# Transformer Compatibility: 208/480 work for 220/440 mill?



## mariner3302 (May 29, 2020)

I have a mill that is wired for 440v, 3 phase at the power box. I have 220v, 1 phase. If I had this Transformer and a VFD to convert up to 3 phase, would I be able to wire it up to the mills power box and it would produce the voltage necessary? I wouldn't have to replace the 2 speed motor on the mill, convert a new motor, etc... 

Please educate me!


----------



## mariner3302 (May 29, 2020)

The guy selling this says it turns 208v to 480v but isn't this tag saying it makes 480v into 208v?


----------



## ddickey (May 29, 2020)

So you want to reverse feed the transformer? You can do that but 208 not 240.
Then feed a VFD 480Vac?


----------



## mariner3302 (May 29, 2020)

Well, no, what I read from that data tag is that the transformer takes 480v and then turns into into 208v. His add says the opposite. I was hoping to find one that actually does 220v stepping up to 440v semi-locally and without the price tag...that and a VFD would make replacing my motor unnecessary because it can't be changed to 220v.

To this point, a motor swap has become the easiest and least expensive route. I have a thread in the Gorton section where we discuss it. This question was more general so figured I'd put it up here to limit the magic smoke escaping my brain housing group.

I'm still unclear on a couple things like if a motor is rated for 1800rpm, can it be run up to 3600 with a VFD?


----------



## Lo-Fi (May 29, 2020)

What mill/motor is it? It is possible to internally rewire (not rewind!) most motors for lower volt operation. Its a bit of a fiddle, but means you can use a common 220v vfd.

I did this to my bridgeport pancake motor which was high volt only, it works beautifully:






I very much take the "you see a mousetrap. I see free cheese and a ******* challenge" approach to these things 

I went through the same process of wondering if I can transform the input to or output of a VFD. In the end, fiddling with a few wires in the motor was cheap and quite painless.


----------



## mariner3302 (May 29, 2020)

A kindred soul! I have the same mindset. Here is the thread that has the pictures and situation. https://www.hobby-machinist.com/thr...or-wiring-hookup-schematic.84330/#post-746288


----------



## mariner3302 (May 29, 2020)

That sounds like something I will try. It will give me a much needed learning curve and the worse that happens is I smoke the motor.. In that case, I am exactly where I am now. Now to start researching! I called the motor manufacturer and the said that couldn't help me with, well, anything actually. I took It to different motor shops, no help. So this will be a great learning experience.


----------



## Lo-Fi (May 29, 2020)

Fantastic, I'll help as much as I can! As far as I know, my method is unique - certainly within the realms of what's been posted online. 400 something volts two speed is exactly the same as my motor was wired, so I'm certain you'll be able to achieve the same. Post some pics of what wires you've got coming out of the motor and we'll take it from there


----------



## mariner3302 (May 29, 2020)

I'm on it! I built everything from scratch on this flight simulator, a scale replica of a F-14B Tomcat front office, except the actual seat so let's do this lol


----------



## Lo-Fi (May 29, 2020)

Nice work! 

The video is crammed with my thoughts and scribbles, but you'll find various drawings and diagrams in the doobly-do down below. Hopefully it'll save you reinventing the wheel! Once I understood the winding scheme that was used, tracing wires and soldering the tails back together in a different arrangement was trivial. With luck, your motor uses the same winding scheme. I'll post up my drawings here too for future reference.


----------



## jmkasunich (May 29, 2020)

mariner3302 said:


> The guy selling this says it turns 208v to 480v but isn't this tag saying it makes 480v into 208v?
> View attachment 325777



In theory (and usually in practice as well) you can run a transformer backwards, feeding the secondary and taking the output from the primary.

However, feeding 220 (or 230 or 240) volts into a 208V winding will at a minimum make the transformer run hot.  Worst case it runs so hot that it burns up.  And since you are feeding 220 into a 208 winding, you'll get something like 508 volts out of the 480 winding.

Next problem: you didn't mention how big the motor that you are trying to run is.  That transformer is huge - 45kVA could run something like a 50HP motor when used as intended.  Because it is a big transformer it will have big inrush current (tripping the 220V breaker), and draw a lot of no-load current.  Not good.

A further complication (and this is the real show-stopper):  That transformer is three phase.  You have one phase power.  You can't feed a three-phase transformer with single phase power.  Period.  Done.  Do not pass go.

In theory you could use a VFD to convert your 220 single phase into 0-208V three phase, then the transformer could step it up to 480 three phase for the motor.  In theory.  I'm an electrical engineer and spent most of my career designing VFDs, and I would try to find another way before I tried using the transformer on the VFD output.  Just too many ways it could go wrong.  For someone unfamiliar with the technology I wouldn't touch it with a ten foot pole.  And the fact that the transformer is still way over-sized makes it worse.

You want a single phase 240-480 transformer.  And not 45 kVA.

You didn't mention the size of the motor you are trying to run.  If it's a typical Bridgeport or similar 1-1/2 to 3 HP motor, you could use about a 5kVA to 7.5kVA transformer.  Something like these:









						Used  Westinghouse Transformer For Sale
					

Used Westinghouse Transformer For Sale




					hgrinc.com
				











						Used  Westinghouse Transformer For Sale
					

Used Westinghouse Transformer For Sale




					hgrinc.com
				











						Used  Acme Transformer Transformer For Sale
					

Used Acme Transformer Transformer For Sale




					hgrinc.com
				




Any of those would convert your 220 single phase to 440 single phase.  Then use a 480V rated VFD to run the motor.


----------



## mariner3302 (May 29, 2020)

Wow, I didn't realize any of that! Thank you!! It is a 3 phase, 2 speed motor, 1800rpm at 1 hp and 3600rpm at 2hp. It came right off a 440v main so it would just need 440v attached to the lines in the box. The motor is a 6 wire. I just took it off the mill and it spins absolutely smooth as silk. 
The link in post#6 above is where the pictures of all the wiring, diagrams, etc are if you could take a look. On these transformers, they all seem to indicate they are 480 to 240 so my ignorance is obvious. How can they make 220 into 440? I think I get the reason and methods to change single to 3 phase but I would love to understand this better.


----------



## Lo-Fi (May 29, 2020)

The motor in my YouTube was originally 400v 2 speed. The switch had five positions: two forward and reverse speeds and off. 

Your motor has to be wound in a similar way. If you've only got six wires presented externally, you're going to have to delve into it, identify the windings as I did, unsolder the leads from the tails of the windings and rearrange them to suit running the windings in parallel delta, rather than switchable series/parallel star configuration that the Dahlander scheme runs. Its really not as scary as it sounds! Mine has been running beautiful for six or nine months now; something like that. I've asked a _lot_ of it on occasion too.


----------



## mksj (May 29, 2020)

The bottom line as I mentioned in your other post for your mill, you cannot use a VFD to provide power to your control box, it is only designed to power the motor directly. So your only choice would be using an RPC to generate 3 phase, then feeding a 3 phase transformer to step up the voltage. You probably would need a 3 phase transformer with adjustable taps, as line voltage is often 240VAC. Using a 480 to 240 transformer in reverse and adjusting the taps you could get around 460VAC on a 95% tap. Motors/equipment is usually rated for +/-5% voltage variation. Some possible examples below, but I would defer to someone with more experience to give you specifics as to KVA and hookup. 

I do a fair amount of VFD installs/work, what I often will see if you are just driving the motor would be to use a single phase step up transformer (like 5-7.5  kVa) to go from 240 to 480VAC or something in that range and feed a 400V VFD (i.e. these are rated for 400-480VAC in) derated for single phase input (so 5 Hp VFD) and the VFD sets the output voltage to the motor (it is directly wired to the motor. The sub systems are run off the transformer tapped for 240VAC single phase input. You CANNOT use the current contactors and motor controls for the spindle motor and the VFD would be directly wired so the motor runs on it's 2 Hp setting.  I also mentioned that there are 230VAC single phase input VFD's that output ~440 VAC 3 phase from China and the UK, how well they will work is just a guess, but the ones from China are around $100 for a 2.2 kW VFD. I wouldn't use one on any of my system builds, but it could work. VFD's for the most part will not drive a transformer on their output, they are not made for variable frequency VFD wave output. My understanding that there are specific transformers for this purpose to minimize the current/size of cables between the VFD and motor, but they are very expensive and application specific.

These might be suitable for 3 phase 460Vac conversion from 240VAC 3 phase RPC.








						Rex 3kva Transformer 3 Phase 480v-230v Delta 460v 240v DCHC1/K4  | eBay
					

If you have to get a hold of us, look us up on the net. Reconditioned, 1 Year Warranty! We can add rain-shields. What is your phone number and extension if you have one?. What is your zip code?. Do you have a forklift, a loading dock or neither?.



					www.ebay.com
				











						Hammond 6Kva Power Transformer 480V High to 240V Low 3 Phase with Taps NEW  | eBay
					

Find many great new & used options and get the best deals for Hammond 6Kva Power Transformer 480V High to 240V Low 3 Phase with Taps NEW at the best online prices at eBay! Free shipping for many products!



					www.ebay.com


----------



## Chipper5783 (May 29, 2020)

As mksj (and others) have pointed out, the phase converter followed by a 3 phase transformer makes a great set up. Most any small transformer that is intended for step down will work fine for step up as well.  My shop ran well for several years with the RPC feeding several 240V machines and a few 575V machines.  When I got a larger machine I needed a larger phase converter and changed to a Phase Perfect - it also feeds the transformer and 575V machines (both options work great - the Phase Perfect works better, priced higher).

I'm not saying the motor rewire won't work.  I can say the phase converter and transformer work great.  Strictly speaking the phase converter is not part of your decision, since the motor rewire still needs a phase converter.


----------

