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Bob La Londe[_7_]

On 6/16/2018 7:11 AM, wrote:
On Fri, 15 Jun 2018 17:25:52 -0700, Bob La Londe
wrote:

On 6/14/2018 10:55 PM, Bill wrote:

I was looking at a jointer with a 3HP 3-phase motor. I'd like to run
this from my home which has 220v. Would I be able to run it on a 20A
(preferably) or 30A circuit?

Can you give me an example of a "phase converter" which would be up to
the task? I saw one for $89, but I couldn't tell whether it would
be up
to the task or not. I imagine it might be wiser to avoid 3-phase and
keep looking, but I thought I would check with the experts here first.

Thanks!
Bill

3hp on 220V is (ideally) only about 10 amps. The reality it may peak a
little higher under a hard startup or if you bog down the motor.

A "good" rotary phase converter is the way to go if you think you will
run much 3 phase stuff. I don't recall the derating, but its something
like 30-40%. ie: Get a 5HP rotary for a 3HP motor. If all you wil ever
run is a motor directly you can probably go with a cheaper static phase
converter. Just remember that the derating is higher. Its best to see
if the MFG says "This converter will run a X-HP motor."

The easiest way for me (and most expensive) is I have dedicated variable
frequency drives on each 3 phase motor in my shop. When used 1ph in and
3ph out they have a 30% derating as well, but they give me infinite
variable speed control. Most are on CNC machines where a 0-10VDC analog
power signal controls frequency and rpm. Others I just use the controls
on the VFD. With most half decent 3phase motors you can run from half
speed (frequency) to double speed without them tearing themselves apart.
If they are inverter rated they may handle more. If you have one of
those fancy new washing machines you probably have a high speed 3 phase
motor controlled by a VFD already. You just didn't know it.

Anyway, even with the parasitic losses it will probably run just fine on
a 20 amp 220V circuit. Should be absolutely no issue at all on 30 amp.

I think 1HP is roughly 750 watts. I always figure 800 and then add a
fudge factor on top of that for safety.

3 X 800 = 2400 watts.
2400 / 220= 10.9 amps.

You will have some loss from your phase converter, heat, wire, etc.
Still with nearly double the fudge factor...

Odds are your 220V is really closer to 230-235 anyway.

In the US, your 220V is even properly called "240V" (twice 120V).

In the US your 240V is anywhere from about 225 to 245 based on actually
sticking a meter on a bus bar once or twice. Mostly I've seen 232 to
about 236. Not counting star which tends to be fairly close to 208, but
if you had 208 from a star transformer configuration you would already
have 3 phase.

In my shop I have 236 on one leg and 234 on the other most of the time.
I have not left my recording meter hooked up as I have not seen the kind
of issues that would indicate I need to.

The gradual shift from 220 to 240 is in part due to the fact that power
companies can transmit net total power more efficiently over lighter
wire at higher voltages. Amps times volts equals total power (watts)

Getting back to the actual issue since I backed it all up with numbers
already...20 amp should be fine, but it pays to have a larger fudge
factor when using a phase converter as there is a bit of loss there.
Particularly with a rotary where you are literally turning a larger
motor to generate 3 phase.