diy solar

diy solar

Failed JK BMS

It soundsl like the one you have is actually booting up rather than not starting at all like mine. It just keeps doing this over and over until I hold the start button down for 30+ seconds after which it might finally stop.
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2022-09-18_19-19-37

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upnorthandpersonal said:
It originally didn't (that's what @Horsefly reported). It powered on when I got it...
Click to expand...
Did you connect it as a 4s or an 8s configuration. It seems like most of the problems I have read about were for 12v packs which prompted me to wonder if it was related to a boost converter that kicks the 12v up to 24v needed to run the internals.
 
It is strange and frustrating that it did not do the same thing that it did for @Horsefly , me and several others. Hard to troubleshoot if it doesn't show the same failure. o_O
 
Wondering how things were coming along on the exploratory postmortem. I need to order a couple bms and the jk was first on the list, but now having second thoughts.
 
Couldn't wait any longer. I've got 2of the b2a24s20p on the way from a reputable retailer, so if they stb maybe I can get them replaced.
 
Ok, I just made some tests. For one, it wasn't the soldering. However, the issue is the defective small six pin SOT buck switchers that @RCinFLA mentioned as well. Cold spray them gets the BMS into a boot loop; I also momentarily managed to get it to behave and the 'buzzing' the BMS induces (on the BMS and in the power supply charging it) goes away.

I'll see if I can find the replacement part mentioned somewhere, and replace those.
 
upnorthandpersonal said:
Ok, I just made some tests. For one, it wasn't the soldering. However, the issue is the defective small six pin SOT buck switchers that @RCinFLA mentioned as well. Cold spray them gets the BMS into a boot loop; I also momentarily managed to get it to behave and the 'buzzing' the BMS induces (on the BMS and in the power supply charging it) goes away.

I'll see if I can find the replacement part mentioned somewhere, and replace those.
Click to expand...
Can they be replaced with better quality?
 
upnorthandpersonal said:
As far as I can remember, yes, the replacements are better - or at least, the correct ones. This is all from memory, I need to look up the details...
Click to expand...
It would be great if you could supply the better quality replacement part#'s. Been a while since I ordered anything from Mouser.
 
The cause might also be related to a switching inductor part substitution of the small DC-DC converters.

I've seen two types of chip inductors used. One is a small bobbin type, one is a ferrite encased block. The bobbin type is likely better.

Bobbin inductor.pngFerrite block inductor.png
 
Thanks for the pictures. I've got quite a bit of experience with DC-DC converters, so one of my goals is to isolate this circuit, compare to previous versions, and find alternative (read: better spec'ed and readily available from Mouser) parts. I just need some time...
 
For reference, the markings on the SOT-23-6: CDFAH. My current thinking is it's probably a Silergy component, they tend to use that pattern of letters.
 
Seen 'BCP2K' marking on 8S version BMS. Fairly sure they are bucking down from total battery stack voltage so likely cheaper, lower max input voltage part on 8S version BMS compared to 16S. Have not been able to cross type to a data sheet.

This part has a boot strap cap between inductor LX pin and BS pin so it is synchronous switcher. I don't trust China IC copy designs so much on synchronous DC-DC converters to avoid shoot through delay crossover gap margin on output devices.

I think the 100 uf 16v alum electrolytics are Vin so there must be a pre-switcher between battery voltage.

1675198439005.png 8S BMS small DC-DC converters.jpg
 
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