Neato D5 li ion battery failure

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Neato D5 li ion battery failure

Postby masterx81 » May 9th, 2019, 9:36 am

Hi!
I have one neato battery pack that have draind out a little bit too much (2.7v/cell), and the onboard battery control logic have switched off the output.
I've tried recharching slowly the cells with an appropriate 18650 battery charger (monitoring temperature, current and tension during the charge) and all of the 8 battery have charged fully with good capacity and good voltage/current matching, allowing me to reassemble the battery pack.
Now i've connected the batteries back on the control logic, connected first ground, then the intermediate connections for checking the series voltages, and for last one the positive of the last 2 batteries of the series (that give vcc to the control ic), but the control logic still not enable the output fets (no voltage output on red/black wires). The control ic is a FM3DXY, that i can't find any PDF over the net, but i suspect that have built in a flash memory that remember the state of the battery also if powered off...
The FETS are 2 AON7426, and over them there is a strange 3pin thing.
Someone have "played" with the safety circuit of the battery pack?
I attach a photo of the control board.
Attachments
20190509_153023.jpg
masterx81
 
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Re: Neato D5 li ion battery failure

Postby valamilamasag » May 15th, 2019, 5:54 pm

That strange 3 pin thing is probably an electronically blowable fuse. Check it for continuity. One of its pin is highly probably connected to the fets or the output or one of the battery terminals.
If you find such connection and its blown then sadly its not repairable. Even if you replace it, the IC will blow it again or simply never enable the output.
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Re: Neato D5 li ion battery failure

Postby masterx81 » May 16th, 2019, 5:44 am

Yes, one side it's connected to the battery output, and the other to the fet. Newer seen this type of fuse :shock:
Normally in the BMS systems that i've seen, the only protection were the 2 fets. I suppose that this will help protect in case of fet in short circuit... I'll try to see what control that fuse...
Thanks!
masterx81
 
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Re: Neato D5 li ion battery failure

Postby masterx81 » May 17th, 2019, 7:09 am

Tried to bypass the fuse (as was blown), but the bms doesn't close the fets.
And also, i get a constant voltage to the control pin of the blownable fuse, so i suppose that the control ic try to blown it.
So it has an eeprom o flash for remember the battery state (as now the batteries are fine, at right voltage)... Maybe can be reset via i2c, but will need a pdf of the device, that can't be found...
masterx81
 
Posts: 7
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Re: Neato D5 li ion battery failure

Postby valamilamasag » Yesterday, 3:58 pm

These blowable fuses are common in smart batteries. Not in the cheap copy ones, but the proper ones that gets all the required certificates to be sold outside of china. Btw this fuse is just a normal fuse plus a heater element.
Datasheet is not required, these talk via SMBus (similar to i2c) and all the commands are standardized (smart battery protocol). Laptop batteries use the same.
If you dont have the keycodes then you cant reset the IC. Its usually a 128 or 256 bit RSA key-response challenge, not crackable. Once the manufacturer locks it and that's it. If you are lucky then they used one of the common codes which are already out in the wild. There are 3rd party tools to work with these IC-s, but they cost far more than a single new battery.
Also even if you know the keycodes to unlock the IC the manufacturer might have uploaded a custom firmware to it which complicates the repair.
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