I just bought 5 different packs of springs (all in 5/16" bolt size) from McMaster Carr. I will let you know what I discover.I was hoping to follow your lead .
Looking forward to what you learn...I just bought 5 different packs of springs (all in 5/16" bolt size) from McMaster Carr. I will let you know what I discover.
I am interested in each versions spring constant. Also how consistent that spring constant is for several examples (I will test 4 of each). And also how linear the spring constant is. I will measure force at 50% and 100% compressed.
I thought I’d checked them, but apparently not...
That’s probably the best deal yet I’ve seen on calibrated washers, but still significantly more than the ‘unrated’ washers.
For example, the 5/16” 110-159 lbs washer is close to perfect, but at $3.36 for 3, that’s $1.12 each.
But with 0.762mm (0.03”) deflection, you’ll need 8 per rod or a minimum of 32.
But $36 per 8S 280Ah battery is a good starting point...
Two in parallel (back to back) equals 70 with twice the displacement.I don't understand how two 70's in series equals 140. if they each compress to max at 70, then two in series will be flat at 70. The force doesn't divide, you just get more deflection before you reach 70.
Thinking about it, I may have the terminology backwards.Two in parallel (back to back) equals 70 with twice the displacement.
Two in series (nestled) equals 140 with the same displacement as a single washer.
Two in parallel << double force when flat.I don't understand how two 70's in series equals 140. if they each compress to max at 70, then two in series will be flat at 70. The force doesn't divide, you just get more deflection before you reach 70.
Now why didn’t I think of using < and > to make a diagram - brilliant!Two in parallel << double force when flat.
Two in series <> = same force when flat, but double the travel to get there (half the spring rate).
I'm not color blind ... but that is hard to see .... maybe bold larger font ...LOLI also think you are not supposed to stack more than 4 washers together. I think that means in parallel so <<<<>>>> is OK. But <<<<<>>>>> is not.
I believe that this <><><>is ok, however.
Here is an idea of what I mean about by a progressive spring:
I am doing an 8S battery with two sets of 4 cells being compressed in the same fixture. Each of four outer threaded rods will have from 140 - 195 lb (exerting from 10 to 14 PSI on the cells). The middle pair of threaded rods will have from 280 - 390 lb which shared by two sets of cells splits evenly into the same 140 - 195 lb.
Looking down on the compression fixture from above.
><>< 140 to 195 lb
><>< 280 to 390 lb
><>< 140 to 195 lb
Key to washer rating (if you are color blind this is not going to make much sense):
< = 140 lb washer
< = 195 lb washer
< = 280 lb (or two 140 lb in parallel) washer
< = 390 lb (or two 195 lb in parallel) washer
This same thing could be done using a wound spring, but it would definitely have to be a custom spring.
I thought of doing something similar and if you are paying full price for fully-rated Belleville washers, that’s probably the best way to go (assuming it works as expected).I am thinking about making a progressive spring. With a single 140 lb washer in series with three 190lb washers also in series.
To set the preload, start with discharged cells and tighten the nuts until the 140 lb washers are flat. The three 190lb washers will allow for 3mm of travel before the pressure reaches 190 lb.
So if I understand correctly, your saying that finger-tightening a socket is applying twice the recommended torque to busbars/terminals, correct?20 in.lb torque is only 2.6 N.m, no wonder people are having problems stripping threads when tightening the screws on their EVE load cells.
I am definitely going to use a torque wrench when installing the nuts on my bus bars. I think I saw a figure of 4 N.m recommended in another thread? That would be 35 in.lb