Re: Wanted - small variable speed inverter

Feb 19, 2011 7 Replies
T


on 19/02/2011, Tabby supposed :


>
> > > >> I'm looking to source a cheap 240v 30watt mains inverter, to enable me
> >> to vary the speed of a peristaltic pump, if any one comes across one o=
r
>> happens to have one surplus to requirements.
>
> > You're not giving nearly enough info here.
>
> Which information do you think it lacks?

Now you've told us its a synchoronous motor, and I'm going to guess a


240v motor. The Range of 6 to 0.2 means a min drive frequency of
1.7Hz, and I cant see any 50Hz motor coping with that without significant complication. I think the only answer that will avoid a good bit of work is forget it, and just use a timed on period at 50Hz, or if you're prepared to reduce voltage to 80-100v you could go down to a fixed 17Hz using triacs to invert every 3rd halfcycle.

Surely there are other options too, but you either need the skills to design & construct a non-trivial circuit, or to buy it ready made. Is changing the gearing instead an option?


NT


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H

It happens that Tabby formulated :

No, I need the full speed range available on the 'dial'.

Regards, Harry (M1BYT) (L) http://www.ukradioamateur.co.uk
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T

I cant see any sync motor working over such a frequency range, not unless you do a lot of careful control & mollycoddling. If you knew how to do that, you wouldnt be asking more basic questions.

Someone suggested a sig gen, audio amp and tranformer, that would fry the motor very quickly, and wuoldnt go much below 20Hz with most amps. The only realistic advice is forget it, your pump can't do what you want it to.

NT

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H

No, not that way perhaps - so back to organising a method to turn it on and off for variable periods of time then.

Regards, Harry (M1BYT) (L) http://www.ukradioamateur.co.uk
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J

Unless, as has been suggested elsewhere, the synchronous motor were to be replaced by a stepper motor. Then speed control from zero to full at

100% torque is available with no problems, and it can even be programmed to single step.

A D.C. or brush/ commutator type A.C. motor would be almost as good with a pulse width modulated controller, but you'd need to keep a close eye on the temperatures.

Unfortunately, sometimes you can't get there from here.

Tciao for Now! John.
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D

The simple solution would be to use a 3 phase motor and a 3 phase variable frequency drive. You can find them on Ebay. They are also used in washing machines and in high efficiency air conditioners. I believe PIC sells a microprocessor optimized for making variable frequency drives.

Dan

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M

I tuned in late here but doesn't the "three phase" preclude a synchronous motor, typically?

Where would this be found in these appliances?

Dan

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D

I might be confused. He wants a variable speed so I assumed that synchronous was what he now had, but not a requirement.

I am also not sure how much power he needs. If only a little power, he might be able to get by with the motor from a CD Rom or DVD recorder.

I have not tried to get a variable speed set up from an appliance, but know they are used in some washing machines and air conditioners.

Dan

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