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cuemaker
04-11-2010, 09:44 PM
With this info on a transformer:

High Volts: 240/480
Low Volts: 208
4.5 kVA

Run a 460 vfd like a FM100-400 n1

Line in is 220 (or is it 230) house current, motor is 230/460.

squirrel
04-11-2010, 09:57 PM
What is your source voltage and what is your target voltage. Most of the time the line is 230 so if you run the 208/460 taps you will have over 530 volts out. Alot of this depends on your input line voltage and do you have 3 phase or is that from a rotary converter.

cuemaker
04-11-2010, 09:59 PM
source voltage is 220 (230?) house current
Target voltage is to run VFD that is rated for 460 3phase...

macona
04-11-2010, 10:23 PM
Running transformers backwards does not always get the results you might expect.

Why not just find a 240v VFD? They are not that much more. Then you dont need to mess around with this stuff. I could see if it was a 460v only motor but its not.

dp
04-11-2010, 10:25 PM
I think the transformer efficiency is going to waste power without providing any benefit.

cuemaker
04-11-2010, 10:25 PM
So the transformer info i have is backwards for what I want to do?

As for finding a VFD.. cheapest I can find for run a 5hp motor is in the $400 range, unless you know of a cheaper option..

And i am just exploring an option, trying to learn and understand... things electrical is my weakest area..

J Tiers
04-11-2010, 10:28 PM
Assuming this is a non-tapped transformer, you will indeed get about 530V out.

That is 15% high for a 460V line, and could be an issue. You can check your VFD and see what it's operating voltage range is.

squirrel
04-11-2010, 10:38 PM
source voltage is 220 (230?) house current
Target voltage is to run VFD that is rated for 460 3phase...
If you have only house current, that is single phase and this will be a big problem. Do you actually have 3 phase coming in?

J Tiers
04-11-2010, 10:40 PM
If you have only house current, that is single phase and this will be a big problem. Do you actually have 3 phase coming in?

He can probably de-rate and use the VFD with single phase in..... depends on the VFD, but most will.

lakeside53
04-11-2010, 11:11 PM
So then he needs say a a 7.5hp vfd, or more.

lakeside53
04-11-2010, 11:12 PM
I think the transformer efficiency is going to waste power without providing any benefit.


Think of it as a nice heater:D

cuemaker
04-11-2010, 11:32 PM
wrong info..

macona
04-12-2010, 01:55 AM
This is going on a lathe?

Rarely will you use that much power. What you can do is use a smaller VFD and lengthen the acceleration time. Thats where your major current draw is. I have seen a 15hp Monarch lathe ran with a 5hp VFD like this.

Black_Moons
04-12-2010, 02:32 AM
You might saturate the transformer running the 208v side at 240v

However, How is the primary setup? you should be able to coax it to be an autotransformer (No isolation)

If its taped, just run 240v to the 240v input and take 480v out the 480v output, should be good for full power rating of the transformer really.

If its two coils designed to be in parallel at 240v and series at 480v, you can still series them and put 240v in and get 480v out.. but im not exactly sure on the math of how much power you can take out in that case.
At very least, it would be 1/2 the power rating of the transformer.. but I think likey the full power rating.

macona makes a good point too, I can chew through 0.1" thick passes in steel at high feed rates and such and just barly start to hear my 2hp lathe bog down. (But then, I do have a gearhead so I get 2hp at any RPM, VFD will lose HP linearly with hz, if you have a few gears or belt change 5hp is insane. If it was direct drive I could see a 15hp motor only doing 2hp at very low rpms)
Especialy if you used a lower voltage VFD, a lower HP VFD would likey be a good match if programed correctly.

Hmmmm... on the other hand, I don't think though that a lower HP VFD would maintain its HP well at low RPMS if mated with a larger motor, due to the high current needed at low voltages, even if the wattage is the same.

J Tiers
04-12-2010, 08:29 AM
The autotransformer idea works also, even if it is way oversized in terms of VA.....

As for the larger motor and current deal... obviously you have to be able to supply the magnetizing current.....otherwise nothing works....