First, crimp sizes are manufacturer specific, so you may find that some SC10-8 lugs from one manufacturer fit, while others form another manufacturer don't fit. So it's hard to recommend a size - other than to say find the one that matches the wire most closely but still goes in easily without stray wires.
Second, short chassis wires may be lower gauge than what your application needs, so if you're extending the wires then you should consider going to a larger wire size to suit your actual application. Not only for safety - which is critical, I'm not dismissing it - but for lower resistance and lower losses. 10mm2 wire is good for 60A in terms of energy loss and heating. Anything above 60A and you'll want to pay very careful attention to your wire selection and how it's routed - can the insulation take the heat? Is it going into conduit? What's the duty cycle for the high power? So if the BMS comes with undersized wires it might be ok depending on their specific wire, and the expected or required usage/installation their equipment requires. But you should transition to a larger gauge wire as close to the BMS as you can if you plan on pulling the full 200A rated current.
Third, you can't tell if a crimp is good or bad externally - you would need to cut across the crimp and look at the cross-section to verify the copper wire and ferrule contain no voids in the crimped area, or run the maximum power through it that it's expected to handle in cycles for a long period of time and confirm that it doesn't become hotter than the wire after all oxidation has taken place. If I had to guess, though, it looks like the crimp isn't completely solid, the SC16 is too large, and you have air gaps between the copper and portions of the ferrule. But again, it's possible that it's good - you just can't tell without destructive testing.
I just had a go at it yesterday with my 2 x JK BMS.
To be "ready" for all cases I purchased both the 10mm2 and 16mm2 cable lug.
After a bit of fiddling, the 10mm2 was "no freaking way". I could not even start pushing the JK BMS ultra-fine wire into it, not more than HALF would even accept to start going in
.
So I had to go to with the
16mm2 cable lug. Afraid of not doing a "proper crimp" and also because the 16mm2 didn't seem to align very well when fitted on the hydraulic crimper, I went with the
10mm2 die set. And I went it all the way to 10 tons ... twice (2 crimps). Well 12-16 tons after the first hydraulic crimper started leaking and I had to switch to its bigger brother for 8-300 mm2 wires
...
As a result quite big "wings" (maybe also called "ears" ?) formed, like this
one on the left for instance (cannot comment on the text of this image, seems a bit weird especially the right one...):
Sometimes the wings came at 90°, but most came at 180° from each other. I guess in some cases the second crimp was angled compared to the first one.
I did NOT file or cut the wings off, as I didn't want to damage the crimp. Gave it a little tug test (pulled "reasonably", but without a "ton" of force
) and it didn't move. Just put heat shrink on it.
I have 2 x Smoke Detectors in that battery. I'm also considering glueing some temperature sensors on the cables and trip the system in case of overtemperature (shunt trip breaker, possibly also open contactor let's see). It's a bit more complicated than just the smoke detector though. Would need some Arduino Code / ESP32 to make use of the DS18B20 sensors
Any thoughts ? I know without destructive testing it's difficult to say. And destructive test when you wire is 10 cm to begin with is a bit hard ...
At that point if issues arise I would guess I would either:
- Replace the 10.5mm2 wires going to the BMS with something proper (e.g. 35 or 50mm2)
- Use terminal blocks WAGO 285-135 for 6-35 mm2 cables instead of cable lugs & busbars. NOT sure they would work very well with ultra fine (class 6) conductors though
EDIT: Image was on "Bad practices Examples" here:
https://etechcomponents.com/crimping-common-mistakes-good-practice/
