[solved] Dyson V6 (DC58-DC62) vacuum cleaner - motor running pulsed

[Greybeard]

I found a Dyson V6 (DC58-DC62) vacuum cleaner in a dumpster.



It is not complete - battery, air hose, nozzles, charger missing.

I found out, what battery voltage and polarity is needed and hooked the motor pcb up to my lab power supply (24V/6A).
The motor is not running continuously, it is just pulsed (about 3 bursts per sec).

I found some reports in the net regarding pulsed motor run - root cause always was blocked air flow (filter).
But that is not the case for this one, because I removed everything but the motor and  the motor PCB.
As I said, the motor is turning for a few 1/10 s, stops and repeat this cycle about 3 times per second.








Has anybody heard of the motor pulsing caused by another cause than blocked air flow?
Maybe over current? Or incorrect over current detection on the board? My supply can just deliver 6A, may be not enough?

PS: I added some pics I found in the net...

[EHT]

If 24V is correct then 6A equates to high power for this small device, so that shouldn't be the problem. I think it is common to find a failing switching regulator circuit behave this way, and could be various causes.
Can you determine the identity of the switching IC? The large IC maybe a microcontroller. What about on the other side of the PCB? Can you identify the power switching semiconductor(s)?
I fixed similar things by finding they were using common switching ICs and then looking at the datasheets for these to determine what the likely circuit is. Unless someone has the actual schematic of course!! (these hoovers are very common)

[Greybeard]

The large IC is a PIC16F1936 controller.
The Li-Ion battery voltage is 21.6V nominal (6x 3.6V). Full charged battery should be 6x 4.2V = 25.2V .
I've tried 20V to 25V - same pulsing behavior.
To look at the other PCB side I have to desolder the 2 massive motor coils.
I've not done yet because my desoldering tools are not the best, so I wanted to wait for some replies first.

[Greybeard]

I've tried another bigger lab power supply (24V/20A) from a friend.
The motor is now running continuously without any pulsing! It draws 17.5A @ 22.0V that's unbelievable 385W in idle (open turbine without filters in the air flow)!
That's over the vacuum cleaner maker's spec (max. 350W) and probably far over the battery cell's spec (it's just a poor 6S1P 18650 Li-Ion pack).
I've tried to slowly reduce the voltage to find the minimum voltage when pulsing returns. At <21.3V pulsing appears again - but in a slower cycle time, about 1 burst per sec.
21.3V at the power supply jacks is not much below the nominal battery voltage of 21.6V but I should have calculated voltage drop over the leads to the load.

So everything seems to be OK.
The problem was just the insufficient current from the power supply.

[uli12us]

Thats not a tension problem, these Motors need a high current and the pulse is typical, if the amps are not enough.

[EHT]

The motor is now running continuously without any pulsing! It draws 17.5A @ 22.0V that's unbelievable 385W in idle

Wow! So in general if it starts pulsing and is not clogged, batterry would be the next suspect.

[Greybeard]

The motor is now running continuously without any pulsing! It draws 17.5A @ 22.0V that's unbelievable 385W in idle

Wow! So in general if it starts pulsing and is not clogged, batterry would be the next suspect.

Exactly.
I later found out, Dyson uses MURATA SONY US18650VTC4 'Konion' cells (max. 30A,  2100mAh), so they could handle the 17.5A the motor needs.
But nevertheless run time shouldn't be very long.