BMS solution and wiring

I've been working very slowly this last couple of months. In part, I think it was due to issues with DC DC converter and also several unsuccessful attempts connecting the BMS to the battery pack.

As you can read here, I switched from a custom battery terminal board to a used one from a Nissan Leaf, which came with all the leads.
I also bought a 32s ANT BMS from AliExpress, after reading a lot about BMSes:

32s Ant BMS
32S BMS I bought from AliExpress

I did look at other solutions but the main factor to choose this was cost. This is a much more inexpensive device and, at least on paper, it ticks all the main boxes. There also seems to be plenty of information around, although the different versions and vendors of this Ant can also be confusing and misleading.

Since the price difference was small, I went for the highest current, 300A, even though I will probably bypass its MOSFETs for discharge if I can implement a reliable way to monitor the current and control the main contactor instead. I did not ordered the screen since I'm planning to use the bluetooth interface (Android APP and a custom program on an Arduino -- an ESP32 with bluetooth).

Connecting the BMS wires to the voltage leads has been quite frustrating and slow!

I first used the information in OpenInverter.org to see the part number for the OEM connectors (here) and ordered some from Ebay (first) and Mouser (later). In my case, I needed a 24 pins and a 32 pins piece.

OEM connectors for voltage leads
Detail of OEM connectors for voltage leads. My plan was to reuse them and find matting connectors for the BMS.

The first issue was that the slots were not exactly the same but I fixed that quickly with a Dremel-like tool. But the real pain in the *ss and what made me give up of that "clean" solution was the difficulty of inserting the pins in the connectors without damaging them. I lost a LOT of time and the results were, well, crap. I also bought a second set of connectors from Mouser, in case the Ebay ones were some bad knockoffs, but they were pretty much the same but pricier.

After some head scratching, I decided to replace the connectors altogether. I considered AMP and Deutche connectors, both used frequently in automotive. But in the end I went for Molex Micro Fit for its lower cost and ubiquity.

It was a slow process because I didn't had the correct tools for the job, namely a good crimping tool and, later on, de-pining tool.

I read a lot of videos about crimping these Micro Fit terminals. Most hold the terminal in the crimping tool, insert the wire and then finish the crimping. However, I found that I couldn't see how far the wire was inserted that way. So I used a small plier to squeeze the larger "wings" (the ones that hold on to the insulation) before inserting the wire and terminal in the crimping tool. That way I was able to have consistent results where the wings are correctly holding to the insulation and bare wire.

I also learned the hard way how to de-pin (remove) terminals from the connectors. Even with care and attention, I made some mistakes in the order of the pins. And a single mistake means all the pins after that are also wrong.
Again, there are some online instructions or videos about this but are suitable for larger connectors and use a two pronged tool. However, the Molex tool is a single prong tool but costs more than 30 euro! After quite some trial and errors and bumping into wrong instructions I finally found this one which explains the (simple) process:

Instructions for de-pining Molex Micro Fit terminals
Instructions for de-pining Molex Micro Fit terminals, taken from Molex Instruction Set

Basically, any thin but rigid flat piece of metal would be up to the job. I ended buying a 5 euro set (see below) with a lot of tips and the process is simple once you get the hang out of it: insert, from the front of the connector, the flat tip on each side of the terminal (at a time) and give it a twist so the side flaps/wings move "inside". Then you can pull the wire. Sometimes the wire would come out of the terminal but it was a matter of pushing it from the front with the same tip used to flatten the flaps.

Finished BMS leads wiring with Molex connectors
Finished BMS leads wiring with Molex connectors (3 x 12 pins). I learned a lot about crimping and de-pining in the process :D

Sorry if this is kind of boring but I hope it helps someone in the same situation. It also reflects my mood when doing all this job. Not fun but important to check the battery health and avoid fires :)

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