How hard to tighten battery nuts

stig44 · Aug 26, 2023

My DIY LFP batteries - 16 cells 200Ah - shall be connected with an 8 mm 15 mm bolt and tightened with 1-2 Nm. How much is 1-2Nm?
I have a 15 cm long spanner, an electric screw driver etc. Tried to Google but no good answer (lb-ft is not my bag). I have tightened with the electric on power number 10, is that OK?
Any suggestions?

sunshine_eggo · Aug 26, 2023

Stop screwing around. Buy a torque wrench.

DIYrich · Aug 26, 2023

2 n-m is about 1.5 ft-lbs. Hang a weight off the wrench?

MattiFin · Aug 27, 2023

1-2Nm is next to nothing for 8mm bolt even in aluminium. Are you sure you got your numbers correct?
For scale you get 2Nm already with smallish size screwdriver handle. Good grip on big screwdriver is good for at least 4Nm

hwy17 · Aug 27, 2023

If you're going to use a budget torque wrench though it needs to be a tiny one, with the target torque in the middle or upper end of it's range.

I've given up on torque wrenches for tiny nuts and bolts in aluminum completely, I can't buy the ones that cost enough to do it accurately, and it doesn't take much error to tighten until they're loose again.

Those threads are coiled at least which will make them slightly stronger.

JJJJ · Aug 27, 2023

I used a torque wrench for my bus bars and inverter. Fortunately the specs were available for the equipment I purchased.

A huge bonus was that I was able to borrow my mechanics high end torque wrench. Just so happens he is a neighbor and a friend.

eemarty · Aug 29, 2023

I agree 1-2Nm is not that tight. It seems like they are warning you against overtightening it. Your electric screw driver is probably not accurate or calibrated to anything but probably in the right ballpark. 2Nm is equivalent to 20.4kg*cm. So if you applied a 1.6kg weight to the end of your 13cm spanner, that would be 1.6kg*13cm=20.8kg*cm or just over 2Nm.

stig44 · Sep 4, 2023

eemarty said:
I agree 1-2Nm is not that tight. It seems like they are warning you against overtightening it. Your electric screw driver is probably not accurate or calibrated to anything but probably in the right ballpark. 2Nm is equivalent to 20.4kg*cm. So if you applied a 1.6kg weight to the end of your 13cm spanner, that would be 1.6kg*13cm=20.8kg*cm or just over 2Nm.

Thanks a lot! I agree, it sounds in the low end, probably no harm if I use just a little more force.

ampsarus · Sep 4, 2023

Watch YT videos where the presenter uses the same 3/8 drive wrench to "tighten spark plugs properly" at 11 foot pounds, and in other videos uses the same wrench to "tighten wheel lugs properly" at 78 foot pounds. no no no

How hard to tighten battery nuts

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