phase converters HELP 6

[anarchist]

HELLO ALL, I HAVE A PROBLEM THAT I NEED TO FIGURE OUT BY MORNING. I HAVE JUST REPLACED THE ELECTRIC MOTOR ON MY FORGING HAMMER FROM A 10 HORSE TO A 15 HORSE AND MY PHASE CONVERTER IS A 10 HP. I HAVE ANOTHER 10HP CONVERTER THAT IS NOT BEING USED. I HAVE HEARD THAT YOU CAN USE THE TWO TOGETHER TO GET MORE HP. BUT DO NOT KNOW HOW. I BELIEVE THAT YOU CAN WIRE THE OUTPUT IN PARALELL AND THAT IS ALL THAT IS NEEDED BUT DO NOT KNOW ENOUGH TO TAKE THE CHANCE OF BLOWING TWO CONVERTERS UP. WE ARE FILMING MYSELF (THE BAREFOOTBLACKSMITH), MY 11 YEAR OLD DAUGHTER (THE BLACKSMITHETTE), AND HERMAN ( THE 100 YEAR OLD FORGING HAMMER)FOR A SHOW ON OLD TOOLS WED MORNING AND NEED THIS HAMMER UP AND RUNNING. ANY HELP IS APPRECIATED. THANX AGAIN, THE ANARCHIST

 

[jraef]

Depends on the type of phase converter. If they are electronic, then no. The phase angles of the 2 converters would never be exact enough and they will damage each other. If they are rotary, then yes. They will just pull each other into synch. So for rotary, wire them in parallel, make sure that the phases are exactly the same, i.e. A to A, B to B, C to C, otherwise you will let the magic smoke out.

Another forum,

http://www.practicalmachinist.com

has people with a lot of practical experience in rotary phase converters (RPCs) as well, you may want to ask in there.

Barefoot? OUCH!

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[waross]

I can make a few suggestions, but I have to make some dangerous assumptions to do so.
Assumption #1. The phase convertors are standard three phase induction motors with enough capacitors between two phases to give enough phase shift for the motor to start on single phase and then produce the three phase running as an induction generator.
Assumption #2. The phase convertors are identical. Not just externally, but the wiring connections are identical internally also.
Assumption #3. The leads can be identified, and matched from one machine to the other.
If we meet all these criteria, we can probably connect the machines in parallel.
Starting both convertors together will be a challenge. You can probably start one and then the other, then start "Herman". Don't forget to check the wire size going to Herman to be sure that it is adequate for 15 HP.
Wait for a few other experts to respond and consider all the advice.
yours

 

[anarchist]

these are rotary converters and they are not of the same brand, one is a phaseomatic and the other is a home made one that has five capacitors, two relays and ? the person that built the home made one has drawn a simple scematic on the housing of the capacitors and has marked the wires red black and blu. the phaseomatic has the wires labeled 1,2 and 3. how woule you go about to find the difference of the two feed wires that are powering the converters, the third leg that they produce is easy to distinguish so i have no problem with that but i am assuming that the two hots coming in would have to be matched to the windings in the motors. is this correct and if so can it be tested with a multimeter. or do you have to use a scope?

 

[jraef]

waross' points were more in depth than mine and in retrospect, I fully agree, especially about them being the same design. I think the risk of negative interaction of the different amount of capacitance in those two would be too great. They can likely resonate between each other and that can lead to extremely high voltages, damaging the motor windings all through the converters and load. I could be wrong though, RPCs are not my field of expertise. waross probably has more experience on them than I.

In that other forum there is also a gentleman with the handle peterh5322 who has a really good handle on designing and building RPCs from scratch. I strongly suggest posting there and specifically asking for his input.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[itsmoked]

Since anarchist is placing a 15HP motor into a 10HP application is there any chance the 10HP converter can run it?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

I think jraef has the right idea.
Check with the other forum. It is a fairly involved process and possibly dangerous to try to match the phase rotation on two disimilar units. Better to get advice from someone who works a lot with rotary phase converters.
Good luck
respectfully

 

[anarchist]

itsmoked asked if the 10 converter would handle a 15hp load so i need to clarify that i am trying to get two 10hp converters to work together to power 1 15hp load. thanx jraef and waross for the imput and i did already get in touch with the other group (great to find another forum to use) so hope for good comments from them. one additional question what are the importance of the capacitors and how many you should run?? is it just about start load?

 

[waross]

Hi itsmoked;
I agree with you, but without being on site to check loading and balances on both the phase converter and the 15Hp. motor, I hesitate to give possibly bad advice. If either you or I was on site, we would probably not have a problem but I think it's more professional to refer our poster to the people who work with Rotary converters frequently.
A lot depends on the load on the "Hammer named Herman". I imagine the load will be cyclic and determining the actual RMS horsepower may be difficult. Another big factor will be whether the 15 HP has the same torque characterestics as the original 10 Hp. motor.
As I understand a phase convertor, it works as an induction generator to supply the current for the third line. If you can get the 15 Hp. motor started and the load is light enough that it draws the same or less current than a 10 HP. motor it will probably work fine. However, if a high slip motor is replaced with a low slip motor all these nice assumptions go out the window.
Like you, I hate to back away from a problem, but in this case I think I'm going to just "lurk" for awhile and see what new stuff I can learn.

PS, Let us now how the movey shoot goes please, anarchist
respectfully

 

[itsmoked]

Points well taken waross.

I was imagining a big flywheel being kept at speed so once it reaches speed the motor does nothing most of the time and grunts briefly after each blow. But as you point out without seeing it I could be way off. Furthermore the original acceleration of the flywheel could be very problematic because the bigger motor will try to do it, (I presume), faster. And this may stall the whole operation creating more smoke then can be attributed to the forge alone.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Warpspeed]

Let's think about this.

These are rotary phase converters, so they will start up and run in either direction, so phase rotation is not really an issue. If you feed one with two 120 degree phases, it automatically generates the missing third phase, just like a Scott T transformer would.

I would connect up both rotary converters to the source and start them up. Then measure the output voltages between the phases of both machines (one machine to another).

The two incoming phases will correspond exactly to two of the output phases, so they can be safely paralleled. The third generated "phantom" phase will differ slightly in voltage and phase between machines, but it should still be safe to parallel them if the voltage difference is only a few volts.

 

[waross]

Hi Warpspeed
If you have two phases at 120 degrees, you don't use a rotary converter, you use an open delta transformer connection, or a Wye-zag connection.
My understanding of a rotary phase converter is that it converts single phase to three phase. It is basically a three phase motor running single phased. The capacitors create a phase displacement to get it started and then act to help supply some of the energy for the third phase, and some of the magnetizing current. The rotation of the resulting field depends on the internal connection of the capacitors. And their values.
Some convertors use a manual starter and some use power factor correction capacitors in addition to phase shift capacitors.
The rotation of the motor shaft is unimportant, but if the rotation of the magnetic field is reversed in one converter in relation to the other converter you can get a voltage between the two third legs in the order of root three times line volts. That would be over 400 volts with a 240 volt supply.
Another factor; I understand that one of anarchist's phase convertors is a homebrew model. The alternate technology people, possibly on the principle that more is better, often connect a second set of capacitors from the second line to the third line. The second set of capacitors balances the first set with no net phase shift but often a very good power factor. They must then add a third set of capacitors to unbalance the first two sets and get the phase shift they need to create starting torque. Once the converter is running, it is an induction generator. It now produces three phase power despite the efforts of the capacitors. I imagine that the extra capacitors do help correct the power factor of the driven motor and so reduce the line current somewhat. The point is that paralleling different phase convertors may be more involved than just starting them and connecting them together.
respectfully

 

[Warpspeed]

All you say may be true, but a simple multimeter voltage test will tell you if it is safe to parallel outputs of two rotary phase converters.

If the voltages coming out of each machine are identical, paralleling them is never going to be a problem. If they are radically different, because of either voltage or phase difference in the third leg, it would probably not be safe to connect them together. Two output legs are always going to be direct hard connections to the source.

I just proposed this as a very quick and simple test to see if parallel operation was feasible.

 

[fsmyth]

To the OP:
Use the RPC that starts the best as the first to start,
then start the second RPC using the motor and contactor
only (from the second RPC). This will give you a 20HP
converter which should start your 15HP machine (unloaded).
It will not be as balanced as it would be if all the caps
were used (assuming both converters were balanced in the
first place), but should be sufficient for your task.
It is highly unlikely that the combination was balanced
for a 15HP load (7.5 + 7.5) anyway. Rotation is unimportant.
<als>

 

[anarchist]

thank you all for the information, it clarified a lot of the unknown. what i wound up doing is to look on the internett and found a simple diagram of how to build a rotary phase converter out of a three ph. motor. i had a 25 horse motor that was not being used and built it acording to the info i had aquired and them added four run capacitors to it ( the info did not tell me to install these ) but feltthat it was important to put these in as the motor that i am using to power the hammer will fluctuate due to a piston that is 16" in diameter being pushed up and down with a crank that is attached to a four foot diameter 1200 lb. flywheel. i have gained more information that i would have ever thought i could in a short time through all that have helped. and it made herman purr, (more like thunder ) the day went well with the film shoot and recomend all involved to watch for a show called the history of tools on the history channel in around three months to see "herman" in all his glory. thanx adam

 

[waross]

Congratulations on your ingenuity. You deserve a star for that.
respectfully

 

[Warpspeed]

Yes, very well done anarchist.

 

[itsmoked]

Three cheers for anarchist!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com