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Dyson v7 Trigger cordless vacuum - TEARDOWN of battery pack

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Lesolee:
I bought a Gtech Multi to clean up after my cat. It  looked perfect for the job, and was a fair bit cheaper than the Dyson. Sadly, having charged it after it first arrived, it failed due to overload the first time I used it with the powered brush bar. It would run for about 20 seconds then cut out. "Oh, it shouldn't do that" said customer services, who immediately shipped out a replacement. Needless to say the replacement did EXACTLY the same thing.  |O

Clearly Gtech had both a batch problem, and a quality control problem. Given that this battery stuff is their core business, for me that is a red flag. I have personally lost faith in them.  :--

Hence I went up-market to the Dyson, at £200. Worked nicely with light daily work, often vacuuming the white duvet cover to clean off the black cat hair. All happy for 9 months then the evil flashing 32 times red flash code of death. This happens when you either try to turn it on or charge it. It was of course still under warranty so they sent out a new one, which worked nicely. Maybe I am just unlucky?

I have seen another site where a small number of people have had the same experience. What percentage of these things fail is of course unknown.

Anyway, a (free) duff battery pack is a valid excuse to tear it down and see what happened.



The battery pack itself is fairly easy to remove (3 screws) but I can't see my youngest Aunt (75) or my mum (85) being able to do so.

Removing the battery pack cover on the other hand is a horrible job, even with proper spudgers/ tools designed for the job.



The battery pack is locked into its cover by the LED light pipe. You have to pry the case away on both side simultaneously to slide it out. I numbered the cells for later use.



The Battery Management System (BMS) is shown on top of the cells. Cell 1 is the low end of the series connected chain, the negative end. The negative battery terminal is circled in blue. There is an interesting looking device circled on the left. It measures as open circuit (maybe). It has a silkscreen identifier as S1. (Thermal switch?) I originally thought it was a fuse, but there is a SM fuse at the positive end of the pack, and it is marked F1. You can follow the tracks easily and the small package would seem to be an N-channel enhancement MOSFET by its location. It is a strange looking package that looks like an SO-8 but the legs on the RHS are all merged into one. The upper three legs on the left are all connected to the 0.002 ohms sense resistor. The fourth lead is the gate. I know because I put some voltage on it via a 3K3 resistor and got it to turn on the supply voltage to the output terminals.

The BMS board in the bottom right corner is marked as 228499-01/03, but a web search did not find anything relevant. :(



This is a close up of the unknown "switch". I searched the unknown part number GD 18-05 and got nothing  :-//



My first thought was that the cells had become out of balance and upset the BMS.
(1)   3.92 V
(2)   4.15 V
(3)   4.10 V
(4)   3.84 V
(5)   4.15 V
(6)   3.92 V

So I put a PSU across each low cell and charged them all up to at least 4.05 V. No change in the flash code, but it is possible that the fault is permanently latched.

Lesolee:
The whole board is covered in silicone rubber, so a bit of digging was required.

The MOSFET is shown as best as I can get it below:



Maybe it is ICD30b  or 1CO30b or some variant in between
Then maybe
Prm
1740

I couldn’t even find this type of package in manufacturers’ data.  :-//

The annoying thing is that the cells all work, the MOSFET works, and something has gone wrong causing it all of it to end up in landfill.  :rant:

Lesolee:
S1 (marked GD 18-05) had 19 V across it. Thinking it was a fuse I tried a “soft short” with 100R, and when that was successful, took the resistor down to 10R. The result was 0.8mV across it. Now instead of 32 red flashes when operating the ON switch I get 32 red flashes, a slight pause and a green flash.  :-+

It still doesn’t work, but the green flash sounds like an improvement!   :clap:

schmitt trigger:
Please continue with your detective work.... I also own a Dyson, and might come back to this thread later.  :-+

Charged batteries give me the creeps when I am poking around on a board. Do you think you could open up a terminal, and substitute the battery pack with a current limited PSU of roughly the same voltage?
That way, you could safely poke around without fear of a major short.

Can you read the part numbers on the ICs?

Lesolee:

--- Quote from: schmitt trigger on January 22, 2020, 03:01:02 pm ---...
Charged batteries give me the creeps when I am poking around on a board. Do you think you could open up a terminal, and substitute the battery pack with a current limited PSU of roughly the same voltage?
That way, you could safely poke around without fear of a major short.

Can you read the part numbers on the ICs?

--- End quote ---
The trouble is, there is not "a terminal". We have the two ends of the series chain of cells, but also all the intermediate taps. Undo the connections in the wrong order and it may cause it to blow up. I designed a large pack, where each cell was 1 kg, and each cell had its own charge balancer between the terminals. Plugging in to the monitor board had to be done in an exact order or the monitor board would be fried. Those cells were seriously scary  :phew:

The ICs are still under the silicone rubber. But they look like FPGAs or micros. If the MOSFET is unrecognisable, you have to figure that they are too.

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