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Dan's DIY ebike blog

 
pollinator
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Location: Jacksonville, FL
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About two years ago I bought the parts to assemble my first DIY electric bike (ebike). I have since built or rebuilt a few more and would like to share my experiences. I started to prepare this info last week but life chaos interrupted me. I'm thankful that Paul brought this topic up on the podcast, as I now have the time to give this the attention it needs. This is such a vast topic and I have tens of thousands of words to write up to convey half of what I want to share, so this is going to be a blog and not a manual. I intend on putting in several hours and dumping several posts in succession.

I want to preface this with two notions. First, I tend to jump into things and figure them out as I go. I have a very strong mechanical and electrical background, as well as experience with construction. I never saw a set of house plans that didn't have at least one discrepancy between different pages and had to figure things out on my own, so I gather information until I satisfy any design questions I have at the outset and run with it. The nature of DIY means using various things of various dimensions. If you need help with that aspect, your best bet is to find someone in person who is handy. This is more of a story of my journey so others can learn from my successes and failures.

Second, I fell (not riding a bike) and broke my skull and other bones in March. If I don't make sense somewhere then please don't hesitate to point it out. I will try to list resources so people can learn from the same places that I did so you can see where I am coming from. I sometimes do things in ways other people wouldn't or even shouldn't, and I will try to point these out and alternative methods to reaching the goal of a functioning ebike.

At the outset of my ebike building journey I was using an old but decent shape mountain bike. I almost made the mistake of buying lead acid batteries because the cost of new lithium ion batteries was too high and you can't tell the quality of the cells from most places. Things seem to have gotten a little better nowadays, mainly because people are willing to pay more for better quality and the market is providing that quality, but it is still possible to spend a lot of money and get ripped off. I guess the easiest way to ensure you get a quality product is to buy a name brand ebike, but those things are thousands of dollars. Most of the ebikes in the ~$1200 and under range tend to not be much better than a DIY ebike, have custom parts that are costly or impossible to find should they break, and you can't just transfer all of your parts to a different bike should you decide to upgrade in the future (I would strongly advise you use a bike with tubes and brakes that are easily sourced. You don't want to have an expensive paperweight because you can't find common parts that wear out from normal use).

Everything changed when I found out about used lithium ion batteries. Most batteries seem to either sit around hardly used/unused or get decommissioned when they have lost less than 20% of their original capacity. You can also greatly extend the life of lithium ion batteries by not pushing them to either extreme of fully charging or fully discharging the cells.

That last point is very important. I almost never fully charge or discharge my cell phone and have little discernable loss in battery life after 4 years. If you currently have a laptop or cell phone and find yourself constantly pushing it to the extreme all the time, and expect to do the same with an ebike, then you won't extract nearly as much value from buying used batteries. Or any battery for that matter. The faster you charge or discharge a battery, the more heat it produces since it is making a chemical change to store and provide power. Always charging to 100% and pushing until the battery is dead will severely reduce lifespan. It's possible to extend the life of lithium ion batteries by 7 times or more if you generally plan to only use around 60% of the total capacity, and only pushing to the extreme when you absolutely need it. Lithium ion batteries are pretty forgiving in this respect, but anything that is abused will have a shorter useful life. I would strongly advise building a much larger battery pack than you generally need, or make multiple packs to switch between versus expecting 100% capacity for every trip. If you plan for where the battery capacity is going to be in a few years then it will serve you well. If you expect more from it than it could ever give then it will be a bad experience from day one.

I caught wind of Battery Hookup on YouTube and followed the advice of someone to buy a certain type of battery pack that had the same voltage (36V nominal) as what I wanted to use on my bike. There were some things I didn't know at the time that caused some headaches involving the battery management system (BMS). Firstly, it isn't advisable to use multiple BMS's in parallel. In some cases it may work fine, but I would personally use one BMS, or use separate packs and switch between them. If one pack can't power your bike by itself then you can combine two packs and control it with a single BMS of sufficient output. Because an ebike motor is an inductive load, it can have current surges that are substantially larger than the nominal current draw specification, so I would recommend going with at least 30% higher BMS capacity. For instance, a 22 amp motor plus 30% (6.6 amps) is 28.6 amps, so a 30 amp BMS should work. A 25 amp BMS might cut out under heavy load. A 35 amp BMS might be an even better idea. You can always use a fuse of the same rating as the BMS or smaller if you choose. Too small of a fuse can be easily replaced. Too small of a BMS will definitely cause a lot of headaches.

The first batteries I bought came in smaller packs with a lower power BMS and the info I was given was, "Put two in parallel and it will work." Well, it sorta worked, but I couldn't hold the throttle down for more than a few seconds at a time, and it was worse at slow speeds where the motor was straining. I initially thought there was a problem with the motor controller and bought a replacement, but still had the same issue. Eventually I figured out the problem and learned enough about building battery packs to make my own. I took 4 of the smaller packs I bought to combine it into one large battery with 40 miles of range. I've tried the pack out on two extremely different bikes and still got the same range when testing. I live in Florida so this was on flat land on days with no strong wind.

Obviously I invested a lot of time learning to make this battery pack, but I probably spent around one third the cost of a new pack to build this one that has about 85% of the original rated capacity. Plus I can carry that knowledge forward to build my own packs and maybe help others to put them on a path to reaching their own ebike goals.
 
Daniel Schmidt
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Location: Jacksonville, FL
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Now that I've given a run down of how I got started, let's take a look at some of the resources I used to learn and what parts I have had success with. I'll start with Battery Hook Up. batteryhookup.com has been great for me. I have purchased batteries from them on several occasions now. Shipping has taken under a week and packages have shown up undamaged. You can certainly find people online complaining about packages showing up damaged, and maybe they weren't as thorough about securely packaging things in the past, but my experience has always been positive.

Because of the nature of the business, they buy in lots and once something is sold they may or may not get any more. There are certain batteries that exist in absurd amounts, but take labor to extract (for example from all of those scooters that got plastered across cities and then banned). Others are backup batteries for critical infrastructure like telecommunications or medical devices, and there will be waves of these hitting the used market as they get decommissioned. Other times there will be packs made for a specific product and because of a design error they don't fit. Instead of redesigning an electric car, it is cheaper for them to sell the battery packs and buy new ones that fit. While you can find plenty of batteries in like-new quality, others may have been more heavily used and are usually sold at a lower price to reflect this drop in quality. For certain applications such as DIY ebikes or small off-grid solar, this can sometimes be one of the best deals. I guess the hardest part is figuring out what you want and waiting for the right time to get it. I've been very lucky that each time I bought batteries was right before they sold out of what I wanted. There are always battery packs of the same or similar type coming and going, and if you miss out it could be months before you find exactly what you want again.

Batteries come in many forms. From massive packs to a single cell. Some come without a case, some have a heavy duty case that is difficult to open or too oddly shaped to use on a bike. Some packs are sold knowing there will be some dead cells and a bad BMS, others have a guarantee that everything is functional. Some cells are metal cylinders, others are pouches. Some are not much bigger than my thumb, others are larger than Kindle tablet.

There are also different battery chemistries. I personally would suggest sticking to lithium ion (Li-Ion) because they are the easiest to use and are perfectly safe when used with proper safety equipment like fuses and a BMS. It is equally possible to make a very safe battery pack or a very dangerous one. Some of the methods I have employed in the past were not at the peak of safety, and you can find many more stories about how not to do something than you will about things actually going terribly wrong. There are far more armchair safety experts that spread doom and gloom without any experience than ones with experience. I will point out my mistakes and encourage others to do what is best for them. I've done thousands of things in my life that weren't by the book, but I had enough knowledge, understood the odds, and take my chances carefully. I briefly played the lottery when I was young and quit when I had more money than I lost. Being aware of the odds of any situation you find yourself in is better than being unaware.

I currently have no intentions of messing with other battery types at this time. Most of them have drawbacks (lower power density, higher price, charging restrictions) that don't fit my gear or my use case. There are tons of resources elsewhere to learn more, just be aware of the pro's and con's before buying.

While I have only used Battery Hook Up, I have seen others on YouTube building packs for various projects from a number of other places and nearly all of them have been happy customers. The vast majority of times that I have seen someone unhappy it has been because they didn't understand what they were buying and were sore about it. Heck, I wasn't the happiest person when I realized I had to reconfigure my packs and buy tools and supplies to make things work properly, but I was fed bad information from a YouTube video. I wasn't really mad at anybody and I'm thrilled with the price to performance ratio with what I have now.

There is another place to buy batteries that I haven't tried, but the guy has tons of informational videos. I do intend on buying from him in the future, kind of as a 'thank you' for the info he provides. Jehu Garcia's channel has lots of info for all sorts of battery setups, from cars and ebikes to power walls for houses. He often has the same types of batteries that many other sellers have, as they all buy by the pallet at auction from some of the same resources.

I already have tons of experience with electrical (2 years of school, 2 years apprenticeship, rewiring cars, 10 years of powering small things from solar in my shed) so the places I go to for information tend to go far above and beyond what is needed to build an ebike battery. I would strongly encourage anyone interested in this to learn all that you can or find someone knowledgeable. These things can be quite complex and require strong math skills and experience with batteries, wiring, and proper safety. I can't tell you how many times I've seen someone with a car try to do what worked for somebody on YouTube, possibly even got things working temporarily, and ended up towing their car or dragging me and my tools to try to fix it. I almost always just undo whatever they did rather than try to make a poorly designed system work. "Everybody's got a car, everybody's got 12 volt systems, this stuff is easy!", and they have an expensive paperweight. The world has more and more paperweights as we use less and less paper.

I don't want to discourage anyone from wanting to try new things, but this is an investment. It takes time, tools, money, and learning a few lessons the hard (and often expensive) way. I've sent a few things up in smoke in my day, but I've gained enough skills where I spend a great deal of time keeping things from being scrapped. If you are only looking for cheaper batteries, but don't want to make an investment of time or money, then I would strongly encourage you to find someone else who can benefit from this information and possibly help you with your ebike goals in the process. The key to cheap cost, reasonable quality ebikes is cheap price, good quality batteries. Buying the batteries is easy, assembling them in a way that suits your needs is the part that takes a substantial amount of knowledge.
 
Daniel Schmidt
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Next up I am going to dive into the non-battery components needed for a DIY ebike build. This is going to assume you already have, or at least have in mind, a bike which will be the platform you build upon.

One of the first things that needs to be decided is what type of drive system you want to use. Old brushed motors made for lead acid systems with a wonky chain drive are out of the question. Every one that I have seen was a far inferior product to a brushless motor, and the minimal cost savings doesn't seem to be worthwhile. With brushless motor systems there are generally 3 types - front hub motor, rear hub motor, and mid drive motor. While there are DIY mid drive options, I will not be covering them. There aren't many DIY options, some of them require frame modifications or a custom frame, they are in general much more difficult to install, and I have never ridden a mid drive bike.

Initially I was going to build a brushless rear hub motor ebike, but at the time the one I wanted was out of stock, I really wanted the cheapest minimal viable product as a functioning proof of concept, and then next one up in price was more than I wanted to spend. I begrudgingly bought a brushless front hub motor kit. I cannot tell you how glad I am that I got that kit! I know things will be different for everybody, but at my age I am really starting to appreciate giving things an honest try before saying you don't like something. If you haven't ACTUALLY given it a seriously try, then you don't ACTUALLY know.

My favorite part right away is that when you hit the throttle, it forces the bike to understeer and stand up straight coming out of a turn. With a rear drive, there is a certain point where you hit the throttle and it wants to fold the handlebars and kick the rear end out from under you. I've purposely pushed my newer rear drive bike to the limit on several occasions and I can tell you if I hadn't been fully prepared for it that I would have been thrown to the ground. I live at the beach in Florida and there is a fair bit of sand at the intersections of every road. This means every turn you make is on ground with less than ideal traction. As long as a car isn't coming the other way I can hit full throttle starting into the turn and the wheel will feel like a front wheel drive car in the snow. It understeers and powers through. Obviously, this isn't something you want to do all of the time as it is nice to stay on your side of the road and spinning your tire will cause excess wear. But it's really nice to know that if my balance is a little off or there is more sand than usual, I can just throttle my way out of the predicament if there isn't any oncoming traffic. Don't get me wrong, I love many other aspects of my rear drive bike, and having a heavy hub motor on the front means using more arm and shoulder strength to control a front drive bike, but I just love the way it feels in turns.

Installing the front hub motor kit was pretty easy. It comes with new brake handles that have cut off switches so you aren't accidentally pushing forward while trying to stop. You don't 'have' to install them but I would strongly advise you do. The kit I got had no display, which was fine by me. I just measured the battery voltage and used a preset path of known length to gauge my range. It came with a throttle and a sensor for pedal assist. Unless you have a problem using the throttle I really don't see the point of pedal assist with this setup. I can twist as hard as I want or pedal as hard as I want, and mix the two as I see fit. Because it is front hub drive and rear pedal drive, it is effectively a two wheel drive system, so you have more traction than a rear pedal/rear hub design.

I already had a DIY cargo shelf on the rear of my bike consisting of 2 aluminum angle brackets tying down into the frame where the rear wheel bolts on, and a piece of scrap pressure treated plywood I found and cut to fit the bike with a funky setup to clamp it to the seat post. This sat a little low down to the tire, so I made a bracket to lift it up a couple inches and cut up a rectangular cat litter bucket to stuff my batteries in and slung it under the shelf, just above the rear tire. I screwed the motor controller to the bottom of the shelf behind the battery box, routed the wires from the front to the back with cable ties, and it worked!

I immediately had to replace the brake cables and pads. The rim brakes are barely adequate at stopping the bike when they are perfectly adjusted. It seems like every bike I've looked at had flex in the frame around the rear brakes when they are applied hard, and as such never seem to stop as well as the front brakes. Maybe the bikes I've seen are just lower quality. It does look like someone with some skill could make a large metal plate with a huge cutout for the wheel to fit in and bolt/clamp to the frame in that area to reduce flex and increase braking power. There are also DIY caliper mounts for disc brakes, and the hub motors all seem to have a place for the disc, but I'm thinking the welded on mounts are far superior to clamp on brackets. My newer bike with front and rear discs is much larger yet slightly lighter, and brakes so much better than the old steel frame mountain bike. The disc brakes come with their own set of quirks, but they stop the bike very well.

As for the actual kit, I just grabbed the cheapest brushless front hub motor kit available on Amazon at the time. I've easily put over 2,000 miles on the setup and other than the battery management system issues with the first battery packs, it still runs great. There are two types of hub motors - geared and gearless. The geared ones are a bit more expensive, smaller in hub size and weight, and have a lower top speed. My rear drive bike is a geared type and does about 19 MPH, whereas the 2 bikes I've built using the gearless front hub motors are heavier, slower off the line, but top out at about 23 MPH. In both cases it seems that the motor controller is limiting the RPM, as I can load the bike up pretty heavily and still reach the same speeds. Both are considered 500 watts, although for various reasons I will delve into later, the rear drive one is more comparable to a 350 watt motor.

The exact kit I bought doesn't seem to be available, and the prices have gone up a fair bit since that time, but most of the kits are similar. Some have different wheel sizes and different voltages. I'm using 26" wheels with 36 volts nominal batteries. It is possible to find a motor controller made to handle a certain wattage motor and different input voltages, which is what I ended up doing with my rear drive, but that story is for another day. I will have to take a bunch of pictures and explain how all of that went down tomorrow.
 
Daniel Schmidt
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Location: Jacksonville, FL
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I'm currently in the process of getting ready to tear down and rebuild all of my bikes at the moment, so I went ahead and took a few pictures to let people see where I came from and where I am headed. I've recently come across a few of older bikes in really good shape with aluminum frames. Some of the old rubber is shiny but cracking, and the brakes need to be replaced, but once fixed up they should be decent transportation for getting around the beach.

This was the bike I started with. It was given to me about 15 years ago by someone moving away. I would occasionally get on a kick of riding it around, always thinking of how to electrify it with lead acid batteries but it never seemed worth the headache. Once I got it set up with the brushless front hub motor, I started riding it around constantly. Rode it so much I wore down the tire pretty far. It wasn't the best tire ever made, but it was soft and grippy. Certainly better than my other tires. Not too bad for something thrown in with the motor kit.

You can see the hub motor up front with a different tire, and the wiring all wrapped up on the handlebar as I start to harvest it for parts. The large gap between the rear deck and the tire held the battery and motor controller. There were a lot of things patched together to make the thing run, and I certainly got a lot of use out of it. The brakes were barely adequate, and one of the main reasons I am decommissioning this ride is because the lighter bikes can stop a lot quicker. There are tons of other benefits, but being able to stop safely from full speed is my main goal.

I'm also really partial to step through bikes when trying to drag any cargo around. It is a major pain having a load tied up high on a bike and having it want to spill over as you attempt to get on. I know there are a ton of other changes I need (and plan) to make regarding cargo and battery placement, but it is really nice to easily step on, and makes it easier for others to try out my bike, especially if they aren't as tall as I am.
FirstBike1.jpg
Old bike now being used for parts
Old bike now being used for parts
 
Daniel Schmidt
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Next on deck is one of a pair of bikes I am fixing up. They were basically bought new and put away in a garage for over a decade. A bit of rust on the chrome and rot on the tires, but the frames are in very nice condition. I currently have it strapped together just to make it work and use it as a backup for my main ride.

The battery attached to the rear tray in the cardboard box is very small for the task (36 volts nominal, 8 amp hours), and it is the first battery pack I built with individual cells and a battery management system. I spent over 6 hours assembling that small thing, but I get about 16 miles out of it, and the high current draw cells have no problem dragging me up and over a large bridge completely by itself if I decide not to pedal. I've had tons of fun piecing things together and pushing them to see what they can do, and so far I've been really happy with the performance.

My goal is to start making front 'baskets' that do not attach to the handlebars, but rather to the frame itself. I hate the feeling of a heavy basket as I try to steer and feel like I can barely control it under any condition that isn't perfectly straight. I've tried making a few prototypes that have all been failures. Not so much that they didn't function, but that they didn't look good. I seem to have a huge disconnect regarding other people's perception of positive or negative looks. I guess there is an uncanny valley where something very 'homemade looking' has a charm to it, but nothing I make ever captures that charm. I usually try to go for more of a professional look, but I don't have a factory of people and equipment to turn out my ideas, just myself and the tools I have on hand. I always go for function first, and most people I encounter seem to be of the form first variety.

After attempting two different styles and having to abandon them due to cost reasons, I extremely reluctantly bought a tool box to store important electrical bits. I'm glad I waited and found something better than the options other people told me to get, but I guess time will tell on that one. I was told to buy a fishing tackle box or some other stuff I though would be terrible. I either wanted something that matched the colors on the bike, or simple plain black. I don't know much about matching colors to make 'pleasing' combinations other than countless previous instances of negative remarks from others for getting it wrong. I couldn't possibly see some random tan, grey, or green (or mix of such colors) looking good, so I got this Harbor Freight Apache Case. I'm currently modifying it so I can add a headlight and turn signals, and bolt it to the front of the bike and possibly make a custom basket on top.

As it is, the bike is really fun if you disregard the horrible beach cruiser handlebars. The sweeping shape may be pleasing to someones eyes, but burying your elbows in your sides like a T-Rex and bending your wrists outward as far as they can go while bounding down the road is unpleasant at best. The acceleration and deceleration are really great, and the only thing missing is lights. Motorists around this area tend to either abandon all reason and slam on their brakes when they see a bike, or get aggressive with yelling and horn honking. And after seeing how bicyclists here tend to also be aggressive or completely carefree, I can see why it is a problem. I feel that if ebikes had turn signals like cars it would grab attention and be more obvious from a greater distance. Being the one with metal between my legs instead of wrapped around me, I want my intentions on the road to be obvious.

I bought several 'used' battery packs in perfect condition so I can add lights to several bikes, and I figure it could be used similarly to a car, where I could add a phone charger, radio, or other small power draw devices of convenience. I even made a power pack with four of those 8AH batteries in series to power a mini air compressor. Not that you need something that overkill for a bike, but it has come in handy on multiple occasions when journeying out to work on a car. I feel like this space has tons of room for growth and innovation, and I want to be there to see and help construct this foundation.

StepThruBC1.jpg
Step through beach cruiser ebike
Step through beach cruiser ebike
 
Daniel Schmidt
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This time around I am going to give an overview of what I did to get a used ebike working. I think this might be the way a lot of people would want to go if they aren't willing or able to afford a brand new ebike, and with sales of ebikes going through the roof, there will eventually be more and more deals somewhat comparable to what I found.

My goal was straightforward - I wanted a fat bike. I was willing to do all sorts of things (and still working down some of those avenues), but after seeing just how absurdly expensive or complicated (meaning special tools, ultimately leading to complicated = expensive) I decided to hunt craigslist to find my fatbike. After many months of searching I managed to find a good deal and jump on it before it disappeared.

While this wouldn't have been much of a deal for someone to fix by replacing with OEM parts, this thing was a screaming deal for me! The reason for the deal was pretty simple - the previous owner put about a thousand miles on it exclusively going up and down the beach, and one day while wading in the ocean a wave hit it and knocked the bike over. It worked for a little bit and then the charger went up in smoke and the thing wouldn't run. I knew just buying the wheels complete with tires and tubes would cost in the neighborhood of what I paid for the whole bike, so I was determined to make this work.

I dragged it home on a Friday and by midday Sunday I was testing it out. The original battery pack had a small amount of water damage, enough to ruin a few cells. Of course I didn't have any cells to fill in for the bad ones, and reconfiguring the pack was a task for another time. So I used what I had on hand, my spare 36V 8AH battery pack from the previous post and a spare motor controller I bought for my first bike when I thought it had a problem. This bike was a 48V system, but I knew the motor would work at 36V and the new controller works with both voltages. The old controller was also messed up pretty bad and was extremely small. The new motor controller was larger, so much so that I had to modify the case and tap it in to place with a block of wood. I do intend on changing the setup down the road since there is no way to keep the large controller in there without the big connectors hanging out the top hole, and it is far from waterproof. Then again the original setup was supposed to be waterproof and the Atlantic Ocean strongly disagreed.

The rear brake cable had completely seized and the front was on its way out, so I ordered new cables. Eventually I will have to replace the pads and the calipers have some wear from the harsh conditions and have to be treated with Liquid Wrench lubricant regularly. I already refurbished one pad that came apart with a piece of automotive brake material I cut out with a coping saw and some JB Weld. It makes a bit of noise at medium brake pressure, but it grabs hard and quiet when more force is applied.

I really like the adjustable gooseneck. This bike, being a beach cruiser style, also had those outrageously terrible boomerang shaped handlebars which were immediately tossed to the side. I had found a mountain bike beaten to bits in an area where garbage is commonly dumped that had a few useful parts, including the handlebars which make this bike feel so much better. The upright riding position and step through design make it so much more enjoyable to ride. No more neck or back pain, no more worrying about spilling over. I do have to be careful with the new battery pack being dumped in the basket the way it is, because if you leave the wheel straight the weight will invariably swing the front assembly to the side with the slightest of disturbance. I will be replacing that with a frame mounted design after I get all of the quirks worked out on the other pair of bikes I am fixing up.

As is, this thing is an absolute beast going down the road. The only noise you hear is the low growling of the tires since they aren't a street tread. The original mountain bike I heard nothing but complaints from people about how it looks and this thing seems to be much more socially acceptable. I'm just so much happier with the comfort. Sometime in the future I will probably buy a new front suspension fork so I can ride a little bit harder without destroying the battery pack. I mostly baby the thing and have probably put around a thousand miles on it this year. It would easily be triple that if I hadn't been laid up with injuries all spring, because this thing feels like a Caddy compared to my first bike. It begs to be ridden and I oblige.
BigCat1.jpg
Refurbished Fat Bike
Refurbished Fat Bike
 
Daniel Schmidt
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Location: Jacksonville, FL
83
tiny house solar woodworking
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Today I want to get into some of the details regarding lithium ion cells and my thoughts on what are good practices for ebikes. There will also be a lot of crossover for solar. I haven't actually made a lithium ion only solar power setup, but I have used my 145 watt panel with a pair of 50AH gel cell batteries that were donated to me to charge my laptop, cell phone, and a couple USB boost packs that all had lithium ion cells, so I do have experience in this area.

I mentioned previously that I had made a smaller 36V 8AH pack as a backup to extend my range. Normally this would be a bad idea with standard output 18650 cells (the kind that look like oversized AA alkaline batteries). The reason for this is voltage drop. Even if you go by the specs of the cells and it says it can provide a certain amount of current doesn't mean you won't have problems trying to design a system that will expect over 90% of that current. Batteries have chemicals in them that take time to react. Pushing them to their limit regularly not only causes excess heating of cells (which is why you mostly hear of high performance EV's and high power electronics having battery fires) and shortened cell lifespan, but the cell voltage will drop substantially. This means under heavy load you won't have the same amount of power that you would with cells not being pushed as hard. It also means that the low voltage cutoff of the motor controller will kick in sooner because the voltage drops below the minimum voltage threshold.

In my case I had bought cells much larger than typical 18650's and they were designed to output much more current than what I use without experiencing significant voltage drop. They had a great deal on them and it's cheaper to ship them in bulk, so I bought 80 cells. I used 10 in series (3.6V nominal for a 36V pack). For a one-off as my first pack it was a good learning experience, and it is great for a secondary pack I can take with me to extend my range. In my case, all of my bikes tend to get about 2 miles for every 1AH of battery capacity (on flat ground and other conditions specific to riding in my area). One of the things about buying used cells is finding good deals when they come along and jumping on them. There are a lot of pro's and con's to using these cells. While I do plan on using the rest for a large trike, I wouldn't use them for a bike because the cells don't lend themselves to being assembled in a shape that is good for most bikes.

The 18650 cells (the number stands for 18mm x 65mm, 0 for cylindrical shape) do have a bit of wasted space when trying to pack them together, but the numerous small cells allow for many different configurations for the overall shape of the finished pack. If you look at the packs made for certain bikes, they are sometimes stacked up to make a triangle to fit inside the frame of a bike. That plus the availability and low cost makes the 18650 cells a good option for an ebike. In my case I have been using 36V systems, and there are all kinds of various scooter packs of that voltage so you don't have to start from scratch assembling each individual cell if you don't want to go that route. Many scooter packs are a bit too small for running an ebike by itself. One option is to get multiple packs and attach the cells in parallel. For instance, I built a pack from 4 smaller packs of 10 in series and 2 in parallel (10S2P) to make one with 10 in series to keep the voltage the same and 8 in parallel (10S8P), increasing the total AH of the pack and all of the benefits that come with it (increased range, less voltage drop, less battery heating and stress for longer life).
 
Daniel Schmidt
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Location: Jacksonville, FL
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tiny house solar woodworking
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The next handful of weeks should be quite hectic. This week I have a few bike specific goals planned and then more bike plans mixed in with other projects. Without getting too far ahead of myself, I'm going to try to rebuild the dead battery that came with my fat bike first, followed by fixing up the sibling of the red and white bike above. I already got most of the parts in for the bike, and everything for fixing the battery pack. I haven't quite figured out how I'm going to go about fitting it back in to the bike, as I rewired things to get it running when I bought it. I might just go ahead and tear the fat bike apart and fix everything some time soon.

But for now the battery pack is on deck. It was going to be around $550 plus shipping to replace it which is why I was able to buy the bike for cheap. Since it had ocean water damage, I opened the pack shortly after bringing it home. Water had damaged the bottom of the pack, causing corrosion on some of the cell interconnects. Unfortunately a few of the cells had also started to leak, and the BMS (battery management system) died as well. I decided the best course of action would be to reconfigure the battery from 48V to 36V.

The original battery was a 13S6P configuration, or 13 sets of 6 parallel cells, each strung in series. I removed 3 sets of 6 cells to change it in to a 10S6P battery. This leaves me with a battery that is still pretty decent (36V nominal, 12AH) and removes most of the corrosion. The areas that were still corroded on top I sanded, cleaned with vinegar, and repeated until it was mostly clean. I may end up having to solder one small spot where the bridge between two cells was significantly weakened, and use a few dabs of anti seize on the other spots to protect it from corroding further. I will have to check it out after a while and make certain it doesn't start rusting again. I'm hoping to get a spot welder and nickle strip for future battery packs, and may need that stuff to go back and fix this correctly. I'm pretty confident it won't be a problem in the short term, but I won't leave it for years on end without giving it a good look.

In any event, I only have two major tasks left to get the battery functional - Add in the BMS and reconnect the cells where I lopped off the end. Because I removed an odd number of parallel packs in the middle of the series string, I have positive next to positive instead of alternating like they used to. I need to run a wire around to the opposite side to reconnect the string and get full voltage from beginning to end. After that I will remove the old BMS wires and put the new ones in place. I've been using XT60 connectors on all of my batteries because that is what I had on hand from playing around with some solar powered devices, so I'll end up using that again. They are common amongst the RC community and with the relatively low amp draw (under 30A) of my bikes it seems to work perfectly fine for my needs.

I also ended up with enough good cells to make a 5S2P pack which would be comparable to a so-called 20V (4AH) pack used on cordless tools. I haven't bought a BMS for doing that yet, but with several different bikes, solar, and tons of cells floating around, that project is going to be put off for a few months.
FatBikeBattery1.jpg
48V battery chopped down to 36V
48V battery chopped down to 36V
 
Daniel Schmidt
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tiny house solar woodworking
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Daniel Schmidt wrote:The next handful of weeks should be quite hectic.



Boy was that an understatement! I got busy with work for a few weeks after being down for a good chunk of last year, caught the plague which put me down for nearly 3 weeks making me even further behind, eventually started to get caught up and had serious plumbing issues which had me redo all the main lines in the house, broke my leg and still didn't have hot water, continued fixing the plumbing, and now haven't been able to walk without a crutch ever since. I still have issues with my leg, but I'm finally able to be upright for more than a few minutes at a time and start getting some things done, so I have been doing what I can and it is time to start this blog back up.

While I haven't completed many projects, I have gathered tools, supplies, and info which is really shaping things up into the form that I have envisioned for a long time. I'm confident that with a bit of practice I can finish converting an electric bike with consistent results and have a finished product that I can genuinely be proud of. Looks aside, I am my own worst critic when it comes to making something perform to my expectations without spending thousands of dollars to get there. Granted, much like the supposed 4 billion dollar electric scooter industry, this isn't infinitely scalable, but I think it will work out and I have some ideas on how to augment things in ways I'm very excited to share once I'm able to get started on those endeavors.

I actually started off writing the last paragraph as, "I haven't completed any projects" but that was incorrect. I had an ebike project thrust on me that I kinda wish I never did, but it galvanized me to stick to doing things the way I have been and not to do something with a low chance of success. Perhaps the things I learned will be even more valuable to others, so I'm going to make the next post about that bike to keep this one from getting absurdly long. I have stuff written up, but still need to take a picture (I'm terrible at remembering to do that) and hopefully make some progress on the next project today.

Overall I'm really happy with the things I have lined up. I rewired my fat bike with a new controller and need to mount the battery box and build a new battery pack for it. I still never finished the other pack, although I now have all the parts to do it right. I also need to work on the headlight and turn signals. I have already tested the parts and very happy with the results, so it's just a matter of setting things up. Since I can't really ride it safely, I am going to put in effort over the next week or so to get a different bike completed. It's pretty close to finished except for the terrible handlebars. I've finally decided to just buy new ones which will take over a week to show up, and with a bit of luck and effort I will have everything else done by the time the handlebars show up.
 
Daniel Schmidt
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This time around I'm going to detail some of the stuff I did to convert another beach cruiser to electric. Someone had gotten the cheapest brushed motor kit as a gift and enlisted me to make it work. Those kits are hot garbage and not meant for beach cruisers with their coaster brake, and I knew this would be a disaster, but they insisted. So I spent a few days fighting with that, making modifications that couldn't be undone without replacing the entire rear wheel, and after getting it really close to working, it reached a point where I would have needed to spend even more money and effort on a bike that was going to need constant attention and tinkering to keep going. In the end I realized it would be cheaper and far less frustration to just set the brushed motor and controller aside for another project and get a brushless hub motor and controller.

One of the reasons I went as far as I did was because I had heard about the first ebike Paul bought which had the batteries walk off. I looked into building a battery pack to ship up there, but apparently I would need a special license to ship a battery of that size. I considered making it as two separate pieces, but thought better of it. The bike also has non-standard connections and the brushed motor issues, and all of that messing around would make it impossible for most people to ride without turning into a disaster. Sometimes discretion is the better part of valor.

At any rate, I went ahead and built a battery box for this beach cruiser of the design I had been wanting to try out. The only issue that I have had so far is that the bike has a short light frame, had no kickstand, and makes the bike a little too front heavy when stopping. If you lean forward at all while trying to use the rear brake, the tire just slides and does very little stopping, and in an emergency it could throw you over the handlebars. The intended use for this bike is to pull a trailer around at the beach, and I added a little tray to the back so it can be loaded up even without the trailer and be safer while braking. It really isn't safe to be approaching any intersection at over 10MPH anyway, so it shouldn't be much of an issue. I may add several ounces of used car wheel weights to the back to help out with the balance. This won't be a problem with any of the other bikes and trikes I plan on building, but still good to know in case I or someone else ever tries this on a bike with similar size and balance issues.

It turned out not to have any understeer. It feels great going through turns, and I can only imagine how it is on a bigger or more balanced bike. After dealing with my fat bike having the battery in the front basket and the steering problems that caused, having the weight firmly bolted to the frame is a complete game changer. To me it completely eliminates steering issues by attaching it to the frame. The only problem I have found is that the handlebars will invade some of the space over your front basket while turning. I'll have to see how the fitment is with different handlebars and goose necks.

I also noticed a certain relationship between the geometry of the bike frame and how I went about mounting the arms that bolt to the frame and stick out over the front wheel. Pretty much everything about this beach cruiser is worse than any of the other bikes I have around, and after playing with it a bit I understand a lot more. Initially I was gong to make the mounting way more complex, but while working on that I realized it worked fine just resting the bars down on the bearing cups and bolting everything down tight so it wouldn't move. This was my first time building it this way, and it fits and functions more than 90% of the way to what I had thought it could. I couldn't ask for much more out of my first functioning prototype.

BeachCruiser1.jpg
Beach Cruiser with Battery Box
Beach Cruiser with Battery Box
 
Thanks tiny ad, for helping me escape the terrible comfort of this chair.
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