Phase converter

I haven't built a phase converter sence Fitch was a regular here. Now I'm building one for "The Kid". He has his eye on a Haas VF2 with a 20
hp. spindle.
So, we've found a 5 hp. and a 20 hp. idler motors. The plan is to start a 5, delay a few seconds then start a 20. I've done this with a 10 and a 15 for years, works great. I plan to pretty much copy the Fitch designed unit but with different motors and circuit breakers instead of fuses.
My questions 1. what size circuit breaker for a 220 VAC 3phase 5 hp motor
2. what size circuit breaker for a 220 VAC 3phase 20 hp motor 2b. what wire size for above motor
3. How much start caps for the 5 hp motor?
4. about how much run caps for the 25 hp system? I know we'll need to tune it. Fitch got my other unit within 10 volts. I had a chance to check it the other day, max volts was 252 L2-L3, lowest was 244 L1-L2, don't remember the L1-L3 but it was in between. Now, I do wish I remembered how he did it.
Karl
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Karl Townsend wrote:

About like this:
http://wpnet.us/FitchWConverter.pdf
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wrote:

BINGO, I never knew he wrote it up.
Thanks
Karl
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FLA

FLA -- but how are you going to run them on two separate circuits, when one starts another?

See FLA and AWG table

Try 100 uF, it differs from motor to motor as to how much will start it

I can find out how much is in my 17.5 HP phase converter (same principle), it balances voltages great.
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On Thu, 20 Jun 2013 18:38:34 -0500, Ignoramus4976

I googled FLA and found 20 amp and 60 amp breakers, sounds about right. Never knew the term FLA before.
Don't see why you think a breaker for each motor is a problem, its just there for a failure. I will be using an entire three phase load center panel so he can breaker all his machines.
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Karl Townsend wrote:

The idlers end up wired in parallel anyway, if each is on it's own three phase breaker in a three phase panel they're still in parallel. The only oddity is that the main breaker into the panel (or main lugs) only has two hot legs connected. You could even wire some run/balance caps in on 2 pole breakers and put a few meters on the panel cover so you can dynamically adjust the balance.
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Putting two parallel connected motors on two panel breakers makes zero sense to me.
i
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its for failures. lets assume a wire insulation fails and contacts ground. what do you want to have happen?.
Or a bearing burns out, or or or
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Try to think how exacTLY the current will flow. For example, it may want to flow to the big motor through the small breaker. Or, if the small breaker trips, it will still get power through the big motor.
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Karl Townsend wrote:

These are two different fault condition and are protected by two different types of devices.
First of all, for motor branch circuit and breaker sizing, consult the NEC, table 430.250 for the proper FLA. Don't use the nameplate. For a 220 VAC 3phase 5 hp motor, use 15.2 FLA. For a 220 VAC 3phase 20 hp motor, use 54 FLA. The
The motor overload protection should be set based upon the nameplate FLA. The reasoning behind this is that, should you need to replace the motor, the table value is conservative. So the conductors will be sized for a worst case. On the other hand, the nameplate value is the limit for that specific motor and needs to be reset in the event that the motor is changed out.
Overload protection is for failures where the motor conductors themselves do not suffer a fault but the motor seizes mechanically. The breaker is sized to protect the branch circuit from an electrical fault.
Also, one must consider the need for a disconnecting means and their requirements when designing a code compliant installation.
All of the above addresses three phase motor protection from a three phase source. Phase converters are addressed by NEC Article 455. But this assumes a device designed and listed as a phase converter. The calculations needed to home brew such a system can be done, but that won't necessarily make for a code compliant installation. Whether an inspector's buy-off is an issue or not, I'll leave up to the individual.
--
Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com
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Hey! It makes perfect sense to me... then, whichever one exceeds the FLA rating of its breaker first, it frees the other one up to fail _almost_instantly_.
What better protection, than to have two breakers that protect one- another? (and do nothing else useful that one couldn't?)
LLoyd
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"Lloyd E. Sponenburgh" wrote:

They let you manually start each motor.
The three phase panel is a nice backplane to build both the RPC itself and the power distribution from the RPC on.
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Breakers are not _usually_ designed to be switches. (some are, but I'm betting this isn't the case, here).
SWITCHES are designed to be switches...
Lloyd
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"Lloyd E. Sponenburgh" wrote:

If he uses a good panel like a QO those breakers are absolutely designed for switching duty. It is very, very common to control warehouse lighting banks directly with the circuit breakers.
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wrote:

Correct.
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children. Thus, for example, there is also the popular tactic of
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"Karl Townsend" wrote in message wrote: <snip>

Don't forget the conversion between 3 phase and single phase amps, 3 phase amps * 1.732 (square root of 3) = single phase amps. Also there is power factor and efficiency to deal with.
RogerN
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If you check the actual hp of the spindle motor, you will likely find you will *never* need the 20 hp idler. Even if the motor were 20 hp, you'd have to be doing some big-time hoging to warrant more idlers. I run a Haas GR510 AND a Fadal 3016 off one 5 hp rpc, no pro'lengs, lite work. If some real work is brewing, I'll stage in another 5 hp. I have over 30 hp in staged idlers, and can't remember switching in the others, except to show off my switching/relay/cap circuitry.
It would be far more economical NOT to run that gonzo idler, but rather stage 2, 3, 5 hp motors, switch them in as is needed. Much more economical, and likely much better overall regulation.
I have my idlers started by motor starters, and breaker the wild legs separately, ultimately feeding into the "main" generated leg supply.
Running big honking idler motors is like having a really big dick -- impressive in the locker room, but almost all women complain. In the rpc case, your electric bill will complain. Esp. when yer doin 1/4 hp worth of drilling/tapping.....

At what load? I've gotten mine and a buddy's within 1 volt, no load, a few volts at about a 1-2 hp load -- different caps switched in, of course.
You should have two idenditcal banks of switchable caps, from 5 to 100 uF. You can switch them in/out to L1-L3, L2-L3 as needed, whether for starting or running, for a variety of load conditions.. Don't, however, switch caps in/out to electronic circuits while the circuits are energized. Best to test with resistive loads. If you test with other 3 ph motors, THOSE 3 ph motors contribute to the generated-leg system, as well, if they aren't directly loaded themselves.
I had a chance to

Trial and error, with the above.
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EA


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