Triacs.

There seem to be problems with all of the triac circuits that they've both tried.

Although Flowering Elbow says he's got good results by using his second circuit to control a DIY pillar drill.

Variable Power Supplies.

I like the idea of using variable switched-mode power supplies to determine the optimal supplies for field coils and armature. And then use slightly less variable SMPSs to provide those supplies.

But I'm sadly lacking in practical knowledge in SMPS design, so there's A LOT of learning to do before I could go anywhere along this path.

Microcontroller.

The washing machines I've taken apart all use a microcontroller (which isn't surprising as they also have to deal with timing and sequencing too).

So, perhaps the microcontroller route is the way to go.

But I'm not that happy with the level of complexity of the circuit that Flowering Elbow has found and the code looks a bit untidy to me.

I think I could improve on the circuit:

1. Replacing the motor's tacho coil with a hall-effect sensor (I've already done a bit of work towards using a hall-effect sensor to determine RPM)
2. Using an ATTiny chip instead of an Arduino Nano - just to cut down on size.

I'd also like to tidy the software up a bit:

1. Instead of using the Arduino framework, use a more "traditional AVR" style and break it down into modules a bit.
2. (This will probably prove unpopular, but it is my obsession) Use assembly language instead of C/C++

Reiteration of the fact that, especially when unloaded, the speed will go up and up and up until the motor eats it's own brushes and/or bearings.

Classic diac/triac circuit seems to be controlling the field coils direct from mains and the armature from mains AND via the diac/triac.

DC diac/triac circuit adds a 240/9V 50VA transformer and rectifier to provide the field coils with high current/low voltage DC. The mains supply to the armature AND field coils is also rectified.

It's not necessary to wire the armature and field coils in series but this gives the benefit of lower starting current and higher ultimate torque.

But at slow speeds the triac can receive phantom triggers which will cause "glitches".

There is a possibility that this can be fixed by using a two-triac circuit. But this is so far untested.

The microcontroller system uses a PID Library for Arduino and hardware from Arduino-Based Universal AC Motor Speed Controller.

A main issue we have to deal with is that these motors are designed for extremely high RPMs and rather low torque which is the opposite of what we need for most practical applications.

In the machine these motors come with drive electronics centred around thyristors or TRIACs.

If you want to run one of these motors on AC, you can use a phase fired controller or using DC through a MOSFET with PWM control.

The machines tend to have rather complex control circuitry and it's probably easier to simply salvage the more valuable components from the control board and build a new circuit than spending ages reverse-engineering (unless, of course, you love a good hardware hack).

It 's a good idea to replace the taco coil on the back of the motor with a hall-effect sensor as this will give us a feedback signal that's easier to use.... pulses at exactly the frequency of revolution.

If we connect the field-coils and the armature winding as a self-excited series-wound motor, the speed runs up and up and up until it exceeds it's rated RPM and destroys it's own brushes and bearings.

Without a control circuit, when we apply just a little load the available torque is insufficient and the speed drops abruptly.

These motors require some means of regulation to use them safely.

There's two paths that can be taken with the control electronics:

• Keep the circuit itself very simple but this is going to take more advanced electronics knowledge to design.
• Keep the design principles simple, use a microcontroller but this will be more expensive and complex to build.

We can use back EMF for feedback to a simple thyristor based controller to keep the speed constant... But this circuit only provides half-wave power.

Better control can be obtained by wiring the motor as a separately excited DC motor and provide the armature with 10 - 30 volts to control speed and 1 - 1.5 amps through the field coils to control torque.

As increased torque results in less speed, we can operate the armature at a fixed voltage and use the field coil current to control the motor.

If we use a fixed voltage on the armature, we still need to switch it off to stop the motor, it will continue to run with virtually zero torque with no power applied to the field coils.