How do you determine this exactly? Your battery is a 36v 8.7Ah and I guess it has something to do with the maximum continuous discharge rate. It would help me (and maybe others) to explain why 30A is more than enough for this battery.
Once I’ve got all the cells I need checked out and ensured they have matching voltages, I like to arrange them on my work surface in the orientation of the intended pack. This gives me one final check to make sure the orientation will work as planned, and a chance to see the real-life size of the pack, minus a little bit of padding and heat shrink wrap.
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Most of the price involved these days in building an e-bike or buying a ready to go e-bike is the size and chemistry of the battery pack. For the consumer its important to understand the difference between a 24V, 36V, and 48V pack. Also know what a 10-Ah pack is compared to a 5-Ah pack.
Test the voltage of each cell to make sure that they are all identical. If your cells came straight from the factory, they shouldn’t vary by more than a few percentage points from one to the next. They will likely fall in the range of 3.6-3.8 volts per cell as most factories ship their cells partially discharged to extend their shelf lives.
You want to use unprotected cells because your BMS will be handling all the protection, and you don’t want individual cell protection circuits getting in the way or limiting current draw unnecessarily. So use only unprotected cells when building big multi-cell packs like these.
Manufacturers usually rate their cells’ capacity at very low discharge rates, sometimes just 0.1c, where the cells perform at their maximum. So don’t be surprised if you’re only getting 95% or so of the advertised capacity of your cells during real world discharges. That’s to be expected. Also, your capacity is likely to go up a bit after the first few charge and discharge cycles as the cells get broken in and balance to one another.
I understand that the Ebay battery may run low, but as it is running in parallel to the “Whale”, I’ simply use the “Whale” LED display as rough guid to both batteries charge state (assuming I fully charge both batteries each time before I ride).
Yea lead acid is a great way to cheaply get into ebikes and test new motor/controller combinations. Keep in mind though that your performance will increase when you switch to lithium. It’s easy to do though, as the bike doesn’t care what chemistry it receives, it just sees volts and amps. Good luck!
At the same time though, think about if that is what you want. It could be that those cells died because of a malfunctioning BMS unit or old wiring. Putting new cells in their spots could just wind up killing those new cells in a few days or weeks. I’ve seen that happen as well. So make sure you check everything and consider all of your options!
Now this step is very important: I’m going to turn the pack upside-down and perform this set of welds between the positive caps on the second parallel group and negative terminals on the third parallel group. Essentially, I’m welding on the opposite side of the pack as I did when I connected the first two parallel groups. Skip down a few pictures to see the completely welded pack to understand how the alternating side system works.
You can also add a label or other information to the outside of your pack for that professional look. If nothing else, it’s a good idea to at least write on the pack what the voltage and capacity is. Especially if you make multiple custom batteries, that will ensure you never forget what the correct charge voltage for the pack is.
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Oh, one last thing. If you have a poorly formed connector or the wires are fraying, that can increase resistance and cause a voltage drop that might trip a cutoff condition. Just another thing to check for.
When you buy a Hobby King pack, it will have a number of these large cell LiPo’s strung together like this 6 cell in-series (6S) pack. The big downsides of this pack is that it will only last you in best case maybe 300 charges and it is volatile, and susceptible to possible fire if not well managed and cared for. When using cobalt-based LiPo, it is best to use some kind of BMS, and also you should charge it in a safe location.
If any one battery cell varies significantly from the others, do NOT connect it to the other cells. Paralleling two or more cells of different voltages will cause an instantaneous and massive current flow in the direction of the lower voltage cell(s). This can damage the cells and even result in fire on rare occasions. Either individually charge or discharge the cell to match the others, or more likely, just don’t use it in your pack at all. The reason for the voltage difference could have something to do with an issue in the cell, and you don’t want a bad cell in your pack.
I’d recommend going with a cell that can output 10A, giving you 40A continuous power rating. You’ll use less than that, meaning the cells will be happier (and cooler). Something like the Sanyo 18650GA or LG MJ1 would give you good power and capacity (both are around 3,400 mAH per cell).
Lithium electric bike batteries are not cheap, they are not perfect, and they are not readily available. Some OEM’s such as BionX sell a moderately sized lithium e-bike battery pack for $1000 plus. Optibike sells their touring LiPo battery as an add-on accessory for their bike for a http://usebikeparts.com $2500. It is surprisingly difficult to find a ready to plug in LiPo battery pack for sale on the internet by any real company. The reason is simply product liability.
Absolutely, a relay is the way to go. Use the keyswitch you bought to activate the relay, then the relay will carry the heavy current flowing through your battery’s positive discharge wire. Alternatively, you could install 9 or 10 of these switches in parallel. Just make sure you mark your keys accordingly 😉
I am new to the ofrum and to the ebike world so I would like to seek some advice please. I have recently bought a sondors fat bike to the UK and want to make some tweaks, I would like to upgrade the battery on a budget, I was thinking of 4 x 12v 5ah lead acid batteries in series, would this give me 48v 20ah or have I got this totally wrong? I want to replace the stock contoller for a 48v 25amp one, would this suffice? lastly it comes with a stock 350w bafang motor, if I make the battery and controller upgrades will the motor handle the increase in wattage? could I drill venting holes in the case cover to expell some heat? Your thoughts and advice would be most welcome,
Once you’ve got 2-3 welds on the top of each cell, turn the 3 cells over and do the same thing to the bottom of the 3 cells with a new piece of nickel. Once you’ve completed the bottom welds you’ll have one complete parallel group, ready to go. This is technically a 1S3P battery already (1 cell in series, 3 cells in parallel). That means I’ve just created a 3.6V 8.7Ah battery. Only nine more of these and I’ll have enough to complete my entire pack.
I don’t think there is any danger to parallel more than 4 cells. Tesla cars have literally hundreds of 18650 cells just like these paralleled. The issue is that if you ever did have a problem with one cell, like a factory defect that caused it to short circuit, it could die and drag all the other cells down with it, killing the entire parallel group. That’s why Tesla uses individual cell fusing, but that’s not really employed on the small scale like for ebikes.
3. Yes, 18650’s with capacity ratings of 6000 or 8000 mAh are fake. The technology simply doesn’t exist to put that much energy in a cell that size on an economical level. In a few years we might be there, but not right now. Currently, the biggest cells are in the high 3,000 mAh range for 18650’s. 26650’s are larger cells and so those can have higher capacities, but there are many fewer options and variety of 26650 cells, so 18650’s are the common cells used in ebike packs.
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C values seem to be as much about cell packaging as chemistry for LiFePo/LiMn/LiNiCoMn Pouch and prismatic cells with high AHr per cell tend to have a C value of about 1 to 1.5. So cheap packs both cased and shrink wrapped or from suppliers like Ping seem to be like this. Cylindrical cells from A123 or Headway tend to have C values of 3C to 5C upwards. And for a fully built pack, C is as much about cells in parallel as anything. eg 10s2p having twice the C of 10s1p Again BMSBattery/GreenBikeKit are now selling LiFePo Headway based packs with a BMS and with C values of 3C to 5C and either cased or shrinkwrap.
Hi I need help! I am building my own battery pack from old laptop batteries (18650’s). I bought the cheep $250 48v 1000w ebike conversion kit on ebay. I have many questions! It seems the perfect number of cells to connect in series are 13! This is a big problem for me because I am cheep and I already bought the Imax B6 battery balancer charger. I also bought 7x 6s balancer leads and 5x 4s leads. The Imax has a max charge voltage of 22.2v (so it sais in the manual), and a max balance of 6 cells at once. I also bought the parallel balance charging board. I don’t want to charge two or three packs at once to just have to turn around and charge one separately. So now I’m faced with the decision of making a 12 series battery or a 15 series battery (I will buy 5s leads in this case). The problem is with the 12 series battery the nominal voltage is only 43.2. Or a 15 series battery with a nominal voltage of 54. Which I’m pretty sure is a big no no because the controller is only meant to handle 48v within reason (13s max charge voltage of 53.3 and 12s 49.2 at 4.1 v per cell). But if I make it a 12s, running around most of the trip at 44v, will this drain the Amps faster because the motor wants 48v? I’m thinking no but just wanted some confirmation on that and if the controller can handle more volts. I could make a 15 series batter and just charge to 3.6 or 3.7 volts. Is this hard on the cells?
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If you are concerned about the speed and power of an electric bike, pay attention to the motor size. Electric motor size is measured in watts and usually ranges between 250 and 750. When deciding on the appropriate amount of wattage, think about factors like the weight of the rider and the desired speed and terrain for the bike. If your child will mostly be on a flat surface, lower wattage should suffice; if they are planning to ride up and down hills, look for a bike with a larger motor.