High Current 18650 interconnects

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BillyJ   1 mW

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High Current 18650 interconnects

Post by BillyJ » Oct 17 2017 5:11am

First post here so don't judge me :D

I'm building a battery pack made of approx. 700 18650 cells split into 4 smaller cell packs.
Each cell pack will be supplying 250A peak and they're all in series to get a total voltage around 400V.

I want to use nickel strips spot welded to the batteries to connect them but the currents get too high, especially at the outputs of each pack...

What is the best way to connect 18650's for high current applications?

Thanks in advance!

Hillhater   100 GW

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Re: High Current 18650 interconnects

Post by Hillhater » Oct 17 2017 6:11am

Buss bars.
But what cells are you using, they will be peaking at 35 amps each ! :shock:
Run a search on this forum, you will find many different options.
this is one simple example..
Image
This forum owes its existence to Justin of ebikes.ca

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amberwolf   100 GW

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Re: High Current 18650 interconnects

Post by amberwolf » Oct 20 2017 2:01pm

THere are a lot of threads on 18650 pack building, I recommend reading thru as many as you can to get all the good info that's already there, then decide which method will work best for your application and budget and skills.

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spinningmagnets   100 GW

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Re: High Current 18650 interconnects

Post by spinningmagnets » Oct 20 2017 6:31pm

I'm building a battery pack made of approx 700 18650 cells split into 4 smaller cell packs.
Each cell pack will be supplying 250A peak and they're all in series to get a total voltage around 400V
Just to be clear, you are building four packs that output 100V and 250A (which will then be 'series-ed' to provide 400V), each one of these packs will be made from 175 cells. I juggled a couple numbers and...the closest I can come up with for a configuration that provides an even number is 7P, and then 175 cells / 7P = 25S?

25S at a nominal 3.7V per cell is 92.5V, and fully charged to 4.1V is 102.5V, does that sound right?

250A peak from 7P is 35A from each cell, and each cell connection. I needed to go through all that to find out how many amps each cell connection would have to carry, which is at the heart of your question.

Hillhater   100 GW

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Re: High Current 18650 interconnects

Post by Hillhater » Oct 21 2017 12:34am

Well SM, you didn't have to go through all that... as I had already done it !
So we must assume he has suitable cells !
This forum owes its existence to Justin of ebikes.ca

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Matador   10 kW

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Re: High Current 18650 interconnects

Post by Matador » Oct 22 2017 9:40am

Hillhater wrote:Buss bars.
But what cells are you using, they will be peaking at 35 amps each ! :shock:
Run a search on this forum, you will find many different options.
this is one simple example..
Image
I recognise my creative touch here :D !

Matador

BillyJ   1 mW

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Re: High Current 18650 interconnects

Post by BillyJ » Oct 23 2017 3:37am

spinningmagnets wrote:
I'm building a battery pack made of approx 700 18650 cells split into 4 smaller cell packs.
Each cell pack will be supplying 250A peak and they're all in series to get a total voltage around 400V
Just to be clear, you are building four packs that output 100V and 250A (which will then be 'series-ed' to provide 400V), each one of these packs will be made from 175 cells. I juggled a couple numbers and...the closest I can come up with for a configuration that provides an even number is 7P, and then 175 cells / 7P = 25S?

25S at a nominal 3.7V per cell is 92.5V, and fully charged to 4.1V is 102.5V, does that sound right?

250A peak from 7P is 35A from each cell, and each cell connection. I needed to go through all that to find out how many amps each cell connection would have to carry, which is at the heart of your question.

Sorry, that would have been useful info. There is still a decision about which cell to use but depending on that decision it will either be 7p100s or 8p100s

You're right though, 35A peak current and 22A continuous. The current solution(no pun intended) is looking like large nickel or nickel alloy strips welded to the cells in turn welded to copper buss bars for the parallel connections. Hopefully that makes sense?

I've run tests on a piece of nickel equivalent to 11mm x 0.2mm and the temperature evens off around 158c so I need to find a supplier who will supply 11x0.2 or some samples of .15, .2, .25 and .3 to test and then bulk order to start pack assembly.

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