One other disadvantage of lithium batteries that isn’t talked about often, but should be, is their potential for theft. Lithium ebike batteries have become huge targets by bike thieves as a result of their combination of small size and high price tags (the same factors that keep shaving razor cartridges behind lock and key at the drug store). Thieves see an easy target and ample resale market, meaning you have to be extra careful about locking your ebike up and leaving it alone in public.
When comparing between battery chemistries, one of the most relevant metrics is the Energy Density in watt-hrs / kg. This figure says how heavy a battery pack will have to be to achieve a certain range. For Lead Acid it is 20-30 whrs/kg, for NiCad it is 35-40 whrs/kg, NiMH is 50-60 whrs/kg, Li-ion is ~110 whrs/kg, and Li-Polymer is up to 160 whrs / kg. Knowing these values makes it easy to project the weight of a pack without having to look up data from the manufacturer.
I would not recommend trying to use a 36V charger. The voltage will be way too high and damage either the charger, battery, BMS or all three. Always use a charger that is matched to your pack’s actual charge voltage, which in your case is 22.2V DC.
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Charge voltage for li-ion cells is 4.2V per cell maximum. So for a 36V 10s battery you’d want to charge it to a maximum of 42V. Charging slightly lower will increase the life of the battery, but isn’t a requirement.
Now you have the required specs on the pack, namely its voltage and capacity, so it’s a matter of finding one that meets your budget and weight restrictions. To a first order, for a given voltage and capacity, NiCad will cost twice as much as lead acid but come in at half the weight, NiMH will be 30% lighter and more expensive than NiCad, and lithium will be twice the cost of NiMH and a further half the weight again.
Nickel Cadmium was the old standard for rechargeable consumer cells in the familiar AA, C, 9V series. They are known for robust characteristics, a good cycle life, and high discharge capabilities. They are still widely used http://usebikeparts.com cordless power tools, R/C toys and similar applications that demand large currents, but for nearly everything else NiCad’s have been replaced by NiMH and Lithiums.
Whether you’re shopping for a turn-key commercially available electric bike, or trying to find or build a good battery for an e-bike conversion, being able to find the right battery for an electric bike is a difficult task. The right battery pack is the most difficult part of the e-bike equation. Keep in mind that even if you’re buying a turn-key electric bike, the lithium battery is more than likely the most expensive component in it, and…not all lithium batteries are created equal, so you should know what you are getting before you buy the ebike.
Why does this formula work? Think about it: heat shrink (unless stated otherwise) usually has a 2:1 shrink ratio, so if I need something with less than twice the circumference (or perimeter rather, since my pack isn’t really a circle) of my pack. Since large diameter heat shrink is quoted in half circumference (flat width) sizes, and I want heat shrink with a circumference of a bit more than the perimeter of my pack, then I know I need the half circumference size to be a bit more than half of my pack’s perimeter, which is equal to the height plus the width of my pack.
It was an interesting project to say the least, particularly how to link the Ch- and the P- from the BMS taking its B- from the 7s negative termination to the positive of the 6s group, given that there are two routes (i.e. charging and discharging), so connecting both simultaneously would override the function of the BMS.
To answer your question, you can definitely build your own auxiliary battery. It looks like they used a fancy right angled female XLR connector, but I imagine a standard female XLR connector will fit just as well. I’m not sure if you’ll be voiding your warranty though by connecting your own battery. Those XLR connectors can be purchased all over ebay and probably even at your local electronics shop.
I have come to the conclusion that a 48v battery would probabky be sufficent for my needs. I need to ride continuously for at least 7-8 hours–but prefer up to 10 hours– at 15-20mph everyday. Although I also need a top speed of 30mph, at times. If my math is right, in order to accomplish this I need to build at least a 14s8p battery. After running these specs through a simulator I found that the power starts to drop at about 1150 watts and 20mph.
So I’m going to first use a wider (285 mm to be exact) but shorter piece of shrink wrap to go around the long direction of the pack. That will seal the ends first, and then I can go back with my long and skinny piece of heat shrink to do the length of the pack.
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I’ve gotten so many different BMS’s from so many different suppliers so I’m not 100% positive, but I believe it was from this source: http://www.aliexpress.com/item/NEW-Battery-Protection-BMS-PCB-Board-for-10-Packs-36V-Li-ion-Cell-max-30A-w/32291193643.html
It’s always hard to say exactly how much AH’s someone will need because every case is different. With that powerful motor sucking lots of juice and big hills though, you are going to want a minimum of 48V20AH. If I were you I would try to go even higher, but it may be even better to simply have two batteries at that point. It’s annoying to swap them, but if you ever had a problem with a 48V30AH battery that destroyed the pack, it would be a big investment straight to the garbage. A problem in one of your smaller packs would mean you still had the other. It’s not likely to happen, but it’s something to think about.
3. There’s something that I think you might be missing here. The factor that actually limits current draw is the controller, not the motor or the BMS. Those are “rated” for 500w and 15A, respectively, meaning they won’t overheat at those values. But both can physically pass those values if you force them to. It’s the controller that is actually “pulling” the current. So you should check your controller to see what its current limit is. If it is a 15A limit controller, then it won’t physically pull more than 15A. The fact that your battery can technically put out 1200W just means that it has “oomph” than you’re using, and you’re giving it an easy, healthy life. But if you switched to a 50A controller, suddenly you’d be pulling the maximum current that your battery can supply (and probably overheating your motor if you pull that 50A for a long time).
For a heavy trailer, I’d add a second brushed motor to the cart, whether the bike has a motor or not. You’d only need 24V, and here’s a discussion about powered trailers. The most important thing for going over sand is to have the fattest tires you can fit onto the trailer.
I don’t know what you mean by saying your battery is 36W, batteries can’t be measured in watts. The only way to know what power your bike needs is to multiply battery voltage by controller current. If you can’t find a marking on your controller that says what its peak current is, you’d have to measure it with an ammeter, like a clamp on DC ammeter that can measure around the battery wire.
My daily driver ebike has 8 cells paralled (14s8p) and it’s been working great for a long time. You can certainly make two 13s4p packs and parallel them after the fact, but don’t be afraid of making a single pack. As long as you use good quality cells, the risk of a parallel group dying is incredibly small.
Lead acid batteries are much larger and heavier than lithium batteries, limiting their placement on ebikes. They almost never come packaged with ebike specific mounting hardware which means that they generally have to go in a bag on the rear rack or in panniers on either side if the rear wheel. Mounting them up high on the rack isn’t a good idea either because it will negatively affect handling. Generally speaking, you want to mount your batteries as low as possible to keep the center of gravity of the ebike lower towards the ground. This will significantly improve your ebike’s handling.
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The Panasonic NCR18650B cells you have are very good quality cells. I used similar cells also made by Panasonic, but mine are the NCR18650PF (not B). The difference is that yours have more capacity (mine are 2900mAh, yours 3400mAh) but yours have a lower constant current draw rating. I don’t remember what it is off the top of my head, but I don’t think it’s much more than 5A per cell. So just make sure that you either use enough cells in parallel and/or limit your controller to not draw more power than the cells can handle. Check the cell specification sheet which you can find on Google somewhere to ensure that you are staying within the cells’ limit.
Lithium Battery technology in a bicycle is still experimental and you have to use a lot of common sense when using these batteries. However with a little education and some end user carefulness, you can use lithium batteries safely, the same as you can safely deal with putting gasoline in your riding lawn mower.
First off: the info you received about a the battery without a BMS blowing your controller is wrong. It’s always a good idea to use a BMS for safety reasons, but as long as the battery is balanced and fully charged, your controller has no idea if it has a BMS or not. All your controller cares about is if the voltage is correct, which as long as the battery is charged, then it presumably will be.
Sorry Benoit, but that won’t work. The BMS will expect the full 10 cells and when it sees that cells are missing, it will assume they are at 0V and not provide any power. You need a 7s BMS, which are pretty commong. 8s will be harder to find for li-ion, but you could do 8s with LiFePO4 and those 8s BMS’s are common.
the problem i have and the bit im confused on is this, i understand the negative on the entire pack goes to the negative on the BMS and the positive of each parallel cells goes to each sense wire but where are the charge and discharge wires going ? am i corrrect in saying that the positive of the pack goes to the charge and discharge socket on the BMS and that when the pack receives its charge it charges the pack and the discharge is when the pack is under load from the output of the pack i.e what ever its connected to for example your bikes motor? in your tutorial you havent shown how you connected the parallel groups of batteries together in series to give you the final pack voltage and capacitance but i’m assuming you linked them in series to get the toal 36v but on the pictures the first and last cells are split compared to the doubled up cells you have through out. am i also correct in saying that if you have 2 batteries connected together to form a cell then you dont need a sense wire on each battery because the two batteries are considered to be the same battery and when they charge and discharge they equalize as one shunts the other ? sorry for so many questions i have googled and googled and googled and as Einstein once said the definition of madness is doing the same thing over and over and expecting a different result, many thanks in advance .