480 to 240 transformer and reversing
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  1. #1
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    Default 480 to 240 transformer and reversing

    I am in need of specific advise for purchasing a transformer. I have talked to local electricians and I dont get any responses because im assuming companies dont want to do odd things.

    What I would like to do is purchase a 480v Y to 240v D transformer that can power 30 amps of 240v (single or 3 phase welder) and also have the possibility of using a 110v stick/tig welder at 20 amps.

    I would also want to be able to reverse wire this transformer to power 480v equipment like conveyors and misc machinery at my shop. Which has a 3 phase RPC at 240v D. I have 2-30 hp RPC connected together.

    My goal is to be able to have 480v at the shop to test machinery and to have 240v in the field when we are 20 feet away from 480v or 300 feet from the truck/240v power source.

    I have read plenty of articles on the web about reversing transformers, and I see what I need to do. But I want to make sure I buy the correct item first since transformers and not returnable once out of packaging.


    Edit- I forgot there is a transformer section on this forum.

    Sent from my SM-G960U using Tapatalk

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    I have a 480v/100A steamjenny that I would love to be able to use at a site where there is only 240v available. Is there a practical way to do that?
    Thanks.

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    Quote Originally Posted by shadow98 View Post
    I have a 480v/100A steamjenny that I would love to be able to use at a site where there is only 240v available. Is there a practical way to do that?
    Thanks.
    Well..."at a site" as-in long-term? Or for a limited-duration project?

    Not cheaply, either way.

    Just on the face of it - simplest of several factors ONLY - you'd need 200 A @ 240 V in the supply-side to provide 100A @ 480 V on the load side.

    That consumes an entire residential-class 200A service.

    So yah - it can be done, but is is WORTH it compared to - for example - a fossil-fuel fired steam source, whether purchased or just rented for the project's duration?
    Last edited by thermite; 06-11-2019 at 06:18 PM.

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    I have a couple machines wired with 240D/480D transformers stepping 240 to 480. Works fine. I don't know how a Wye/Delta transformer will work, if any differently.

    I was told to derate the transformer by some magical amount running it backwards.

    Only bad experience I had with transformers was trying to hook up control transformers backwards to turn 240 into 480. Didn't work. Let the smoke out of a bunch of little control transformers I had saved for years trying to make it work.

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    Quote Originally Posted by Garwood View Post
    Only bad experience I had with transformers was trying to hook up control transformers backwards to turn 240 into 480. Didn't work. Let the smoke out of a bunch of little control transformers I had saved for years trying to make it work.
    The reason why, is pretty fascinating.

    A control transformer has a primary winding, magnetics, and secondary winding combination which is intrinsically capable of transmitting ONLY_SO_MUCH_POWER. When you reach the limit of secondary current, it will NOT pass any more... the core goes into saturation, and impedance effectively STOPS carrying any additional current.

    This is the very essence of a control transformer's existance- it is intended to power CONTROLS, not 'loads', and as such, if some control element becomes damaged (i.e. shorted by rainwater, etc), it will not be able to supply tons of current to 'feed' the short circuit.

    Now... when you run a transformer backwards to STEP UP voltage, you're asking the transformer to do what it's design effectively rejects.

    To make the reverse transformation, a 'control transformer' isn't the right design... it'd only be good for oh... mebbie HALF of it's nameplate VA. A 'Power Transformer' though, will usually do just fine.

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    Quote Originally Posted by DaveKamp View Post
    The reason why, is pretty fascinating.

    A control transformer has a primary winding, magnetics, and secondary winding combination which is intrinsically capable of transmitting ONLY_SO_MUCH_POWER. When you reach the limit of secondary current, it will NOT pass any more... the core goes into saturation, and impedance effectively STOPS carrying any additional current.

    This is the very essence of a control transformer's existance- it is intended to power CONTROLS, not 'loads', and as such, if some control element becomes damaged (i.e. shorted by rainwater, etc), it will not be able to supply tons of current to 'feed' the short circuit.

    Now... when you run a transformer backwards to STEP UP voltage, you're asking the transformer to do what it's design effectively rejects.

    To make the reverse transformation, a 'control transformer' isn't the right design... it'd only be good for oh... mebbie HALF of it's nameplate VA. A 'Power Transformer' though, will usually do just fine.
    I'm sorry but this isn't accurate.

    For a typical transformer used to convert one voltage to another based on the ratio of windings (this excludes resonant, shunted, and current transformers) magnetic field strength is based on primary voltage and primary voltage alone. (There is a tiny region where an overvolted transformer can come out of saturation because of a heavy load, due to the resistive losses in the primary winding, but transformers are not operated in this region).

    The amperage that a transformer can carry is dependent on how much heat the transformer can dissipate, and in pulse applications is limited by the resistance of the windings.

    Control transformers must output fairly stable voltage from 0 amps to its full load rating. That necessitates a low winding resistance. A while ago I tested a 12V 4A control transformer and it provided 30 amps when shorted. Control transformers are supposed to be protected by a fuse or breaker, and many have fuse holders premounted to the transformer core.

    The reason that transformers need to be derated when run in reverse is because the primary handles total output power plus the primary ohmic losses, secondary ohmic losses, power factor, and the magnetic losses. The secondary handles total output power plus secondary ohmic losses.

    So a transformer can have an output of 10A at 240V, but it will draw 6 amps from 480V because this hypothetical transformer is only 80% efficient. If you want to use it in reverse, since the secondary is only intended to pass 10 amps, and the transformer will still have about the same losses, you will only be able to get 4 amps out of the primary. In practice you can get a bit more because the total ohmic losses are reduced in the second case.

    For efficient transformers, the difference between power handling ability between the primary and secondary is so little that it makes more sense for the manufacturer to make them equal so they only have to stock one transformer for both use cases. That, and they are limited by available wire gauges so the difference may get lost when they round to the nearest standard size.

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    I have a 480 to 240 step down 3ph transformer that I have been using to bump 240 single phase up to 440v 1ph (It's still a 3ph transformer, I've just used the taps in creative ways ;-)
    The transformer powers VFDs to drive a few machines in my shop. Was running the 7 hp Lathe that way for a while, but I switched back to 240v for a few reasons unrelated.

    At any rate, I believe it would do all you require, I would live without it, it takes up room I could use otherwise. It could be yours for a price, but it's heavy, and you are in NJ......

    Alas.

    Comments about 100 amps were not part of the original post as far as I can read....right?

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    Thanks.
    I do have a diesel-powered steam cleaner and it is satisfactory, but the SteamJenny 400v is a big beast and it would be fun to find something to clean with it!
    Oh well, I'll list it for sale someplace and see if I can get anything for it.

    Thanks, again.

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    If somebody on this thread actually wants a 30+ kVA dry 240-480 (taps up to 600) buck/boost transformer, I have a brand new one on a pallet, (never used) that I’d love to provide to a good home.

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    Quote Originally Posted by shadow98 View Post
    Thanks.
    I do have a diesel-powered steam cleaner and it is satisfactory, but the SteamJenny 400v is a big beast and it would be fun to find something to clean with it!
    Try the crack of Dawn.

    Age-old challenge, but if yah can git 'er clean enough, might even take a weld proper-like.


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