Question about Phase Converter

[JessEm]

Hello, I'm looking for some feedback on a phase converter. I just picked up an awesome, older Baldor 1/2 HP pedestal grinder, 3 phase. Does anyone have experience with the cheaper, "static" converters? My understanding is that they are somewhat misleading, in that they only provide 3 phase on start-up, to get the motor going, and not continuously, which doesn't seem good... Then I read that it's fine for a grinder, because it's not constantly starting and stopping, and it doesn't run unattended. Can someone shed some light on this? Do they work? I don't want something that will damage my motor, or burn it out.

Also, this grinder came with 2 diamond wheels. I should be able to swap them out for regular, amum oxide or stone grinding wheels, correct?

Thanks in advance.

[rusty]

The problem with the el-cheapo phase convertors is they don't produce balanced 3 phase power, so the motor runs with unpalanced phases. Mor\tors don't like this, and try to balance the 3 phases by shifting current from one phase to another, which increases the winding currents and generates heat.

However, the motor on a grinder isn't very heavily loaded, and the Baldor motors are rather over built, so I suspect it will work ok, provided you can find one the right size. That's the other problem, they have not only a maximum HP rating, but also a minimum rating, if it's too big, the motor can't load it enough to make it work right. Most of the convertors floating around are 5HP because they were very popular with folks who wanted to run horizontal milling machines in their garage...
(many of whom also fried the electronics in their milling machines, electronics don't a like funky power ; P )

>Also, this grinder came with 2 diamond wheels. I should be able to swap them out for regular, amum oxide or stone grinding wheels, correct?

Depends, what speed is the thing? Some diamond wheels are designed for high speed operation, you need to match the wheel to the grinder to use it safely...

PS: Don't assume you won't find a small rotary phase convertor surplus somewhere, computer rooms were still using them for UPS service untill fairly recently, now they are all obsolete, , I havn't gone looking for one, but I bet they are out there...

[rusty]

PPS: Make sure you fuse the *motor*, if the phase convertor fails, it will toast the motor ; P

[JessEm]

Thanks a lot for all the info, rusty. ... I wouldn't know where to start looking for one of those used rotarys either, but I'm on the lookout from now on. ... From what I've read about those statics, I'm just not sold on it.

Thanks,
Jesse

[Aunt Phil]

Don't discount static capacitor type converters too heavily.
Bridgeport has been supplying them for years to customers wanting single phase machines.

There is an entire section of fairly good information on phase converters on Practical Machinist.  You can also look into a VFD at relatively cheap money, ebay is loaded with them and they keep getting cheaper.

[rusty]

>There is an entire section of fairly good information on phase converters on Practical Machinist.

Seconded, very good site with sharp folks : )

>You can also look into a VFD at relatively cheap money

Now there is a *very kewl* idea. A variable speed grinder. It always annoys me when grinding something small and the wheel wants to light it up white hot and instantanously take the temper out of it, Slowing the grinder down to a few hundred rpm would be interesting, tho I dunno how slow you can go and still have the VFD still be able to excite the motor...

hmm...