A new co-worker was about to replace a system board in a laptop when it would not power on. He checked the voltage from the brick and it was at 19.5 volts (as it should be). I told him to remove extras (battery, drives, etc). He brought it to my area so I can show him how to take apart a clip and the laptop worked. Went to his desk and nothing.

It appears that the brick was no longer suppling the needed voltage or amperage when under a load. I've seen it before, but not very common.

MY question:

I would like to build some simple load testers. I searched the forum and have an idea of what to do and have seen some interesting projects.

Adapters: 19.5v 65watt and 19.5v 90watt ratings are what I use most.

Just to use the 19.5v 90 watt adapter as the main example what are some choices?

19.5v / 90 watts / = 4.61538 amp / = 4.222 ohms.

Simple power resistors? what values do you suggest to be safe?

More elaborate setup to cover a range (65 - 120 watts)? Pots, meter hookups?

This would not be constant but just a quick and dirty tester to check for operation when in the field.

 

Light bulbs are a lot cheaper than power resistors, and they give visual feedback. I think with a little experimentation, you could find the right bulb to give an easy check for a working versus non-working brick.

But, don't some bricks require data communication with the laptop?

 

For versatility, I would consider a large variable resistor.

http://www.vishay.com/docs/50020/50020.pdf

 

Searching for 20 volt light bulbs doesn't work. Single resistors for 30, 60 and 90 watts are going to be expensive and bulky. 3.2 ohms, 250 watts, special order, $116.47 plus shipping. This is not practical!

http://www.mouser.com/ProductDetail/Vishay/RH2503R200FJ01/?qs=ozkTL/Uej0RYjrsXw1RAXg==

 

If all you need is a short term load for confirming output from a 60 or 90 watt power supply, I think this would work.

http://www.digikey.com/product-detail/en/AVT100-10-10%/AVT100-10-ND/257640

 

Best one yet by tracecom. 100 watt limit means you should restrict your test time to only a few seconds.

 

My approach is still 5X cheaper. For example.

 

A 24 volt car headlight? I didn't know there were 24 volt cars.

I learn something almost every day on this site.

 

Ha ha, I learned it only minutes earlier myself. I was thinking two 12v bulbs in series but figured, why not first see what google can find at 24V. Voila. I was amazed it even goes to 100W.

 

Light bulbs are a lot cheaper than power resistors, and they give visual feedback. I think with a little experimentation, you could find the right bulb to give an easy check for a working versus non-working brick.

But, don't some bricks require data communication with the laptop?

You are correct sir. Some 'smart' power adapter plugs have three wires. Although the jack looks like a standard two wire plug. There is the outer shell (usually ground), inside shell (usually Voltage), and the center pin - (usually has the same voltage) if tested with a meter will be for communication(controls/limit power I believe based on need). Not all may be the same.

I believe that you can put a small resistor between the last two pins if you had to use a non-smart adapter (or fixed voltage source) for a temporary fix.

 

I will try some of these suggestions.

I do have a fix, I just ordered a few extra supplies, but where is the fun and learning in that.

I am keeping the bad supply to compare it with one of the new ones against some of these suggestions.

After I order some parts I will post my findings.