Please review my battery pack so I don't make a 🔥

[Scream]

Ok battery build thread here goes:

Here’s the gist of what I’m trying to achieve:

I grouped the cells in threes and glued them with black hot glue, plus taped the positive ends with kapton tape. Then I spot welded a length of 0.15x8mm pure nickel strip to the positive and negative terminals of each p group. I used fish paper rings on the positive terminals, and trimmed the corners of each strip.

To isolate each p group from its neighbour (and the cells above or below) I cut a piece of 1mm pressed insulation board (like presspahn), and scored a fold in it. Then I shrink wrapped each p group.

I then connected each p group using flat, braided copper speaker wire

For the connections between 3 and four, and 7 and 8 I stripped the insulation from the speaker wire and just wired two lengths of copper braid straight down between the groups. Between 5 and 6, I folded the speaker wire in half.

Complete pack photos:

Link to BMS used:

US $15.75 12% OFF|10S 13S 36V 48V 40A 60A Lithium Battery Protection Board...

BMS wiring diagram:

It’s going to be hard to check my BMS wiring, but the key point is that b0 (Black balance wire) is wired to pack negative, and all subsequent balance wires up to b10 have voltages increasing in increments of 3.42v(ish).

One thing that happened when I was wiring up is the battery charge negative made contact with the BMS body and sparked. The balance loom was also loosely touching the BMS balance pins. Because they were only loosely touching, it’s possible the current sparked across from the balance leads to the wrong part of the bms.

I think this short significantly damaged the bms. When I connected the balance plug (I think with everything correctly wired) it sparked and smoked.

I’m no electrical engineer, but I believe it’s a blown fet?

If the brief short isn’t to blame, the other explanations are:

• I made a mistake in my wiring; or
• The BMS is junk, and what did I expect for the price?

If the cause of the fault was in fact the short while I was wiring up the bms, this begs the question - what is the recommended order for wiring up a bms? Battery negative first, or balance leads?

[Andy87]

Usually first the main leads than the balance leads.

[lrdesigns]

Just dropping these here as they are so nice. @akhlut did a great job!

[b264]

@Scream

When I went to plug in the balance wire loom it sparked and the BMS smoked. I did check the voltages on each wire and they were in order (from B0 to B10):

4.38 9.37 14.08 18.77 23.4 28.1 32.8 37.5 42.3 47

Something’s not right though

@Scream

Balance loom from b0 to b10 goes: 3.42, 6.86, 10.29, 13.71, 17.13, 20.4, 23.8, 27.3, 30.7, 34.1.

Both of these have 10 numbers but you’re saying B0 to B10 which is 11 wires.

This sounds like an off-by-one error.

Also the diagram you posted is not correct, B0 should at the same tension (voltage) as B- and B1 should be about 3.5V higher to the positive side

So measuring from B- you should have (assuming all cells are at 3.5V charge level)

(eleven numbers, eleven wires) B0 - 0.0V B1 - 3.5V B2 - 7V B3 - 10.5V B4 - 14V B5 - 17.5V B6 - 21V B7 - 24.5V B8 - 28V B9 - 31.5V B10 - 35V

What is the voltage between the big B- wire and the black balance wire (B0) ? Do you have a photo of the bottom of the BMS? How about a photo of the plug the balance connector goes into?

@Scream

what is the recommended order for wiring up a bms? Battery negative first, or balance leads?

I think battery negative first

[Scream]

@b264

Both of these have 10 numbers but you’re saying B0 to B10 which is 11 wires.

I thought someone might mention this… i wasn’t sure how to write it in a way that wasn’t confusing.

I left one leg of my multimeter connected to b0, then measured the voltage to b1, b2… b9, b10. I can confirm no voltage drop between battery negative and b0 ( the other end of b0 is soldered to the negative terminal lol).

Here’s the bottom (other side) of the bms:

[b264]

@b264

a photo of the plug the balance connector goes into

This would help, but I don’t see anything wrong at the moment…but I don’t know which way the plug orients and I need to know to help any more

[Scream]

[martijntje42]

Out of curiosity I removed the shrink wrap of a cheap Chinese xt-90 splitter. I was kinda surprised to just find solder in there to bridge the gaps. Is this an ok method of doing it? I was going to make my own one of genuine xt-90s and was wondering if I should use the same method or just make a regular y harness using wires.

[bigben]

Rainy day today so I’m making a battery. All and any advice welcomed.

[moon]

What soldering iron do you use?

[bigben]

Antex 100W. Very quickly because it’s a beast. Less than a second.

[moon]

Ok I’m looking for one since the one I just bought was awful. Where did u get it

[bigben]

ebay. This is just for big stuff though. I’ve got a smaller one for other stuff.

Antex Sr8w270 Hp100 Soldering Iron Blue for sale online | eBay

[moon]

Well ok I bought this

https://www.amazon.co.uk/Sealey-SD100-Soldering-Iron-Silver/dp/B000R9Y0ZK/ref=mp_s_a_1_4?ie=UTF8&qid=1544888344&sr=8-4&pi=AC_SX236_SY340_FMwebp_QL65&keywords=100w+soldering+iron&dpPl=1&dpID=31IxDbQSXTL&ref=plSrch

Looks almost the same but for some reason the tip deteriorated within like 10mins of soldering

[moon]

As for the spot welding. It’s not pretty but I don’t see anything alarming

[deucesdown]

The Weller 100w has a temperature controlled huuuge tip, great for big stuff (terrible for non-big stuff).

https://www.amazon.com/Weller-W100PG-Farenheit-Soldering-Degree/dp/B07C43TSFK

[deucesdown]

@bigben

any advice

I don’t think it’s necessarily a problem, but something to be considered. Some of the series connections are 2 x nickel, and others are wire braid? I suppose the nickel ones will just bottleneck the pack as a whole rather than causing some kind of uneven discharge.

And I know usually everyone does the parallel welds as first layer, series welds on top of those, but for me I find the nickel-to-nickel doesn’t stick quite as well as the nickel-to-battery. I think, I could afford to lose a parallel connection but losing a series weld would be no bueno. So I would do battery → series weld → parallel weld. Someone correct me if I’m full of shit.

And something I do when I’m making packs, I put tape on all exposed contacts that I’m not currently working on. I know you’d remove all that for the photo shoot, but thought it might help someone.

I like the welding jig

[bigben]

The nickel is 12mm x 0.15mm so I thought that would be ample for the size of the pack? 1 strip should be good for 40A or am I way off?

[UKRider]

Batteries looking good, Nickel should be enough… I bought some 15mm wide 0.2mm thick nickel.

Yet to put my DIY welder together.

I will be using one of these butane soldering irons

[J0ker3366]

@martijntje42

Out of curiosity

Yes this is acceptable.