# Odd Multimeter Reading



## jimtyp (Jan 2, 2008)

I have a multimeter, pretty cheap one. I hook it up to a 9V battery and it shows 9V (or very close). I have a power supply that can be switched between 13v, 18v and 23v. I have a controller hooked up to the power supply. When I set the power supply to 13v but only have the controller set to 50%, the meter reads 13v. When I hook up a lamp to the controller it dims when I turn the knob down and brightens when the knob is turned up. 

Somehow the multimeter reads the source of the power not what is actually being provided. It works the same when I use the 18v or 23v setting on my power supply, i.e. it shows 18v or 23v, respectively, no matter where I set the controller knob. I know the controller knob works because of the lamp test.

Is there a way to test what voltage is really being provided? Is it a problem with this cheap multimeter or do all do this? 

I'm setting it on DCV 200 for testing.


----------



## grsman (Apr 24, 2012)

jimtyp
You need to hook the meter the same place as the light bulb.
The output of the power supply will not change. The controller
takes the power supply output and changes it to the desired output
at the controller output terminals when you turn the knob.
Tom


----------



## jimtyp (Jan 2, 2008)

Tom, I am placing the volt meter at the same place as the light bulb. That is what is so confusing to me. I know the controller is working as I see the lamp dim and get brighter as I move the controller knob. But the volt meter always reads the max power no matter what position I have the knob at. I assume there is something wrong with the volt meter?


----------



## CliffyJ (Apr 29, 2009)

Jim, what type / brand of controller is it?


----------



## Totalwrecker (Feb 26, 2009)

Aren't you playing with a square wave? The longer the pulse of the set voltage the brighter the bulb. You meter still reads the top voltage, how long it is applied matters not.


----------



## toddalin (Jan 4, 2008)

The meter is measuring the peak voltage, but the light is responding to the average voltage.


----------



## jimtyp (Jan 2, 2008)

Thanks all. So I need to use a meter that measures the average? The one I'm using is pretty cheap - Cen-Tech. I may have gotten it at Harbor Freight.


----------



## CliffyJ (Apr 29, 2009)

If you're measuring DCC, you might want to see my (quick and) "dirty meter" thread: 

http://www.mylargescale.com/Community/Forums/tabid/56/aft/129114/Default.aspx


----------



## jimtyp (Jan 2, 2008)

Thanks Cliffy. I went ahead and bought a low-end True RMS meter - DIGITEK $40 on Amazon. Even simple electronics seem out of my league- but I'm trying to learn. I've got a handle on resistors  

Also like your shapeway products  Going to have to learn sketchup.


----------



## CliffyJ (Apr 29, 2009)

OK Jim, I'll have to look that up, good tip.

As for me, the only electronic components I've got a handle on are relays, diodes and a can of beer.


----------

