Box to measure loaded wart current & voltage?

[Paul Perry (Frostwave)]

I often want to measure battery (or AC plugpack drain), especially when prototyping or debugging. What I'm about to make, is just a little box, with a few different input power sockets, and a power lead coming out. Plus a switched phono jack.

The idea is, with the phono jack out, the power just runs straight thru. But, you have a "phono to two banana" test lead that you plug in to your current measuring multimeter! It's going to be pretty easy to measure current now
And maybe I'll even have another socket across the power input, so I can see the wart voltage under load!!!!!! got a few of those $5 tiny DMMs, plenty good enough for this

[zachary vex]

excellent!  it's incredibly useful to know exactly how much power is going into any given circuit.  it's an invaluable diagnostic tool, and it always keeps you honest.  8^)

[Nasse]

Don´t know what they call these, a lab supply or what. Don´t know if an older pro repairman some kind of way left a nice power supply for me (been sitting on my table at work for more than a year and a half...) He just left it there, said he don´t need it just now, use it if you need, we will look some day later... Last time long ago we talked at phone he happily told he got his pension, I should call him...

Really I don´t know how such things are used but we tested some electronics stuff about 12...15 volts voltage and the current consumption , we perhaps had some idea what it should be... Well the supply has adjustable voltage, adjustable current limiter and both voltage and current display (huge analog meters). He told you just hook the device under repair to that supply and by just looking the meters you see very quickly if something is wrong, and you can use the voltage adjusting and current limit setting when locating the fault

So I think yes you could use two multimeters, one for voltage and one for current

[niftydog]

three words; electronic dummy load.

I built one for work, two actually. A huge MOSFET sinks all the current, driven by an op amp with reference voltage that keeps the current being sunk the same regardless of the supply voltage. We use it to calibrate power supplys here, you set the current just below the trip point with the multi-turn pot, plug in the supply, adjust the voltage and bob's my uncle! I built it with a voltage and current panel meter for each end of the bipolar supply, so now it's just a matter of plugging in the supply to the dummy load and tweaking a couple of pots.

It used to be a case of three or four multimeters strewn accross the bench, a tangle or banana leads, an incredibly hot passive dummy load sinking almost 140W sitting on my bench next to me and a really fickle 100W rheostat to adjust the current to two decimal points! Thank god those days are over!

[Paul Perry (Frostwave)]

Nasse & niftydog, you are thinking about things far more complicated than I had in mind! In the first case, I already have a lab power supply wiht a meter (but, the resolution is two low for guitar fx, unless there is a short!!) and I want to see the current & voltage from an any wart.
And in the second case, it isn't a dummy load i want (though I would, if I built amps).
All I was suggesting, was a little junction box that made it easier to measure power supply current and voltage, instead of having to cut wires, unsolder stuff, use alligator clips.

[niftydog]

yeah, I can see the need for such a box, but I was just mentioning the dummy load because I use it to evaluate wall warts for ripple voltages and stuff and your post just kind reminded me of it.

[Paul Perry (Frostwave)]

Right you are Niftydog, it definitely would be a good idea for me to test warts on a fat resistor rather than on a working box!!!!!!!