Isolation Transformer (multi-winding transformers)

[acceler8]

I have 2 identical unknown transformers that I'd like to wire back to back to make an isolation transformer. They are both from the same model UPS (battery back up) and I haven't been able to find ANY information on them (markings include 430-2060B; E184736; DV-130-1). Since they are the same, I'm not worried about getting a 1:1 ratio. My question is, can I hook up all the different windings back to back, or should I just use a single winding? I haven't measured the voltages yet, but I have 3 large wires on the output side that are Red, White, and Black. My thought is: MAINS (110v) ---> xfmr1 Input --- xfmr1 Red Output ---> xfmr2 Red Input --- xfmr1 White Output ---> xfmr2 White Input --- xfmr1 Black Output ---> xfmr2 Black Input --- xfmr2 Output (110v)

Does this sound right?
Thanks!

 

[mickeymoose]

Draw a pix.
Transformers are not 100% efficient. You will loose 10% ore mor of the voltage (depending on the load) on the output of your contraption. E

 

[bear]

Hmmmm... interesting to think about.

It should work IF you get the phase correct.

You might get some bucking because of slight phase differences between the sets of windings. That being due to the variance in inductance and interwinding capacitance.

I'd fire it up first with just the heaviest windings connected, and use a LOW voltage xmfr as the source (like 12vac) and see what the output looks like compared to the input. Then try it the same way with the rest of the windings. Finally, try it with some sort of current limiting (a lightbulb for example - or a variac with ammeter) on full mains power.

I doubt that any voltage will be lost, but some power may be eaten up in the xfmrs, but who cares...

_-_-bear

 

[acceler8]

MM, Here is a hastily drawn diagram in Paint. I'm not too worried about voltage loss, as this will be (Before???, After???) my variac.

Bear, I'm not sure which windings are the heaviest, as all three wires shown are the same gauge. Could it be center-tapped? If so, would it damage anything if hooked up as shown in the diagram?

Thanks Moose and Bear! Lot's of animals around these parts....

 

[mickeymoose]

Asumptions: You know which side is the 110 volt and that the 2 xformers are the same model, than you can figure out what should go where. I would not use the centre (I spell that the Canadian way) tap of the secondary. E

 

[Speedskater]

Are UPS transformers wound the same way that typical linear power supply transformers are?

 

[mickeymoose]

On the input of a UPS you most likely have a HF switching supply to charge a battery. The core would be a powder-iron design. On the out you could find a ferro-resonant transformer. And than, maybe not. E

 

[acceler8]

So I finally had a chance to actually test the transformers in question. Both tested the same, and all results were at 60hz with 110V in.

Red-White: 15.7vac
White-Black: 7.85vac
Red-Black: 7.85vac

Blue-Brown: 19vac

I didn't mention the blue/brown wires before as they are quite small compared to the rest so I'm not planning on using them no matter what.

So what's up with different values between the first three sets of wires? Can I still use this as an isolation setup? Help and thanks!

 

[Spiny]

You have a 7.5-0-7.5 volt transformer I guess allowing for mains variations (otherwise a 0-15 volt with a centre tap - same thing)

connect the red and white on one to the red and white on the the other and insulate the centre tap wires.
That will work fine. Will work as back to back transformers at the full power rating

 

[acceler8]

Spiny, thank you! That worked! I measured 110vac in and just a little less on the output (with 2 multimeters).

Next question, can I (or do I want to) connect the smaller wires in the same way to get a little extra capacity? Seems a shame to have an unused coil just going to waste.

Thanks!

 

[Spiny]

I would just insulate the thinner wires, I doubt it would make any difference and if you get the phase reversed could cause problems.

Perhaps use the 19v coil to light a lamp to show its live

glad it worked

 

[Davis Lambert]

I have the same transformer and you can also get a voltage of similar to 33 vac and 66vac if you swap the primary and secondary; the primary wires for this are the thick black and white wires on the side with the yellow wire.

 

[gmphadte]

You should not swap the windings of the first i.e. input transformer. CAUTION

Gajanan Phadte

 

[Davis Lambert]

I think that the coils are reversed for different sets of wires.