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Help with battery calculations

Im trying to decide on a powertrain for a new build.

Can anyone help me with the math for determining watt hour and amp rating for a 8s8p battery made with samsung 30q 18650s?

I want to compare that to a lipo setup.
(4) 10,000mah 4s 50c batteries wired 2s2p.

If you help me with the maths, I’d greatly appreciate it.
Batteries aren’t cheap and I don’t want to make a big mistake.

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@Soflo

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Any reason you’re going 8s8p specifically? That’s a weird config

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http://esk8.it/

Relatively novice calculator to get you started.

Probably because he’s comparing it to a lipo 8s8p setup. The lipo setup could be because of enclosure space constraints.

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Ratings are one thing but another factor of comparing lipo packs to liion cells is cycle lifes. Of which you will usually get more out of liion so that adds value to an often higher price

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There’s a calulator linked in the top bar above :wink:

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@Flasher thank you, what site is that?
@tipsy I’m considering doing a moe stooge 8s build, but that 8s8p amp rating is waay too low for my needs.
@KfromtheBay thank you, I have a couple 12s 30q packs, jusr didn’t know how to math.
@Avio thanks man, I’m comparing it to (4) 4s 50c 10,000mah lipos connected 2s2p. I still need to do the math on the lipo setup

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I definitely agree with @KfromtheBay that the length of service life should be taken into account — lipo don’t last very long, li-ion last a decent time, and LiFePO4 last a very long time

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30Q has been accepted as a 20A cell. So you could probably reach bursts of 160A without big problems. As long as your series connections can take it

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I would start by deciding how many miles of range you want to get out of your pack.
Also make an educated guess on how much power you want (for acceleration and top speed).

For range: you can guestimate ~25Wh/mile. (For moderate riding, search people’s measurements)
So, for 20mile range you’d need 500Wh.

Now, you get to this number by:
Wh = Pack voltage (V) * Pack Capacity (Ah)
For a 10s5p Samsung 30Q pack that would be:
Pack voltage = 10 (series)* 3.6V (cell nominal voltage)
Pack Capacity = 5 (parallel) * 3Ah (cell capacity)
That gives us 36V * 15Ah = 540Wh

You will not want to drain your batteries entirely,
and capacity is lower when used at high discharge currents, soo you will have a slightly lower real world range.

You can use the same logic for Lipos.

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@PrivacyDoctor thank you!
How does C rating come into play for the lipo?

Power, C-Rating and Amps:
Depending on your ESC and motors, you have an upper limit. Let’s say you have 2 motors that you want to run at 40A each. So, you want 80A cont power from your battery.

You get that by multiplying number of parallel groups by capacity and discharge rating.
For 30Qs and above example, that’s
5 (parallel) x 5C (discharge rating) x 3Ah = 75A

But you’ll have voltage sag when you draw at Max discharge, so, increase your pack by say 20% of what you want to draw.

30Qs can do a bit more than 5C, so, in this case, 5p might be enough.

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@PrivacyDoctor
my math can’t be right…
So let’s go with the 4s 10,000mah 50c lipo example
I’ll have 2 parallel and 2 series.

So (2 parallel) x 50c x 20ah= 2000a???

Almost. Corrected for you:

Yes, Lipos can be amazing in terms of discharge.
They suck for safety and life (cycles).

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Im a little lost again
(4) batteries @10ah each, 2 parallel, 2 series would make a 20ah battery correct?
@PrivacyDoctor

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For real power it matters, yes, but in terms of current, no.
Power is Amps x Voltage
But for battery dimensioning, stick to the two procedures above. Tip: don’t go beyond 10s. Or read up on ERPM and VESC versions…

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@PrivacyDoctor I have (2) 12s builds right now.
One is 12s4p 30q dual 6380, the other is 12s2p dual 6374… I’m actually not new to this. I just don’t do math well. Im wanting to go with the Moe Stooge components for the new build to go real fast. Was trying to see if it was feasible for me to make a li-ion Nese pack that I could travel with.


This is my latest build.

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It’s not a website. It’s my battery pack calculator app :slight_smile:

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That’s some solid motors!
I think you are really limited by your battery here.
The 4p delivers like 30A per motor, while they can take the double. You might as well have used cheap racerstars. So, making a more potent battery sounds like a solution.

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