Milwaukee 18V Li-ion Cordless Compact Vacuum Cleaner Repair - M18CV-0

[greencardigan]

Hi,

I'm looking to repair an 18V Milwaukee vacuum cleaner (Model M18CV-0).

Symptom: The vacuum motor usually runs for 20-30 seconds then cuts off completely. If the power switch is kept held in, it restarts after 10-15 seconds and repeats.

Diagnosis: I have determined that the thermal switch attached to the side of the 18V 220W motor is opening (see photo attached).  I can hear it click closed about 10-15 seconds after a power cut-off and a continuity check confirms this. The unit also has some cut-off circuitry monitoring battery voltage (I think) and the MOSFETs on this board do not seem to switch off during the power cuts described above.

With the motor unit completed removed from the main unit housing, I was able to get the motor to run for multiple minutes with no power cuts, suggesting it was in fact the motor over heating. I have removed the main filter, and with the motor back in the housing, the power cuts are back even though there seems to be plenty of cooling air flowing through and around the motor.

The motor casing beside the thermal switch only reaches about 30 degrees Celsius when it goes open.

Questions: Is it common for these thermal switches to fail? Can they be easily removed/replaced? What would be a normal cut-off temp for these (I'm finding it hard to read the text on the switch). Should I just bypass the switch?

[m3vuv]

Are you sure its not a mechanical fault ie a partialy siezes bush/bearing causing excessive current draw causing it to get to hot?

[perieanuo]

mechanical thermal switches are 'almost' science, their precision may alter up to 20C error margin, I saw this on heating mechanical thermostats (dunno if this word is in englisk ).
yes, it may be de-calibrated
you may check with some themp meter, but anyway 30C seems toooo low imho, for apliances like this for me 60C-70C is ok
if you live in some countries, 30C may be ambient temp in the summer, whare is the heat margin for the motor, between 30 and 30?
just get him out, test the motor, if it's shorted anyway it will die, watch him spinning for 30 minutes and see how hot it gets

[greencardigan]

Are you sure its not a mechanical fault ie a partialy siezes bush/bearing causing excessive current draw causing it to get to hot?

I'm not sure.  The motor seems to spin pretty freely. It's taking about 7 seconds to come to a stop after releasing the power switch. And the motor casing doesn't seem to get more than very slightly above ambient.

Or do you mean the thermal switch could be getting hot and opening due to excess current?

[greencardigan]

I removed the thermostat switch from the motor and left it hanging freely outside of the vacuum cleaner housing but it still goes open circuit. The switch itself is getting hot with the current flow through it.

The switch is labled BR-S 120°C which is strange as it looks like a BW-S to me.

http://electricprotector.com/1-10-bws-thermal-protector/

I can't find a source of these exact switches locally but found some on eBay that should be compatible.

I'll bypass the switch and flatten a few batteries to confirm that the motor is actually OK.

[amyk]

A 120C switch shouldn't open even when put in boiling water. If it's opening at far lower temperatures it is defective.

The fact that it is itself heating up suggests the contacts inside may not be making good contact.