I’m working on my first build and have run into a roadblock with batteries. I have a degree in applied physics and feel very confident that I could build a battery from individual cells, however as I look through cells that cost anywhere from $3-8/cell, and do the math of a 12s12p or 14s14p battery, plus a BMS that’s capable of handling the amperage required, I find myself running into a coupe of questions like:
How much does a battery typically cost people?
Are people really spending close to $1,000 for a battery?
Are there suppliers that people are getting them from that are simpler/cheaper than building one yourself?
Do you need a BMS for discharging the battery, or only for charging it?
Anyone able to answer some/all of those questions from their own experience?
I built a 14s14p battery pack which ended up costing me 900$ so yes most people are spending close to 1k on battery packs. To my knowledge, there are no reliable supplier of ready-to-go battery packs. As for the BMS, some people are breaking their big packs into two (ex: 2*7s14p) so they can use balance chargers instead of BMSs. However, I bought a smart BMS for my pack which is able to handle charging and discharging. I think this is the safest way to go about it as you can monitor the battery pack at all times with the app and it also protects it from discharging too far and permanently damaging the cells.
You don’t necessarily need a BMS for discharge but it’s usefull for controlling max Amps and also the overdischarge protection feature is handy.
It does typically cost 600-800 without a BMS
800-1000 with a BMS
Yes they spend close to a 1000usd for a battery except if they buy a pack from aliexpress.(I’d rather build one myself, i don’t really trust chinese batteries)
If you need a good BMS check out voltaplex website (www.voltaplex.com)the bigger ones you can even customize…
Is there any reason I couldn’t build a 14s2p or 14s3p battery out of SPIM08HP cells? Also, how many Ah do you need to get 45-60min of ride time? The only reason I see is that their Ah/kg isn’t as good as 18650 cells. However they are way cheaper too…
Thats a nice way of saying “your battery is going to be double as heavy”. A 18650 cell has roughly 45g and 3Ah. Those got 300g and 8Ah. So same weight for 18650 would be ~20Ah…maybe a bit less because of more pieces => more cell holder and connectors.
Also I would trust a cell with a steel housing a lot more than a coffeebag/pouch…no matter if it is LiPo, LiIon or LiFePO4.
Also did you see any datasheet, discharge tests or cycle tests?
I agree with the first argument but I disagree with the second.
Pouch cells are not so easy to use for the 0815 mechanical expert but they can handle a lot more than a cylindrical one.
I am using a pouch cell which deliver over 250A continiously…1 cell in Series😃
No joke but you need some skills and not a China BMS and not a RC toy charger…
Electrically, yes
but how do you fix them inside the board? How do you connect them? How do you isolate the connections?
How do you ensure that nothing spikes or rips at the thin foil?
I connect them with industrial cable stuff. Wach cell ist wrapped in a polymide film. The cells are connected in series with a screwed bar made of aluminium.
which is also just a thin foil, one spike and the party starts… not so easy with a steel cylinder.
and how do you isolate those busbars against each other? I mean sure you put tape around them, but while driving they will wobble and maybe even rub against each other…again a party starter…
No there is no wobble. This kind of pack is user in Paragliders. I have crashed the board twice on a rock…the most important is a good compartement.
But if you use the cylindrical ones it is also good. But if one cell is damaged in a parallel row have some fun
hi, what Kind off brand? kokam?
thanks for info. my level of knowledge after 8 years of building aircraft: so far there have only been cells up to 150 A continuous load and 40 Ah in aviation. Of course, the cells can only deliver up to 220 A for a short time, and the cycles / life is then reduced dramatically.
have some fun
