Bosch WFF1201 washing m/c, no spin - controller or motor?

[741]

After perhaps over-filling the machine, and initiating a wash cycle, at some point a circuit breaker opened in the consumer unit. When power was restored, eveything (other than the motor) seemed normal. I could hear the relays clicking and the pump going.

I do not really understand the way the motor should work, it has 6 power leads (3 orange, 3 brown). I guess there will be 3 pairs of coils and each should read low (but no 'too low') ohms?

Quite how speed is controlled, other than PWM and how the the (presumably out of phase) 3 coils are driven I do not know. I wonder if, say the triac on the controller is worth desoldering & testing?

PS: I guess I should also inspect the brushes.

[abraxa]

Does the motor still spin during the washing cycle? Is it only the high-speed setting that doesn't work?

If the motor doesn't turn anymore at all then yes, the Triac is what I'd check first.

[741]

The motor never spins.

I have checked the brushes (very worn) so that is a possibility - I have ordered a spare set.

The fault that tripped the circuit-breaker has not re-occurred - therefore the "current overload" was directly linked to the motor.

Also, a motor uses maximum current when stalled.

[JFJ]

... the "current overload" was directly linked to the motor.

As the motor is powered via a PCB, it's worth checking the track side of the PCB - just in case a trace has been burnt through.

[741]

I replaced the brushes and nothing happened.

How do I test the big AC motor? Is an inductance test better than a resistance test maybe: look for 3 inductances...

The motor has 6 wires. I guess that is 3 windings. The brush wires are brought out from inside the motor, perhaps the commutator is in series with the windings - so that the AC magnetic field on the rotor maintains a known relation with the rotor (and so logically it is a bit like a DC motor).

Then the triac controls the phase at which current flow starts in the windings I guess. Looks a pretty small triac (on an admittedly large heatsink) to drive such a motor.

I wonder why there would be 3 separate windings though; what is different about the supply to each set?

The controller looks a major effort to remove; once it's out I can test the triac.

I'm puzzled why the PCB has a big rotary timer thing plus what seems to be a microcontroller. Perhaps it was to simplify the front panel back when it was designed, maybe late 90’s.

I suppose I'd be struggling to get a circuit diagram of the PCB.

[mikeselectricstuff]

There's probably a triac in the motor controller - replacing that would probably be a good place to start

[JFJ]

... The motor has 6 wires. I guess that is 3 windings...

Usually, two wires are connected to the carbon brushes (to energise the armature/rotor), two wires connect to the field coil/stator and the remaining two wires connect to the motor's tachometer.

... How do I test the big AC motor?

You may find this video useful:
https://www.how-to-repair.com/help/how-to-test-a-washing-machine-motor/

[741]

Usually, two wires are connected to the carbon brushes (to energise the armature/rotor), two wires connect to the field coil/stator and the remaining two wires connect to the motor's tachometer.

Thank you - very useful info

• Would any speed control typically be a "burst fire/phase angle" type to the stator via a triac?

[mikeselectricstuff]

First thing to try is replacing this triac

[741]

I have it desoldered (BTB16 800W) and admittedly it'd be quickest just to 'swap and try'.

However I will try to test it first, so as to understand things a bit better. So far I can make it trigger in 2 quadrants, plus I gather 'commutating' types (turn off reliably with reactive load) typically only manage 3 quadrants.

I'll borrow a proper triac tester later this week.

This whole area, big motor control and the motors themselves is new to me and I've long been aware it's be something worth understanding more about.

[shakalnokturn]

Replacing brushes was a good start, make sure they can slide freely right to the rotor's collector sometimes they will jam due to carbon powder aggregating.
Is this one of the motors with clockwork style springs to push the brushes?

Identify motor connection layout, connect motor  disconnect at controller and measure on the connector, measure stator resistance, measure rotor resistance (confirm it is always approx. in same range while spinning motor slowly by hand), measure tacho resistance and confirm it produces some voltage while spinning fast by hand.

Common problems are: Cut wires (due to vibration where they get the most bend, or where they enter the connectors), bad solders on relays.

More seldom bad relays and bad triacs.

[shakalnokturn]

If you have no luck with that you can also consider checking solders to the rotary cam switch.

[741]

Thank you - I will have to get around to the motor tests, they sound sensible.

The brushes do have springs, but these are simple "corkscrew/spiral" springs. I have sprayed electrical contact cleaner on the commutator itself, and hand-turned the motor a few times.

Would the triac supply the stator windings?


PS: I think the issue will not be the contacts on the rotary switch, because bad solder joints here would not cause the circuit breaker to trip?

[IanMacdonald]

The leads will likely either be commutator and two sets of field coils, or commutator, field and tacho for speed monitoring.

Often there is a safety feature that the controller will not attempt spin speed if the tacho output is missing.

[741]

I think the motor might be at fault, see diagram. For the tests I did, I disconnected the connector 'spades' from the carbon brushes. There should be some way to apply a differential voltage across those spades, and there is not. Looking closely I'd say the internal black lead that ties to spade B1 (I named the brush on the same side as the connector "B1") looks a bit heat stressed.

To review: The machine tripped a circuit breaker in the consumer unit, (and there is some discolouration at one of the mains input tabs on the PCB). So at that time I assume a fault current, possibly a heavy current, was flowing. I'm not sure if it would be L-N or 'earth fault', or one leading to another?

My "wild guess" is the internal connector.pin5-to-brush-spade leadout has melted / 'fused' (is that plausible?) maybe if I run a wire direct to spade B1 the motor might work. However, if the internal black wire lead-out to brush B1 has some inaccessible "last-gasp" fuse, it'd be wrong just to bypass it.

It'd be nice to know of a place doing reconditioned motors, as they cost £200 new.

[mikeselectricstuff]

Have you replaced the triac yet?

[741]

Not yet because Farnell charge for delivery under £20, and I'd like to test it first, hope to borrow a tester ("Peak SCR") soon.

[mikeselectricstuff]

What's the part no. ?

[741]

I've tested the triac; it works OK it all three (#1,#2,#3) of the quadrants the DS specifies it should work in.

The motor part # is 141344.

[741]

Looks like an internal thermal motor protector has blown, type "15AM253A" by Sensata (formally, and surprisingly, a TI product it seems). One side goes to the "no connection to brush #B2" terminal, the other side goes to brush #B2.

Also shown are shots of tacho etc.

http://www.carbonbrush.com/klixonam.htm stock the 15AM253A, but the repair - a connection to springy brass contacts - looks difficult. Not obviously soldered, more like a spot-contact micro-weld; I wonder how I'd do it? I can imagine buying the protector, then being unable to effect the swap-out.

It is meant to automatically reset, but has not done so.