> 1. always use 1N4007 for mains rects!

Okey doke

> 2. Some sync motors always run the same direction like in record
> player turntables, others as in microwave turntables randomly pick
> a direction when they start. exactly what type of motor is it?

It's a Brevel 40W (not 60W, possibly a BT40, the ink is smudged),
with "Model 715" on the gearbox, and the motor windings have a
label with "715-982568" printed on it. The gearbox IIRC is >100:1.
That would be a shaded pole motor ? Just wondered whether the
direction is set in the windings or some how you can give it a kick
to make it go a certain way. My original wood lathe motor (1/6th HP
washing machine motor) could go backwards if you had the wontons
to flick it that way when you put the juice on, but the last thing you need
is the lathe going backwards and all the wood flying back on to the job

I haven't checked prices out recently but large AC motors were
always much cheaper (and commoner, eg fans, washing machines,
driers, turntables etc) than large DC motors, and I doubt if that has
changed. The only drawback is that anything you put them into isn't
very mobile. In the past though I've picked up second-hand cordless
drills and for $20 these are good value for a pretty gutsy DC motor
and gearbox. Universal motors from mains tools like drills and
circular saws are easy to control but, oh, the racket !! Would they
be any quieter on DC or is it not worth the bother ?

> 3. I have seen a similar circuit that worked, instead of a full wave
> rect giving 320vdc, keep the neutral as "earth" and use two 1N4007
> diodes and two filter caps to give +320vdc and -320vdc

Yes, I realised that today when I found a second big cap in the box.
There were also a couple of 0R47 5W resistors too but I don't recall
why. No provision for negative rectification on the board so have to
assume I was not going to get it right the next time either ;-(

> Also use 2.2ohm 5w resistors in series with your diodes to make the
> whole thing last longer with diode switching currents and mains spikes.

Each diode ? How about protecting the semis (FETs I presume). Poly
switches ? Varistors ? Zeners ? The board so far had a diode and
varistor across the FET and it lives on. I'll have to get into the archives
and refresh myself on FET protection, they don't last long with a spike
in the right/wrong place

> Once you have +/- supplies, you can use 2 switching semis, to switch
> alternating + and - dc to the motor, like this:
>
> 25% duty off
> 25% duty on+
> 25% duty off
> 25% duty on-

> If I could use ascii art I would put a pic but I think that makes sense.
> I have repaired a couple of really cheap 12v to mains inverters that
> used this system, if the motor has enough inductance this will work
> as good as from the mains.

The 12VDC - 250VAC inverter I have uses a two-step wave (ie 0V
50%+ 100%+ 50%+ 0V 50%- 100%- 50%- 0V) to drive the Tx and
I notice in the text it says that some motors and appliances don't
care for this too much, even though it's closer to a sine wave than a
square wave is

> If the motor has very little inductance, you may need to add a simple
> inductor in series with the motor, (and maybe a resistor of a few ohms),
> I have used the low-voltage winding of a small mains transformer for
> similar things, they make a pretty heavy duty inductor and are cheap/
> free if you have a good parts bin.
>
> If I knew exactly which motor you have I could suggest more?

> -Roman

And now you does

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