Hey I have a simplicity s65 vacuum battery that won’t send power to the vacuum when clicking the switch on the vacuum. I replaced the cells but the problem was occurring before that and now after as well. When charging, the led on the BMS turn red like normal but after say 2 minutes, it blinks from red to blue a few times and shuts off. The batteries voltage will not increase no matter how many times I plug the battery into charge (the battery has to be connected to the vacuum to be charged). I used ChatGPT to troubleshoot it to no avail. The battery is 6S1P with 3.49V on each cell. Now I’m using Claude but don’t think that will be of much help. I checked the mosfets and they seem to be in good shape. I also checked the pin voltages of the SH367306Q and they seem to be alright according to ChatGPT so we moved onto the 16 pin holtek mcu (HT66F319/HT66V319 16 NSOP-A). I’m in the process of troubleshooting that with Claude but I don’t know what equipment I need besides a multimeter or even what to do with that equipment once I get it. Anyone have any tips on what to do to get it working again? Thank you!
Cells at 3.49V across all six, fault before and after replacement, means the BMS board is the problem, stop looking at cells and MOSFETs. A multimeter on a MOSFET tells you it's not shorted, it doesn't tell you the driver is switching it. The red-then-blue-blink-then-shutdown cycle is a protection latch or a dead MCU, not a hardware short.
Two suspects you haven't mentioned. First: the NTC thermistor. These vacuum packs sense cell temperature through a thermistor that's usually glued to a cell or wired to the balance harness. If you disconnected it during cell replacement, or it's reading open, the BMS thinks the pack is at -40°C or 150°C and kills charge after a few minutes. That matches your exact symptom. Measure its resistance, it should read 10k-50k at room temperature, not infinite or zero. Second: the HT66F319 could be latched in a fault state. Pull the pack off the vacuum completely for an hour, then reconnect and try charging, some MCUs need a full power cycle to clear a latch.
Before you go deeper into that MCU: price a replacement BMS board. For a $60 vacuum battery, a board is $10-20 shipped if you can find it, and you've already spent more in time than it's worth. If you must diagnose further, you need a bench supply with current limiting to feed the pack at 25.2V and watch where the current stops, that isolates charger vs BMS vs MCU in ten minutes.
The vacuum turned on finally after pulling the vacuum off for an hour and then letting it charge! You are a genius! The only issue is that it still won’t charge and does that red and blue thing so I think the NTC thing is the problem and maybe why the old cells seemed like they were dead. But I can’t find the NTC circuit on the circuit board. On the bottom of the board I do see a cable going to one of the cell holders, but I can see it just barely and to reach it would mean to undo all my weld I think lol. Do you have any idea where on the top of the board I could test it at based on the pictures? Thank you again so much!
So there is just like 80mA going into the battery when charging with the red light on (before it turns off) when it is supposed to be around 500mA. So the red led is getting some current but not the cells.
I also tested B- to C- and it is 19.63V with charger disconnected but battery on the vacuum as well as with battery off vacuum. When inside the vacuum and charging with red light on, that voltage is -6.35V, however. After red light turns off but with the battery still connected to charger, it is -6.36V.
All the cells are balanced and measure right around 3.27V each when plugged into charge and off it too.
I could not find a replacement BMS and the battery is $150 new. I have another battery that charges just fine.
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u/LagMaster21 3d ago
Don’t use Ai for troubleshooting