How does a machine ACTUALLY detect an out of balance load?

[wrigpm]

I am looking for a real technical answer here as it may help me diagnose why my machine just starts to spin then drops out with the timer going slowly! (This is on an AEG L64810 BTW).

I have had a really good look at the controller PCB and now have most of the circuit drawn out! There is a pretty standard Triac phase controller driven directly by a uC logic output and open collector trany. The speed sense for this comes from the tacho (AC) and is rectified and smoothed and fed straight into the uC (to an ADC I assume). There is a feed from the cold/N side of the motor (other side is hard L) that is potted down and also fed to the uC – what for, I do not know. There seems to be no accelerometer or way of detecting the current to the motor so I do not understand how the controller/uC would decide when the load is unbalanced.

Can anyone shed some light?

Paul

[Penguin45]

Re: How does a machine ACTUALLY detect an out of balance loa

Basically, speed variation against fixed vaules programmed in. Wash speed doesn’t matter (50-60 rpm), but the OOB system is usually rigged for the “distribute” phase prior to spin. This is where the drum picks up enough speed to stick the load to the drum, rather than letting it tumble. Typically 80-90 rpm. A significantly offset load will require an increase of power to lift it at the required speed, but when it goes over the top and starts to come down, it is trying to accelerate under its own weight and there are no brakes……. The tacho generator on the end of the motor is signally back the speed variations to the pcb, which is in turn comparing them with its programming and trying to adjust accordingly. The distribute sequence may well stop and a period of slow tumbling take place, to try and re distribute the load in the drum, before trying again. If it’s too far out, the spin sequence may be aborted all together.

Similarly, a “run away” motor due to a defect in the tacho circuit or triac switching circuits will be read as an inappropriate response by the pcb and the motor will be sgut down completely.

HTH,
Penguin45.

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