For a long time, lead acid has been the defacto standard for EV’s. The cost is low and the chemistry well understood: Always charge up the lead acid battery whenever you can, never leave it in a flat state, expect only 60-70% of the rated amp-hours, and be glad if you get 200 cycles in a deep discharge environment. Probably 80% of all ebikes sold around the world still use lead acid battery packs, but their days are limited. The weight of lead needed to propel a bicycle for a decent 40-50km range is simply too much for a bicycle to easily handle.
My thinking is that because each of the batteries is only 50% stressed, that the probability of problems due to overcurrent, etc. would be negated and I wouldn’t use a BMS for the supplementary battery.
Finally, have you used the type of spot welder shown with hand held probes? Can see the benefit of greater reach, but do you know if this gives as neat a result (my spot welder there is a very firm press up to activate, hence the discharge only occurs when the tips of the welder are pressing the strip firmly against the top of the cell so i assume ensuring a tight weld)
This page is embarrassingly old, referencing chemistries that are completely obsolete, and is due for a rewrite. In the meantime, we recommend checking out our Battery Kits Product Info page for a more current explanation on lithium specific battery packs.
Remember, if a battery with a certain chemistry can “survive” at 2C, it may actually last much longer if it is sized so that the amp-draw from the controller/motor is only 1C. If it can actually be run at 2C, but it dies in a month with daily use…and yet if sized to run at 1C it lasts a year? Legally the manufacturer is not lying by calling it a 2C battery. There is nothing wrong with that, but…we here want E-bike customers to be aware of the real-world results so they can make an informed decision, and avoid the disappointment that could turn off a lot of potential E-bikers to a wonderful sport and hobby.
To calculate the max amps the battery can deliver, you have to know the max amps of the cells you used. For example, Panasonic 18650pf cells can deliver 10A continuous, and I used 3 cells in series in this battery, so the battery can deliver 3 x 10A = 30A. However, you also need to know how much current the BMS can deliver. If I put a 15A continous BMS on this pack then that would be the “weakest link” so to speak, meaning the pack with the BMS could only deliver 15A continuous.
I think it is much better to use a purpose built CV-CC (constant voltage, constant current) ebike charger. I 100% understand the desire to complete the project on the cheap, but I think that sometimes it is worth a few extra bucks as insurance to protect your battery which is worth many hundreds of dollars.
I finished an ebike yesterday, but i found some major problems on it, The problem is while i riding the bike by throttling, some times the display light dims and low battery voltage caution icon is displaying in the display. and than display shutting off. after that if i try to turn it on again it wont work, so i removed the battery from controller and installed it again than works perfectly, it happens always so i want to remove and install battery again and again, so what is this problem, is this problem is in battery or controller?? Please give me a solution.
I’ve been building a 13s6p Li-ion battery based on your article, and everything went swimmingly (except underestimating the amount of nickel I’d need) until I started hooking up the BMS. I was in the middle of hooking up the sense lines, and the BMS smoked. Opening it up, it looks like a few of the caps that couple adjacent nodes burned. Have you seen this before? Any thoughts on what I may have done wrong, or does this just happen sometimes when a cap’s voltage tolerance is outside spec?
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You can use any connectors you like. I’m a big fan of Anderson PowerPole connectors for the discharge leads. I used this other connector that I had in my parts bin for the discharge wires. I’m not sure what that type of connector is called, but if someone wants to let me know in the comments section then that’d be great!
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.
Amazing article, just what I needed. Have been batteries for electric scooter LOTS of research but have struggled to find any real answers on which charger I should buy for my homemade battery. I am making a 48V 13s4p battery with a BMS (with balancing) like yours but am stuck as to whether I need to buy a normal bulk charger or a ‘smart charger’ that will balance the battery. My question is will the BMS balance the battery on its own or will I need to get a charger that balances also?
I’m wondering, what do you do for 6V or 12V applications where the correct number of in-series cells is ambiguous? For example, if I’m replacing a 6V SLA battery, it seems like the existing charging system would set a 1s battery on fire, but wouldn’t be sufficient to charge a 2s battery. Are there BMS’s that have VRs to step up the voltage from the charging system to the battery, and step down voltage from the battery to the charging system to facilitate a 2s battery for the application?
If I regroup my 12 paralled cells in 10 modules, can I then join these in series using single wires (one for neg, one for pos) between modules, instead of wiring each terminals of each cells like you are doing. Could this affect BMS and/or have any negative impact on cells balance?
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.
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I want to build a 36v ebike battery for my 36v 500w motor. What battery you recommend for me which gives the enough current and capacity. My plane is to build a battery with 40 cells 10 in s and 4 in p,
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.
LiMn/LiMnO2-Lithium Manganese Oxide. Adding manganese to the cathode made this chemistry more stable and less sensitive to individual cell balancing issues. If you were using LiFePO4, and one cell began losing its amp-hour capacity, the rest of the pack would get dragged down to the weakest cells level. Demanding high amps with one weak cell in the pack would cause the entire pack to wear out much earlier than it should have. With LiMn, the packs just seems to stay in balance, with all the individual cells aging equally.
You want to be really sure you get this part right, and if you aren’t certain, I’d recommend having an electrician or the company help you. But you can determine positive and negative on the charge port by using a digital multimeter on the DC voltage setting. Probe between the three pins on your bike’s charging port to find which pins give you a positive readout of between 30-42V (Depending on level of charge). When you find it, the positive pin will be on the red probe and the negative pin on the black probe. Be careful not to short the pins together or touch the probes together, those XLR connectors are cramped quarters. And again, make sure you’re certain you’ve got it right – connecting something backwards could damage your bike’s battery.