Li18650 module: nickel plate size calculations

1968 Views 4 Replies 3 Participants Last post by mmark666, Jan 11, 2011

JimDanielson

Discussion Starter · Jan 4, 2011

I am working with a company that has donated battery thermal management to my friends electric motorcycle project. The company is AllCell Technologies and it is a graphite wax material that holds the 18650 cells. as the cells heat up, the phase change material acts as a heatsink but does not raise above 55 C until it absorbs a considerable amount of heat. Everything this company has done is for much lower current then we are looking at (scooters at ~50amps).

My friends motorcycle is going to have an AC 20 or 35 with the Curtis controller. I think this is a peak of 550 amps.

We have set his bike up for 28s56p. The cells are 3.7v nominal and 2Ah each. We are creating 28 modules that are each 56p, so a nickel plate will be tabbed to every cell on a side putting them all in parallel. In trying to determine how to connect each module together and handling 550amp peak I am having trouble. All the calculators online are for copper and aluminum.

Pictures attached are of one module and the planned arrangement. The nickel is 5 mil thick. It is set up to have a connection 5.75inches long between each series set. We have a couple spots where it would be better to connect on the short side of the module. But then, the connection would only be ~3.75 inches wide.

Please help me calculate how much current this nickel can actually handle.

Thanks

If the embedded pictures dont work, click this link: http://picasaweb.google.com/lh/photo/LtFhUIyqSZgijbjBFP6b-w?feat=directlink

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JimDanielson

Discussion Starter · #2 · Jan 4, 2011

Found this: http://www.mogami.com/e/cad/wire-gauge.html

My wire size ends up being 18.548 mm^2 which comes out to 5 AWG. Note, the travel distance between modules is <1inch.

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vpoppv

· #3 · Jan 10, 2011

Sorry that I don't have any helpful information to give, but are there any plans for having these blocks to hold the 18650 batteries available for sale?

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JimDanielson

Discussion Starter · #4 · Jan 11, 2011

The technology is patented by AllCell, so you wouldn't be able to make it yourself. We worked directly with them at their place in Chicago. It took about 1.5 weeks to fully assemble a 11.6 kwh pack for the motorcycle.

They might be willing to make a custom pack for you

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mmark666

· #5 · Jan 11, 2011

Nickel has a 4 times higher specific resistivity than copper. This means that the power losses due to the resistance of the interconnects are increased by 4! (see http://en.wikipedia.org/wiki/Resistivity)

The 5.75" wide segments would have a resistance of around 0.1mOhm/inch, leading to a power loss of around 30W per inch at 550A. So if the total length of your interconnects would be 30", you would convert 900W into heat!

AWG 5 solid copper wire is rated for currents up to 40 - 120A (depending on specification and usage). Divide that by 4 and you should have a good estimate of the current carrying capability of your 5 mil nickel foil.

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