What 18650 batteries would I need to use?

Batteries, Chargers, and Battery Management Systems.
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Zeus99   100 µW

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What 18650 batteries would I need to use?

Post by Zeus99 » Apr 04 2021 12:49am

Hello,

So I would like to create 72v 63AH battery

example:
https://voltaplex.com/20s18p-72v-63ah-l ... mj1-cuboid

72V 63AH - 20S 18P
3150mAh batteries x 20s = 63AH

Am I calculating this correctly? and what would be the best 18650 batteries to use?

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amberwolf   100 GW

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Re: What 18650 batteries would I need to use?

Post by amberwolf » Apr 04 2021 3:20am

Zeus99 wrote:
Apr 04 2021 12:49am

72V 63AH - 20S 18P
3150mAh batteries x 20s = 63AH
Ah is cells in parallel, voltage is cells in series.

20s x 3.7v = 74v

18p x 3.15Ah = 56.7Ah

You also have to have enough parallel cells to handle the current (A, amps) you will draw. If you needed 100A, then for 18p it would be 100A / 18p = 5.6A each cell. For 3.15Ah cells, that's under 2C (5.6A / 3.15Ah =1.78C), which many new cells can handle fine. If you needed 500A, that would be 500A / 18p = 27.8A per cell, which would be pretty extreme, at 27.8A / 3.15Ah = 8.8C.

Keep in mind that generally, the higher the amps a cell must supply, the more the voltage will sag, and the less total power (watts) you will get from the pack under load (and the more likely cutouts / shutoffs are at low state-of-charge). Also, the cell will heat up faster and stay hot longer, which is detrimental to lifespan.

So you need to decide what the pack has to do for you before you can pick which cells, and how many parallel cells to use--knowing only the capacity you want isn't enough.

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flippy   10 MW

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Re: What 18650 batteries would I need to use?

Post by flippy » Apr 04 2021 9:03am

first you need to know what the battery needs to do before you can pick a cell.
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Chalo   100 GW

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Re: What 18650 batteries would I need to use?

Post by Chalo » Apr 04 2021 10:03am

What they said.

Also, what's the purpose of massively parallel pack construction when you can get 65Ah cells? It's like you want to build a barn but you assume you're going to use Lego.
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Zeus99   100 µW

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Re: What 18650 batteries would I need to use?

Post by Zeus99 » Apr 08 2021 1:56pm

Thanks guys. I'm not 100% sure which battery to use, any suggestions? I only know that the physical size needs to be 18650s.

I need it to be 20S 18P, nothing more, nothing less, because that's what's in my ebike right now.
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flippy   10 MW

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Re: What 18650 batteries would I need to use?

Post by flippy » Apr 08 2021 4:39pm

Zeus99 wrote:
Apr 08 2021 1:56pm
Thanks guys. I'm not 100% sure which battery to use, any suggestions? I only know that the physical size needs to be 18650s.

I need it to be 20S 18P, nothing more, nothing less, because that's what's in my ebike right now.
still dont know what controller you are using and what you expect to get the battery to do for you.
Lithium beats liquid dinosaurs.

Zeus99   100 µW

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Re: What 18650 batteries would I need to use?

Post by Zeus99 » Apr 08 2021 10:35pm

flippy wrote:
Apr 08 2021 4:39pm
Zeus99 wrote:
Apr 08 2021 1:56pm
Thanks guys. I'm not 100% sure which battery to use, any suggestions? I only know that the physical size needs to be 18650s.

I need it to be 20S 18P, nothing more, nothing less, because that's what's in my ebike right now.
still dont know what controller you are using and what you expect to get the battery to do for you.
Sorry, I'm not sure what controller it has, I'll have to take the lid off and take a look. I would like to get longer range with the batteries if that's what you're asking. Based on my calculations and what I see\experienced, I have 18650 (2100mAh) batteries right now. With higher mAh batteries will I get more range or is it just for power?

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Chalo   100 GW

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Re: What 18650 batteries would I need to use?

Post by Chalo » Apr 09 2021 3:01am

Zeus99 wrote:
Apr 08 2021 10:35pm
With higher mAh batteries will I get more range or is it just for power?
Higher capacity cells give more range at the expense of less power.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

mxlemming   100 W

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Re: What 18650 batteries would I need to use?

Post by mxlemming » Apr 09 2021 1:48pm

You probably want cells with 10A+continuous discharge, decent quality and can expect 2500-3000mAh per cell.

Try:
Sony vtc6 or Sony vtc5
Samsung 25R
Samsung 30Q (some seem to think these self discharge randomly, mine don't but :?:
Molicell p26 or p28
The lower mAh ones have higher power, but with 20s18p that's already 13kW at 10A/cell.

You don't really sound like you know what your doing so... Read lots, be careful and good luck.
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Zeus99   100 µW

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Re: What 18650 batteries would I need to use?

Post by Zeus99 » Apr 09 2021 7:31pm

mxlemming wrote:
Apr 09 2021 1:48pm
You probably want cells with 10A+continuous discharge, decent quality and can expect 2500-3000mAh per cell.

Try:
Sony vtc6 or Sony vtc5
Samsung 25R
Samsung 30Q (some seem to think these self discharge randomly, mine don't but :?:
Molicell p26 or p28
The lower mAh ones have higher power, but with 20s18p that's already 13kW at 10A/cell.

You don't really sound like you know what your doing so... Read lots, be careful and good luck.
OH trust me I'm been watching videos and reading forums, but I haven't found, or maybe I haven't read enough to see the details that I need. This, what you have provided helps a lot for me to determine which batteries to use. Cheers.

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