diy solar

diy solar

Compress or not, flexible busbar or not

I've read some of this topic thread, can people confirm to me what the recommended clamping force should be for a 280ah cell in Nm & do you multiply this by 4 cells for a 12v battery pack?
Nm being applied with a small 'bicycle tool' 1/4" drive torque wrench, clamped between 2 suitable metal plates with suitable studding.
Thanks

My fixture is using 2 yellow pine pieces of wood 1 inch x 10 inch cut to length with 4 holes drilled in each piece (2 top 2 bottom holes). Four 1/4 inch course threaded rods with 1/4 inch nuts & washers are used through the holes of the wood on each end of the 8s Lifepo4 battery banks and snug the nuts down.

This is Info I used and torqued a little less at 5 Inch Pounds with a torque wrench at about 3.2 to 3.3 volts charge in each cell. The cells are essentially just held in place.

The spec from EVE was 300 KG force which rounds off to 660lbs. Battery face is approx 6.85"x 7.874" = 53.94 sq inches
660lbs/53.94sqin=12.23 lbs per sq inch
Divide 660 by 4 bolts that's 165 lbs Axial (clamping) force per bolt.
Using 4 course 1/4 in threaded rods that should equate to roughly 8 INCH pounds torque per bolt. Realistically, that's a snug twist of the wrist on a regular nut driver for the average build mechanic.
 
So how do you measure the clamping force applied? To work out the stud
My fixture is using 2 yellow pine pieces of wood 1 inch x 10 inch cut to length with 4 holes drilled in each piece (2 top 2 bottom holes). Four 1/4 inch course threaded rods with 1/4 inch nuts & washers are used through the holes of the wood on each end of the 8s Lifepo4 battery banks and snug the nuts down.

This is Info I used and torqued a little less at 5 Inch Pounds with a torque wrench at about 3.2 to 3.3 volts charge in each cell. The cells are essentially just held in place.

The spec from EVE was 300 KG force which rounds off to 660lbs. Battery face is approx 6.85"x 7.874" = 53.94 sq inches
660lbs/53.94sqin=12.23 lbs per sq inch
Divide 660 by 4 bolts that's 165 lbs Axial (clamping) force per bolt.
Using 4 course 1/4 in threaded rods that should equate to roughly 8 INCH pounds torque per bolt. Realistically, that's a snug twist of the wrist on a regular nut driver for the average build mechanic.
Only problem is a tiny bit more oil or even rougher threads on one of the pieces of all thread or nut and all bets are off on where you are compression wise.
 
Rig up a test with two blocks of wood that straddle a bathroom scale. Put a hole in each end of each block and you can test out the torque for just two lengths of 1/4-20 all thread, nuts and washers. A dry run will know if the math is correct for your hardware. 330lbs for two? Also, if I were you I’d probably error on the lower side of compression for WHEN the cells try to expand. Who knows what kind of pressure it’ll see. A 3/4” thick pine end plate will bow with time. I suggest to double it or use a couple of aluminum angles 1/8x1x1 at each end that the studs go through to backup the plywood. If you must remove the cells from the fixture after use, only do so when cool, a lower state of charge and re-fixture within an hour or so. Don’t let them relax too much. I use springs in my fixtures but there’s plenty of people that have rigid. Haven’t heard anything bad one way or the other which is best so I’m not judging anyone.
 
Only problem is a tiny bit more oil or even rougher threads on one of the pieces of all thread or nut and all bets are off on where you are compression wise.
That’s a concern with moving, mechanical things like bearings or a pressurized vessel of some sort.
It would seem to me that battery compression fixtures to a manufacturer’s specification or recommendations is less about the exacting torque of fasteners and resulting clamping force and more about creating a containment mechanism from everything I’ve read or seen.

One shouldn’t position themselves to drown in the details when the details are only one inch deep. In other words, one shouldn’t overthink the details if one is debating with a talking sparrow.

The idea is mere containment - and think of how many manufactured batteries are essentially not compressed at all!
 
That’s a concern with moving, mechanical things like bearings or a pressurized vessel of some sort.
It would seem to me that battery compression fixtures to a manufacturer’s specification or recommendations is less about the exacting torque of fasteners and resulting clamping force and more about creating a containment mechanism from everything I’ve read or seen.

One shouldn’t position themselves to drown in the details when the details are only one inch deep. In other words, one shouldn’t overthink the details if one is debating with a talking sparrow.

The idea is mere containment - and think of how many manufactured batteries are essentially not compressed at all!
I find it interesting that we are almost 1,000 posts deep in this thread and still debating whether compression is needed.

You mention pressurized vessels needing proper pressure, then say that you just want containment for batteries. The EVE specification is pressure. That part is stated very clearly.
 
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