Going from 240v to 480v with a transformer

[930dreamer]

Has anyone used a transformer after a rotary phase converter to go from 240v 3 phase to 480v 3 phase?

 

[wyliesdiesels]

I’ve seen it done... on youtube videos

 

[ddawg16]

You won't have much power.

If you're trying to power a 480Vac motor....i'd check to see if you could wire it for 240.

Personally, I think it would be cheaper to buy a new motor than the transformer.

 

[930dreamer]

I have plenty of re-connectable motors, just thinking about a larger air compressor and being able to cut the amperage in half on 480v. Thank you.

 

[Bad Habit]

Transform before the phase converter? 6 of 1, half dozen of the other. May be a cheaper phase converter.

 

[Bert_]

I have plenty of re-connectable motors, just thinking about a larger air compressor and being able to cut the amperage in half on 480v. Thank you.

The reason for higher voltage is smaller wire and control equipment. The amount of power used is the same. Half the amps but double the voltage.

 

[ycgoat]

The reason for higher voltage is smaller wire and control equipment. The amount of power used is the same. Half the amps but double the voltage.

This is fact, your 240 source would have to supply all of the power needed for the motor, plus the energy losses at each device between the 240v source and the final load. It would be a huge waste of money, space, and power.

 

[930dreamer]

This is fact, your 240 source would have to supply all of the power needed for the motor, plus the energy losses at each device between the 240v source and the final load. It would be a huge waste of money, space, and power.

But the only way to have 480v.

 

[ycgoat]

But the only way to have 480v.

You could get a commercial service. If your reasoning is the equipment you need is only available in 480, then I would start with the power company (I have known 1 person who did, but the power company was reluctant). If its just cause you can or you want to, go for it. If you are trying to save energy or money get the equipment that will work with what you have available. I have also known people who rented commercial space for their hobby. The guy I knew who got a commercial service was a self employed machinist and had to get special use zoning permits from the city, and he worked with the set up you are talking about for a while until he got the commercial service. All of his stuff was second hand, but he did good work at a reasonable price.

 

[wyliesdiesels]

You won't have much power.

If you're trying to power a 480Vac motor....i'd check to see if you could wire it for 240.

Personally, I think it would be cheaper to buy a new motor than the transformer.

He'd have the same power he has @ 240v. remember the power (watts) stays the same and the amps are cut in half.

You could get a commercial service. If your reasoning is the equipment you need is only available in 480, then I would start with the power company (I have known 1 person who did, but the power company was reluctant). If its just cause you can or you want to, go for it. If you are trying to save energy or money get the equipment that will work with what you have available. I have also known people who rented commercial space for their hobby. The guy I knew who got a commercial service was a self employed machinist and had to get special use zoning permits from the city, and he worked with the set up you are talking about for a while until he got the commercial service. All of his stuff was second hand, but he did good work at a reasonable price.

not every PoCo will give 480v service to every building. I'm guessing the OP isnt eligible to get 480v service from the PoCo hence the reason for the post

 

[Bert_]

But the only way to have 480v.

If your machines can be easily changed to 240 that would make the most sense. The only reason to put in a transformer to step up to 480v would be a machine that cannot be changed. Even then you should look at the cost of a transformer and decide if it would be cheaper to just buy a machine that can run on 240.

 

[ddawg16]

He'd have the same power he has @ 240v. remember the power (watts) stays the same and the amps are cut in half.

not every PoCo will give 480v service to every building. I'm guessing the OP isnt eligible to get 480v service from the PoCo hence the reason for the post

The OP would need about 30+ A @240 Vac to drive a 3ph 5HP motor....going thru a step up transformer......and not including losses.

That makes for an expensive rotary phase converter and step up transformer

Hey....Grainger has some step up transformers starting at $3800

 

[930dreamer]

A bunch of used transformers in the $800-$1200 price range.

 

[wyliesdiesels]

The OP would need about 30+ A @240 Vac to drive a 3ph 5HP motor....going thru a step up transformer......and not including losses.

That makes for an expensive rotary phase converter and step up transformer

Hey....Grainger has some step up transformers starting at $3800

unless you have a free donor motor... but the OP never said anything about price factors so....

 

[Norcal]

Unless you need 480V there is no advantage to it over 240V if you have to step it up.

 

[American Locomotive]

As mentioned, there is no advantage. You halve the amps, but double the voltage. So the power consumed is the same. You will still need a "15 HP" idler to power a 7.5 HP compressor, regardless of voltage.

I don't think a 3 phase transformer would like the power that comes out of a rotary phase converter very much. A better way to do it (if you wanted to power 480v-only equipment) would be to use a single phase transformer to step the 240v up to 480v, and send 480v single phase into a 480v RPC.

 

[nadogail]

The answer will depend on your ability to locate an unwanted transformer in somebodies
junk or Bone Yard.

 

[ycgoat]

As mentioned, there is no advantage. You halve the amps, but double the voltage. So the power consumed is the same. You will still need a "15 HP" idler to power a 7.5 HP compressor, regardless of voltage.

I don't think a 3 phase transformer would like the power that comes out of a rotary phase converter very much. A better way to do it (if you wanted to power 480v-only equipment) would be to use a single phase transformer to step the 240v up to 480v, and send 480v single phase into a 480v RPC.

Interesting, I would think the transformer after the phase converter would help clean up the power and be better for the load equipment.

 

[mike93lx]

480v is not something I would want to have around a non commercial or industrial shop. That's definitely not a home-gamer voltage.

That said, how long are these wire runs that all this messing around gives a benefit?

 

[PoorUB]

I have plenty of re-connectable motors, just thinking about a larger air compressor and being able to cut the amperage in half on 480v. Thank you.

If you have not bought it yet there is no advantage going to 480 volt, certainly if you need to get a transformer to go from 240 to 480 volt. The amp draw on the 240 phase converter will be the same, even a bit higher with the tramsformer than just running a 240 motor.

If you have the motor already then perhaps, but used motors are easy to find, and your system will be simpler.

 

[MBfreak]

930.
Unless you can find a used/cheap 480 3 phase with same frame.
Take the 240 you have to a mom and pop electrical shop and ask them to rewind to 480 , and at the same time check bearings and the squireel cage rotor. It is a job of less than 4 hours.
A transformer will probably cost more.
As to 480 vs 240 and safety, I FREELY admit that I have NO KNOWLEDGE whatsoever re US rules and the byzantine local electrician friendly rules
In IEC countries rules for AC installationa are the same from 50 V to 1000 V. 380/400 and 690 Volt are common 3 phase voltages in most of Europe. UK and the Netherlands stick out, though.
Ola

 

[nadogail]

120, 208, 220 & 240 can all shock you unpleasantly, 480 will knock you off your ladder. Been there and done that.

 

[Norcal]

120, 208, 220 & 240 can all shock you unpleasantly, 480 will knock you off your ladder. Been there and done that.

Pretty much impossible to get shocked with 208 or 240 volts unless you grab both legs, 220 volts is a line to neutral voltage in the parts of the world who use 220V, in the US, the only way to get hit with 208V is contacting the high leg of 240V 3 phase, otherwise contacting one leg only results in getting shocked by 120 volts. Canadian electricians can talk about 347V, like 277V they are line to neutral voltages.

 

[jabberwoki]

Has anyone used a transformer after a rotary phase converter to go from 240v 3 phase to 480v 3 phase?

Yep i have . No problems with chit

 

[rlitman]

I have plenty of re-connectable motors, just thinking about a larger air compressor and being able to cut the amperage in half on 480v. Thank you.

How far will the compressor be from your panel? Unless it's hundreds of feet, the thicker wire will still be a better and cheaper option than any transformer. Keep in mind that the transformer will have standby power losses that are not insignificant too.

 

[alfredeneuman]

In addition to the transformer you'd also need grounding, and disconnects on both the low and high voltage sides off the transformer.
You'd need a 480 volt panel and breakers.
All things 480V are mega$$$. Here's the fusible disconnect alone>
https://www.grainger.com/search/ele...480+v++fusible+disconnect&sst=4&tv_optin=true

 

[Bert_]

In addition to the transformer you'd also need grounding, and disconnects on both the low and high voltage sides off the transformer.
You'd need a 480 volt panel and breakers.
All things 480V are mega$$$. Here's the fusible disconnect alone>
https://www.grainger.com/search/electrical/fuses-circuit-breakers-safety-switches/safety-switches-panel-and-door-disconnects/safety-switches?attrs=Protection+Method|Fusible&filters=attrs&searchQuery=480+v++fusible+disconnect&sst=4&tv_optin=true

Let's be honest, that's Grainger's pricing, which is well above the rest of the industry. I can get a 600v 30A fused N1 disconnect for $175 from an electrical supplier. That's regular stock pricing.

 

[alfredeneuman]

Let's be honest, that's Grainger's pricing, which is well above the rest of the industry. I can get a 600v 30A fused N1 disconnect for $175 from an electrical supplier. That's regular stock pricing.

Yes, that's the list price. (I used to charge the "Grainger price" for billing service call materials).
But it is well above the price for 240 volt equipment.

 

[FredWanaker]

My instinct from having been around electricity most of my life is that unless there is no other way, the cost to implement this will outweigh the benefit. And, when using a bone yard transformer, one is using old windings that have been subjected to unknown transients, having unknown oils in them ....... it can go down hill from here if poor decisions are made.

 

[wyliesdiesels]

My instinct from having been around electricity most of my life is that unless there is no other way, the cost to implement this will outweigh the benefit. And, when using a bone yard transformer, one is using old windings that have been subjected to unknown transients, having unknown oils in them ....... it can go down hill from here if poor decisions are made.

most indoor transformers are dry type so there wouldnt be any oil

 

[ycgoat]

If you get a used transformer. Make sure both the line and load are over current protected. try to megg the windings before hooking it up, let it sit energized with no load for a day to dry up any moisture absorbed into the windings and insulation.