PCB 18650 connections

Batteries, Chargers, and Battery Management Systems.
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AEM   10 mW

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PCB 18650 connections

Post by AEM » Jul 20 2018 3:14am

I have no idea about the ultimate validity of this form of interconnecting 18650 cells, and I would like to know what you guys think. Using the printed circuit boards, is interesting but I feel like I’ve misunderstood something. I remember I read once that the model 3 battery pack and modules used a six foot long flexible circuit board with spot/bond weld cell fuses and held together with a silicone material. But I’m not used sure whether the PCB was just for measuring voltage and temperature or as a busbar. I’ve seen potted and single cell fuses 18650 batteries but never ones using a PCB in either manner.

https://m.youtube.com/watch?v=SaRQub9Sg7c

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jonescg   1 GW

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Re: PCB 18650 connections

Post by jonescg » Jul 20 2018 7:39am

The flexible PCB is definitely only used for the BMS.
The Model 3 battery uses proper busbars with cell terminals wire-bonded to them. The encapsulant ensures uniform temperature and vibration protection.

AEM   10 mW

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Posts: 20
Joined: Nov 17 2015 9:25pm
Location: Chula Vista

Re: PCB 18650 connections

Post by AEM » Jul 20 2018 11:13am

Ok thank you, that makes way more sense, with the pictures I’ve seen of Model 3 modules. Do you think a flex PCB could be used in a similar way for a smaller pack? The model 3 modules seem pretty dense, 200wh/kg +. Not including the mass of the outer protective casing as well as the penthouse that contains the bms controller, the charger, and the dc/dc converter.

Another question for Jehu’s PCB idea what possible problems do you see with his pack design. I already see issues with the use of normal battery holders in the first design, while the second design I think glues them together, and then welds/solders them to the board. Other than the low power output of the board of course.

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jonescg   1 GW

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Re: PCB 18650 connections

Post by jonescg » Jul 21 2018 8:38am

I think I did see a video of his single cell holders - fine if you never ask more than half an amp from the cells.
Flexible printed circuit strips are only good for sensing - milliamps at best. Even thick PCB traces would require lots of copper area to carry more than a few amps without heating up.

Ultrasonic wire-bonding of small cylindrical cells to a solid busplate seems to be the best termination solution I've seen. Tesla does it in all their vehicles and in their BES systems.

Personally I would just get large prismatic cells - my time is worth more than 5000 tiny cells!

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