Have 240 3 phase need 440 3 phase

A buddy of mine has a larger pedistel grinder that is wired 440v 3 phase. He said he has 240v 3 phase but know means to get the higher voltage. I have been doing a lot of research and found that I can use 2 single phase transformers to get the 440. Just not sure on how to do this. I haven't been able to come across any wiring diagrams or schematics. I also don't know exatcly how many kVAs is needed or if I can take one transformer at 1.5 kVA and another one at 1.5 or 2kVA and get 3 or 3.5kVA. Any help would be greatly appreciated.

Have you looked inside the box on the motor where the wires go in. When you do there is usually 9 wires inside and sometimes a diagram to show you how to hook it up for low voltage or 240v it will draw more amps that way but is much easier and cheaper than xfmrs. It would also be on teh motor nameplate volts 480/208-240 something like that and there will be 2 numbers for amps 10.4/20.8. If it is able to run both voltages the wires will be need to be re-arranged for the lower voltage leads 4-5-6 need to be tied together under one lug, and wires 1-7 go to one incoming hot wire, 2-8 to another and 3-9 to the third. If you have 12 leads or they are not numbered stop and pm me or make another post. All of this is also in a book called and uglys book you can find at most electrical supply shops or you can look it up online of course theres probably a you tube video for that.

Thanks for the reply. I haven't yet stopped by and checked the motor myself to see if it can be wired for low voltage. I also have an uglys book, just don't know that much about using the transformers. I wanted to have a better idea before going over there and maybe a couple of transformers just in case. He told me before that he looked and it looked to him that it couldn't be rewired for low voltage, just not sure on his electrical experience.

Check the motor tag to be sure.

It probably more economical to find another grinder than to invest in a transformer.

3 phase transformers are available second hand in most areas, and 220/440 is a common configuration.
Talk to some of the comercial electrical shops and motor rewind shops.
One of them the should be able to point you in the right direction.

Three phase transformers usualy look like three single phase transformers built side by side and are usualy in a big metal enclosure.
If you go that route any reputable shop will be able to tell you how big a unit you need based on the HP of the unit.

Doing the step with two single phase transformers seems a bit odd to me. I would certanly want to know more about how to size the components.


If your really adventerous, and dont mind letting the smoke out of the grinder, it is possable to go in and tease out all the connections on the windings and figure out where to add the extra taps to make it a 220 V motor (assuming its single speed).
Most rewind shops wont do it, too much liability and headache, but it can be done.
Cutting the voltage in half is accomplished by splitting the mid points of the fields and putting them in paralell instead of series.
Thats an over simplification, but its the basic idea.
There is always a chance you get something backwards or dammage the windings insulation, so dont atempt it if you can live with the consiquences of frying the motor.

Thanks for the info. I guess my first step is going to be finding out for sure if the motor can be wired for low voltage. If so headache gone, if not then I will have to see what I can find for the transformer configuration I was talking about. I know he doesn't want to spend a lot of money and I really don't either. I can probably come across a couple or a few single phase transformers pretty cheap compared to a 3 phase for the means I need. With that being said any more advise would be great, especially on using single phase transformers to accomplish this task.

Be sure to look at the motor wires. I have a 12" Queen City Grinder that sat in the corner for 2 years because the nameplate said it was 440 volts. I finally decided to take the grinder off the stand and have it rewound and discovered it had all nine leads tucked into the stand behind the manual starter. I simply reconnected it for 220 volt 3 phase and it works.
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As to transformers, the two transformer method is call an Open Delta. I used to have a handbook with these connections and the corresponding rating but can not find it. You may be able to find this on line.
Since this is only a 2 hp motor, you can use 3 each, 1 KVA single phase transformers and have a 3 KVA system which is about right for a 2 hp grinder. The transformers must be oversized to handle the motor's starting requirements.

I tried to post this earlier, but the system rejected it. Open delta transformers are connected with their primaries to phase A & B, the second transformer to B & C. Secondaries are in the same sequence. Each transformer should be half the KVA needed. Open delta doesn't maintain balance quite as well as a three phase transformer, but in this case it shouldn't matter.

I also have a 12" Queen City grinder that has been running on 240 V 3 Ph for many years. Easy conversion.

Bill

Thanks for the replys I will definately have to look into the motor and see if all nine leads are there or not and take it from there.

Thanks Bill for the info. It now points me in the direction I was needing if I have to go with the transformers. I at least now know what size I should be looking for.

9100 said:

I tried to post this earlier, but the system rejected it. Open delta transformers are connected with their primaries to phase A & B, the second transformer to B & C. Secondaries are in the same sequence. Each transformer should be half the KVA needed. Open delta doesn't maintain balance quite as well as a three phase transformer, but in this case it shouldn't matter.

I also have a 12" Queen City grinder that has been running on 240 V 3 Ph for many years. Easy conversion.

Bill

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Bill
I got to thinking about it, but does it matter that if I go the transformer route that I will probably be using step-down transformers but reversed so it acts like a step-up. Will the kVAs I need for each change then or would it still be half on each for what I need. I could also use a wiring diagram, I kinda have an idea of how to do it, but I don't want to let the smoke out either.

Thanks,
Nick

bucknv30 said:

Bill
I got to thinking about it, but does it matter that if I go the transformer route that I will probably be using step-down transformers but reversed so it acts like a step-up. Will the kVAs I need for each change then or would it still be half on each for what I need. I could also use a wiring diagram, I kinda have an idea of how to do it, but I don't want to let the smoke out either.

Thanks,
Nick

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If you are being super picky, there is a difference because the manufacturer may have built in compensation for the small losses in the transformer. Like anything else, you never get quite as much out as you put in, but as a practical matter, running a grinder, don't worry about it. You won't be able to tell the difference. As to KVA, multiply the voltage, 480, by the amperage listed for that voltage and divide the answer by 1000 to make it kilovolt-amperes instead of volt-amperes and divide that by 2 for each transformer. A little extra is fine, the grinder will draw only what it needs and extra capacity in the transformers may make it start a little quicker.

Here is a discussion in another forum. I have not heard of the 87% rating, but then, there are lots of things I haven't heard. I have never run an open delta that close to its rated output, so it never was an issue. I have the book they cite and can scan pages if you need them.

Open delta transformer

Bill

Thanks Bill, I really hate to be a bother, but it would be great if you could scan those for me. It will help tremendously. Thanks again for the information.

Nick