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Reply by Mainiac Matt

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Posted on 3ph 5hp Powermatic 66

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Mainiac Matt

9238 posts in 2783 days


#1 posted 06-14-2017 08:19 PM

We run a 5 HP 3 ph PM66 at work and it’s a great saw.

and Jim is right, 3 ph equipment sells for a lot less.

I’ve looked into it several times and your options are pretty much as follows:

1. replace the motor with a single phase motor. But a good single phase 3 HP motor will run you upwards of $300.
2. Buy (or make) a static invertor. This uses a capacitor to create an artificial third leg to get the motor rolling. The you have two poles driving the motor and the third pole acting as a generator. You take a hit on the overall HP rating, but a lot of people do this. Phase-o-matic sells them for ~$150 and they have to be sized for your machines HP rating. the starting capacitor is often on a timer circuit and then a smaller run capacitor is used to balance the phase angle between the legs. BUT… if the machine has contactors that run auxiliary functions (limit switches, coolant sump pumps, etc…) you will often find that the invertor will not properly trigger those contacts and drive those functions.
3. Buy (or make) a rotary invertor. This uses a 3 phase motor and static invertor to get it rolling. This motor then generates the third leg which can be wired to run multiple 3 phase machines. The prices on these have come down, and Grizzly sells a nice ones for ~$500-900 depending on the HP rating. This will allow you to run multiple 3 PH machines, just as if you had it coming in from the utility company.
4. Use an DC invertor. This option is definitely the way to go for variable speed applications (think drill press or lathe). Getting the right invertor specified for you motor is crucial. And if you buy the wrong one, they won’t take it back. For a 220 v 5 HP machine, you’ll wind up paying ~$400 or more, but the prices on these have also come down in recent years.
5. Pay to get your shop wired for 3 PH and get a 3 ph drop from the utility company. The price of this depends on how far you are from then nearest 3 ph pole. But it will easily run thousands of dollars.

My personal pic would be to build a rotary phase convertor, as I salvaged a 7 HP industrial duty 3 ph motor several years ago, and the plans for convertors are readily available on line.

HOWEVER…. if you screw it up and burn your house down, your insurance company may well deny the claim.

-- Matt -- I yam what I yam and that's all what I yam


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