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Re: [TCML] Variable RSG
Kris,
Yes, you can use an angle grinder motor and a variac. The VFD is
better because it gives you precise control (on some you can simply set
the frequency in Hz.) If you already have the parts, I say go for it.
Just intuition here, but I would suggest you use 4 or 6 flying
electrodes for a higher BPS, that way you do not need to run the motor
full bore for your 330-390 bps. Just my two cents.
Scott Bogard.
P.S. Test it first to make sure your motor does not have an
interference problem, you should be ok, but just run it next to your
coil and make sure. I have had troubles in the past, so now I test
everything I use next to the coil to make sure it is alright.
Kris Grillo wrote:
> So an angle grinder with a variac wouldn't accomplish this? I have a heavy duty 5A 4.5" Dewalt grinder and a 10A variac. I was thinking of making a 6" long bar of G10 stock with 2 flying electrodes for 333 - 390 bps between 120 to 140 volts, if rpms are somewhat linear with voltage input. I also have a couple motors from wet saws. They look like big angle grinders and turn 9" blades. I'm not sure of the rpms, I'll have to check today at work. After that, I also have 4 or 5 single phase motors ranging from 1/16 horse to 1/2 horse. I believe that they are all 1750rpm. Would any of these suffice? Just asking before I spend the time and money to make something that won't do the job.
> Between still needing to get a larger variac and spending so much on the Teletype motor and rotor, I don't have much left in the budget to buy a whole new motor setup any time soon.
>
>
> bartb wrote: Hi Scott,
>
> I meant to reply to your thoughts about Grainger, but deleted the email
> and emptied trash. So writing this under and new subject.
>
> Anyway, yes Grainger does have some decent prices. But, for AC speed
> control, price is HP dependent (even at Grainger). If motor is under
> 1/4HP, you can pick up a speed control for $34. But for something like a
> 1HP motor, you head to the $170 range minimum. I use a 2HP Baldor
> myself. This of course gets even more expensive for speed control. Even
> at 1HP, your already at VFD prices. The motors themselves are cheap and
> 3-phase is likely the least expensive. For DC motors, the price can get
> very high in the 1HP range. This is where eBay comes in real handy.
>
> Adam and myself are using a VFD to control a 3-phase motor and vary
> speed with a simple potentiometer. My Altivar31 2HP VFD is expensive at
> $300 each off the shelf. No matter how you slice it, as HP is increased,
> variable speed will cost a bundle between the motor + controller if
> purchased as new (even at Grainger). I think eBay is still probably the
> best way to beat these enormous prices.
>
> BTW, I should let everyone know I have a brand new (in box complete with
> 375 page manual) ABB 3HP VFD for sale which list in the $500 range. I'm
> letting it go for $200. P/N is ACS350-01E-09A8-2, 1-phase 200 to 240,
> 21A and 3-phase 230V out, 9.8A, 0 to 500 Hz variable frequency. I
> haven't used it and I don't know any of the details. Should not be too
> difficult to figure out.
>
> I also have a used 2HP SquareD Altivar 31 VFD for sale for $125. Works
> perfect! Don't have the p/n handy, but it's 1-phase 200-240 in and
> 3-phase 230V out with 0 to 500 Hz variable frequency.
>
> If anyone wants these, they should contact me at bartb@xxxxxxxxxxxxxxxxx
> I will also offer a money back guarantee that these VFD's are "both" in
> new working order. In order to use these VFDs, it is necessary to pick
> up a 2HP or 3PH 3-phase motor for them (as appropriate to the VFD HP
> rating). Check eBay. Sometimes these motors can be found for around $50.
> I have only one spare 1HP 3-phase motor on hand, but it doesn't match
> these particular VFD's. However, if you come across a VFD or speed
> controller requiring a 1HP, 3-phase motor, I will sell it to you for $50.
>
> BTW, for those that don't know, Leeson (major motor manufacturer) just
> announced that they are off to Mexico to build their motors! Cheaper
> labor I guess.
>
> Take care,
> Bart
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