have transformer - no specs

[Maran]

Well, this is my first post. I want to make psu for my 6A 3.3V steppers. I have a transformer ( 4 of them) from computer UPS, but I do not have any specs for transformer. I am not at home with electronic, so I am not sure what is primary and what is secondary winding. On one side there are two thick wires, one red other black. On the other side are two pairs of wires. My guess is thick wires are primary, other two pairs are secondary. Can I use multimeter to measure secondary windings? Can I just connect primaries to AC outlet and then measure V on secondary? Or it will blow something? I will try to upload pics also.


Maran

[Maran]

Here is a pic of transformer ( I hope ).

[Al_The_Man]

One way is to check the resistance, and find the highest reading pair, you have some pretty low resistance windings there.
Then if still not quite sure, feed the highest pair with a low voltage AC from another, say 5 to 25v source and see if the voltage is lower on the other pairs than the voltage you are putting in. if a pair is higher than the input pair then that pair would most likely be the primary.
Al.

[Maran]

Al, thx, will try this.

Maran

[Maran]

Here are the readings.

One side:
Black-White = 3.5
Brown-Red = 0.4

Other side:
Black-Red = 0.2

So, primary should be black-white.

Can I just connect black-white to AC outlet (220V here) and measure with multimeter voltage on other pairs? What if I am wrong and this is not primary?




Maran

[NC Cams]

Did you think of contacting Startron???:

Startron@ms15.hinet.net

They might blow you off as the import companies tend to do but you never know

The following website does indicate that they speak English:


http://translate.google.com/translat...lr%3D%26sa%3DG

Looks to me like it is more of an isolation transformer than a step up/down piece as denoted by the Voltage/current in versus E/I out ratio.

[Maran]

NC Cams

Mail sent. Hope there be an answer.

If it is an isolation transformer is it useles?

Maran

[Al_The_Man]

Here are the readings.

One side:
Black-White = 3.5
Brown-Red = 0.4

Other side:
Black-Red = 0.2

So, primary should be black-white.

Can I just connect black-white to AC outlet (220V here) and measure with multimeter voltage on other pairs? What if I am wrong and this is not primary?
Maran

It looks most definately that black white will be the primary, I assume there is no continuity between any of the pairs?
Looking at the label again I see that it mentions 240 in and 230 out? which implies an isolation transformer, but I don't see any way that is actually what you have looking at the windings, and the readings you got.
I would power up the high resistance side with a suitable low fusing, not too low as it may blow from the inrush.
Note: if you look at the secondary in the picture and assuming it is an isolation transformer with approx. 2turns/volt then primary and secondary would have to have ~480 turns, there is no way you would get 480 turns of the square section wire shown.
Al.

[Maran]

Al,
What will be adequate fuse size?

Maran

[Al_The_Man]

No larger than 10a I would guess.
I would think that any of the windings are going to handle that current without damage, the fuse should blow before anything drastic happens, if you have the fuse in the correct primary winding it should remain intact.
Al.

[NC Cams]

If the input voltage/current versus output voltage and current (as clearly posted on the label) meet your needs, it is NOT useless.

If the input voltage/current versus output voltage current values (again as clearly published on the label) do NOT fit your needs (as in the need to step up or step down voltage), the answer should be intuitively obvious.

Putting more or less voltage in won't change the net output - it will be a function of the turns ratio of the transformer. Since the turns ratio appears to be about 1:1, I'd strongly the transformer is an isolation transformer - no more no less.

Thus if you put 240 in, you'll get about 240 out - likewise if you input 110 or whatever - what goes in will come out voltage wise....

[Al_The_Man]

I would say that the label applies to the input/output of the UPS is was in, NOT the voltage of the transformer secondary, those winding in the pic. would be rated at least at 20~30amps.
Probabally very low voltage.
Al.