Advice on testing a trasnformer
 

just back from holiday and found my cctv has gone wrong.
I need some advice on testing a transformer/power supply. The label on the back calls it a switching adaptor. model FJ-SW4802000F
240v input. The output should be 48v DC, 2000mA.
should I get a fixed AC voltage reading? I think not but I do.

thank you

macafee2

I would expect what it says on the box. 48V DC.
A bit above or a bit below would not surprise me.
If AC maybe a blown diode or rectifier.

But what did you measure?

I think in excess of 100v ac. if this means the transformers duff I hate to think what it has done to the unit it powers

macafee2

Ian; read under ‘Modes of Operation’ here for an explanation!

Simon

It is best not to think of this as testing a transformer.

A switched mode PSU should be tested with some load as otherwise the switching elements can misbehave depending on the design.

Put a small load on the output, say a 5W 1k ohm resistor, and test the output.

The output of a 48V DC supply should be close to 48V DC.

Damn you all with your helpful answers. I was going to suggest hitting the transformer and seeing whether it changed into a car, boat or plane:getmecoat:

Let's not jump the gun.

Yours is the third phase of the analysis! :bowdown:

You cannot test a switching supply off-load. Doing so will only give you wildly out of range results if any at all. If you do get a reading it will normally far higher than you would expect. Testing on-load is the only way to accurately check for correct output. Secondly, why do you suggest the output is AC ?

Some SMPSU's even shut down completely if they are presented with no load.



Can you test the 48v with it actually powering the CCTV?

Yes and that tends to be the rule rather than the exception.
That would be the route I would take. If it has gone faulty in operation and left that way, any damage done has already been done. If the supply was not overly hot to the touch with no odour of burning, hook up your meter first, plug in the SMPS to the main box then turn it on briefly and see what you get.