How To Build An Ebike From Scratch

You want build an ebike, but the project seems overwhelming. Lets de-mystify the entire process, including planning, parts and perfecting the end result.

Introduction (you are here)
Step 1: Planning
Step 2: Hunting
Step 3: Tinkering
Step 4: Buying
Step 5: Assembling
Build Day 1
Build Day 2
Build Day 3
Step 6: Perfecting
Tools List

This is Going to be a Big One

As writing projects go, I’m expecting there’s going to be a LOT here. This is an ambitious topic. Organization will be a challenge, but I think I’ve laid it out in reasonably broad brush strokes that make sense. The Tools List will be organized one section for each Step/chapter. I intend to release these Steps individually across a couple of months. Since 11 steps are planned, thats going to be a pretty fast production schedule. For the initial stages at least we’ll be seeing two drop per week.

What Does ‘From Scratch’ Mean?

I’m going to go through a complete project build that starts with a bare frame, to which I add all the parts to that frame to make a fully functional electrically-assisted bicycle. We won’t be concentrating so much on electrical / motor specifications as we will picking out every single part that is needed to build a bicycle. Right down to the shifter ferrules and cable crimps. Building a bike is a lot less intimidating when you have a complete list of everything that is needed, along with the tools you have to use to install them.

This will be a ‘frame-up’ build: start with a bare frame and make it into an ebike.

I originally planned this article long ago. It was obvious to me there was a need for a sort of ground-up tutorial based on a lot of conversations with a lot of folks who wanted a fun project, but realized quickly they were in over their heads.

Thats kind of where I was myself the first time I did it – back before ebikes, in fact. I built my own analog bicycles back in the day, and so when it came time to join the Dark Side and switch to electrically-assisted bikes, I leveraged what I already knew and just added a few things to the parts list to account for the electrics.

You know what? You can just as easily use these articles to build a regular bicycle; never mind the ‘e’ part.

Throughout this series, I will be trying to balance the value of taking a deep dive on a specific task, to just referencing that something needs doing and trusting you to use the many better, existing resources out there in the world to get a step-by-step tutorial (I will also sometimes point you straight to one of them). I plan on referencing many of the detailed articles I’ve published on this site to cover a lot of ground in this regard.

Where am I cheating?

I didn’t build the wheels. Really… wheelbuilding is a fairly advanced topic. For a person who needs help from a ‘how to build a bike’ article, that person should probably not also be taking on learning how to build wheels. Let a pro do it for you (I do).

In my case, supply chain issues compounded by my regular wheelbuilder’s busy schedule meant I needed to find another way to get the wheels made for this bike within a specific time frame, with specific parts. I’ll get into the wheel parts saga in detail in the assembly sections.

Anything Else?

Yes, I’m describing how to build THIS ebike from scratch: A full suspension, BBSHD-assisted, mid drive e-MTB. I chose this bike because it is a pretty generic animal. Its not something weird like one of my gargantuan cargo bikes, or an all-wheel-drive beast. Those are great bikes, but they are not projects that would appeal to the first time builder, nor are they of mainstream interest.

So… you aren’t going to see me discuss building a hub-assisted ebike. I’ve stated publicly in other fora that I am done building hub bikes (and I have no plans to change this). However, I would like to, at some point in the near future, add a supplement to this build series to discuss what is done differently if building a hub-motor’d ebike from scratch.

Its not a major departure from this instruction set (if anything, its simpler) and only involves a few different specialty tools – chiefly a crank puller and a bottom bracket tool. And we’ll need to address torque arms. And…

.. Never mind. Lets save that talk for later.

Oh And There’s Also This

Lets call this a Mission Statement: DIY Does Not Have To Mean Half-Assed.

Look around on the internet for awhile and you will know exactly what I mean by this. This project is intended to build up a bike that is as close to factory-quality as possible. There will be things I deliberately do that will spoil that look, and its a standard we will know in advance we can’t reach. But when the Perfecting stage is posted with the final production pics (and that is not the bike shown below) you should be seeing a bike that is awfully close to that ideal.

Background on the Subject Bike

As mentioned above, I wanted to do this series some time ago. Unfortunately, after trying to get it off the ground, I realized I needed a reasonably generic build in-progress to reference as I went along and described the build. It took awhile before that opportunity presented itself.

Recently I decided to build a small, self-contained, full suspension bike for use around town on short errands and maybe for light trails. A bike I could easily toss into my car and haul back out again. Finally, this was a ‘normal’ bike I could use as the backbone of this writing project.

The Apostate is the result.

Our finished product will be a simple, full suspension ebike – using high quality components – with a mid drive and a mounted, in-frame battery.

Quickee General Layout:

Lets take a brief look at how this is going to go down:

Step 1: Planning

Decide what kind of bike you want to build: Cargo? Full suspension mountain bike? Hardtail fatty? Put together a preliminary parts list to give yourself a ballpark idea of cost (don’t worry there’s a sample list ready for you to customize). Your parts list will be the backbone of your project management too. What kind of motor are you going to use? Hub (geared or direct drive)? Mid drive (from what manufacturer?). Where is the battery going?

Your parts list is the key to project management

Step 2: Hunting

Step 1 told you what kind of frame you want, in at least general terms. Now you get serious about buying one. Looking around the marketplace at real products will teach you new things you didn’t realize you needed to know. Read specs closely. Buy the frame that meets your needs.

Step 3: Tinkering

Now that your frame has been delivered, you can start confirming measurements so you know for-reals what the dropout widths are, seatpost diameter and so on. With the frame in your hands, you buy parts with confidence knowing they will fit (and this includes your chosen motor, battery and controller). Having the frame in front of you rather than just in pictures is likely going to give you new insight on what kind of bike this is going to be. You may change some of your parts decisions mid-stream.

Step 4: Buying

Now that you have looked long and hard at your frame, and made your final (?) parts decisions, its time to cast your net wide and start buying all the parts. This is where the parts list you roughed out in Step 1 and finalized in Step 3 becomes crucial. It will manage the entire process of buying, waiting and tracking parts shipped from myriad locations.

Step 5: Assembling

This is the big one. You’ve been receiving little boxes from all over for weeks. Now that you have everything in hand, here’s where the rubber meets the road: Put that pile of parts together into an electric bicycle. Because of all the ground we have to cover, this step couldn’t fit into a single article. Since I did the actual build in about 3 days, I split up the assembly discussion into three parts, each covering what was done on Days 1, 2 and 3.

Step 6: Perfecting

Once you finish the core assembly step, the chances are near zero that you picked all the right parts the first time around. Expect to learn new things when you actually ride the bicycle. Maybe the handlebars would be more comfortable if they were a little wider, or the stem was a little shorter. Or longer. There’s almost always something that needs a tweak.

The Apostate was no exception. Right after the first test rides were complete I knew I wanted to make a couple of sizing changes. From there it went straight into the back of a car where it went riding daily for a week in The Grand Canyon. After that fairly extended initial period of use, I had a few additional things I wanted to change.


Are we ready to get started? Lets go!

Step 1: Planning

Range Anxiety? Be Prepared (and Stop Worrying)

Want to take a long trip with an ebike? Just want to proof yourself against running out of juice on your commute? Here are a variety of solutions.

I’ve put rather a lot of effort into proofing myself against running out of battery juice. In all the years I have been using an ebike as a daily driver – almost always for utility rather than for recreation – I have never run out of battery power. Even when I’ve forgotten to charge before a ride (more on that below).

There Are Solutions

Lets explore some range-extension options. Hopefully you’ll come across something here you hadn’t thought of and can take advantage of.

Use a Big Battery

This is the most obvious one. If you don’t want to run out of gas, put in a big gas tank. This is not a new idea. Nowadays when a gearhead hears about a Corvette Z06, a super fast, light and powerful version of that car comes to mind… but back in 1963, if your option code was RPO Z06, that meant you had the “big tank” Corvette… with a freaking 36 gallon gas tank to minimize refueling stops during races. Or Cannonball runs.

So not a new idea.

If you are doing a DIY ebike conversion, unless you have specific weight goals, you typically want to fit the biggest battery you can afford. Same goes for a manufactured ebike. If it has a larger battery option… you want that. Whether you can take advantage of an option will boil down to the size of your wallet. An XL-sized battery will also let you preserve your battery by charging it to 80% or 90%, but thanks to it being oversized you still have enough in the tank to go wherever you please.

I am all about big batteries on the bikes I build. The Great Pumpkin has a 31 amp-hour, 52 volt custom triangle pack. The Lizzard King has a 32ah/52v brick hiding under its floor. The biggest in the fleet is 2Fat – now a recreational bike, it needs big power to run through remote stretches of beach without inland access. That bike has two parallel’d 16ah/52v packs joined together to make a single 36ah battery.

Bigger is better only up to a point. Big batteries equal big weight. So there’s a limit to what you can and should get away with. You can’t go this big on normal neighborhood ebikes, nor should you.

With all that said, going big on a battery can also save your bacon when you do something like forget to charge your battery… there’s enough extra capacity to eke out a ride home rather than having to figure out a way to sleep over at the office.

Bring Along a Spare Battery

This is my least favorite solution, but it may work for you. If you have a battery, buy another one just like it and toss it into a backpack or pannier. Swap it in when needed. This is probably most likely going to appeal to folks with a manufactured ebike and thus no other options. Unfortunately with a solution like this, you can’t get anywhere near as much out of two batteries as you would be able to for a big single one, or for two joined together in parallel (you can to only partially drain each of your packs, hence the loss in capacity). But you suffer the same weight penalty.

Sidebar:
Don't parallel batteries together unless you know EXACTLY what you are doing.  Running packs in parallel increases the potential for danger dramatically, and should only be messed with by folks with the experience to know how to mitigate those increased risks.

Onboard Charging (Permanent Mount)

I have written up my experiences with using Mean Well power supplies as CC+CV ‘smart chargers’, and mentioned they are fanless and weatherproof. This and the fact they have mounting tabs means they can be mounted permanently. Assuming the bike is large enough to have a brick bolted on without anyone really noticing. That can mean cargo bikes and any bike with a front rack – the charger works great as a rack deck. And on the front, you don’t really miss the fact you can’t put a rack trunk on.

Pictured above on the left: The Big Fat Dummy and its 185w/3a charger gassing up at the park. The charger is bolted onto the lower deck, up front on the rack. On the right: The Great Pumpkin‘s 320w charger on the front rack is good for 5 amps.

The 480w monster now on the front rack of 2Fat is good for a whopping 8 amps. Its supersized, as when I need a recharge on that bike I am in the middle of nowhere and facing darkness, fog … and may need to negotiate with an unpleasantly high tide if I dawdle.

Onboard Charging (Carried in a Bag)

You don’t always want to be lugging a charger around; nor do you always have a place to bolt one on. I have both 185w and 320w portables that I bring along occasionally on bikes that don’t have a permanent charger mount. For instance, I didn’t want to add a heat-generating charger to the largely enclosed basement battery box on The Lizzard King. So I carry the 320w unit you see below when circumstances warrant (not the shoe. Thats just there for size comparison). Being able to pump in 5a into any battery is going to add a whole lot of range if you plug in while having lunch.

Speaking of open outlets, where are they best found? Here in the USA I have really good luck with public parks. Oftentimes a picnic canopy will have a working power outlet. You can also stop at a roadside cafe, shop or gas station and ask the owner if you can plug in while you are there visiting. This works best if you are stopping somewhere for lunch and will be there for awhile. I’ve also found plugs attached to the outside of restroom buildings at state parks.

Obviously, this approach works best on regular routes where you can determine in advance what is available. Keep your eyes open, scope out your options and file that information away for the time when you need to use it.

I include a ‘Y’ plug in my kit so if I am asking someone to plug into their AC power, I am proposing to share it, not take it over.

Don’t Be Such a Pig

This next one is obvious… or is it? Its a technique I have used and it gets the job done so here goes:

Use less power, as in dial back the assist. My Bullitt with its Great Big Battery was about 3 miles into a 16 mile Saturday morning Costco run when I realized I had forgotten to charge it after work on Friday. Its 52v/14S battery reads 58v when its full, and was already down to 52v when I realized my mistake. Not only would I be blowing my morning turning around and going back home, it would be hours before that battery was charged. I decided to just go for it. So I reduced my assist to the minimum and continued. When I returned home with a cartful of groceries stuffed into my cargo box and panniers, I was down into the mid 40’s, voltage-wise – and more than a little worn out.

But I made it. I wouldn’t have if I had not gone overboard with the size of the battery.

After this I made sure I carried a charger with me on these trips. There is a park midway on the journey with a publicly available power plug. I can plug in, sack out and catch a nap next to a water fountain and be on my way. Late… but I’ll have beaten the system.

Charge at Public (J1772) EV Charging Stations

Yes really. It may be difficult to find an open plain vanilla AC power outlet that you can use… but nowadays electric vehicle (as in automobile) charging stations are popping up all over the place.

If you do not live in the USA, you will want to find a different adapter than what I am describing below (from what I hear non-USA charging stations in the EU are much more likely to have an ordinary, separate outlet available for public use).

But in the Land of the Free, this may be the only obviously available power plug you can get hold of. I’m seeing them increasingly in parks and ordinary store parking lots. Likely they are also springing up at the more refined campsites and national parks.

This is my J1772–> Nema 5-20 adapter for plugging into an EV charger

This is an option that hasn’t been available until recently, and is still not widely known or even understood. Above is a picture of the adapter I have. It plugs into a USA-standard J1772 EV charger plug and terminates in a female NEMA 5-20 plug on the other side. NEMA 5-20 plugs are also compatible with NEMA 5-15 plugs. Folks in the USA know of the 5-15 as your garden variety 3-prong grounded electrical plug. Using this adapter, you now have a bridge directly from a 240v EV car charger to a plug that you can connect your charger into.

Fzzzzzzzz… BOOM!

Thats what could happen if you just plug in without making sure your charger can handle 240 volts of current versus the usual 120.

Here’s the thing: Many ebike chargers are manufactured to run on global power grid voltage. In the USA, we use 120v. Much of the rest of the world uses a lot more volts. 240v in particular. So if you are manufacturing chargers and want to sell them everywhere, you make one that can handle the various voltages right out of the box, so you only have to make one model. However, you can’t count on this feature being there. So check first.

How can you tell? Look at the fine print on the label. The really tiny print that you never read. In the case of the Mean Wells I use, its written clearly in big letters, since they are meant for commercial use and nobody cares if they look pretty.

Yup it’ll handle 240 volts, alright. Since I have also made chargers for relatives who use them on their ebikes in the EU, I know they work just fine on the higher EU voltages.

But thats me. YOU have to figure this out for yourself on your own charger. You won’t know until you go look.

So Much For The Good News…

Here comes the bad news: These adapters are expensive. I have seen them selling for as much as $200. Oddly enough, after some googling I found a seller only an hour or so down the road from me who seems to have the lowest sale price on the web. I paid $85 for mine. Thats still a lot. Lets hope the price is only going down as these types of units become more common.

Or better yet, lets hope that EV charging stations in the USA start commonly having normal AC plugs available.

Whether that happens or not, you should be able to do one or more of the things above, and turn range anxiety into something you used to have … but don’t anymore.

How To: Safe, Reliable Electrical Crimp Connections (part 2 of 2)

in Part 1 we introduced the topic and assembled our tools. This time, we’ll use them to make something and show how its done, step by step.

So after having gone through Part 1, we assembled our gear and have what we need to get a job done.

What are we going to do? I have an article on how to create an ultra reliable ebike battery charger (which also works as an AC charging brick for a solar generator like a Bluetti AC200P). Since I have an extra one sitting and gathering dust, we’ll make some plugs for it here. That will serve the dual purpose of giving readers of that other article a step-by-step construction guide.

What do we need to get the job done?

Everything we saw listed in Part 1. Our project device will be a Mean Well HLG320H-54A LED power supply.

The Mean Well power supply with bare wires. If purchased new retail, both ends will be stripped and tinned.

We will also need a 6-foot-long, 3-prong AC power cord with an open pigtail on the female side. Never seen one before? Don’t worry they are commonly available. Apparently a lot of construction workers tear up the cords on their power tools, so replacements are easy to find and cheap.

Lets get started.

Step 1

Size the heat shrink you will need at the very end of this process, and run it down along the wire NOW before you need it. I cannot even begin to count the number of times I have gotten wrapped up in making a cable and then realized I forgot to size and place the heatshrink for that last step. Do it now before you need to do it and before a connector is on and its too late.

The heat shrink has been added – nice and long – and you can slide it well back from the connection as needed.

Put it on the side that you can slide the furthest away from the heat gun for when we have to take that step later. You don’t want to be shrinking this one up when its out of position so it needs to be away from the heat.

Step 2

The wires on the pigtail side of the power cord are already stripped and tinned so they are easy to work with. Lets use those to teach ourselves how deep the butt end connectors are. We can trim these wires so their insulation fits right up to the edge of the metal connector insert. Once we do that, we’ll know how much we need to strip off the wires on the other side of this connection.

Dip the wire into the connector. The insulation on your wire should seat against the metal butt end connector inside. How much extra is there? Snip some off so the insulation fits right up to the end. Repeat for all three wires on the power cord.

Step 3

Next, we strip the wires that go into the other end of these butt-end connectors. The lengths we snipped down to in Step 2 give us an easy visual guide to how much we need to strip back on these wires.

A note on wire stripping: There can be a little more to it than just picking the hole that matches your wire gauge and biting in. I like to spend a little more time on the job so I don’t lose a single wire in the bundle (if I can help it).

Here’s the way I did this particular wire: I picked the 18 ga slot and was able to clamp down hard on it without damaging the wire underneath the insulation. Its a size up from where I’d get a clean, complete cut, and gave me a safe cut of maybe 80% of the insulation. Then I shifted down a size to the 20 ga slot and – very gently, clamped down on the same spot. Just a bit. While slowly spinning the cutters radially around the wire (again, just a bit). This cut the insulation without cutting any of the wires underneath. Until you get a feel for it, put the wire into a hole thats too big for it and work your way to smaller holes from there.

From there, I hand twisted the now-exposed wires so they bunch together and I’m ready for the next step.

Step 4

Crimp connectors onto the wires on the power cord. For this article I am using my new handy-dandy semi-auto crimping tool for the first time, rather than my manual commercial-grade crimper (i.e. giant pliers). The ‘semi-automatic’ part of this crimper is you just squeeze until the crimper releases, and you have a good crimp that is solid, and uniform with every other crimp you make for this job. Because of the small wire size, we can use the pink 18-22 gauge connectors.

Something to remember when you do this: While you are fumbling around the wire can slip partially or even fully out of the connector. Because of this I like to grab onto the connector with my crimper – without squishing it any just yet. Once I have it fixed in place, I use one hand to push and hold the wire end into the connector so it can’t slip back. Only then do I squeeze the bejesus out of it to make the final crimp and permanently connect the two wires.

Step 4 Complete. The semi-auto style crimper with its dual crimps was almost too big for this small 18-22 gauge connector.

Another something to remember: When doing one of these 3-wire connections, things can get awfully tight when you start finishing the connections in the next step. There may not be enough room to stuff the crimper’s jaws in between the wires to get the job done. Solve this problem by stripping enough of the plastic sheathing back from each side so you have enough open space to work with when things start getting crowded. If you can’t do that (I couldn’t here) then you’ll have extra effort in store trying to get the crimper’s jaws in the right spot while the wire stays in place inside the connector before the crimp.

Step 5

Now crimp on the wires on the other side – the charger side. This time, you have to pay close attention to which wire goes where. Since I live in the USA, our power cords do not adhere to the international standard for wiring colors. Connect:

  • The green wire on the cord to the green wire on the charger (GND)
  • The black wire on the cord to the brown wire on the charger (AC+)
  • The white wire on the cord to the blue wire on the charger (AC-)
Step 5 complete. Note the dual crimp lines on each side. The 18-22 ga crimper jaws were almost too large for this connector. You have to go right to the edge of the metal connector inside.

If you live pretty much anywhere else besides the USA, the wire colors will all match and what you connect to what will be obvious.

If you happen to screw up making one of these connections: Bite the bullet. There’s no uncrimping one of these. You have to snip off any crimped connectors at their very edge. Then snip down any wires you haven’t connected yet so they are all still the same length. Then re-strip and try again from scratch.

Step 6

Now you heat shrink the individual wire connectors. Remember the big heat shrink you put over the wire in Step 1? Make SURE you keep it well away from the heat gun while doing this. Let it get warm in the slightest and it’ll stick itself to wherever it is now, and not where you want it to eventually be.

I use my heat gun on its lowest setting, which is much slower going, but it lets me very carefully heat up my connector. I like to push the wires – and the connections – together a little, which spreads them out more or less evenly. Then I slowly rotate them around under the heat so every side of each connection gets heated up. You’ll be able to tell when you are done on each side because you will see a little bit of the internal adhesive squeeze out and form a bead on the wire. When you can see that – AND the air bubbles inside the connector disappear (this is another reason you slowly rotate while heating) you are done.

Ready to begin Step 6

Heat up each END of the connector. Stay clear of heating the center over the metal connector. That center section is where you stressed the adhesive covering by smashing the hell out of it with your crimper. If that stressed area shrinks and tears, it will expose the metal underneath, and thats a bad thing. Let the center section shrink down thanks to the indirect heat coming to it from each of the two ends. Also, if you use a manual crimper, which is much more likely to cause a tear if you are a little overzealous, then staying away from the center will let the adhesive inside liquefy and seal up the hole you created rather than spreading it open via shrinkage.

Step 7

Let the wires cool a bit. Our next step is to slide the oversized, overly long piece of adhesive heat shrink over the connection we just made. If you try and slide it over while the connectors and wires are still hot… it’ll stick to them, shrink up a touch … and you’re screwed. So walk away for five minutes and be patient.

On this power cord, I am using an extra long piece as I want this to be a strong connection. I am also using an oversized tube that will just barely shrink down to hug the power cord, which means it will be very thick once it gets to its minimum diameter. I did this because this cord is going to take abuse as its going to be pulled, coiled and stepped on. Hopefully for years (it turns out when this stuff cools after shrinking its also completely rigid, which is a good thing for protecting my connection).

Step 7 complete. That little red ring of heatshrink near the plug is just a test I did to make sure the big size I used would shrink all the way down to hug the cord.

Application of heat is the same process as it is for working the connectors. Regardless of whether or not it looks like the heat shrink has shrunk down enough to do its job, take the extra time to apply heat to the every angle of the exterior of the strip. Slowly go around all of it in even, top-to-bottom strokes. It may look like its fine halfway thru the process, but going around it and heating thoroughly it at every angle will shrink it down tight on top of the other work you just did.

And… pay attention. Keep the nozzle moving and keep it on low heat. Its a whole lot easier to melt your cord than it is to unmelt it.

And thats the end of the AC cord input side.

The Power Output Side…

We did the power input cord in step-by-step detail. We won’t need to go into that same level of detail on the output side, since its almost the identical process. But there are a couple items worth calling out.

We need step-down connectors this time

The XT60 we are using for power output is a nice beefy 12 gauge, which would need a yellow connector. The Mean Well’s power wires are 14 gauge. Thats ordinarily a blue connector. So we need a step-down (yes, I could have used a 14 gauge XT60 – I do have them in my shop – but I prefer the heavier wire).

We do the same trimming to size the wire in the connector as before. However the 12 ga wires on the XT60 have enough fudge in the 10-ga-capable wire connectors that we can leave the tinned ends on. So no need to snip them, we just take some insulation off and job done. If you can leave the ends of a wire tinned, do it and make your life easier.

Bigger connectors = more room to work with

On the 18-22ga pink connectors, we almost didn’t have enough room to work with. But with the larger yellow 10-12ga connectors that wasn’t a problem.

You can see how the crimping jaws are within the borders of the metal segment on this larger connector; ending fully to the left of the slot in the middle. Lots of room.
The connectors, after applying heat to shrink them down onto the wiring, just before having the external sheath shrunk down over them. They essentially glue themselves and the wire connection together, providing a second of three layers of stabilization to the connection.
The finished product. I used red heatshrink over the wire on the output side simply so my stock of heatshrink (red and black) gets used up at about the same rate.

How To: Safe, Reliable Electrical Crimp Connections (part 1 of 2)

Solder or crimp? Debate on that can be fierce. After more than 7 years of daily commute riding, I have never had a crimped connection fail. How is that reliability accomplished?

We’re going to add this to the growing list of topics I never thought I’d be writing about. But it seems to need discussion quite a lot, and not just in ebike circles. I come across it frequently in the world of solar generators too, from folks who have zero experience with or initiation into the necessary skill of making extension cables. So while I am typically discussing DIY ebike topics, this subject crosses over into a whole lot of other areas.

Should I Solder or Crimp?

If you know how to do a good job of soldering, chances are pretty good you already know your answer. There’s nothing incontrovertibly bad about doing a proper soldering/wiring support job. At the same time, if you make good crimps that never fail, then there’s nothing wrong with crimping, either.

Can a case be made that either method is superior? Yes. I’m going to ignore the existence of this debate and instead focus on showing my tools and methods, which have resulted in a perfect reliability record so far. You decide for yourself if you want to go this route, or another.

What Tools Do We Need?

As is always the case, your success will be entirely predicated on using the right tools for the job. A crimping tool is not a pair of pliers for instance, regardless of the fact that you already own pliers and crimpers sure do look a whole lot like pliers.

Wire cutters

I use a dedicated set of wire cutters. Yes you absolutely can find yourself a single combined tool, or press tin snips or scissors into service if you already have those. I suggest you resist that temptation. Right tool for the job… remember? I use these, which I bought from Amazon.

You can find what amounts to the same cutters with a different label on them under about a zillion different brand names. These are actually cable cutters (not wire cutters) and they serve a good dual purpose in that they also work great for cutting bicycle brake and shifter cables (did I just violate the right-tool schtick I went on about just a second ago?). The best way to make a cut is to put the wire in their jaws and use a sharp, fast hand squeeze to snip the end off lickety-split. Trying to cut slowly and deliberately will give nothing but trouble with leftover wire strands. These bigger cutters will work especially well on the 10 gauge wire that is common on ebike controller input and battery output wires.

A good, strong pair of industrial scissors – with tiny serrated edges on the cutting surface to grip the wire – can work in a pinch. Regular household scissors… not so much.

Wire Strippers

Here again, you want a dedicated tool. I mostly use this one, again purchased from Amazon. I also have one made by Klein Tools that is marginally better… and double the price. While I like the Klein tool a little better, reality is I use the cheapie almost exclusively. So it must not be so bad, right?

Wire crimpers

Here’s where the magic happens. Its another tool you’d be tempted to not buy and just use a pair of pliers or something, but its very important to use actual crimpers. We’ll get more into why in Part 2 when we look at actually making crimps.

For the most part I use a 9 3/4″ manual crimper that I bought from Home Depot. I like it because I am used to it, but its probably better to use something like this Klein Tools semi-automatic crimper. It makes a uniform crimp that is perhaps more likely to leave the outer heatshrink surface of the connector completely intact – something you have to learn how to do after some experience with manual crimpers.

While the manual crimpers have been my tool of choice for years, I have the Klein tool on order right now and we’ll see how it goes when I use it in Part 2 when we get hands-on with crimping duties.

End Connectors (Pigtails)

So you have your wire on one side. You need a connector of some kind on the other. For an ebike, the common choice for a battery charge connection is an XT60 female connector with a 12-gauge wire. For the battery output its typically an XT90 female connector. A larger, more power-capable version of the widely-used XT60. Better yet, instead of using an XT90, make the connector an XT90S, where the ‘S’ signifies the anti-spark feature of that otherwise identical-to-XT90 version.

Tinned XT90S pigtails. The green paint signifies the connector is the anti-spark variant.

The cheapest way to create connector ends is to take a soldering iron and directly attach a connector to the destination wire. But an alternative shortcut is available to folks who may not be up for that, and its ideal for folks who are crimping connections. “Pigtails” – a connector professionally pre-soldered to a short length of wire – are commonly available, ready to crimp on with very little preparatory work. I use them almost exclusively.

My box of XT60 and XT90 pigtrails, along with some pre-made extensions. Crimp two pigtails together you’ve made a cheap, short extension cord. You can see one in the center of the box (an XT60).

How much preparatory work is ‘very little’? Well on a pigtail, the bare wire ends are ‘tinned’. Essentially this means the bare wire has been dipped in solder, which makes it a single piece that cannot fray. You almost always have to snip off that end bit before you strip them. But we’ll get to that in Part 2.

Wire Connectors

All of the connectors I use are 3:1 heat-shrink adhesive ‘marine’ grade connectors. There are non-adhesive connectors (usually employing a 2:1 heat shrink ratio) which you should avoid. There are also connectors that do not employ any heat shrink at all. Same deal: Stay away from them and use only the adhesive marine grade version (unless you are an experienced hand at this, in which case there’s no reason for you to bother reading this article in the first place).

Why? Well, the heat will shrink tightly around the wire insulation on each side. This firm, adhesive grip will strengthen the connector’s bond, and support it. The adhesive liquifies under the heat and then dries, forming a strong gripping bond that ends up being stronger than the plain wire. Whats not to like about that?

You can find a variety of crimp-on ends. These two make up a detachable bullet connector that can be manually separated.

While there are a variety of connector types, including spades that let you screw a wire down, or bullets that let you uncouple and re-couple a connection manually, I almost always stick to butt-end connectors that just connect a length of wire to another wire. I do any form of quick-detach connections with proper connectors like an XT60 or XT90.

There are two sorts of butt-end connectors you should know about:

Straight-thru same-gauge connectors

These are pretty straightforward: You have the same thickness of wire on both sides. Or, more accurately, the thickness of one wire is within one size of the other.

Your yellow connector works for 10-12ga wire. the blue ones work with 14-16 gauge and the pink ones work with small 18-22 gauge (thats actually three sizes). But what happens when you have a bigger difference in the wires on one side or the other? You need a special kind of connector that has a smaller hole on one side.

Step-down connectors

This is the solution for connecting two wires of different sizes that exceed the ordinary tolerance of your standard straight-thru butt end connector.

The yellow connector is ordinarily used with a 12-10 gauge wire. But notice the blue band on the left? That side has a narrower opening that accepts a wire of 14-16 gauge. The right side, banded in yellow, takes the standard-for-that-connector 10-12 gauge.

The blue step-down connector has a blue stripe on the left for its normal 14-16 gauge wire. The red stripe on the right means its suited for an 18-22 gauge wire.

Here’s a connection using same-gauge connectors:

Above at left, I’ve connected a three-prong (grounded) power cord to a power input cord on an ebike battery charger I am making. The connectors have been crimped together, but have not yet been heat-shrunk. On the right is what the adhesive connectors look like after careful application of heat from a heat gun.

Notice how the adhesive covering of the connectors has not been broken or split despite being smooshed by the crimper. This is a big deal as if you split the adhesive shrinking surface, the split will widen when it heats up and make a hole with the bare metal of the connector exposed: an uninsulated path to a live connection (more on that in Part 2).

All this wire needs need now is some adhesive heat shrink covering the entire connection to finish off the job. And yes depending on where you live thats a funny looking plug. Its a ‘Schuko’ type plug and I was making a charger for someone living in the EU.

Heat Shrink

Once we completed the crimps as seen above, we need to cover it. This is to further stabilize/support the connection and protect it. For that I am using heat shrink tubing. Once again, there are two kinds of heat shrink: 3:1 marine grade adhesive heat shrink is the best. Stay away from the thinner, less sturdy 2:1 non-adhesive stuff unless perhaps you are putting on an external layer in a pretty color – over top of the 3:1 stuff – for the sake of cosmetic appearance. I have orange, green and white 2:1 heat shrink rolls for use on cable coverings for orange, green and white bikes I have built. But its just for show.

You can buy heat shrink in little pre-cut bits, but I much prefer uncut lengths so I can snip it to exactly fit the job I am doing at the moment.

By using the thicker adhesive version you add another significant layer of protection over your connection. If it wasn’t going anywhere before (it pretty much was already unbreakable) its completely safe and protected now with a crimp, an adhesive grip on the crimp and another adhesive grip completely over top of that.

Left (above): the same plug already illustrated, with the wire now covered in adhesive heat shrink. Without looking right at it you might miss that its not a factory-made cord. See the red/black wires? That is the bare wire on the other end of that same charger (its not the same wire).
Middle: We take the two output leads on that black/red wire and graft on an XT60 plug to connect to our ebike battery. We use blue connectors this time because of the thicker 14 gauge wire.
Right: After shrinking the connectors, we slip a long length of 3:1 adhesive heat shrink over it all to strengthen and stabilize the new connection. Job done.

A Heat Gun

This is what does the shrinking. You might be able to use a hair dryer for this job instead of a proper heat gun. And it may work.

For whatever reason, I don’t own a hair dryer

One benefit of a heat gun is you can stand it up vertically on the garage floor, so you can use it hands-free. That gives you two hands to slowly rotate what you are heating up over it, to get a uniform effect without burning or melting stuff.

This is the heat gun I use. It has two heat settings and I almost always use it on ‘low’, which is slower but gives me lots of control over what is happening (its a lot easier to melt things than it is to un-melt them).

I keep the leftmost adapter permanently on the nozzle to concentrate the heat as much as possible. This minimizes the possibility of collateral damage to nearby wiring and connectors.

Quality Bulk Cable

One of the spiffs of having all this cable- and cord-making gear on hand is the ability to make just about any cord your heart desires. To do that conveniently, it will pay in the long run to buy the cable you are most likely to need in a spool. Say… 250 feet of the stuff. Thats going to seem expensive until you need a 50-foot extension for your solar panels and snip-snip-poof you have what you need in 30 minutes.

Sadly, the 250-foot spools don’t seem to be available at the time of this writing, but you can still get 100 feet of oxygen-free copper wire in 10AWG for under $1 per foot. You can spend more than this for bonded, PVC-coated wire that can take the outdoor weather and even be buried.

A quick morning’s work: A 50-foot extension out to my portable solar panels, sitting in the blazing summer sun. The short factory cable connects to a watt meter that I added to measure current, and that connects to the actual extension which leads outside to my solar panels. Created entirely from parts I already had in my garage workshop.

Next: Part 2 of 2. How To Do The Work, Step By Step

A Backpack Ebike Battery… Are You Insane?!?

If all I did was write internet posts, I’d still hate this idea. But circumstances made me try one. I knew almost immediately how wrong I had been.

Brace yourself, because, if you haven’t already tried it, and you are like most people, you probably think this is the worst idea, ever. I was one of those people. Then I built a bike that simply had to use a backpack battery as its power source. I held my nose, gritted my teeth and just did it. I dreaded the result right up until I rode it for the first time.

Look at the two pics below. Where’s the battery? Nowhere. Nowhere in the picture, at least. I was wearing it. In the image at right, I have used subtle visual cues to highlight the silicone-insulated XT90 connector I plug into.

By the way, that is a Cyc X1 Pro Gen 1 motor. The little bag houses a BAC800 controller that reached 60 amps of continuous output before I chickened out and lifted.

What problem are we solving?

A backpack battery should obviously not be your first choice, so why do one at all? When doing a DIY ebike build, there are some donors that just don’t have space for a battery.

Where the hell am I going to fit a battery on this bike? I will deliberately NOT answer that question here.

Fresh out of the box from Guerilla Gravity: My Smash 29er; one of their very last alloy frames before they switched to carbon fiber. The tires aren’t even dirty. Lets take a picture cuz it will never be this clean again.

In an earlier draft of this post, I wrote up all the different things I thought of or actually tried, and abandoned because they sucked for one reason or another.

But that is going off into the weeds as this discussion is about backpack batteries, not build or donor choices. So lets table all that talk and just stipulate: We have this bike that we have to work with. we looked at alternatives (remember… I hated this idea at the time), we are left with one choice:

The battery has to be in a backpack

Once I accepted the fact I was stuck doing a backpack, all that was left were materials and ergonomic/mechanical choices. i.e. just make it and do it right.

Pack Choice

If you listen to the experts on the internet (thats a joke in case you missed it), whenever the subject comes up you hear all about how a battery on the back of a rider is a bomb just waiting to go off. There is some truth to this. Flying off the bike and landing on your back on sharp rocks is a really bad thing made a whole lot worse if a li-ion battery is your crash bumper.

There’s also a lot of talk about how the world will end if you put your battery weight up on your back, but we’ll get to that one later.

The solution for safety is to use a hardshell pack of some sort, of the kind you see used on sport motorcycles. I picked a 20L Boblbee GTX from Point65.

Nope, it sure as hell isn’t cheap, but remember that unexploded bomb thing? Its for real and a hardshell pack solves that problem. It also provides you with spinal protection in case of a crash. And you also get something that addresses another negative the villagers are shouting about: A pack like this form fits your spine, hugs your body and never shifts – not even a little.

I suppose if you had to, you could use a soft pack and then stick your battery into a 30 cal or 50 cal ammo can. Drill a hole in a corner for the power cable exit and it would work, but that can is going to be a lot of weight to carry. Still, if you want a cheap, safe solution that uses a conventional pack… thats it. I’m sure you will figure something out on the shifting thing. I know I have packs that don’t shift. Much.

Really though… this is a problem you need to throw money at to properly solve. In my case I spent about half of retail by finding a vendor closing out an old model and blowing them out at a big discount.

QUICK NOTE:
I take a lot of pics of my stuff, but for some reason, besides whats above I have never done any of my backpack setup.  In the near future (the pack and bike are hundreds of miles away from me right now) I'll get pics of everything.  Especially the wiring/keyring/ball stuff below.  That is a lot simpler to just look at than it is to write up intelligibly.

Battery placement inside the pack

You do not want the battery bouncing around freely inside that hardshell pack. Each battery and backpack combo is different, but the core of the solution is to stabilize it with dense, closed-cell padding. I didn’t say wrap it tightly in foam so it overheats (put down that pitchfork). However, part of a smart DIY plan is to use cells that can take a murderous flogging without heating up in the first place. I used the old standby Samsung 25R cell for mine. For my pack, I have enough extra room to fit my pump and tire change tools.

Some judicious padding. Sprinkle some tool bags in there (so no little bags on the bike). Job done. Its not moving around.

The Smash, post build but before the first real ride (its too clean). All those bags violated my Anti-Festooning Rule and went into the backpack, although the top tube bag only contained soft towels meant for nutcracker protection. Maybe I should have left that one.

Figure out the wiring / connection

This is the tricky part because if you get this wrong and stay aware of the cable, you will hate your ride. First off, I used a short 8ga XT90S extension directly off the main battery output. I pretty much do this on every battery connection on any bike so, when connecting and disconnecting the pack, I’m visiting the wear and tear on a cheap replacement connector and not a live cable soldered into the pack. I also use a pair of XT60 pigtails to make a similar extension cable for the charge connector. Same idea. I’ve had my bacon saved doing this and the experience of just being able to throw away and replace a cheapie extension made this a go-to for me on everything.

The short XT90S extensions are at right. You think thats a lot of pigtails? Doesn’t take much to run out of spare parts… especially these days.

Next comes a long length of true 10ga power cord, made into a long XT90S extension cord. This is what will go from the battery to the motor and its several feet long. How long exactly? I measured out enough to exit the pack, run down my back, down thru my legs and still be long enough to never tug if I am standing on the pedals and bouncing around at the same time.

OK… great… what if I’m sitting down? A cable long enough to stand up with is going to be all kinds of awkward when doing what you do most: Sitting. I spent a fair amount of time trying to figure out what to do about this. A lot of others have done some sort of elastic bungie contraption. I tried that and felt it needed too much strain to extend, and carried a risk of pulling apart the connection at the motor. I needed something that reliably retracted my cable and extended it without much resistance.

And here’s the solution: The Key-Bak Super48 HD. This is literally the direct descendant of that chromed steel extendo keyring thing that every janitor in the United States has on his belt. Except they aren’t chromed steel anymore.

They’re kevlar.

The model I bought has a 48″ extension length, with their lightest 8 oz pull and a kevlar cable. Its so lightweight, it doesn’t impart the same feel of indestructability that the old steel pucks had, but I have been using it since mid-2019 and so far it shows no sign of wear. You can see from the Amazon link above that there are other models of varying lengths and pull weights. You can even get one with a steel cable. Since I’ve been using mine, I can say its 48″ extension is plenty, and the light 8 oz pull makes its operation completely unnoticeable.

How do you make the Key-Bak work?

What you need is a ball attached to your power cable. The cable threads through the key ring and stops at the point where the ball – which is bigger than the ring – is reached. You place the ball at a point down your back and to the side, so there’s more than enough cable slack to let you stand on the pedals, but not so much it gets in your way.

When you stand up the keyring lets the cable extend until the ball stops it. When you sit back down, it retracts back up behind you. Simple and effective. You never have excess cable down around your legs getting in the way. If you need more, the light 8 oz pull lets it happen without your even noticing its there. In fact, you really don’t know its there at all because its placed where you can’t see it, behind you and to the side. Out of sight and out of mind.

Once I spent some time figuring out the cable length needed to do the job right, and where the ball needed to be, I built and positioned the ball as follows:

  1. A strip of leftover silicone handlebar grip roughly 1.5 inches long. Since I have used Wolf Tooth Fat Paw grips and ESI Extra Chunky XXL grips with my Jones bars on various bikes over the years, I have leftovers from grips that were cut off.
  2. Plenty of silicone X-Treme sealing tape.
  3. The silicone grip segment – since it was already sliced off a set of handlebars – already had a slit in it to let it slip over the cord. Wrapping silicone in silicone tape sticks instantly, and doing so – with overwrap onto the adjacent power cord, tightly affixes it so its not moving, ever.
  4. Silicone tape fuses permanently to itself and isn’t going to unravel.

The above is just one way to do this. In my case with spare stuff laying around in my garage.

What is it like when you ride it?

I wasn’t expecting a good experience. The idea of being tethered to the bike and having a power cord running down off my back… I hated everything about that. Boy was I ever wrong, and if I hadn’t built the solution and gotten on the bike and tried it, I’d still be just as wrong. This is something you have to experience to fully understand and appreciate.

The Good.

You are still tethered to the bike. But the smart setup mitigates this so thoroughly its unnoticeable when you ride and requires very little extra effort to deal with.

Not having the battery weight on the bike makes it behave… like a bike. Internet experts will jump up and down and point to the higher center of gravity that comes from putting the pack on your back. But reality is that without the weight of the battery, smashing thru a rock garden or challenging singletrack is like doing it on an unpowered bike. Since in singletrack you usually only use (or want) power when going uphill, that means your ride everywhere else is exactly like you want it: Old school analog. Your suspension acts like it should… but with a rider who’s eaten too many cheeseburgers.

Having the battery on your back means you can shift its weight from side to side just as you already do with your body. See the above point, because that one and this one together completely undo the whole ‘center of gravity’ argument, and put the backpack setup in the ‘superior’ category when it comes to all-around performance. If you are wearing a 10 lb backpack… so what? You spent the money to buy a pack with a completely form-fitting back panel, that attaches firmly to you so its an extension of your body. No shifting of any kind whatsoever. You did that, right? Bought the really good pack? Cuz if you swiped your kid brother’s lunch pack or figured out some other way to cheap out… you’re screwed. Proper packs are not just ones that shield and pad the battery. They shouldn’t fidget.

Holy crap I totally forgot about that cable! I thought that was going to suck so hard, and I don’t even know its there! Thats you after your first ride. My first config ran the cable around my side and did not go thru my legs. I was concerned (and rightly so) the cable could flop away from my side and hang up on a bush. So I took the plunge and ran it between my legs like the experienced builders say I should. Sure enough it works perfectly.

We have addressed the safety/crash issue by using a hardshell pack, with some dense foam around it but not smothering it (and used a battery cell that doesn’t heat up under extreme load). That makes the battery safer than it ever would be in a ‘traditional’ battery bag.

The Bad.

You are still tethered to the bike. I never said a backpack was the best solution. Its just the only one sometimes. Its not the end of the world if you do it right.

When you stop the bike, you have to disconnect. Its not difficult, but you have to do it so it goes on the list. I keep XT90 safety caps in a little pouch and use them to cover the open connections on the bike and my battery cable. When I mount the bike, I first lower the dropper post all the way. Then I straddle the bike from behind, standing over the rear wheel. I connect the power and, since the seat is so low, I can just step forward and be right over it. I then raise the dropper and I’m on the bike. Dismounting I have some options. I can be standing and reach down, disconnect and just throw my leg over like usual, or do the reverse of the mount from the rear. In practice I’m about 50-50 as the rearward exit is easier but I need to think about it to do it.

And The Ugly

Whats ugly is I used that unoriginal cliche for those pro and con section titles. Lets take a break, sit down with a plate of spaghetti and enjoy the movie!