Transformer to get 440 3PH or re wire motor?

jhg · Feb 8, 2007

I have a 10hp 220v RPC. I have a newly aquired machine with a 440 only motor.

What is my path of least resistence cost & effort wise?
Is it to build a 440 capability into my RPC, or can/is it feaseable changing the motor to accept 220?

I will do a search in the mean time.

Thanks in advance.

jhg

johnoder · Feb 8, 2007

If you know motor is 440 only the thing to do is look for a General Purpose Dry Type Three Phase Transformer and use it as a step up. KVA of transformer needs to be about twice the machine HP. I.E., if machine is 5 HP, get a 10 KVA transformer.

Tag on transformer must show it to be three phase and 440/220 or 460/230 or 480/240

John

jhg · Feb 8, 2007

Dumb question- why can't the motor be wired 220? Does it care as long as it sees the voltage it needs?
jhg, thinking that he'll get out of this somehow...

Bill Simmons · Feb 8, 2007

Well you can have the motor rewired (most likely rewound) for 220. But it will probably cost about the same as a new motor. Assuming the motor is of common physical characteristics and is not special (such as a 2 speed motor) I would look for a used replacement motor. Check your surplus stores and ebay. You will want one you can pick up because the shipping will be similar to the cost of the motor. The shipping on a transformer will not be cheap either.

johnoder · Feb 8, 2007

why can't the motor be wired 220?

Maybe it can. You can check if you want.

Open terminal box on motor. See if it has nine numbered leads coming out of motor. If it does, it can be reconnected for 220/230/240.

If it does not, it can't

Something to keep in mind is that changing a motor from high voltage to low voltage will always require replacement of the heaters (thermal overloads) in the magnetic starter because you have doubled the amps going thru.

John

jhg · Feb 8, 2007

Thanks for the tip. I was just doing a search and just found that. I will see this weekend whats inside. Hoping for the best. I am on the hunt for a transformer too, just in case.
This machine has two motors- a 4hp and a 2 hp.

jhg

Bugpac · Feb 8, 2007

http://s139.photobucket.com/albums/q316/bugpac/Mill%20project/?action=view&current=Picture024.jpg

will i have to change something in this pic if i swap voltages then?

toolnut · Feb 8, 2007

Changing motors would be the preferred option if the cost is equal or less. Since you have a 4 hp motor I suspect something special as 4 hp is not a NEMA size motor (2,3,5 but no 4s).
I have used the transformer option for a special motor and you need to be aware the tranformer will double the error in your voltage imbalance. It does not change the percentage but will change the numbers. It is important to balance the RPC to within 5% to give the best performance. I have 245 volts single phase so I ended up with 500 volts after the transformer and RPC. I consider that to be high although it is within the 10% of a 460 volt motor. It is too high for a 440 volt though. I had to balance the RPC better to solve this situation. You can use 3 each single phase transformers of about 3 KVA each if you do not find a 3 phase one. This works just fine.

dkos · Feb 9, 2007

toolnut..

i just purchased a transformer from 'livewire' and bumped my 240 volts up to "440volts" for my surface grinder.......but, since my voltage was also a bit high, i am ending up near the 500 volt mark as you did. is there an easy way to balance down my voltage? can you explain?

thanks

toolnut · Feb 9, 2007

dkos,

all you can do is to balance the phases produced by the RPC so there is little difference between phases. There is a good description by Fitch Williams on this site. Search for "Fitch RPC" or "Fitch Converter" and you should find his plans for building a RPC. The balancing instructions are in the plans.
For example: if you have 245, 250 and 255 as the three phases you will end up with 490, 500 and 510 after the transformer. If you balance the RPC output so you have 245 to 250 maximum then you will not exceed 500 volts.
The only other method is to use a transformer with multiple taps so you can get a 1.9 : 1 increase instead of a 2 : 1. I do not know where to get these.
I suspect a Buck and Boost transformer could be used to reduce main transformer output but have not tried this. Maybe someone else will chime in.

jhg · Feb 9, 2007

My RPC is under 250 all three legs. IIRC they are 246-248 or so, load motor running.

I think I am dreaming that this machine is going to have nine leads hidden under the box. Its a special motor on a wood morticer. There would be little reason for them to provide any flexability.

jhg

toolnut · Feb 10, 2007

JHG,

You should be ok with a transformer and your RPC. There are two other alternatives if you need them:
1. have the motor rewound for 230 volt, 3 phase. Cost will be about $300. We had a 2 hp Oliver mortiser rewound recently for $250 so I am guessing at the cost.
2. use a single phase transformer(5 Kva or larger) and a 460 volt VFD(probably a 7.5 hp one that will accept single phase input)and add a load reactor. This will be more expensive than the transformers and your RPC but it is the route I use to power my 440 and 460 volt machines. I currently have a 1.5 hp geared head drill press on one VFD and a 2 hp patternmakers lathe on another. I have a 2 hp mortiser and a 2 hp grinder yet to hook up.
send me a private message if you want more information. I may not see a post here as I am not online every day.

J Henricksen · Feb 12, 2007

If you rewind the motor to run on 240 v, the heaters ( thermal overloads) on the starters will ned to be changed for a higher ampreage load.

jhg · Feb 12, 2007

Ha Ha- it turns out the motor has been re-wound already- changed to 220!

Thanks everyone. I'll be able to use what I learned here anyway- one day there will be a need for 440 in my shop.

Quartersawn · Mar 13, 2007

How do you know that it was rewound for 220? was it labeled as such?
...Rod

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