Washing Machine Motor Tacho Testing

[Ray Pooley]

Hello all

Just looking at a Samsung EcoBubble washing machine that's fairly new and been an issue for some time apparently.

It's in the sister-in-law's garage. She says she's had the Samsung guy out to it 3 times under warranty and it still doesn't work.

She has no idea what was done to it when the guy came out.

It's now out of warranty and it has been brought to my attention. I hate to let good challenge go to waste.

It is behaving exactly how you would expect a machine with worn brushes or a failed tacho would behave.

At least according to what they tell me. That's full cycle but no drum turning.

I haven't run the diagnostics test routine yet because there are no services in the garage so I have whipped the motor out
to do a physical with a multimeter.

The motor is as clean as a whistle, coils are fine and brushes look like they were fitted this morning they are that good.

So that leaves the tacho. I am getting 40 ohms resistance across the tacho. I have had a good look around
the net and some say it should be 60 - 70 ohms others as high as 200 ohms.

Anyone got any thoughts about this?

Also, when I spin the shaft I should get some voltage output from the tacho. That's going to be DC output. Right?

Any idea what kind of voltage I should expect? I am getting 1 to 3 mVDC. That wouldn't be much use I reckon.

Thanks for your time.

 

[Lucien Nunes]

No a normal basic tacho on a domestic appliance will be AC output, it's just a permanent magnet rotating in a wound stator. The actual resistance probably isn't very important provided there is a circuit through it. Tachogenerators on industrial servomotors etc were usually DC but at 50 times the cost per unit.

 

[Ray Pooley]

I know what you are saying but there are a few motor testing vids that tell you check the resistance, not just the continuity, and specify a specific range the implication being that if your resistance is outside that range it is faulty.

 

[Ray Pooley]

Just thought I would update this in case someone else comes along later with the same question.
DSO confirms that the output from this tacho is AC. I don't know whether that's always the case. There is plenty of room in this particular tacho's casing to accommodate a full wave bridge rectifier. So use a DSO to be certain. In this particular application it produces 2.9 VAC at 1400 RPM. 0.83 VAC at 400 RPM. Whether this ok I am not sure (I think it probably is) but I have ordered a new one for comparison.

 

[wheeto]

I know you've mentioned brushes in your post, but to help others with a Samsung machine, bear in mind that a lot of them are now inverter-driven, for an extra layer of excitement.

 

[Pete999]

Hello all

Just looking at a Samsung EcoBubble washing machine that's fairly new and been an issue for some time apparently.

It's in the sister-in-law's garage. She says she's had the Samsung guy out to it 3 times under warranty and it still doesn't work.

She has no idea what was done to it when the guy came out.

It's now out of warranty and it has been brought to my attention. I hate to let good challenge go to waste.

It is behaving exactly how you would expect a machine with worn brushes or a failed tacho would behave.

At least according to what they tell me. That's full cycle but no drum turning.

I haven't run the diagnostics test routine yet because there are no services in the garage so I have whipped the motor out
to do a physical with a multimeter.

The motor is as clean as a whistle, coils are fine and brushes look like they were fitted this morning they are that good.

So that leaves the tacho. I am getting 40 ohms resistance across the tacho. I have had a good look around
the net and some say it should be 60 - 70 ohms others as high as 200 ohms.

Anyone got any thoughts about this?

Also, when I spin the shaft I should get some voltage output from the tacho. That's going to be DC output. Right?

Any idea what kind of voltage I should expect? I am getting 1 to 3 mVDC. That wouldn't be much use I reckon.

Thanks for your time.

Have you checked the belt for tension?

 

[Ray Pooley]

Have you checked the belt for tension?

The belt is fine. The problem is that the motor isn't running.

 

[Lucien Nunes]

Is there a circuit through the motor?
Does it run OK outside the machine?
Is the speed control integral with the programmer or separate?
What it its output device, a triac?
Is there any drive to the triac gate?

 

[Ray Pooley]

Is there a circuit through the motor?
Does it run OK outside the machine?
Is the speed control integral with the programmer or separate?
What it its output device, a triac?
Is there any drive to the triac gate?

No wiring diagrams are available.

 

[Lucien Nunes]

Sorry, my careless use of English: Is there continuity through the motor?

It should be possible to discover all that with just eyes and a meter. If the programmer is electronic, then we can't tell what its preconditions are for enabling the motor, but it is reasonable to think that if it isn't enabled and driven because the conditions aren't met, the programme won't advance or it will throw an error. Therefore the problem is very likely to be outside the programmer. If it is electromechanical, then you can reverse-engineer it.

 

[Ray Pooley]

Sorry, my careless use of English: Is there continuity through the motor?

It should be possible to discover all that with just eyes and a meter. If the programmer is electronic, then we can't tell what its preconditions are for enabling the motor, but it is reasonable to think that if it isn't enabled and driven because the conditions aren't met, the programme won't advance or it will throw an error. Therefore the problem is very likely to be outside the programmer. If it is electromechanical, then you can reverse-engineer it.

The motor runs well outside the washing machine. With an 18VDC supply across the coils and brushes the tacho produces 3.53VAC output. I will test it again when the new tacho arrives which isn't going to be until early December because the only place I can find a compatible one is South Korea where the machine and motors are manufactured. I suspect though that it will be the control PCB at the end of the day. But I will run diagnostics first when the new tacho arrives to see if it reveals anything.

 

[Ray Pooley]

Update for those who are interested. New tacho arrived. Resistance 68 ohms. That's obviously a lot more than the 40 ohms I measure on the old one. It's also in keeping with the 60 to 70 ohms healthy range suggested by companies like eSpares in their videos. Output from old tacho 3.53VAC with 18VDC across the motor. This is now 6.00 VAC. So. Looks like the tacho is dodgy.