40T, neodymium magnets, plasti dip cycle test

started a 5 cycle test. temperature starts at 72F, after a 7.5amp discharge temp reachs 91F magnet and wire temp drops to 88Fonce discharge ends and battery remains 91F but slowly drops after 5minutes rest, charge starts and Battery temp will drop to 84F eventually reaching 86F by end of charge


heres the readings of each step D-CC is discharge 7.5a to 3.0v, C-CV is charge, to 4.12v with 0.35a cut off
capacity is mah, energy is wh



TheBeastie said:
People seem to forget that the Tesla EV battery pack runs off this level of thinness connections, clearly the philosophy of Tesla battery packs is "many hands make light work".

Yes, but there's still a large current collector in the nickel-plated aluminium busplate. After all 42-odd cells are delivering 5 A each, that's 200 A and it's the busplate which takes this current.
I moved the tester and battery to a different spot started cycle test went to bed when I woke up and checked the test the fan had been blowing on the battery and it was at 5 minute rest phase of cycle #7. checked battery temp and it was 71F/21C.

at end of discharge #8 battery temp was 92F/33C, negative magnet was 91F/32.7C and positive magnet was 88F/31C
jonescg said:
Yes, but there's still a large current collector in the nickel-plated aluminium busplate. After all 42-odd cells are delivering 5 A each, that's 200 A and it's the busplate which takes this current.
So Tesla wires its packs "parallel first", to build Ah capacity at 1P, and then the plates get serial'd to increase the voltage?

you can see after 7-1 is when I stopped the fan from blowing on the 40T and then capacity and wh recovered. after this test completes im going to do 1 cycle test with battery in cardboard box to see if increasing cell temp will increase mah/wh







battery temp was 73f after final charge

if you look at tesla wire and and stuck it in the hole with conductive adhesive click it on battery and solder to bus bar

heres the 3 magnets little one is 3/16x 1/16x1/16



ill order some adhesive and test it

I was thinking of silver paint between magnet and battery


feel free to ad suggestions

I think im going to order this one, its the fastest delivery time. so if someone here thinks its a bad idea just say so
heres the charge

when the 5amp charge hits 4.12v and starts to taper down to 0.35amps the temp is 87f


end of charge temp is 76f


ill do a 5 cycle test in box to see if the warmer temperatures help
I think the acrylic base is not ideal, designed as "paint" on a 2D surface, likely forms the conductive layer along the top

I believe other solutions ?? epoxy based ?? wojld allow for conducting through the gap-filling mass, 3D.

Good company though.

Maybe they have techs to talk to?
id like to find a conductive liquid, not an adhesive. just put a pin drop on the battery attach magnet and then plasti dip it. maybe silver conductive paste instead. I was looking at conductive epoxy to glue an electrode into the hole but i see temperatures of 200 for curing, might be too hot for the magnet.

could also wedge the 16 gauge copper in the hole with something like a thumb tack
you could tell the battery was running bad, too cold but now at end of discharge, temp hits 99F and after charging lowest temp is 76F. its putting out a steady result for now.

yes, my first thought was do either magnet or adhesive rather than both

thermal paste to increase surface area contact

so long as you get a good resistance measuring setup to verify these various options
What exactly are you trying to test here ??
Magnet connection system ?
Glue/adhesive conductivity ?
Cell thermal properties ?
Cell capacity/discharge ability ?
..you seem to be mixing a combination of variables and objectives.
A couple of suggestions.
1) ANYTHING ( paint , adhesive, paste etc ) you put between the conductor and the cell surface, will reduce conductivity !
2) read up on how to do accurate and repeatable cell IR tests..its not difficult.!
Use IR testing to check the effectiveness of your different magnet connection methods compared to a direct cell contact method.
3) there is no reason to expect those magnets to heat up other than simple thermal conduction from the cell internal heat. They are not part of the electrical conduction path
I like pure soft copper foil as the bus contact to the cell-end. This way it can conform to the shape of the cell-end. They appear to be flat (and most are very flat), but there may be irregularities that are not obvious on every cell.

A discussion about using copper contacts to allow for high amps in a no-solder/no-weld contact brought up the subject of copper oxidation in harsh environments. Polished copper will eventually turn brown, and its' skin conductivity will get worse. It's not horrible, but...not good. Even worse if you live near the salt-air of the beach, copper will have its skin turn green with the copper-oxide cancer. So to protect the contact point from oxidation, there was a discussion about DIY conductive paste (to hermetically seal it).

"Conductivity improving paste project" (liveforphysics, 5 pages)
im doing a cycle test but I wanted to experiment with magnets. John asked about the resistance of the magnets but im doing a copper electrode which touches the battery and I think from what you say if I put anything in between battery and electrode it will add resistance but im worried about oxidation

so this will be my no solder solution for my next pack,just working the kinks out right now, if im going to buy 68 40t. I want to run them the way I think theyre designed to be run so I had to buy a tester to see.

I live in a cooler climate so I want a battery that can maintain its 100%t temperature while riding in cooler weather. I think if I run my 4p pack at 50 amp burst and about 30 amp continuous then that's 7.5a to 12.5a/cell. then if I charge at 5amps in 1 hour I just need a 20 amp charger for fast charging instead of a big battery. I think 100%a is 10 amps but???? I don't know what im doing but if the 40t can get 750 cycles and be 80% ill buy them if not, buy a different cell and make bigger battery at 3.5a/cell.

in the above test by putting the battery in the box to increase temperature the battery is providing better results. the previous tests I think the wh was dropping 0.02 every cycle same with capacity every cycle. but now its better.

I pulled that battery to plasti dip the ends and then ill just let it cycle.

I could do another 10 amp discharge on the plasti dipped battery under the above charge/volt condition to see what the mah and wh is. I think temp hit 106F on last test, I wonder if the extra heat ate up some mah? ill do another test, takes 2 hours
Great thread.

My thinking is

A. thin-stranded tinned boat wire strands "splayed" out flat in a short fan

(don't like the umbrella/angled splay shown here)

or perhaps crimped into a solid very flat copper "disk / coin"

B. physically held in place against the end of the cell*

(as with foam-pressure in other solderless, role of the magnets here)

C. the whole assembly then encapsulated per-cell in non-conductive permanently flexible sealant/adhesive, gas-tight and waterproof, preventing oxidatiin of the copper against the cell ends

(role of plasti dip here)

* in B above, role possible for soft copper foil disk with conductive adhesive/paste

**not** to go between the primary contact surfaces

just to hold the splay/disk in place securely on the end of the cell from a lateral location POV, preventing slipping during the assembly process, gluing the foam, putting in the case etc
I did not ask about magnets' resistance, I understand they are not in the flow path.

But overall resistance A/B comparing different methods / materials, and of course compared to spot-welding.
between you and beastie, john. might be able to splay wire then wrap magnet and wire in that copper conductive adhesive kinda like a Hershey kiss?
did the 10 amp discharge forgot to save screen before charging, temp hit 106f mah was around 2900 but at rest volt had sprang back to 3.411v once discharge stopped. im going to do it again but save and share, I might be able to find the mah of 3.411v in the 7.5a discharge to see if its the same?

spinning magnets brought up an old thread about magnets, he bumped 2 threads back into the battery threads
see that bump in the blue line, I bumped the gator clip. I need to replace the clips with good ones I guess. looked at data for 7.5amp but it didn't give mah but this test the volts came back to 3.374v at rest


okashira mentioned copper anti-seize, im going to look into what she was talking about, haven't yet just brought link over
john61ct said:
jonescg said:
Yes, but there's still a large current collector in the nickel-plated aluminium busplate. After all 42-odd cells are delivering 5 A each, that's 200 A and it's the busplate which takes this current.
So Tesla wires its packs "parallel first", to build Ah capacity at 1P, and then the plates get serial'd to increase the voltage?

In the case of a Model S/X battery module, yes it's about 74 cells in parallel, and the bus plates complete the series links to build up to 6s.
mrbeastie mentioned cw7100
I will see what I can find today, pretty sure I can get copper anti seize locally and possibly cw7100. if I can use it to fill the air gaps with splayed wire connection to keep the plasti dip/air out of connection and do some tests to see what happens.