Re: [CAD_CAM_EDM_DRO] 3 Phase rotary converters

Using a potential relay, and starting caps is easier to set up and would
appear to be safer than the starter motor and belts. Doesn't dim the lights
and takes only about 0.5 second on my setup. A added plus is if you happen
to stall one of your machines and pull down the line voltage the potential
relay will kick back in and give you added capacitance to get the machine
pulled back up too. Not a recommended situation, but it will work. Have
stories of a working machine shop starting and running 10hp + machines on a
5 hp converter, utilizing this method. I don't recommend it but it will
work. (rule of thumb, is the phase converter should be as big as your
biggest starting load, but can run up to 3 times its size in total hp load,
as each 3 phase motor running is also like another converter on the line)
Also, I have started a converter with just unbalanced run capacitors on the
line, starts kind of slow, but it will.

Beau

----- Original Message -----
From: <bobmcknight@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, May 08, 2005 6:56 PM
Subject: Re: [CAD_CAM_EDM_DRO] 3 Phase rotary converters


>I am running a rather large motor (10 Hp) and decided
> that the easiest way to start it was to mount a 1/2 hp
> motor and belt connect it to the rotary convertor. To
> start, I turn on the 110v 1/2 hp motor and tighten the
> sliping belt with a handle on the idler pulley. This only
> takes a few seconds. When the rotary motor comes
> up to speed, I release the handle and the belt slips.
> then I switch on the single phase power to rotary convertor
> and it goes on its merry way. No high starting current, or
> prolonged waits for the convetor to come up to speed.
> I just have the run capacitors to the third leg. I could deal
> with the mechanical starte a lot easier than going thru all
> design and experimentation. I use it to run a 300 amp MIG
> welder which will never see close to that output, but it was
> dirt cheap and in excellent condition. I also have a 17" lathe
> that can use either a static or rotary convertor, and a 10 grinder.
> So if you have a small electric service to your shop and don't
> want to dim the lights while starting the convertor, there is an
> alternative.
>
> Does anybody know for sure about the voltage rating of capacitors?
> I read someplace that the voltage printed on the capacitors is not
> the voltage that they should be operated at on a rotary convertor.
> A capacitor for a 220 VAC rotary convertor should have approx
> 370 volts printed on its case. ???????
>
> Bob McKnight
>
>
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