Re: "54Vac Three Phase" means what?

From: Zak (jute_at_zak.invalid)
Date: 07/12/04 

Date: Tue, 13 Jul 2004 00:29:20 +0200

Scrim wrote:

> I don't plan to try running the turbo pump beyond short tests until it's
> under vacuum.

Don't run it in air. It doesn't run very much at all in that case, and
agood enough starting vacuum will not be that hard to reach.

> Yes, I'm trying to build a power supply for it. I really want to try to keep
> it as low cost and easy to build as possible, but I don't mind spending time
> on the design and I'm patient. My original plan was to use the 3 phase
> variable frequency digital sine wave generator I've designed (with help from
> this group - see thread: Digital Sine Wave Generation) to drive three audio
> ic power amps. Unfortunately I now realise that the required 3 phase 54Vac
> means I'll need an 88Voutput swing, which is beyond the IC's I've been able
> to track down. There are plenty of high power audio amp chips and power op
> amps able to provide far more than the 35W max I'll demand from each, but
> none at sensible prices that will work with 90V-100V supplies :-( I'm a
> little concerned too about how these devices would behave when driving a 3
> phase induction motor anyway.
>
> The alternative idea I've been considering is to use some logic to produce
> 3 square wave signals which overlap in the required 120 degrees (3 phase)
> fashion. I'd connect these to something like the HIP4086 3-Phase Bridge
> Driver and 6 FETS.

This would be a whole lot easier. I'd make high side drivers myself and
run the whole thing on square waves. Use the desired RMS value as DC
power voltage. 31 V RMS to neutral means + and - 31 volt power.

To drive you could even use optocouplers. 3 phase can be generated with
a 4017...

But run the thing in vacuum only or the motor will burn out. You may be
able to find data sheets on line of these pumps - I found them at least
for Alcatel pumps.

Thomas