Testing AC/DC adapters/chargers

[Jeff Ivers]

Wanted to try some electroplating and needed a DC power supply. Have a couple dozen AC/DC adapters/chargers. Thought I should check them to make sure they were working and to select the best actual voltage one for my experiment. Got out my 30 year old multi-meter and tried to check voltage and amperage rating of all the adapters I had in stock. On about 75% of them, I could attach my test leads to the power plug from the adapter (that was plugged into a working outlet) and get a voltage reading. On some, I was not able to get a reading, but thought the adapter should be good, so cut the plug off the end and bared the two wire leads and re-tested. If I didn't get a reading, I reversed the pos/neg leads and tried again, assuming I may have mis-interpreted the polarity. Still no reading. Since this one (that had no voltage reading) had the best voltage rating based on the label, I decided to go ahead and use it on my electroplating experiment. It obviously was putting out current as the electroplating worked. I could see the voltage flow as indicated by the bubbling on the anode.

Why am I not getting a voltage reading on a device that is obviously putting out current? Is there something about the internal design of some of these adapters that prevents testing them in the manner indicated?

I also tried to check amperage output and my readings started getting even more weird. In one case, I obviously had the test leads in the wrong range on the multi-tester (too low - potential overload). Decided the multitester might have a problem, so took the back off and discovered corroded batteries. I removed the batteries and cleaned off the corrosion and installed fresh batteries. I then commenced re-testing and still was getting no voltage readings when I thought I should.

Once the new multi-tester came in, I rechecked my previous tests and still could not get a voltage reading on the adapter that worked for the electroplating.

To get an accurate current reading on these in a test mode, does the adapter have to be plugged into a load?

Thanks, in advance, for any insight.

 

[justsam]

Most of these 'wall warts" today are switching supplies, and may not be pure DC or sine wave AC for that matter. They may also want to sense a load before providing an output. When it is functioning for your electroplating do you see a voltage? Try both AC and DC. Confirm your meter is working properly by measuring a battery or door bell transformer so both AC and DC are verified.

 

[usa#1]

To check amperage you have to put your meter (assuming it's not and amp clamp) in series between the power supply and the load using either the + or - leg of the power supply. If you put your meter in "amp" mode and connected it directly across the + and - legs of the power supply, you put your meter across a dead short which typically causes the internal meter fuse to blow. Check to see if your meter fuse is blown.

 

[Jeff Ivers]

Most of these 'wall warts" today are switching supplies, and may not be pure DC or sine wave AC for that matter. They may also want to sense a load before providing an output. When it is functioning for your electroplating do you see a voltage? Try both AC and DC. Confirm your meter is working properly by measuring a battery or door bell transformer so both AC and DC are verified.

I didn't think to try to test the voltage when using it on the electroplating. I will try that. I did test the meter with a battery but did not have a known AC transformer to test against.

To check amperage you have to put your meter (assuming it's not and amp clamp) in series between the power supply and the load using either the + or - leg of the power supply. If you put your meter in "amp" mode and connected it directly across the + and - legs of the power supply, you put your meter across a dead short which typically causes the internal meter fuse to blow. Check to see if your meter fuse is blown.

Thank you for the clarification on testing under load. Sure wish my instruction manual bothered to explain that. I did change the internal fuse, but did not test the replaced one.