Battery Basics for Beginners Wiki [Serious]

Is it just me or are C ratings totally backwards and unintuitive when you just want to know how many amps your battery can handle? This is a great suggestion.

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Agreed, Voltage and Ah are already in the text, might as well define Wh.

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Thanks for this writeup, Justin :smiley:

More information about cutoffs can be found over here

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This is kind of like soldering on cells. You should never do it. Those that do it, know exactly what they are doing and why, and what damage it can cause, and how to solder in a way that drastically minimizes that. But I would still recommend never doing it. Anyone who knows enough about it to do it, knows they can disregard that advice, because they know enough about it and what’s happening inside the cell.

Yes, this :arrow_up: So basically, never do it.

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Dude, this is awesome! Thank you for putting the time into this❤️

Would a discussion on capacity vs discharge of a pack be helpful? For example, I often figure on more P groups in a battery because I want it to be able to dish out them AMPS. Range is nice too…
:beer:

Edit:
Seems @bonesaw and @Rojitor had similar recommendations👍

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excellent work @Venom121212 and @b264 i linked to this page in the glossary of terms with the other Math and Science of Electric Skateboarding series @mmaner published

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Also there is the ESK8 CALC in the banner that will help with estimating battery use. And @thisguyhere 's tool http://esk8life.com/batt/index.html

perhaps its too advanced but we could also discuss discharge rate and data sheets for above mentioned cells

18650-Samsung 18650 30q
Capacity: 3,000mAh
Constant Discharge: 15A

18650-Samsung 25r
Capacity: 2,500mAh
Constant Discharge: 20A

18650-Samsung 40T
Capacity: 4,000mAh
Constant Discharge: 30A

18650-LiFePO4
Capacity: 1350mAh
Constant Discharge: 50A

20700-Samsung
Capacity_Nominal: 3500mah
Constant Discharge: 30A

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I tried to write something similar, take as much as you want
http://esk8.uk/#/wiki/batteries

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I am working on another thread about how to set up your esc. This will be focused on there.

@krindor yeah yeah less amp draw I get you :wink:

@Rojitor C value is the most inflated battery measure Ive ever seen. I personally hate it and try to avoid using it as it’s a controversial topic.

@wandagoner that would make an awesome topic. Inviting you to a pm chain shortly

@anubis thank you, I will happily use that and give you credit for saving me work haha

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Does that also apply to a 40T battery, i.e. if I have a 40T 12S2P battery I have to charge it with 2.7 A, since [2]*[4000/3000] = 2.66?

I’ve heard “2 amps per parallel group” thrown out as a theoretical safe max for 30q.

40T has a higher discharge current so I imagine it can handle a higher charge current as well but I’ll call on @MysticalDork and @BluPenguin for some back up advice / clarification.

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Okay I’m so confused by that formula. General rule for charging is 0.5c or less per cell for longevity. C rating being the capacity of the battery. I would say that for optimal speed vs life, 0.2c-0.5c multiply by # of cells per P group is a good place to be. So for 2P of 4Ah cells, you can charge it at 2A x 2 so 4A charger. Less is better for cell life but will take longer.

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As mentioned above, I hate c ratings as they are often inflated and confusing. They seem like a floaty variable that changes based on usage case.

I’ve always understood it to be a discharge rating over time at a standard amp rating.

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It seems to me like a battery can really be any c rating within reason regardless of what the manufacture recommends. That formula was a quick, multiplying factor to avoid using c ratings.

Thank you for clarifying on the amp charge of the cells.

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Discharge C ratings can be inflated, but the C number itself is a constant. 1C = Ah of the battery. 3Ah cell at 1C is 3A, 0.5C is 1.5A. The C is just a multiplication of the cell’s capacity. So it’s easy to claim 0.5C charge rate because it works for any cell. Just divide the cell’s nominal capacity by half and charge at that amp rate.

In a perfect world, 3Ah cell discharging at 3A (1C) gives exactly 1 hour of use. In real life due to losses and inefficiencies, it comes to less than 1 hour.

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Hi, quick question
how many bms do i need to connect 2 6s lipos in parallel?
can i connect both batteries in parallel to the bms
or
connect each lipo to a bms and then to the VESC/Charge cables in paralllel?

Thanks in advance for your answer

Just one. You will always only need 1 BMS per set of battery. For example 10S battery requires 1 BMS just like 12S battery requires just 1 BMS. The only situation for 2 or more BMS is if you have 2 or more 10S batteries in use. Even then, depending on wiring, you could probably get away with 1 BMS.

Yes, you can connect 2 6S lipo in parallel to a single BMS.

What are you running that’s only 6S though? I think 6S is the bare minimum for vesc to operate?

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thanks for your reply @annihil8ted
i’m upgrading an old e-scooter and i’m trying to get more distance range.
at this moment i’m using 2 lead acid batteries in series with the vesc so i’m looking lipo to accomplish that

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What might be the safest way to have a dual battery setup so you could ride with a 12s4p battery one day and two 12s4p another day? I understand to connect them in parallel. But in doing that would I just make a cable xt60 connection going to the esc that has both positives on one side and both negatives on the other with another xt60 connection before the batteries so I could choose if I want one or two connected?

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What you described is a valid way to do it, but be ware that the batteries should have equal voltage when you connect them! Otherwise the higher charged one will rapidly charge the other one, which might cause a fire. If you connect both after charging them to 100%, you should be good.

You can search around on this forum for other ways people have connected batteries together to avoid this problem. (Usually it involves using one battery to charge the other through the BMS)

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Hey how much should the discharge rate be? Is 60A ok?