The battery builders club

If you can do the serial connections by wire

Could i do away with 14 AWG? My width space is limited that’s why i thought of connecting via nickel strip.

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Yea it will do :slight_smile:

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Nickel alone, no. Don’t do that, nickel is a poor conductor, and those strips are very thin. Either copper wire, or copper braid is what you want. If you can’t fit a single piece of 10-12awg, then two or three pieces of smaller wire in parallel will also work. Look up the cross sectional area of different wire sizes, and you can see that 12AWG has about 3.3mm2 of area, where 14 has about 2mm2. So two pieces of 14AWG will be even better than a single piece of 12.

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Hey battery gurus, I am trying to decide between Samsung 30q cells and LG MJ1 cells. I am interested in the MJ1 because people say it has a higher cycle life than 30Q but is that really true under our use case?

I know 30q is considered very durable compared to others but that is at 15amps. I wont be going that hard on them.

The easiest to find info shows 30q at 300 cycles and MJ1 at 400 cycles.

Although when looking at the data sheets of the two, the cycle life test have been performed at different amp levels. The MJ1 was tested at a lower amp level making it naturally have a better cycle life.

Can anyone find cycle life test for both done to the same standard?

LG MJ1 - 400 cycles, charge 1.5A, discharge 4A (80%)
Sam 30Q – 200 cycles, charge 4A, discharge 15A (80%)

Seems like the cycle life for both is close to 300 if the test was the same around 10A?

My planed use is for a commuter, each cell will be discharged regularly at 6-7a and occasional peaks of up to 10a. Charged @0.5c. Low voltage cutoff 3.3v

Although I did find this comparison from NASA although the discharge rate appears to be only 0.58A?

image

image

This is 30Q from Samsung’s data sheet, discharge at 15A and strangely charge at 4A.

Although MJ1 at 80% capacity has more left than 30Q at 80% Still I have not seen MJ1 life cycle tested at a decently high rate of draw to draw a conclusion for my usage.

Might want to have a look at Sony vtc6 as well.
They seem to have a better cycle life than 30q, do perform similar and depending from where you order are priced similar as well.

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I haven’t used the MJ1, but 30q seems overkill for your use case and the MJ1 also has a higher capacity…

I’d be going MJ1 if I were you.

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Hey bro! I like to do series connections with braid in tight situations like that. I weld tabs to the cells and then fold the tabs back over on top of the cells, but leave an airgap there while I solder the braid to the tabs.


I use the forceps for multiple reasons;
A) they hold the shit to the tabs
B) they help stop the solder from wicking through the braid
C) they act as a heatsink

many thanks and appreciation to the mighty @Arzamenable for this absolute gem of a technique :ok_hand:

Once the soldering is done, I use a quick grip clamp to squash the nickel back down against the cell for the tightest possible pack. If there are any high or sharp spots in the solder to the braid, I hit it with the cutoff wheel on the dremel.

Whenever you are soldering to nickel, be sure to rough up the nickel surface. It is crucial for a good bond. I use the cutoff wheel on the dremel on a low speed

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Thank you for the great info! I might go with the braided wire, or 14 AWG.

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Strip the silicone from the wire if you are really tight for space :ok_hand:

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Hey all, I’m in the process of building my first pack and figured I should see if I missed something and QC here before I finish it. See first pic for design + 80a discharge BMS.

Thoughts:

  • Are spot welds OK? At first I thought they were but noticed on closer inspection that some welds have a slight crack around the center, guessing slightly too high power (~27J on kWeld). Are they OK to keep or should I redo?
  • Did I under dimension the series or parallel connections? Two 12awg wires for series and single 10*0.15 mm nickel on parallel. Referencing amp chart suggests series connection to be fine but parallel to be questionable. Improve in any way or will it be safe as is?
    -Lastly, solder joints. Made them before welding them to the cells. Do they look okay or should I revisit? Clean them? (if so how?)

Tell me what I did wrong and I’ll be super happy,
Peace

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Looks a hell of a lot better than my first pack :joy:

The welds look great dude, some of them are maybe a tiny bit too hot, but all in all it looks good. No need to redo them.

Your solder looks pretty well saturated, if you want to clean up the flux you can use some isopropyl alcohol. I usually blow the joint until it solidifies and then just wipe it with a wet rag while its still hot, this gets most of the flux off and cools the joint at the same time.

2 x 12awg is ample for series dude, probably could get away with 2 x 14awg even. As for parallel, also ample.

You’ve done an excellent job for your first pack bro, keep us posted with the balance wire progress and your final insulation :ok_hand:

I’m gonna add this as a constructive criticism because its been all praise so far… you could improve the rounding on your nickel. As it is, its far safer than a lot of packs I’ve seen, but I feel like I had to pick on you for something :joy:

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Thanks man, appreciate it! Nice to hear some reassuring words :grin:

Will see if I can pretty up the remaining tabs and clean those joints a little bit.

For balance cables, I want to wrap some nickel around from the open cell. I’ll update with pics shortly!

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I chop my balance tabs small, like chop the strip in half, they are easier to keep tidy.

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Cheers, gonna split the pack and plug in when both are charged fully I think. Keep costs down. And ofc make sure the cells are the same voltage before plugging in

Does a little bit of magic smoke mean your bms is completely toast?

Lmao probably, did you check the board?

The bms board itself if fine, but the little bms resistor that had 101 on the front has since burned off the 0 in the center. Kinda wack. Might be able to replace

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Built my first battery
12s5p and 2 of the packs are at 2v
Would like to slow charge the battery up but haven’t wired bms or main negative or positive yet
What is the best way to charge it
Should I wire the whole thing first?
Thanks