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On Tue, 19 Jun 2018 10:39:35 -0700, "Bob La Londe"
wrote:



wrote in message ...

On Sun, 17 Jun 2018 18:42:32 -0700, Bob La Londe
wrote:


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.

OK. Is the mains voltage precise anywhere in the world? The US
specification is +/- 5% (228V to 152V), at the source (i.e. at the
transformer). Losses in the wiring will put it on the low side of
those numbers.

********** No its not and arguing about whether its 220V or 240 is just
arguing because you want to argue when in most places it is actually
neither.

NO, I'm pointing out that the tolerance is 5% and hardly matters in
this discussion.


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.

Different kettle of apples. That's not "204V" and rarely, if ever,
found in residences.


********** Just being thorough since you choose to pick at nits. LOL.

But it has nothing to do with the discussion.

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.

Sure, you have an load imbalance. Not surprising but hardly relevant.

*********** Relevant? Sure it is. Its nt 240V. LOL. 2 volts is hardly a
significant imbalance though. Its the same at the lugs with the main
breaker off. So... if anything the "neighborhood" has an imbalance. LOL.

That's what I said. It's not relevant.

No, it's probably in your house.

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)

OK. But here we are.

************ Yeah, but any electrician will recognize that arguing over
whether its 220 or 240 is pointless. An engineer might note that you can
carry more net power at 235 than at 220. Again. LOL.

But the issue is a 3HP motor. The difference between 220V and 240V,
or any tolerance of the 240V is irrelevant. A 20A circuit is good
enough.

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.

Agreed. 20A single phase should be good for 5HP but I prefer a bit
more overkill also. I usually do a home-run from the tools back to
the panel, unless I know that two outlets can never be used at the
same time. ...and with 240V circuits, usually then, too.


************* I think we mainly agree and are just quibbling over
minutiae.

No, the point is whether 20A 240V circuit is enough for a 3HO motor.
It is. Period.

************* That may be the point of the OP, but you are the one who chose
to establish himself as a self appointed egotistical god of all things
electrical and argue over every little thing. My very first post
established with facts and numbers that conservatively a 3HP motor could be
run on 220 or 230 or 240 under or whatever arbitrary number you choose to
claim at under 20 amps and I noted it has a particularly large safety
margin. I'm not sure why you are even arguing that point. I established it
before you even let your fingers spew across your keyboard. However, You
seem to pigheadedly refuse to acknowledge that there is more in the OPs
circuit than just a motor. He asked specifically about a phase converter
which is notoriously in efficient. Rotaries and static converters are both
inefficient. Even VFDs are very inefficient when used as phase converters.
It almost seems like you are against the very fact that I choose to be
conservative and safe with my calculations and choosing unimportant things
to argue about like whether or not the established standard of 220V or the
closer to 240V actual (but almost never exactly) is correct. Its like
arguing your Chevy is better than mine because yours is blue. You can go
out and find new outlets for example that are labeled at different primary
voltages even today.

One also needs to recognize that bogging down the motor at the tool may
have
a net current draw that is higher than its nominal or even rated current
draw unless loading it up until it bogged down was how the motor was rated
to begin with. Then its really not a 3HP motor. Not 3 useable HP anyway.

What? That makes absolutely no sense. A 3HP motor will draw its
rated current *AT* 3HP. It will be "bogging down" ("slipping phase")
at that point.

************* I suppose with the number of crap motors on the market today
that is true. Between cheap import motors that are literally rated by
loading them down until they stop and measuring the current, and name brand
motors struggling to compete with cheap imports very few electric motors
today are capable of putting out their useable rated power for even a
fraction of a second. That wasn't always the case. Like your petty
argument about 220V vs 240V to make yourself feel superior, or whatever it
is that motivates you, that wasn't always the norm. There are still motors
out there that don't lie on their data plates. I have 3 phase spindle
motors that I have literally run at their rated horsepower. Not for very
long, but they can actually run at rated power for a short time. No I
didn't run a recording meter on them (and current is actually NOT an
accurate factor to measure of horsepower), but when calculating cutting
loads mathematically I found corners and sharp inside turns calculated right
at their rating, and the motor didn't bog down or die. Of course I value
those motors very highly, and I try not to ever run them like that as it
shortens their life and particularly bearing life substantially. As I have
learned more about machining techniques I try to keep my motors well under
their ratings. Heat buildup is the killer. However I have to acknowledge
that even 35 years ago machine builders questioned the output of their
motors and designed machines with a safety margin. I have a 1984 (I can
never remember for sure the year) 2 ton CNC mill (light weight by today's
standards) with a 5HP spindle motor and the mill builder rated the mill at
4HP. Of course they are running a 3.7Kw (5HP) VFD to control the
spindle.... hmmm not quite a 30% derating, but they probably intended the
machine to actually be run directly on 3 phase. I have never ever bogged
that motor down at normal speeds. I do run it as low as 96RPM at 3hz where
it can bog down if you don't plan well, but if you can't do that you
shouldn't be running it at all. I suppose I have to add another caveat.
Many motors are capable of their peak horsepower for a second or two, but
often not at their standard line frequency speed. I have several 24K rpm
400hz motors that peak around 19000 (+/-) rpm. They are not as linear as
people would like you to believe. I've found similar results with more
conventional motors running at the 30-120hz that most 3Phase motors are
capable of running. Again, just being thorough. Want a great example?
Open one of those high tech modern washing machines I mentioned in my first
post and read the voltage and frequency tag on the basket motor.



Also start up of the that 5HP (or larger) rotary may draw more than its
nominal rating at peak load as well. In rush of the caps can be quite high
and initial inertial load can be higher than expected. The odds are 20
amps
at the range from 220 to 245 (there you happy now LOL) is adequate for the
job anyway. Especially since breakers do not trip instantly at peak
rating.

Hardly. The start capacitors are irrelevant.


*************** Any current draw even for a fraction of a second is
relevant. Although as I stated before (so you don't have to argue an
established point all over again) even IF (=big if) the total circuit hit
near peak current for a fraction of a second it probably would not trip the
breaker as modern breakers (most) do not trip instantly at peak current.
GFI breakers do tend to be more sensitive, and there is always the chance of
a breaker that isn't quite up to "spec." Of course like my mention of 208
to be thorough I am just mentioning this to be thorough.


TO THE OP... get a phase converter rated to run your motor at peak and hook
it up. Even a cheap-ish one will do if you follow the usage
recommendations. Hook it up, and if you ever have any issues you can always
upgrade the circuit later. As both Mr know-it-all and I both agree. Its
unlikely you will have a problem. Of course I said that in my first post.
LOL.