Suggest a dummy load please

bonzodog2

I have a car charger for a laptop, plugs into a lighter socket, adjustable volts 15-24. Rated at 80W. I want to run it off the 12v output of a computer PSU, for indoor use.

No-load voltage at the output is about 40V, and i'm wary of plugging a laptop into it. What can I use as a dummy load?

edit: the laptop I want to run is 19V

whizbang

is the 12v computer psu thats giving 40V, or the output of the laptop charger ?

Either way, use the lowest current you can get away with, I would aim for about 100Ma to start with. At 19v that's 190ohms, or 200 is a nice round value.
A 24volt 1watt bulb (Christmas tree bulbs!) might be just as good. Double up if you need. Your charger can handle loads!

If its the 12v output you are loading, you may have to load up the 5v or even 3.3v also. And some computer PSU's need lots of load before they are stable.

bonzodog2

Its the car charger thats reading 40V-ish. Thanks for suggestion, I don't have any xmas lights.

I run a 120W 12V laptop PSU off a set of deep cycles. Set to 19V no load voltage is 19V.

bonzodog2

I was initially thinking of some kind of lightbulb, but it was suggested to me that the resistance when cold would be a lot lower than hot, and this might draw too much current from the psu.

True it's not hugely significant. Your laptop battery charging would be a lot greater in terms of fluctuating load. 2 x Stop lights (car brake bulbs) in series = 50W max.

Careful with those cigarette lighter plugs they're a bittova joke, I wouldn't rate them higher than 3A. They're absolutely dreadful connections. They love to melt and start fires; it's all spring loaded point contact with no thermal relief. I've swapped mine for Hella/Din connections (16A). That or hard-wire it.

ZENER

Definitely do not connect the laptop to it for a start.

When it's plugged into the car what does the output voltage rise to ? I would expect it to be stabilised and give the selected voltage +/- .5V even without a load connected. If it doesn't then bin it, I wouldn't risk an expensive laptop on it.

As a load I would set it to 15V and use a 55W car headlamp bulb. Normal voltage in a car electrical system can be up to 14VDC so the extra volt shouldn't cause the bulb much harm in the time it takes you to measure the voltage with a multimeter.

Ken

Johnboy1951

There is some good info in this clip regarding starting and stopping an ATX power supply and placing a dummy load on it to get it operating properly.

https://www.youtube.com/watch?x-yt-ts=1421914688&x-yt-cl=84503534&v=z2oSFpKh_Uw