Triac motor control question

You may want to read some of the items in

if you are building a lifting type application.

The type of motor used in a washing machine would NOT be a brush type motor. A drill motor doesn't use polyphase, it is a straight universal type motor.

Nonsequitor.

Please post 'after-failure' pictures. The more blood the better.

PeterD Inscribed thus:

Not really relevant to the OP, but brush commutated motors are common in domestic washing machines. Hoover, Philips, Hotpoint just to name a few. As are electronic speed control modules.

Indeed Hoover made the motors for the "Sinclair C5"

Probably the difference between domestic and commercial motor applications.

Purely from a safety point of view you need a mechanical brake mechanism that will stop things dead, particularly if there is a power failure.

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The washing machine motors that I'm aware of are brushless types (cage induction motors) that use a capacitor to provide the extra phase. These motors cannot safely and reliably be controlled by triac circuits using phase proportioning. Their speed is related to the frequency of the AC-current rather then the voltage.

Drill motors are often controlled by triacs allthough the electronics use feedback to maintain the speed set when under load.

Lifts tend to use counterweights to keep the load more or less equal for up and down.

petrus bitbyter

I am aware of the dangers and official regulations in this particular type of application.

I've been doing electronics design and repair work for some 30 years now, and all washing machines I've seen in the past fifteen years or so have a brush-motor, with a tacho encoder on the axle and a triac-based speed control circuit. These are front-loaded washing machines, with a horizontal drum and a single bearing at the back. The motor is responsible both for the washing action and the dry spin cycle.

All motors selected so far incorporate a mechanical brake, which engages as soon as the power to the motor is cut off.

Richard Rasker

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There is a separate mechanical brake that is released when the motor receives power. When the power is cut, this brake engages.

Richard Rasker

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Interesting -- all washing machine motors I encountered in the past 15 years are brush type (and I had to replace worn out brushes on quite a few occasions) with a triac-based speed regulator (and yes, I have replaced those triacs on a few occasions as well).

The application of this lift system makes the use of counterweights impossible (I can't elaborate further on this). Most of the mechanical system has already been designed, but we're still looking for a suitable motor + speed controller.

Richard Rasker

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Hmm... 15 years. Makes me realize that time flies. It has been quit some years that I replaced my last washing machine motor. Which was a slow turning one that has a separate spin drier. Guess newer, multi speed machines use the motors you mentioned.

What power do you need? Can't you get either an obsolete washing machine or a (not too expensive) drill? Both with control electronics connected already?

petrus bitbyter

On a sunny day (Sat, 17 Oct 2009 00:01:26 +0200) it happened "petrus bitbyter" wrote in :

Never mind, my old Zanusi-913 has no triacs and no brushes that I know about, here is the diagram (well, I think it is like that, original got lost): ftp://panteltje.com/pub/wasmachine_diagram.gif They do funny things with the capacitor, electrical clock sequencer, no electronics. Well, originally, I replaced the temp sensor by a diode, transistors and relays. It is also almost 30 years old.. Those motors just keep running. And it has dual speed, washing and centrifuge,

These are uncommon in the US. At least over the past 30-40 years, the vast majority of washing machines here are top loaders with a vertical shaft. [Front loaders are again appearing on sales floors.]

Some machines use transmissions, others [Maytag] have simple belt drive and reverse the motor to get different functions.

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I don't understand?

You state that the gear box is holding it back for you at full load with no power. So why do you need a brake?

Maybe what you should be using is a Helical gear box. This will back spin on the other side when motor isn't driving up. This may not be applicable in your situation how ever. You may actually need that load locking you're achieving now in case the power is lost. I guess you could have some kind of mechanical locking pin to solve too.

For braking to reduce down acceleration, you can use DB (dynamic Braking) resistors that apply some DC current in the motor windings which will cause the motor to create a drag on the drive shaft.

Normally, DB control is applied at full motor rated current and some times higher for short periods. For long periods, 50% of the motors rated current is normally ok.

You can also keep the motor in the forward position with a slight up drive on it, using a Helical gear box to slowly let it down..

But then again, there's that possibility of losing control! (power)

I guess if you're not in a dangerous situation, it wouldn't matter.

"Richard Rasker"

** ???? Brush motors use DC or single phase AC.

Reversing is by internal switching of the stator coils.

** AC motors can be held stationery by applying DC - but the motor you have operates from DC or AC, so no luck.

A spinning brush motor will stop quickly if the supply terminals are horted - but to hold it steady against an external force requires use of reverse drive.

If you want good speed control over a brush motor, using SCR drive ( ie half wave power with back emf sensing) is the way to go.

..... Phil

Not a word.

The ones i've seen in the uk are all belt drive, with either series universal motors using triac control, or switched multipole (2/4/8) induction motors to get the speed control.

I hear that more modern machines (and refrigeration), are using small solid state vector inverters and 3 phase induction motors. The reason is better efficiency, reliability and lower cost...

Regards,

Chris

Understandable. You can drive the thing backwards between forward pulses for braking while the load is going down, control either torque or speed, change direction, sense current, RS232 control, yada yada yada with a good PWM controller & appropriate motor.

(and are probably better for sales too).

I've no personal knowledge of the sales side, but it seems probable.

Ed