Since we started building our own batteries we have been using custom busbars made of Klauke DIN 46235 M6 compression cable lugs and Eland 35mm2 H07RN-F copper wire cable. The initial reason for this having no busbars that really fitted the way we arranged the cells in our utz RAKO boxes (see here, here and here).
I never actually measured the difference in internal resistance of the ones we built and some we got with our EVE LF280K cells. Time to correct this …
The flexible busbars delivered with our cells have approximately these dimensions: 105mm * 20mm * 2mm. This should give us a surface area of 40mm2 and an ideal internal resistance of around 0.045mOhm (according to some online calculators).
When measuring this with our trusty and highly precise TR1035+ the result displayed is 0.08mOhm.
The Klauke version which comes with tinned copper lugs gives us a reading of 0.06mOhm – despite the smaller cross-section of 35mm2. The ideal internal resistance of the copper wire could be expected to be around 0.051mOhm (according to some other online calculator), so we are much closer to the measured value.
The display error of the TR1035+ is expected to be similar as the measured range of both busbars is quite similar. There is certainly quite an amount of uncertainty (not only due to the maximum resolution of 10uOhm) to it. But it is interesting to see that the resistance of the custom busbars seems to be lower despite its smaller cross-section – while being better insulated (not seen on the picture) and more flexible at the same time (as it can be bent in more directions).
Producing these custom busbars is certainly more expensive (a single lug costs around 1.17GBP or 1.27CHF) and involves more manual and time consuming labour. However, it is quite easy to double them and/or increase its cross-section to up to 70mm2 per wire (when using multi-stranded DIN EN 60228 conductors).
So, this is it for today with fascinating facts about busbars for LiFePO4 cells.
Our Journey to Scotland 