Re: [CAD_CAM_EDM_DRO] Re: 3 Phase rotary converters

Wally

I think it is the square root of 3 or 1.732
instead of the square root of 2 or 1.414
no big deal cause the capacitor mfg seem to eithe r
rate them for 220 AC or 370 . I bought a bunch from
surplus center that are working fine. I don't find
the extra trouble of starting manually to be a problem.
With manual starting, I have to make sure that the
convertor is up and running properly. With a homemade
convertor of this size, I am a little leery of what might go
wrong if I try to automate too much.

bob mcknight

On 9 May 2005 at 0:21, cnc_4_me wrote:

> 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

I think that is a peak rating. Peak is 1.414 x 240vac = 340 volts
peak. This gives a 30 volt safey factor. I used 240v because this
is what the lines are supposed to be.

Wally






--- In CAD_CAM_EDM_DRO@yahoogroups.com, bobmcknight@c...
wrote:
> 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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