I'm a young player and I found a trap!

[ElectroNub]

I'm working on a power supply project using a few cheap ebay parts and I found a problem that is stumping me.

Using a $2 dollar panel voltmeter with 3 wires. Common ground with separate power and sense wires.

And a $2 dollar 3 amp PWM module.

I'm making a little power box that I can plug in any of my wall warts and make it adjustable.

Anyhow, I was whacking my brain against the wall  trying to figure out why this simple circuit was not working correctly. It turns out that my PWM module is switching the LOW side!

My panel meter is not happy with this configuration. I can hook up all the meter wires to output and it works OK but the meter shuts off under 3 volts.  My PWM control goes down to 1.2 volts and this meter is capable of reading 1.2 volts.

Is there a trick to wire this up and make it work as intended?

Or is this low side switching with a common ground meter pooping on my parade?

[kjs]

that's an unusual setup. Most of these switchmode controllers have input and output ground completely and hard connected. What type is it? The usual LM2577 and LM2596 ones would work just fine..
If it really has a separation there you unfortunately are hosed with that DVM as the supply ground and test ground is identical.

Edit: just remembered.... I had several of these 3-wire DVM's (38 out of 50!) which had the jumper (solder) for the 2-wire version still in. You better check whether yours has that too. That would also hose up things if you short input and output. The solder jumper is just after the pads where the + and test wires are soldered to. Looks like they use it for faster testing and then sometimes forget to take it out for the 3-wire version.
(picture is of a 2-wire and I circled the "jumper")

[NiHaoMike]

Use a diode and capacitor as a charge pump to power the meter.

[Zero999]

that's an unusual setup. Most of these switchmode controllers have input and output ground completely and hard connected. What type is it? The usual LM2577 and LM2596 ones would work just fine..

I doubt it's a switch mode controller. It seems like it's a PWM control unit designed for motor speed control and is completely unsuitable for use as a switched mode power supply.

[NiHaoMike]

Maybe that's his intention. Apart from motor and resistive loads, there are a few electronic loads (e.g. some LED modules) that are designed specifically to run from PWM.

[kjs]

Looked to me like he's intending to build a power supply (lab) but let's wait until he comes back...... Could well be that he has chosen the wrong module or wants to use it for something different.