18650 battery busbar

Batteries, Chargers, and Battery Management Systems.
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electricbiker1   1 µW

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18650 battery busbar

Post by electricbiker1 » Mar 13 2019 12:56pm

Hello, i have a battery design in mind and was wondering if i am misunderstanding something regarding the busbar. So the battery will be a 20s20p battery of Samsung 30q cells. From what i hear 30q cells are very similar to lg hg2 cells, which means its possible to discharge it at 30a each for a few seconds. So now you have the 20 cells in parallel and you want to draw about 500-600 amps. So now you put a long copper bar parallel to your battery main positive and you connect each cell to the copper bar with ( 2 ) 0.3 (thick) x 8mm ( wide ) nickel strips which from what im reading are each capable of 15 A each. Now for my main question, the copper busbar that you are connecting to is 0.5mm thick 6.3mm wide and a total of about 16 - 17 in long. Now from the chart that tells you the Amps measurements of strips, it says for those copper measurements i should be able to get 36A for every 3mm squared. So now at the end of the 16 inch bus bar, cant i just connect my 4/0 wire with a nut and bolt, and draw about 500+ Amps? If im reading/ understanding everything correctly.





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flippy   100 kW

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Re: 18650 battery busbar

Post by flippy » Mar 14 2019 4:31am

If you make the battery 20 cells wide you dont have to use busbars. Just simple nickel strip 0.2mm by 8mm. Prehaps 0.3mm if you are cranking lots of amps. the bus bar should be fine but i would recommend tapping off from the center or have 3 smaller taps with lower gauge wire to make contruction easeyer

Bear in mind that those cells will not survive those stated currents and the pack will heat up considerably. Active cooling is needed.
On the ends if the pack (pos, neg connection) i would use busbars just to make connections simple as there is a lot of parralel current flowing. In the rest of the pack you have virturally no parralel current flow so a simple nickel strip will suffice
Lithium beats liquid dinosaurs.

electricbiker1   1 µW

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Re: 18650 battery busbar

Post by electricbiker1 » Mar 14 2019 11:20am

flippy wrote:
Mar 14 2019 4:31am
If you make the battery 20 cells wide you dont have to use busbars. Just simple nickel strip 0.2mm by 8mm. Prehaps 0.3mm if you are cranking lots of amps. the bus bar should be fine but i would recommend tapping off from the center or have 3 smaller taps with lower gauge wire to make contruction easeyer

Bear in mind that those cells will not survive those stated currents and the pack will heat up considerably. Active cooling is needed.
On the ends if the pack (pos, neg connection) i would use busbars just to make connections simple as there is a lot of parralel current flowing. In the rest of the pack you have virturally no parralel current flow so a simple nickel strip will suffice
Yes i agree at that kind of amp draw it would get very hot. I would only be doing it for a short time if ever and keeping constant eye on it. Now if i am understanding what you are saying correctly, when i use a copper bar to connect the main positive of the battery, i mean only the main positive of the battery ( like only one row of 20 cells ) because i think what you are saying is there is no need to put bus bars ( several ) of them in the battery pack to connect several positive ends... The reason why im using the one copper bar is because i wanted to use a big 4/0 wire, and typically what you would do is solder the wire on to the positive end but the 4/0 would be to big to solder. So if i have a copper bar that connects to the ( main positive of the pack ) i can put a whole at the end of the copper bar and with a nut and bolt connect the 4/0 terminal. Does that make sense? And then you mentioned i could solder several smaller wires to make it easier, but my only problem with that was, when it comes to making the battery box, i would have to make several holes for the terminals to come out... instead of one for the positive and negative. Sorry if i make things hard to understand lol. To sum it up, i will be connecting the entire battery from start to end with nickel strip. But when its all connected, and i need to connect my main positive and negative leads, i want to draw a lot of amp from the pack and so i wanted to use a big terminal ( 4/0 ). And thats why i wanted to use one copper bar next to the positive and negative end of the pack.

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flippy   100 kW

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Re: 18650 battery busbar

Post by flippy » Mar 15 2019 3:47am

a short burst is one thing, but you are also heating the pack up with regular driving. to drive a regular motorbike at regular highway speed you need about 5kW in general. with a 72v pack that means already 70+ amps in steady state driving. that is 3.5A per cell. aka: more then 1C just in holding highway speeds. that will heat up the battery on its own. once its saturated and start pulling 500A from it the temp inside the pack (especially the center cells) will heat up more and cant lose that heat. constantly pulling more then 1C will also kill the cell decently fast. think 500~700 cycles at best.
Lithium beats liquid dinosaurs.

electricbiker1   1 µW

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Re: 18650 battery busbar

Post by electricbiker1 » Mar 15 2019 12:57pm

flippy wrote:
Mar 15 2019 3:47am
a short burst is one thing, but you are also heating the pack up with regular driving. to drive a regular motorbike at regular highway speed you need about 5kW in general. with a 72v pack that means already 70+ amps in steady state driving. that is 3.5A per cell. aka: more then 1C just in holding highway speeds. that will heat up the battery on its own. once its saturated and start pulling 500A from it the temp inside the pack (especially the center cells) will heat up more and cant lose that heat. constantly pulling more then 1C will also kill the cell decently fast. think 500~700 cycles at best.

Ok, so lets say we draw 20A from each cell, thats a total of 400A. My question is whats a neat, and effective way of drawing that kind of amps, does my idea of having a copper busbar next to the positive terminal, then connect all of the (20 main) positive cells to it, and from there connect the proper sized wire, 4/0 awg work? Again im going to be very mindful of cell heat and not push my limits, and work on cooling. My question is the battery layout, and setup.

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flippy   100 kW

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Re: 18650 battery busbar

Post by flippy » Mar 15 2019 2:31pm

you can do it with a single cable and a big fat busbar. no question about that. but such a heavy and stiff cable might be cumbersome to deal with.
i would use the "square" cell holders, not the honycomb. the latter gives more energy density but is very poor in cooling. due to the heat creation i recommend using the square cell holders, that creates a lot more air gaps between the cells so they heat up more evenly. they will heat up more but the temperature in the pack will be much more even compaired to the honycomb setup, that will concentrate all the heat on the inside of the pack.
Lithium beats liquid dinosaurs.

electricbiker1   1 µW

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Re: 18650 battery busbar

Post by electricbiker1 » Mar 16 2019 9:53am

flippy wrote:
Mar 15 2019 2:31pm
you can do it with a single cable and a big fat busbar. no question about that. but such a heavy and stiff cable might be cumbersome to deal with.
i would use the "square" cell holders, not the honycomb. the latter gives more energy density but is very poor in cooling. due to the heat creation i recommend using the square cell holders, that creates a lot more air gaps between the cells so they heat up more evenly. they will heat up more but the temperature in the pack will be much more even compaired to the honycomb setup, that will concentrate all the heat on the inside of the pack.
Thank you for clearing that up, and yes i will use the square cell holders, i already have them.

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flippy   100 kW

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Re: 18650 battery busbar

Post by flippy » Mar 16 2019 1:21pm

might want to consider putting some fans on the pack to blow air into the pack to cool it.
Lithium beats liquid dinosaurs.

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