Why I don't like wall warts

[tedstruk]

I think this is one of those check the specs of the wart online and then buy the right one questions but....
Why can't I read the 2a that the wart is supposed to be delivering? I metered it and it just fluctuates between 0 and 0.8a?
12.29v .08a out of a 12v 2a wart

 

[AnalogKid]

Linear or switching?

 

[kellys_eye]

The 'ohms' readings.... are these your calculations or are these the actual resistors you used to load the output?

Per usual specifications you have to account for a 5% drop in output voltage at the maximum load before specifying the actual rating. In other words, load the output until it falls to 11.4V and see what current is flowing at that point.

 

[BobK]

Tell us exactly how you did this measurement. Please say it is something other than "I set my multimeter to the 10A range and connected the probes to the wall wart."

Bob

 

[Terry01]

I predict more burst fuses!

 

[Terry01]

Does that apply to all PSU if your looking to find the max output current Kellys eye? Sorry if it seems like a silly question but it makes sense now you say it.

 

[kellys_eye]

Not just power supplies - everything is built to 'standard's that you need to know about if you want to meaure them or incorporate devices into your own designs. In the UK, equipment is usually to BS**** (not a swear word!) British Standard which, if you can get hold of them, tell you what you need to know.

But for electrics it's fairly well known that all power supplies have such specc's as 5% regulation (for a basic power supplies - test equipment power supplies are much more regulated than that). The cheaper the power supply (wall wart) the worse the regulation is - and it's not just output voltage/current that is affected, you get problems with ripple and noise too.

You could do your own tests and derive the full specc's for the power pack you have there. It would be a useful learning exercise.

 

[Terry01]

Yes,great idea!

I also have a cheap boost converter I was sent by mistake. I ordered a pack of capacitors and received a boost converter! http://www.ebay.co.uk/itm/150W-DC-D...750920&hash=item2ee05788af:g:aKwAAOxyyFhTeWWb

I can do the same with this too. Thanks for the info and idea.

 

[kellys_eye]

Producing the specc's of such PSU's uses pretty much the techniques but the larger the PSU (in terms of power output) the larger the load needed to test it. You can add simple loads like light bulbs (car bulbs are good) but it limits you to doing it in steps rather than a continuous sweep. Nothing really wrong woth that as you interpolate the missing bits.

The converter will require a suitably rated input source though...... you would normally test it's efficiency at various input voltages but even doing it for one 'fixed' input voltage will give you some basic specc's.

 

[Terry01]

Cool. I've just been using my bench PSU to run the BC. The caps discharging after i cut the power caught me for a second but then I caught on. Thought I'd broke another meter
Just been watching what's happening with the Volts and Amps as I change both outputs. I've been using 2 meters,1 for Volts and 1 for Amps.

I made a simple signal generator using a 555ic on my breadboard,again using my meter but on the Hz setting this time. Its really for when my oscilloscope comes to tinker with. I'm going to wire a potentiometer in later today so I can change the frequency around. I'm having lots of fun with it.

 

[jedro]

Please tell us that you are applying a 2 amp load to the output leads of the wall wart.

You apply a .5 amp load, that is what it will provide. You apply a 1.0 amp load and that is what it will provide.