Help on this transformer (make work)

[Pranav A S]

Please help me out how to make work this transformer?

I don't know it's primary connection, or secondary.
It's from a UPS, Please help me out

 

[kellys_eye]

The thickest winding - and lowest resistance - will be the secondary.

 

[Pranav A S]

And the primary? It is an autotransformer with a lot of connections.

 

[(*steve*)]

If it's an autotransformer then it doesn't have a primary and a secondary. Autotransformers have just the one winding.

 

[kellys_eye]

Actually it IS a 'sort of' auto transformer in that many UPS devices regulate the input/output throughput voltage by switching in primary winding taps to boost or cut the output within a narrow range. Outside those controllable ranges the system switches to full UPS mode (battery derived AC output).

Taps on the primary allow these small variations to occur but it doesn't distract from the fact that the system is primarily 'transformer' based.

If you identify the primary and secondary you can apply your local AC mains to the primary side and measure the secondary voltage. Change the primary supply connection points and re-measure. When you get your full range of voltages (from highest output to lowest output) then the 'middle' voltage tap will be the most appropriate one to use if you intend to use the transformer for 'permanent' use.

Although using the other taps as the input won't (shouldn't) really matter, these types of transformer are only really meant for intermittent use at full load. If running them at below their 'expected' rating then they are safe to use constantly.

 

[Pranav A S]

So I can connect at any 2 points between the primary without killing the transformer?

 

[kellys_eye]

No, not 'any' two tabs.

Measure the winding resistance to find the highest ohmic value. This will be the 'top' setting i.e. highest voltage on primary.

Using one of those two connections, measure the other connections. You should get a 'lower' resistance - not TOO low. If it's too low then use the 'other' connection you first identified.

What you're trying to do is measure the winding resistance to determine where the taps are.

T1---------------------T2-----T3-----T4-----T5

(N)--------------------(L)-----(L)-----(L)-----(L)

T1 would be the mains neutral (N) and T2-T5 the other taps - mains live will connect to any of the (L) points.

You do NOT want to connect mains neutral to any of the (L) points or you're applying mains straight across some very small portion of the primary and smoke will ensue.

The resistance from (N) to any (L) connection will be successively larger whilst the resistance between any two (L) connections will be 'small'.

 

[Pranav A S]

Thanks!! Now I am confident to do this!!