Battery Technology – Tales On Two Wheels

Create a Battery DIScharger

Letting an ebike battery sit and stew in a high state of charge accelerates its march to end-of-life. Here is a straightforward, albeit unusual way to help with that.

This short article is going to describe something you probably never thought you had any use for, and maybe still won’t. I read about them for years, but didn’t realize how handy they were until I finally took the plunge and put one together. This is one of those gadgets where you won’t really appreciate its utility until you have one available to take advantage of.

Here’s an example:
Just yesterday after a very long ride and recharge, I pulled my Bullitt out of the garage to do some basic maintenance. Rain was unexpectedly pending and set to last a few days. My 14S/52v pack was up to about 57.5v, which would have been fine if my planned daily ride was not cancelled, and the battery will now sit for a few days. So I plugged in my discharger, set it for 10 minutes and while I did some minor work on the bike, the discharger brought my pack down to 55.0v.

Whats The Problem?

Your typical ebike battery is called “lithium ion”, but in fact that term covers a variety of chemistry variations that behave differently. Ebikes typically use a variation known as “Li-NMC”, which translated means “Lithium Nickel-Manganese-Cobalt oxides”. If you charge up a Li-NMC battery and let it sit, doing so accelerates its march to the end of its lifespan.

In an ideal world, you never charge a Li-NMC battery up and let it sit. If you do, the battery isn’t going to die today, but it will happen sooner thanks to this.

How to make a lithium battery last, or…kill it, if you like

The article above is quite technical. Skip forward and start reading at the heading “Amount of TIME at HIGHER VOLTS is BAD”. Then go further down to the header that says “Don’t charge to 100%” and read that. Or take a bigger shortcut and just read the Conclusion section. Its worth noting this article was written in 2017, about a video lecture given in 2013… None of this is up for debate, or new news despite what you may hear from the self-appointed experts on your favorite internet forum.

Google Search: “How to make a Lithium ion battery last longer“

So… Extended time sitting charged up high is bad. Got it. I try and charge to full voltage only just before I ride. If I have a ride planned for the morning I charge most of the way the evening before. As soon as my alarm goes off in the morning I plug in my charger to top off while I perform my morning ablutions.

But what if something comes up and I can’t ride? Or I get lazy? Or whatever. Now I have a battery pumped up to 11 and its going to sit like that. It would be nice if I could back that battery voltage back down some.

To be perfectly clear, using this discharger concept (aka “cycling”) does put mileage on the battery. We won’t fix that. But this is the lesser of two evils. Better to plan charging better so you don’t do this at all. But we live in an imperfect world, so…

Time For The Solution

The key component of this gadget is for us to find a load we can place on our ebike’s battery, to drain it down to a more palatable level. There are a couple of ways to do that.

Method 1: The Cheap, Slow Way

Do something like hook up a string of light bulbs to your battery. Let them blaze away for awhile and slowly drain your power back down. The ones I have seen like this use a wooden plank and old-timey ceramic bare light bulb sockets.

A REALLY cheap way would be to get

an extension cord with multiple outlets, or a power strip
some plug in bulb sockets
some 48v low voltage camping light bulbs

Plug in the sockets into the extension cord, screw the bulbs into your little sockets and voila, you have a basic battery load (and off-grid campground light). Now… 48v bulbs only eat a very few watts, so this is going to be a pretty slow drain, but its cheap and it will work. And you can always add more sockets and bulbs.

Next, you want to address the issue of potentially draining the battery down too much. Going the cheap route, since the timer has to be wired into a gadget that is not plugged into a wall socket, I don’t have a fail-safe solution to recommend. However you could set a stopwatch timer on your cell phone, or a kitchen timer that you keep nearby, pay attention when the timer goes off and go manually disconnect the discharger.

What follows is the method I chose, which includes a built-in cutoff timer. You could include such a timer in a cheapo light-bulb-based solution no problem.

Method 2: The Fast/Convenient Way.

Use a Load Resistor. This method will take more effort to put together, and costs more, but will be a lot more convenient to use in everyday life.

Grin Technology makes a 6.8 Ohm, 400w load resistor designed specifically to soak up current from an ebike battery. A load resistor works by turning electrical current into heat. So these suckers get REALLY hot. How hot? Well, my 52v packs will heat one of these little buggers up to around 450-500 degrees, fahrenheit.

You want to be very thoughtful about what you set this unit on when you plug it in. That includes leaving free space around it, and ensuring no one will accidentally stumble upon, sit on or otherwise touch it.

I like to set mine on top of a brick, with the brick sitting on a concrete driveway or patio. I set one on a painted garage floor once and the grey paint on the garage floor burned a little bit brown from the heat. So a brick insulator is a really good, almost-free enhancement.

NOTE: This whole assembly is sitting on a concrete patio outdoors. NOT a shag rug or anything else remotely flammable.

Above you see the complete discharger. A Grin Technologies load resistor sitting on a brick, connected to a 60-minute timer, connected to a 6-foot or so cable, connected to a watt meter which finally has a connector that lets it attach directly to one of my batteries. Since much of this gadget is made up of various bits and pieces I had made up for other things, you see I had to use things like gender benders to get the connections right. The watt meter has a corrective note on its face letting me know how far off of true voltage it is, and what it needs to read so I have a true 55.4v (which is meant for low amperage charging and not much use when I am yanking 7.5a out of a battery on a discharger).

I made a relatively long cable to give myself the freedom to ensure the load resistor – which again will become dangerously hot and must be put in a safe-from-causing-a-fire place – is located safely away from everything and everyone when in use.

Using a 36v battery, this load resistor will drain the battery at a constant rate of about 5 amps. Connected to a 48v pack, it will drain the pack at a rate of 7 amps. My 52v packs pull about 7.5 amps. I have two of these load resistors, and a Y adapter that lets me plug them together in series for about a 15 amp draw. This is acceptable load for a big 52v battery, but I’ve found that in practice running two of them like that is too much of a good thing. It only takes twenty or so minutes for just a single unit to pull a volt or two out of even the biggest batteries and that is plenty fast.

This is a fairly heavy duty solution, and I used the heavy duty timer described here (a quick-finish 60-minute version) to limit the discharge time so the battery doesn’t drain down too far.

An additional article related to putting together one of these for yourself:

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

To Sum Up:

In an ideal world it is better to never need one of these discharger kajiggers. You’re better off riding the bike, and never charging the thing up high and letting it sit in the first place. But in real life things don’t always go as planned. Having a discharger on hand – regardless of whether you go all in or do it on the cheap – can be a handy way to do penance for the occasional sin.

Ebike Battery Charge Safety: Heavy Duty Cutoff Timer

Add a safety layer to ebike charging practices, with residential/commercial grade components rather than the cheap stuff.

Nip It!

In my previous post I dug into the subject of using a mechanical cutoff timer plugged between your ebike charger and the wall. It gives you an added layer of safety when charging your ebike battery. Using a timer, coupled with some advance planning and brain power, you physically cut the power to the charger. In doing so you prevent even the possibility of a charger or battery malfunction. I went into the details thoroughly in that post.

To do this job I used a cheap, basic timer bought online that I have been using for years. Recently, others who also use this timer have taken it apart and looked inside. The verdict: It will do the job, but it is not particularly robust or fault-tolerant.

How Do We Beef It Up?

Use a better timer. Chances are pretty good if you live in the USA you have already seen and used this exact timer many times. They’re on the wall in almost every hotel or motel bathroom: The timer that turns your heat lamps off after a short while so the bulbs don’t burn out. You also see them on whole-house fans in private homes (you have to live where it gets hot to have these).

The one brand that seems to be everywhere and in use for decades is Intermatic. They seem to last forever, so the hope here is it will also last forever with your ebike charger. Since it is made to conform to residential electrical codes, its internals should be safer and more robust than any teeny tiny timer you bought on the internet.

Following that, what will we use to go along with it? After all they’re called ‘wall timers’ because they are usually built into walls and connected to your power grid. We want this thing to be reasonably portable, and still safe.

Lets Make A Parts List

I have built a few of these. I have bought parts from a local Home Depot, or from Amazon. Neither is the best place for everything. Some parts are cheaper at one source than they are at the other, but the bargains are all different parts. Buying everything from just one or the other, you end up spending the same amount of money. If you want to save a few bucks, shop around locally and buy a few bits in town. You should be able to save about US$15. I am going to stick to using Amazon on this parts list.

Project cost if bought from Amazon is about US$75 if you buy the 10-foot cable. Thats a lot more than the cheapie timer but it is WAY less than your fire insurance deductible on your garage.

Intermatic 12-Hour Spring Wound Timer

Different versions of this timer exist to span ranges from a few minutes to a few hours. This 12-hour version (Model SW12HWK, Single Pole Single Throw) is less common. It is usually an order-in item if bought locally. I chose 12 hours because I like to charge big batteries (35ah!) at low current rates, so a long timer works better for me. Its also almost guaranteed to work for a variety of other jobs, so I am not blowing US$75 on something that is only good for one thing.

The image above is what you will see on order pages. It is a bit deceptive as the timer does NOT come with the decor-style faceplate seen in the product image. You have to buy that separately.

Alternatives:

The commercial series by Intermatic has a slightly different look and a faux brushed-aluminum 1-piece faceplate (In days of yore it was made of metal. In modern times its plastic). These are available in a 4-hour version (model FF4H) and a 6-hour version (model FF6H).

Both models, like the 12-hr version, are SPST

This shorter duration may be a better choice, timewise, for more mainstream, manufactured-ebike batteries that tend to be in the smaller 12ah to 20ah range. That is the good news. The bad news is these versions cost more money and can be difficult to find, even on Amazon where you will see some sellers wanting ridiculous prices for them (the links above are the best prices I could find).

This increased cost is slightly offset by there being no need to buy the next item on the list, the decor-style wall plate cover.

White Decor-Style Wall Plate Cover

This is what you’d think the timer would have come with above but doesn’t. I chose white to match the inner timer plate (which DOES come with the timer). The inner plate fits directly into and onto the ‘decor’ style wall plate.

There is no requirement to buy the linked Leviton brand as all decor-style covers are a standard size.

1-Gang Weatherproof Deep Wall Box

This is what we are going to mount the timer into. Heavy duty aluminum boxes like this are ordinarily used to surface mount a switch onto a wall, like bolting one onto a metal wall or similar. The box will come with little screw-in plugs so the big extra hole in the back will be easy to seal up.

I chose to use the ‘deep’ version of a wall box so I have more room to work in. I also used the larger 3/4″ hole version as again bigger holes are easier to work with.

Two Strain-Relief Connector Fittings

One of these comes out the top of the wall box, and one comes out the bottom. They have rubber gaskets inside and when you screw them down, the gasket tightens onto the cord running thru so it is held fast and can’t be pulled apart without deliberate malice aforethought.

The pictured part above has a metal ring that could be used inside some wall boxes, but in this case we’ll discard it and just screw it tight to the box. I have bought this exact pictured part and used it, but in the pictures below you will see I used a slightly different version I bought locally.

Lighted 12-Gauge Outdoor Extension Cord

Read the specs on this cord via the Amazon link above and you can see it is quite a beefy cord. The SJTW rating means its meant for hard-service, rated for 300v and approved for outdoor use. The one I linked is good for 15a and 1875 watts. As importantly, since I am going to be splicing this cable into a residential/commercial electric timer switch, and those switches typically use 12 gauge wiring, I wanted a cord that also used that same thickness of wire, even though it is by necessity stranded and not solid copper wire.

The seller I linked sells the cord in a variety of lengths. You can decide whether you want a short or long one. I went for 10 feet when I put mine together as that is what fit best from my outlet to my charging station.

Lastly, notice the cord has a lighted end. This will be handy for when the timer turns on the power. We know its hot by seeing the light at the end of the plug.

If you live outside the USA, your electrical cords will be different, so you’ll want to find a similarly overbuilt cord for your project.

Aside from two heat shrink butt-end connectors we will need, thats it for the parts. There is a complete tutorial on how to make reliable crimp connections here. You can refer to it if needed.

Lets Get To Work

Step 1 is to figure out just where on your power cable you want to place your timer box. For my project, since I was mounting the box in my garage I had to measure from the wall plug, to the place I was mounting the timer. I also had to be sure I had enough cord to reach from the timer to my ebike’s charging cable.

So… Using a sharp and sturdy cutter (12/3 cord is not going to cut cleanly with ordinary scissors) cut your power cord completely in half at your desired spot.

Next, cut back the cord insulation without slitting the insulation on the inner three wires. I used a utility knife blade held in my hand, and cut very carefully. Just as important to not slitting the insulation on the inner wires is to not slit yourself, either. This process requires considerable caution. There are specialized cord stripper tools out there to take the danger out of the process.

After this, strip a short length of each inner wire on each side of the cord. The end result should look like this:

With your two stripped ends ready, thread the strain-relief connectors over each end of each cord. Now run the two cords thru each side of the box, one from the top and one from the bottom. Screw down the connectors into the box, but do not tighten down the outer rings, so it is still possible to move the electrical cord back and forth thru them. When you are done it should look like this:

Now its time to re-connect the cord and put the switch in between. Here’s where things get tricky if you intend to mount the box vertically on a wall, as I did. This is where the deep box giving extra room comes in handy.

You only need to plug the hot wire (black) into the switch. The neutral (white) and ground (green) wires can be connected right back together again (note to folks outside the USA, your wire colors will be different and will match an international standard that – of course – we don’t use here in the States).

The neutral and ground wires are reconnected with simple heat-shrink, adhesive marine butt-end connectors. The hot wire is attached to the switch via its simple teeter connectors, which work fine on stranded wire even though they are meant for solid copper. This connection is a big part of the reason I chose thick 12-gauge electrical cord.

When deciding what side goes where, the Line side (male plug end) goes to the power source (the wall). The Load side (female plug end) goes to your charger.

Because of this Line and Load business, and the fact that I was mounting this switch vertically (notice the directional Top markings on the front of the switch) I had to run the top cable to the bottom of the switch (Line) and the bottom cable vice versa to the top (Load). Thats why everything is running around in a circle inside the box.

If you look to the right side of the switch you’ll see Line (2) and Load (2) plugs are there and reversed, which would solve this alignment issue. However, this second set of connectors are dummies lacking the hardware to be usable. They’re just blanks not used by this Single Pole, Single Throw switch.

Once you get to this step, all the real work is done. Carefully move the switch into the box, ensuring the connected wires are not subject to any pulling stress. You’ll want to be tugging back the still-loose electrical cord a little to help make room, but again don’t overdo this. You don’t want to cause any strain on the switch connections, and you have a deep-version of the box so there’s room to fit the cable behind the switch.

Screw it down carefully once its fit into place. The screws to do this came with the switch.

And now screw down the decor cover. Take care not to torque it down too hard as it is a delicate part and you can crack it if you go too far. Next, tighten down the two strain-relief connectors, which fixes the cord in place so you can’t tug it apart.

Those last two steps took only about a minute, and we’re not going to need much more than that to finish the job: The switch comes with a little cheapie hold-down ‘nut’ that is little more than thin bent metal. It needs to be that thin as there are almost no threads available for it to grab. Drop the inner timer plate onto the opening. Tighten down the nut so the inner plate is now fixed to the timer face.

Don’t overdo the tightening. You will figure this out as you see the plate bend inward as you tighten. I used needlenose pliers as fingertips don’t quite have enough grip to do the job.

Next, press on the timer knob. You’re done. You just created your heavy duty timer, that you can use to plug in between your ebike battery, or anything else you want to provide time-limited electrical power.

Now What?

Plug that sucker in and make use of it! This is the part where it becomes handy to have the lighted plug end. Turn the timer on and you’ll see the power come on via the little light. Come back a few hours later and the presence of a light at that plug will instantly confirm the power is on before you even glance at the timer dial.

Ebike Battery Charge Safety: Use A Cutoff Timer

Lets easily add a layer of extra protection to help safeguard your home and loved ones from a battery fire.

We’ve all seen the news reports. When compared to the number of ebikes out in the world, battery fires are extremely (EXTREMELY) rare. But when they do occur they can be catastrophic to life and property.

As a daily commuter who also uses an ebike for an auto replacement, I have been charging daily for years. In fact, since I charge at home and at work, I am generally charging twice daily. So I do a lot of charging, which increases the possibility of a failure, even if it is a small one.

Lets skip to the good part first:
Here is the light-duty timer I use. It costs a whole US$9.99 on Amazon. I have several scattered around at my home, my office and in a couple of garages.

With that out of the way, I’ll spend the rest of my time telling you how to go about using it.

What Kind Of Failure?

I have had chargers fail to stop at the target voltage on three separate occasions: They kept on charging. In one case I was using a premium charger with an 80%-charge setting, that was supposed to stop at 55.4v on my 14S/52v pack. A 52v pack is really fully charged at 58.8v. I walked into my garage and saw the charger with its fan merrily humming along; its little red light telling me it was feeding current into my battery… and it was now at 59.5v. Luckily for me it wasn’t enough to cause the battery to combust, which it could have if I hadn’t walked in and reacted appropriately

The second time it happened was almost exactly the same story. Diagnosis worked through with the charger manufacturer determined an internal component failure. They were prompt with warranty replacements, but who is going to warranty my garage?

What About The BMS?

All drama aside, the BMS likely stopped the battery from accepting the current from the charger at 59.5v. This second layer of safety prevented disaster.

Whats a BMS? There is a layer of protection inside the battery. Ebike batteries typically have a Battery Management System inside that is supposed to stop accepting current if an overcharge is in progress. But if you read the headlines, you already know those can fail too.

As part of my solution to this problem, I started using chargers made for outdoor commercial and municipal use. These units have Mean Time Between Failure ratings in the hundreds of thousands of hours. They are built to work trouble-free for decades.

That is a whole different story explored here: An Ultra-Reliable Ebike Battery Charger.

Add Another Layer To The Onion

We’re going to address the failure-to-stop risk specifically: Plug a countdown timer into the wall, plug the battery charger into it, and set the timer to physically cut the AC power clean off before the battery even has the chance to reach a 100% state of charge, let alone an overcharge. If everything works correctly, this adds significant safety to routine charging.

Whats a Countdown Timer?

Think of a kitchen timer. You want something to cook for 10 minutes, so you set your timer to ’10’ and when 10 minutes expires, you hear the timer going off with a bell. If you have an oven with a cooking timer, it will also shut the oven off.

So What?

Thats what we’ve got here: An oven timer that plugs into the wall, and instead of going ‘Ding’, cuts the power from the wall socket to the charger when time runs out.

What that will do is stop a charger from even enjoying the possibility of failing and overcharging your battery. So we will be gaining two things: First, we’ll be making it more difficult for the charge process to induce a battery to combust. Second, we will be creating a way to charge the battery to a less-than-100% level, which will lengthen its lifespan.

Extending Battery Life

This second benefit is optional, but makes sense to take advantage of if you can. If this is a new topic for you, here is a good explanation of the plusses and minuses of the practice. I have cue’d it up a couple minutes in to skip the technical portion of the explanation.

How Do We Set The Timer?

You may have to go on a short fact-finding mission. You need to know how much voltage your charger puts into your battery in a given time period. You need to either have a charger that displays the current voltage level, or an ebike display on your handlebars that shows current battery voltage (i.e. the display shows something like “46.2” volts instead of showing five bars in a pictograph, which is functionally almost useless, but not uncommon). If you don’t have a voltage display, you will want to fudge one.

Two DIY ways to do this

Use a Multimeter/Voltmeter and take a reading off of your battery leads
Use A Watt/Voltage Meter and plug it inline to your charge plug or cord

I describe the Watt/Voltage Meter in a fair bit of detail in the ultra-reliable ebike battery charger article, so I will, for now, just link you to it and let you take it from there. You can use that information, along with the separate instructions on how to make dependable crimp connections, to put together an inline meter fairly simply. Additionally, you may be able to come across a meter that just plugs straight into your battery.

When we get into the description of doing a robust DIY timer, one of the optional ways to do it will let you directly attach an inline meter.

We’ll discuss an inline meter as seen above, when we describe a custom timer build in a separate article.

You could also use a multimeter, or voltmeter. Those are pretty simple devices you can get for cheap online, or in your local hardware store. You don’t have to spend a lot of money to get one much more accurate than the typically marginal accuracy of ebike displays and watt meters.

Here is a cheap multimeter (US$9.99 at time of publication) that will do the job. I am linking it here chiefly because it has an instruction manual written in understandable English.

For about US$35, you can get hold of a much higher quality product. This unit has a neat feature where the leads you need to plug into for a given job are lit up with little LED guide lights so you can’t screw that part up.

Since I do a fair bit of hobby work around electrical things, I use this slightly fancier model, that runs about US$60. Its a little more accurate, and has a couple of added bells and whistles. Using it I found my voltage display on my Bullitt hill climber was consistently 0.5v lower than the actual battery voltage.

Find Volts-Added-Per-Hour

Now that we have a method of determining battery voltage, lets figure out how much our charger adds in an hour.

I plugged my multimeter’s leads into my battery charge plug. I get a reading of 55.8v. Thats my starting point. I plug in the charger and set an alarm to come back in one hour. My alarm goes off and I hustle back to the bike to take another voltage reading.

57.2-55.8 = 1.4. My charger puts in an additional 1.4 volts into the battery per hour. It is not such a bad idea to run the battery back down and test it again. Go for a third time on general principles. See if you come up with the same number or maybe you want to average three slightly different numbers.

A Worthwhile Detail To Note:
Ebike battery chargers use a method commonly referred to as “smart charging”. Technically speaking, this is what is known as “CC+CV Modes”, where the Constant Current mode pumps power into the battery at the charger’s full current level (usually something like 2 amps). But when the charge starts approaching the voltage limit the charger is set to reach, it switches to Constant Voltage, which slowly ramps down the current being fed into a battery until it gently stops at the final target voltage.

So, bearing in mind the above, we don’t want to be measuring the rate of volts-added-per-hour when we are up near the top of the battery’s capacity, because we will be measuring when the charger is in a ‘slowing-down’ mode.

Now What?

Well, in the above example, if my battery is at 55.8v, and I want to charge it to 100%, I now have an idea how long it should take to fill it up. My 52v battery is fully charged at 58.8v. So 58.8-55.8 = 3. I need three volts. My charger charges at 1.4v per hour … and I know CV mode will slow the charge rate down near the top.

I could be conservative and just set it for two hours, knowing 2.8v is close enough to 3v, and its safer to come up to a bit less than 100%. Or if I need that 100%, I can set it to 3 hours. That is too much time, but not by much thanks to the CV mode slowdown at the end.

In practice, this is a lot more thought than you will need to put into the process on a routine basis. What you’ll be doing is ballparking what you set the timer to, and even if you go over or under by a bit, if you do your part on the math it will not be enough variance to matter if Something Bad happens.

And if you use the timing method to cut power off at a lesser charge state of, say, 80%… you can routinely be off a bit and instead of risking a problem, you’ll end up with maybe an 83% charge. Or 78%. Not enough to matter on most rides.

Myself personally this is exactly how I ballpark my charges with my timer: I don’t worry about getting anything exact and I shoot for 80%-ish.

We Are Ready To Use A Timer

So we’ve done all of our homework. Its time to plug in a timer. What timer should we use? I personally prefer mechanical timers. The old-school spring-wound kind that are immune to weirdness like power interruptions. The kind that are not programmable and are thus not subject to programming mistakes. The kind that need a positive action to set, and are not so susceptible to a little oops like pushing the 4 hour button instead of the 2-hour button. Also a mechanical timer is more granular in how you set it. If you want an extra 10 minutes on today’s charge you just turn the dial another click or two.

Here’s the timer I have been using. Amazon tells me I have bought five of them over several years.

Picture taken at my professional photo studio (i.e. on my garage floor)

Its a whopping US$9.99 at the time I am writing this. I have been using them for years and they work easily and effectively. Is this a robust solution? No it isn’t. Its just a super cheap little timer. Folks on the internet have taken theirs apart and reported the mechanism inside is not very sturdy. In recent weeks I have found my main one at my home is feeling a little worn out when I turn the dial.

BUT its one hell of a lot better than nothing. And if its this or nothing, spend the ten bucks, get this and hopefully you will be a little safer for having it.

If instead you want to try and do this job with something a little better made, then read where I

Build a Heavy Duty Countdown Timer

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. That ties for biggest pack in the fleet with 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 32ah 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.

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 (I paid about $200 for mine which is way less than they are now), 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.

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 add in a little judicious padding. Then 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:

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.
Plenty of silicone X-Treme sealing tape.
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.
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.

Here’s the whole setup, laid out so the cabling is visible (right side). Note the key ring and the little foam dingle-ball that makes the whole idea work. Click to zoom in.

A close-up of the keyring retainer in position. Note the inert (siliconed) XT90 cap over the otherwise open, disconnected battery-to-motor connection.

Whats With The Cargo Net?

With a 20ah battery, two small tool bags (one on each side of the pack) and an electric pump, the interior of the backpack is pretty much full. I found some hooks that work well with this pack on Amazon, and applied them to the pack and the net. Now I have the ability to stuff something onto the exterior of the pack. Usually that is my veteran Condor Summit Zero and maybe a small, flat pouch for wallet and phone if I can’t stuff them into the handlebar bag.

Funky hooks. Kind of a specialty choice that work just for this particular pack’s oddball equipment slots.

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.

Do NOT forget to carry along a safety plug to cap your pack’s power cord when it is disconnected. I am using an extra XT90 male plug where I siliconed over the power leads (and I added another bead once I saw the gap in this pic)

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!