10S5P Battery Pack build log. 50 pieces of Samsung 35E cells

Btw, do your welding cables start heating up after a dozen welds? Mine are ~7 AWG and they do start getting progressively hotter with the welds. The below IR picture is from after about 2 dozen closely done welds.

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I´m using 8 awg and they are getting warm after 10 welds and hot after about 20 welds when I´m fast

yeah they get noticeable warmer but not hot.

@The_Dude has exactly the setup you proposed: car cap with timed mosfet switch instead of a car battery. Seems to work well: https://www.electric-skateboard.builders/t/dude-hubs-in-depth-dual-hubmotor-build/21519/55?u=maxid https://esk8content.nyc3.digitaloceanspaces.com/uploads/db2454/optimized/3X/8/8/8821dd89b27ab0e0b89511d008f39cdd470e36a7_1_666x500.JPG

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Im not a spot welding expert, but my audio cap works very well and it was a very cheap spot welder in total: https://endless-sphere.com/forums/viewtopic.php?f=35&t=70435&hilit=evolve+at#p1062504

not perfect, but I got pretty fast with batteries by now - would say I made about 10 batteries in total. my welding spots seem less pronounced & deep than others, but when I tried to separate the nickel strip from a cell, I tore off the strip and the nickel at the weld spots was still on the cell.

btw, my discharge wires are 25mm^2 (!!) and my copper rods are 5mm thick and they get quite warm to the touch after fast welding.

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How would a setup like this perform compared to a sunkko 709?

@Maxid @whitepony @TarzanHBK Now the question is whether a 1 Farad cap is going to be enough, because that I can go get immediately in a local shop. Otherwise I’ll have to order it and wait for it to arrive and I’d like to get this pack welded together ASAP.

im interested in this too. Get more info, please share it here, maybe :slight_smile:

Well I just ordered a 1 Farad cap from UK for 14 £ with shipping so at least if it doesn’t work at all, I’m not making a too big of a dent in my pocket and if it does work I can order a second one to connect in parallel :wink:

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Any Update? :frowning:

Update.

This process has been a b***h and a half, if I’d have to sum it up. Not going smoothly at all.

So what’s been going on?

Well, I ordered the cheap car audio cap from ebay, waited a couple of weeks and was starting to wonder why the item had not been shipped. I go check the order on ebay and discover that the seller account I ordered the cap from has been terminated. Ok? I contact ebay support about not receiving the item and that the seller account doesn’t exist no more, so I can’t contact the seller anymore. Couple backs-and-forths with the support and they cancel the order and refund. Ok, wasted a lot of time there…

I go and find another audio cap that’s the same model, but more expensive, but whatever I just want to get this project rolling forward and I order it. It finally arrives couple weeks later, so at this point I have already lost a month of time. I make it part of the system and replace the car battery with it. I test it. Nope, nothing, barely making a dent in the strip. Well just what the cuck man? When I give the welding pulse the voltage just crashes back to zero on the cap. I test the thick strips more, but they just don’t weld, they simply don’t heat up enough to get welded. Then starts the other part of this delay. I go to test the strip one more time and just by touching the welding anode and cathode on the strip causes suddenly sparks to fly. Wut?.. It also turns out that I had borked up my grounding on the welder, which left the logic side partly floating and caused one the gates on the mosfets to basically fail, so it short circuited the mosfet internally (Or that’s what I post-mortem believe to have happened). Shooooot… And I tried to see if I could get the mosfet desoldered, but with the large gauge wire soldered to the back of the board, it just sucked away the heat and I decided to just start designing a new one instead.

So then I spend a couple weeks designing a couple different PCBs for my different projects and sent them to manufacturing. 3 weeks later I got the new boards. Now I’ve gotten the new board assembled and just did a couple test welds with only the audio cap. Nope, still nothing. Well, s**t. I hook up the car battery in parallel with the audio cap. On max pulse length of 16 ms, there is a little bit of welding going on, but not something I’d trust to put under any sort of vibration. Hmmm… what to do?.. Increase the length of pulse ofc. Crank it up to 64 ms and oh yes, we are welding boys.

Then I started to wonder why in world do I need such a long pulse length? Well, TLDR: The car battery is not stronk enough. Picture below of my oscilloscope attached to the terminals of the car battery.

So the battery floats at about 12.6 Volts, then comes the first short pulse and the voltage dips to 8 V it then bounces back up during the short pause and then when the main welding pulse comes it dips back down to 8 V, so what does this mean?

These strips are goooood man. They conduct well so they don’t heat up as much relative to the current and they sink the heat very well, due to them being 0.2 mm thick. The car battery simply can’t provide the strong current pulse, because the voltage dips down, meaning the welding current also dips down, meaning that I have to use a loong pulse to get the contact points to actually heat up to welding temp. I guess I’ll have to invest in a beefier battery at some point as @TarzanHBK

The spot welder itself has no problems, barely heats up. I guess I’ll try to finish this pack finally this weekend!

EDIT: Ok, I need another battery, because it still can’t weld 2 strips on top of each other…

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yep, it´s like our lipo batteries with to low c rating :wink: The poor car battery is simply not strong enough. You could use 2 or 3 of them in parallel or get a bigger one.

This thing pumps out some real angry pixies!

The red lead jumps when I pulse the thing and I can now actually weld the strip on top of each other.

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Nice :slight_smile: Always funny when cables are jumping around because of high current :clap:

I can’t edit the original post anymore to add the rest of the build log, so I’ll just have to add it here.

Continuing Time to add the parallel tabs… finally. I first finish 4 easy identical packs, which will then be assembled into a bigger pack.

Now here’s the both halves of the pack done. There are also parallel tabs on the bottom to complete the circuit.

Time to prepare the balance leads Now comes the interesting part of the build, which I don’t think anyone here has done it like this before. First we need some small nickel strips. I cut the pieces in half lengthwise.

Now we can solder the balance lead on to the strip.

Money.

And then finish the leads by heatshrinking the ends for a neater look.

Now I can weld the rest of the pack and I can just weld the balance leads onto the strips. No soldering iron anywhere near the pack at any point.

I then folded the pack out just like shown in the original post’s planning stage.

Close-up.

I then routed the balance leads to the front of the pack and taped everything together to add some rigidity.

It fits so snuggly into the board. Although it should, because I designed the board from the beginning for this battery pack.

I’m most likely going to go with a XT60 power connector, which will plug into my own BMS module. I have XT90-S loop key, so I don’t have to worry about the in-rush currents.

Summary and afterthoughts: I think I’ll have to admit that I used too thick of a nickel strip. The 0.2 mm thickness is just overkill for the currents I spec’d this battery for. Mind you this is genuine pure nickel that I tested and verified. I’m still not 100% happy with the welds and their penetration. They could be better, but would require a complete rework on the pack, so I plan on going with what I have now and seeing if it survives. If the welds come undone, I’ll rebuild the whole pack with thinner strip (0.1 or 0.15 mm).

The most challenging part of the build was in the assembly stage after I had folded the pack out and needed to route the balance leads to the front. Problem was flipping the whole pack neatly onto it’s pack, while it did not have all the tape giving it some structural support. Ideally at the point you see in the last picture, would be to shrink the whole pack with a big PVC heatshrink sleeve to give it a neater look and give more mechanical support to the pack. I do believe that the strips will stay connected as long as there isn’t any rotational or twisting motion applied to them.

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Figured out in part why the car audio capacitor did jack squat for the spot welds.

Being bored in the evening, I decided to strip the capacitor down to the cap itself. So I removed the voltage display module and removed the PVC shell with the “1 Farad - 1000 Watt audio capacitor” text on it. We’ll see about that…

I decided to test the real capacitance of the capacitor by doing a RC time constant measurement https://en.wikipedia.org/wiki/RC_time_constant

I set my power supply for 10 Volts and connected a 10 Ohm resistor in series to the capacitor, So if the cap really has 1 Farad capacitance, the voltage should rise to 6.3 Volts in 10 seconds…

Except it only took 2 seconds…

THIS FRICKIN’ THING IS ONLY 0.2 FARAD CAPACITANCE!!! NO WONDER IT DIDN’T DO ANYTHING TO THE WELDS!

Color me semi peeved off…

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But wait! There’s more!

Decided to cork this POS open to see what is inside…

So I mangled the end of it open.

That looks like… cement?..

Oh, it IS cement. I can now guess where this is going…

Did two long cuts length wise on both sides to start cracking it open. Hmm… those look like normal small caps…

MotherF****!

With a god dang cement puck at the other end!

I already wish I could shove this up the arse of the chinese bastard who made this scam…

Welp, it’s a fake confirmed. So maybe a closer look at these el.caps explain why the measured capacitance was only 0.2 Farads from the promised 1 Farad one…

16 V 10000 µF caps.

And there’s twenty of them… Well, THERE’S MY GOD DANG 0.2 FARADS OF CAPACITANCE ALRIGHT!

@Okami @whitepony @Maxid @TarzanHBK

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wow - reminds me of these:

Glad you at least got some welds done

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WTH is that supposed to be? A powerbank?

Either a “high-capacity” usb storage device or a power bank.

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these are chinese usb drives that are obviously sold with much higher capacity as they actually have just like @SimosMCmuffin said.

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