Phase converter help

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Forum topic by William Shelley posted 03-30-2017 06:19 PM 502 views 0 times favorited 5 replies Add to Favorites Watch
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William Shelley

587 posts in 1613 days

03-30-2017 06:19 PM

Hi all,

I’d like to get some real-world information on sizing a phase converter for my new 5.5hp jointer/planer machine.

The standard sizing charts would recommend a 10HP phase converter to start a 5HP motor. A jointer is quite a soft thing to start up as far as I know. The only load on the motor is getting the cutterhead moving.

Could I get away with a 5HP or 7.5HP phase converter?

-- Woodworking from an engineer's perspective

5 replies so far

View Aj2's profile (online now)


1717 posts in 1942 days

#1 posted 03-30-2017 07:45 PM

My experience with Phase Converters is it depends on the manufacturer.Some do recommend that.
The trend is to use Vfd but not me.
My jointer has a pretty good inrush to start but it’s a direct drive.
Make sure your single phase service can handle your choice.
Good Luck

-- Aj

View bonesbr549's profile


1576 posts in 3211 days

#2 posted 03-30-2017 08:21 PM

I would think depends on the converter type, and mfg. They are not the same at all. If you want a RPC, call They know their stuff and great company to work with. Talk to an expert.

-- Sooner or later Liberals run out of other people's money.

View Loren's profile


10477 posts in 3792 days

#3 posted 03-30-2017 08:45 PM

I think you’ll be fine with 7.5hp.

Money savings won’t be much if you’re
building a 7.5 converter over a 10hp.

I found my used 10hp idler for about
$100 on ebay and picked it up (weighs
over 100 lbs). I got the box from Phase-craft
on ebay.

View alittleoff's profile


541 posts in 1421 days

#4 posted 03-30-2017 09:30 PM

If you go with a VFD you only need it rated for 5 hp.phase converter you probably need to go 25% more for the starting load. I’d call the manufacturer before I bought one.

View William Shelley's profile

William Shelley

587 posts in 1613 days

#5 posted 03-30-2017 11:50 PM

I would have liked to use a VFD to act as a phase converter for this unit, but it has an electronics panel that is quite complicated. Has an AC->DC switching power supply to run the control board, also a powered raise/lower mechanism for the planer table. What I’ve read of VFDs is that they’re not supposed to be connected with any type of switch between the VFD and the motor load.

I might be able to rewire the panel to single-phase and add one or two VFDs as necessary, one for each motor. That seems like it might be more trouble and expense than just buying a 7.5HP rotary phase converter.

-- Woodworking from an engineer's perspective

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