Mystery Transformer on CNC

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WakelessFoil

Joined Apr 16, 2020
1
Hello I’m new here but I’m in need of someone more experienced than I am.

I’m working on a Japanese CNC mill from the early 1980s for my boss and I cannot figure out how this transformer is supposed to be wired. It has two inputs either 220v or 480v. We are feeding it 220 and that comes out true when testing the primary voltage at the top. But when I test the secondary I keep getting half the voltage I need. Any ideas?
 

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Dodgydave

Joined Jun 22, 2012
9,459
Are the Primary windings wired in Phase Parallel , if not they will be subtracting the input voltage, thus lowering the Output..!!

Looks like the Transformer is wired for 440V in series.!,!
 
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Tonyr1084

Joined Sep 24, 2015
5,080
I can not say this for certain, but it appears that U1 and V1 are jumped together, putting the mains on V2 and what is probably U2 (under S4). That's probably where the key lays. The configuration of those jumpers will probably select between 220 and 440. And I have no idea if there's another voltage possible.

If it were my project I'd get a small 12 volt transformer and put it in on the secondary side, the side with five posts. The two boards on the transformer are marked with a P and an S. Probably Primary and Secondary.

I would probably use the two most furthest posts and input 12 volts, then measure AC voltage at the primary side. Measure between U1 and V1. U1 and U2. U1 and V1. Then V2 and U2, V2 and V1. Then U2 and V1. Carefully note the voltages on each post without anything connected to it. No loads, no jumpers. Then report back here with what you found. Some real smart and savvy AAC user will be able to tell in a heart beat which wires you should input your mains voltage to get the prescribed outputs.

WARNING! Messing with line voltages is hazardous. BE VERY CAREFUL.
 

MaxHeadRoom

Joined Jul 18, 2013
21,431
Typically those dual voltage single phase transformers are parallel or series primary.
They have to be phased correctly however
Sounds like you are putting 220v into the 480v configuration
Max.
 

MisterBill2

Joined Jan 23, 2018
7,033
Hello I’m new here but I’m in need of someone more experienced than I am.

I’m working on a Japanese CNC mill from the early 1980s for my boss and I cannot figure out how this transformer is supposed to be wired. It has two inputs either 220v or 480v. We are feeding it 220 and that comes out true when testing the primary voltage at the top. But when I test the secondary I keep getting half the voltage I need. Any ideas?
Do you have a circuit drawing of the transformer part of the system? What I see is the very typical really poor Japanese labeling. It would help a bit to be able to see the voltage labels on the terminal boards, and also to see the label tag on the transformer.
But it looks to me like there is a jumper between U1 and V1, and that puts the two windings in series. So you need to use an ohm meter to first verify that there are two separate windings.
My guess is that what you need to do might be to apply the voltage to U1 and V1, and then the other side to U2 tied to V2. But first try that with a very current limited AC voltage and the secondaries disconnected.

Another option would be to check the transformer maker's website for connection information. That might possibly be useful.
 
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MaxHeadRoom

Joined Jul 18, 2013
21,431
The link is already there on the primary, all it needs is to remove all primary conductors and identify the two winding's, although they are marked!
Then power one winding with 220 and connect one of the other primarys to a terminal and then check for zero voltage across the ends of the other two, it should be near zero in order to connect in parallel , otherwise swap the first two
It is plainly labeled so should not be difficult.
Max.
 
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MisterBill2

Joined Jan 23, 2018
7,033
The link is already there on the primary, all it needs is to remove all primary conductors and identify the two winding's, although they are marked!
The power one winding with 220 and connect one of the other primarys to a terminal and then check for zero voltage across the ends of the other two, it should be near zero in order to connect in parallel , otherwise swap the first two
It is plainly labeled so should not be difficult.
Max.
Max, that plain label is confusing because U1 is tied to V1. If they are both "Start" ends then it sould be U2 to V1 to put them in series for 480, giving the half-voltage outputs being complained about.
My experience with Japanese made robots was that wires were tagged with the terminal they went to, NOT the wire number. That makes assembly easier and servicing very challenging, even with a circuit schematic. There is a good reason for our NEMA standards.
 

MaxHeadRoom

Joined Jul 18, 2013
21,431
But if in doubt, or in the absence of any label, it is very easy to find out by connecting one winding and phase the second correctly.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
21,431
OK my guess is that as is typical, you have two primary windings, either series for 460 or parallel for 230v.
As it is you have V1 and U1 connected so this would be the 460v (series) arrangement.
The other option is parallel for 230, U1-U2 & V1-V2, I would however test the phasing of them first to ensure the prevention of short circuit.
Max.
 
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LesJones

Joined Jan 8, 2017
2,698
Remove the link between U1 and V1 and wires R4 and S4 from U2 and V2. Measure the resistance readings between all 4 terminals. (U1, U2, V1, V2) You should get two pairs with relatively low readings (Single figure or tens of ohms.) There should be almost infinite resistance between the pairs. (Your meter will display the same as it does with the test leads not connected to anything or each other. (This will probably be something like OL) Report the results of these tests. I would have guessed that U1,U2 was one winding and V1, V2 was the other but the way the phasing is marked with U1 as the end of one winding and V1 being the start of the other we need confirm that this is the case. We will need facts not guesses to tell you how to connect the windings in parallel for 220 volt input.

Les.
 

MaxHeadRoom

Joined Jul 18, 2013
21,431
The way to phase them is to identify the two windings, connect 230v power cable to one pair, also connect One terminal of the second winding to one terminal of the first.
Leave the other lead of the second winding open.
Power up using 230v, measure the voltage between the open end of the second winding to the single connected terminal of the first winding, you need to obtain close to zero volts.
If it shows much higher, then swap the second winding connections and re-read, at this point it the open end test should be close to zero and capable of being connected to the single connection terminal, placing the winding's in parallel.
Max.
 

LesJones

Joined Jan 8, 2017
2,698
Hi Max,
As we know how it was phased for series operation and working we should be able to tell the TS how to connect it for parallel operation when he has given us the result of the resistance tests.

Les.
 

LesJones

Joined Jan 8, 2017
2,698
Hi Max,
I agree that is the most likely numbering but it is just possible the windings could be V2-U1 and V1-U2. Another reason that I think you are right is that the strapping would be tidy. The power input would remain on V2 and U2. The U1-V1 stap would be removed and straps added between U1 to V2 and U2 to V1.

Les.
 

MaxHeadRoom

Joined Jul 18, 2013
21,431
I am guessing they did not use the 'convenient' method using the typical way the studs are layed out.
IOW instead of using the outer two for the link the centre two would be used and power into the outer ones.
If using 230, then a strap across the left two and the right two and 230 power in to each.
This is clearer on the common layout of the one in post #8.
Max.
 
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