Advice on a 48V pack from E-golf battery needed

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HrKlev

New member
Joined
Jan 13, 2020
Messages
4
Hi guys!

I got a great deal on a 24kwh E-golf battery pack a couple days ago. Unfortunately I didnt have too much time before I had to jump on the deal, and one of the few pictures that came up on google showed a cell with threaded studs, so I took the chance. I have been spoiled working with the Yuasa cells from Outlanders before. They have M8 studs and are super easy to build whatever size and shape you want with. After disassembly, I realized that this was not the case with these cells. They have no threaded studs, and are assembled in 17 packs of 4s3p, and 10 packs of 2s3p. The bus bars seems to be crimped on to the cells, and it looks like they are made of aluminium. It is impossible to solder anything to them (at least with what I have available). The lugs for the balance cables are spotwelded, and it is possible to solder a cable to these.

The battery will be hooked up to a Multiplus 48V 5kva, so a 14s configuration seems like the best shot.

Now the question - how do I do this?

  1. 6 strings and a batrium K9 cellmate would be my first choice. Only problem is that the BMS would cost as much as the battery, so its not that tempting....
  2. 6 strings and 6 chinese BMS's, and a victron smartshunt to keep count of the battery status. I have several small battery packs running with ANT's and Xiaoxiang BMS's running and have had zero problems. However, I would like to try something little more tried and tested for this size of a battery. Or am I being overly sceptical and should just go ahead with this solution?
  3. Connect the 6 strings in parallel and use one Batrium K9. This was my plan if the cells were studded, but this situation makes it a little harder. I cant seem to find any other way for parallel wires than soldering a cable to the little balance lug that is spotwelded to the bus bar. So what I wonder is, could I get away with it? I would probably use a 2.5mm2 cable, and I was thinking of maybe using 16A inline fuses on the balance cables to protect them in case of a cell failure. The cells was perfectly balanced when I disassembled them, and I would imagine only a small amount of current will be flowing in normal running conditions. In case of a cell failure, the fuse would blow, and the parallel bank would lose 1/6th capacity, so the batrium would catch it on cell imbalance. Something I am missing here?

Any advice would be appreciated! I have attached some photos of the modules and how I would like to configure them. And just a really quick test solder on one of the modules that will be spare anyway (I have also tried to thread one of the bus bars. I think they are a little bit too thin and soft to get a decent mechanical connection).
 

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OffGridInTheCity

Active member
Joined
Dec 15, 2018
Messages
1,862
Hi guys!
  1. Connect the 6 strings in parallel and use one Batrium K9. This was my plan if the cells were studded, but this situation makes it a little harder. I cant seem to find any other way for parallel wires than soldering a cable to the little balance lug that is spotwelded to the bus bar. So what I wonder is, could I get away with it? I would probably use a 2.5mm2 cable, and I was thinking of maybe using 16A inline fuses on the balance cables to protect them in case of a cell failure. The cells was perfectly balanced when I disassembled them, and I would imagine only a small amount of current will be flowing in normal running conditions. In case of a cell failure, the fuse would blow, and the parallel bank would lose 1/6th capacity, so the batrium would catch it on cell imbalance. Something I am missing here?
This logic is perfectly sound. You can definitely share sense leads across multiple parallel batteries - and (as you say) as long as the cells aren't way out of balance the power will flow thru the main load wiring rather than the sense leads.

@LithiumSolar did fuses / longer-wire sense leads on his K9 setup to LifePo4s.
View: https://youtu.be/m0Z25-jqLrs
 

HrKlev

New member
Joined
Jan 13, 2020
Messages
4
Thanks for tour feedback! Im struggling to make a decision now. I am not confident about the current carrying capability of the soldered cable lugs... And if the parallel cables should be fused or not.
If a fuse goes out because of a partial cell failure, there are no 100% way of detecting that, and one of the strings could potentially go way out of balance without me knowing.
And in case of a total cell failure and no fuses those small 2.5mm2 cables would get quite toasty....

It almost feels safer to do 6 strings with ANT bms's and mcb's on each strings.

Its a hard decision... Kind of wished I had gone for the slightly more expensive I-miev packs now 😂
 
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