Using two transformers to get needed voltage?

[Rapid_Tech]

Hey Guys,

I recently purchased a cnc lathe (2003 Gildemeister CTX310). Being a European built machine it requires 400V/50Hz. From everything I've read, the machine will be okay running on 60Hz. Even the shop I bought it from ran it on 60Hz with no problems.

I have 240V at my place but having difficulties finding a 240V to 400V transformer. The transformer I got with the lathe is a 25kva 600V to 400V and I have another 30kva 600V to 240V transformer as well which I'm not using. Would it be possible to use the 600V to 240V in reverse so I get 600V out of it and then feed the power into the other transformer to get it back down to 400V? Other than being slightly inefficient would I have any problems with this setup?

Thanks for any help you can offer.

 

[CarlBoyd]

Each transformer will dissipate some power so it is not the most efficient solution, but it will work.

CarlBoyd

 

[TDegenhart]

It ran fine on 60 hz, but perhaps a loss of some power. To duplicate the same running conditions as the lathe was designed for, you should run it on 460/480 volts, 60 hz. That way the motor has the same flux density. To simplify your setup, I would just find a 240/480 60hz transformer and be done with it.

Thats for the motor. If there are electronics wanting 400 volts and there is no easy or clean way get from the 480 to 400, then go your route. Not the best, but it should work.

Perhaps someone else can offer a better solution.

Tom

 

[billzweig]

Hey Guys,

I recently purchased a cnc lathe (2003 Gildemeister CTX310). Being a European built machine it requires 400V/50Hz. From everything I've read, the machine will be okay running on 60Hz. Even the shop I bought it from ran it on 60Hz with no problems.

I have 240V at my place but having difficulties finding a 240V to 400V transformer. The transformer I got with the lathe is a 25kva 600V to 400V and I have another 30kva 600V to 240V transformer as well which I'm not using. Would it be possible to use the 600V to 240V in reverse so I get 600V out of it and then feed the power into the other transformer to get it back down to 400V? Other than being slightly inefficient would I have any problems with this setup?

Thanks for any help you can offer.

Your connection of the two transformers will work fine. And if you power needs are below the rating of the transformers, it will be actually quite efficient. I have a 240-480 transformer I am using at less than 1/2 capacity and the losses are negligible.

 

[rwbaldwin]

There's no real problem, but you do have to be careful about circuit protection. You do need a breaker between the two transformers.

 

[mike_kilroy]

I have 240V at my place but having difficulties finding a 240V to 400V transformer.

difficulty finding a transformer? Did you call Rex Transformer down the road from you in Ontario?? Ask them for an AUTOTRANSFORMER 240->400V? They have good prices, quick delivery, will make exactly what you want!

 

[motion guru]

400V / 50Hz x 60Hz = 480V . . . use 480V and never look back.

 

[Rapid_Tech]

Good to know that it will work but I have some concerns about the suggestion of using 480V instead. Wouldn't that be harmful to the electronics since they're designed to run on 400V?

Mike_Kilroy, I've found another place online that manufactures transformers and it would be a little over $1000. I don't want to spend that much if I already have ones I can use.

 

[Mud]

I have a 380V CNC machine running on 2 transformers - 240 to 480 then 480 to 380, it's working fine.

 

[SAF]

You never stated what your loads were only voltages. 380V volt can be obtained from single phase four winding transformers. Two of them could be configured in the open Delta bank for three-phase operation. Only one required for single phase controls, and run the motors from 480V. SAF

 

[JST]

Check the specs for the unit, don't assume . A lot of european VFDs and machines have a range of voltages. One range covers 230V, the other tends to cover 380 to 500 or so.

If the range of allowable voltages covers what you have out of your transformer, don't fiddle with more transformers, you can hook it up as-is .

 

[Rapid_Tech]

Sorry for taking so long to reply. I checked out the electrical cabinet and the Fanuc power supply module has a input voltage between 400-480V @ 50-60Hz. The machine doesn't have taps for different voltages, unlike my Haas mill which has four (I think) separate taps for voltage between 195-260V.

For now I'll hook up the machine with the two transformers as this has two benefits, first I don't have to buy another transformer, second I'll have 600V to power my surface grinder.

SAF, the label says 21kVA and the power supply shows 13kW.

Thanks for the help gentlemen.

 

[Rapid_Tech]

I talked to a guy at work who understands electrical stuff a lot better than me and he told me the setup won't work because there is no connection for the X0 wire now that the transformer is being used in reverse. He talked to an electrical engineer as well to confirm this. I'll take his word on it as I really don't want to take a chance with damaging anything. It looks like I'll have to buy a new transformer as used 240-400V transformers are nearly impossible to find. The closest I found was a 208-400V transformer but if I feed 240v into the 208v side I would have nearly 460V coming out of it, correct?

Also, I don't think I can feed 480v to the machine either since the small transformer inside of it only has 400v(-7%/+5%) taps on it, even though the power supplies can go up to 480v.

 

[mike_kilroy]

1) I talked to a guy at work who understands electrical stuff a lot better than me and he told me the setup won't work.... because there is no connection for the X0 wire now that the transformer is being used in reverse.

2) He talked to an electrical engineer as well to confirm this.

3) It looks like I'll have to buy a new transformerw

4) if I feed 240v into the 208v side I would have nearly 460V coming out of it, correct?

5) Also, I don't think I can feed 480v to the machine either

Whew! SO MUCH misinformation & questions in a single post!

1) You got yet another uneducated opinion from that shop guy. He is wrong.

2) I absolutely HATE it when a supposed electrical engineer gives wrong data! How the he11 did they graduate? He too is wrong.

3) That may be best since you do not believe any of the opinions given here and prefer to believe the nonsense spewed by that shop guy. If you do buy, give Rex a chance - they prob will be quite a bit less than your other $ 1000.00 - be sure to tell them the description I gave in eralier post or the price will be $ 1000! (I have no relation to them)

4) Your math is good: put 240 into a 208 tap and whatever rating on the output side will be 240/208= 1.15 times higher also. So 400*1.15= 461 volts.

5) There is no law stating you cannot feed 480 to your 400v machine; sometimes folks do that. Their next step is usually to call the scrap iron place to come pick up their blown up machine and get paid 10 cents a pound for it.
5a) Of course you cannot feed 480 into a machine expecting 400v.
5b) A previous poster, without the benefit of all the info after you have dribbled it out in many posts, said you would get less performance if you feed 400v 60hz into your machine that expects 400v 50hz. Now that you gave more info - you have Fanuc servos and spindles that simply rectify the ac input to dc - you should ignore that comment too: you will get 100% performance out of that machine with 400v 60hz.

I have an idea for you: instead of vacillating back and forth between the generally informed and correct replies here, and your shop friend idiot, why not do as others might: simply hook your two transformers and MEASURE THE OUTPUT VOLTAGE YOURSELF?? If you don't have a voltmeter, go buy a sports Illustrated magazine and rip out the free meter coupon at Harbor Freight and go pick one up. This way, you can be SURE what you will feed that beautiful machine and KNOW you will not harm it!

 

[JST]

The only thing I would add, is to LOOK AT THE MACHINE SPECS. I know you wrote some of them, but you also listened to the crazy EE.... So I dunno.

Anyhow... FEED THE MACHINE A VOLTAGE THAT IS IN THE ACCEPTABLE RANGE GIVEN IN THE SPECIFICATIONS FOR YOUR PARTICULAR MACHINE.

I don't think any of us know for sure what that range is.... if you got your data from a "blurb sheet" it may be wrong. The thing to do is to look at the machine data plate (and hope some moron did not change something without marking it if the machine was obtained used).

IF the data plate says 400 to 480VAC, you should be good for any line voltage that is between those two, and does not vary more than 10%. The 10% is the usual amount allowed for variation, BUT see if the data plate confirms that. Some things quote 5% tolerance, in which case you need to figure the nominal voltage as lower.

Maybe you should take a photo of the dataplate and post, because without speaking for anyone else, I would not commit on anything with the data so far. Sorry, but that's the way it seems.

If it were hard limits at 480 and 400, the best you could do is likely to aim for 440V and go. You can count on the voltage varying, and the usual UL limits are 10% up and down. That's not limits for correct operation, but rather for "no hazard", which is a different thing, although usually interpreted and implemented as "works right". There's no "hazard" if it faults out on overvoltage and shuts down safely at 460VAC.......but it does not help you much.

 

[Rapid_Tech]

Mike_Kilroy,

The shop guy is a millwright but even he wasn't sure which is why he asked the EE. If the EE is wrong, I wouldn't know.

At this point I'd rather just buy a new transformer if it will simplify things. You mentioned previously I should ask for an Autotransformer. Is there a reason for an autotransformer vs an isolation? I've googled the differences but still don't completely understand the difference between them other than an isolation having a common winding.

Last question I have, if I wire up the transformers where do I connect the ground wire in the first transformer (back-fed 240-600v), just to the case?

JST, the label on the machine says 400V, 21Kva. There is a small transformer inside the lathe which steps down the voltage to 230v and 24v for the control and other things. It is this transformer which has taps for 400v -7%/+5%. The actual Fanuc power supplies and servo amplifiers have 400-480v markings on them. So I think it would be safest to feed the machine 400v.

 

[mike_kilroy]

You mentioned previously I should ask for an Autotransformer. Is there a reason for an autotransformer vs an isolation? I've googled the differences but still don't completely understand the difference between them other than an isolation having a common winding.

Last question I have, if I wire up the transformers where do I connect the ground wire in the first transformer (back-fed 240-600v), just to the case?

The autoxfmr has a single winding, not the iso mode. But reason is the auto uses part of its pri as the secondary: result is smaller tansformer. an 21kva auto 240->400v 3p xfmr will actually be only (1-240/400)*21= 8.4kva in size. I am sure you realize an 8.4kva xfmr (but still rated 21kva) will cost less than a 21kva.

If you connect ANY terminal marked X0 to ground in your 2 transformer set up, you will get VERY LARGE sparks and may blow your 240v CB apart in your supply box. In other words, do not use the neutral of either transformer and all will be wonderful. after you do this and prove the concept, come back with a wiring diagram of how you have it and folks here will show you what to ground, if anything.

 

[JST]

JST, the label on the machine says 400V, 21Kva. There is a small transformer inside the lathe which steps down the voltage to 230v and 24v for the control and other things. It is this transformer which has taps for 400v -7%/+5%. The actual Fanuc power supplies and servo amplifiers have 400-480v markings on them.So I think it would be safest to feed the machine 400v.

Machine is labeled 400V.... so YES feed it 400V.

Always believe the machine label UNLESS you have KNOWLEDGE that it is no longer correct....

 

[Rapid_Tech]

My apologies again gentlemen, I've been on vacation the past few weeks. First, as Mike_Kilroy suggested, I contacted Rex but they don't sell direct and I have to go through a distributor. The local distributor offered a 30KVA 400V to 240V autotransformer and said to run it in reverse. Mike_Kilroy mentioned that I can used a lower rated transformer and they have a 15kva model for about $850. Would there be a problem with running this 15kva model in reverse or would the 30kva be required? I'm not sure if the amperages through the lower rated transformer would cause any problems. Thanks for the help.

 

[mike_kilroy]

...Mike_Kilroy mentioned that I can used a lower rated transformer and they have a 15kva model for about $850. Would there be a problem with running this 15kva model in reverse or would the 30kva be required?

I did NOT say you could use a lower rated xfmr; I said the same rated autoxmfr of same rating would be smaller physical size and thus lower cost of the isoxfmr.

You read the machine nametag; thus you know you do not require 30kva but only 21kva.

I will ask a detroit xfmr mfgr I know send you a quote.