Advice on testing a trasnformer

macafee2 · 2nd October 2018, 16:31

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

kaiser · 2nd October 2018, 16:38

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?

macafee2 · 2nd October 2018, 17:02

Quote:

Originally Posted by kaiser

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

SD1too · 3rd October 2018, 07:37

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

Simon

MSS · 3rd October 2018, 08:41

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.

Groundsman Willie · 3rd October 2018, 12:46

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

MSS · 3rd October 2018, 13:04

Quote:

Originally Posted by Groundsman Willie

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

Let's not jump the gun.

Yours is the third phase of the analysis!

Ennine · 3rd October 2018, 19:51

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 ?

HarryM1BYT · 3rd October 2018, 20:44

Quote:

Originally Posted by Ennine

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?

Ennine · 3rd October 2018, 20:53

Quote:

Originally Posted by HarryM1BYT

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.

2nd October 2018, 16:31	#1
macafee2 This is my second home Rover 75 Saloon & Tourer Join Date: Sep 2012 Location: Lincoln Posts: 14,911 Thanks: 1,630 Thanked 3,032 Times in 2,181 Posts	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

2nd October 2018, 16:38	#2
kaiser This is my second home 75 Tourer 2.5 Auto, 1.8T, 75V8ZT Join Date: Jun 2007 Location: Johannesburg ZA Posts: 6,200 Thanks: 1 Thanked 859 Times in 613 Posts	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? __________________ Worth his V8 in gold

3rd October 2018, 07:37	#4
SD1too Doesn't do things by halves Rover 75 2.5 Connoisseur Auto (1999) Dealer launch model. Join Date: Mar 2007 Location: Former Middlesex Posts: 20,338 Thanks: 1,587 Thanked 3,749 Times in 3,181 Posts	Ian; read under ‘Modes of Operation’ here for an explanation! Simon __________________ "Whatever is rightly done, however humble, is noble." Sir Henry Royce.

3rd October 2018, 08:41	#5
MSS This is my second home Rover 75CDT, Jaguar XF-S 3.0V6, V'xhall Omega V6 Estate, Twintop 1.8VVT, Astra Estate and Corsa 1.2 Join Date: Dec 2007 Location: Suffolk Posts: 7,083 Thanks: 283 Thanked 624 Times in 440 Posts	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. Last edited by MSS; 3rd October 2018 at 10:09..

3rd October 2018, 12:46	#6
Groundsman Willie Gets stuck in Rover 75 1.8t Join Date: Dec 2017 Location: Newbury Posts: 842 Thanks: 783 Thanked 423 Times in 264 Posts	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 __________________ Dave

3rd October 2018, 19:51	#8
Ennine Posted a thing or two Ford Join Date: Nov 2012 Location: Portmahomack Posts: 1,330 Thanks: 545 Thanked 317 Times in 193 Posts	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 ? __________________ Ni9e How to: Replace touch screen Navall II [SIGPIC][/SIGPIC]

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode