Measuring current to daisy chained pedals

[stallik]

I wanted to measure the current being drawn by the 9v pedals on my board just to make sure that I wasn't over running my power supply but ended up with surprising results.
All the pedals are run through a ps daisy chain so I split the + cable at the ps end and measured the current by connecting my dmm in series. I tried A & mA and the readings were the same - 320mA
I was expecting more as I'm powering:

TC Electronics tuner
Lightwah
Vox Valvetone
Spitfire
Zendrive
SHO
2 mayqueen circuits
PT80 delay
Chasm reverb
Ditto
And the LEDs in an ABY

They're all on, surely they can't be consuming so little - or have I missed something?

[anotherjim]

Average about 32mA per unit  - that could well be right.
If you don't trust the DMM on amps, put a small value 1/2watt resistor (10ohm would be easy) in series instead of the meter. Measure voltage across the resistor and do a bit of ohms law calc'. It should come out a bit lower than the ammeter reading on account of the series resistor dropping the power a bit.

[GibsonGM]

Funny thing is, I'm betting the major current eaters in your chain are the LEDs in the pedals!   

[stallik]

Thanks guys. Jim, I'll check that out when I get home tomorrow.
I don't know why I had it my head that each pedal would be in the region of 100mA or so. You should see the size of the transformers I've been using

[davent]

To make things easy I put a small box together with a 1r resistor between two power jacks, just measure the mV drop across the resistor for a direct reading of mA's being consumed.

The tuner, the Ditto, the delay and the reverb i think would be the  power hungry pedals, the others squat.



dave

[GibsonGM]

Thanks guys. Jim, I'll check that out when I get home tomorrow.
I don't know why I had it my head that each pedal would be in the region of 100mA or so. You should see the size of the transformers I've been using

Funky box, Dave!  Good idea

Yeah, often we start out thinking we need AMPS when really, the mA are what does all the heavy lifting!  If I had a penny for every time I tried to talk a person into making a 9- or 12-volt, 1A supply instead of some insane 30V, 5A thing....for some reason, it's instinctive to want "more power" when you're getting started.

Now, I spend all my time trying to DECREASE current consumption, at least for things i want to use with batteries! 

[anotherjim]

Also, when you build pedals, if they have a series resistor in the 9volt feed, you can measure current off that the same way - write it on the bottom of the box for future reference.

[karbomusic]

I built one that goes inline at the beginning of the power chain and is now a permanent fixture on my pedal board so I always know volts/mA. It's powered separately so that the reading is accurate and the unit doesn't draw power from the line I'm measuring.



Also remember most of them are "on" even when bypassed.

[anotherjim]

Karbomusic, that's very nice.
I take it that the green numbers are milliamps
Davent's bit of test gear is very good too. 1ohm - even I can work the current out from that. 

[karbomusic]

Karbomusic, that's very nice.
I take it that the green numbers are milliamps
Davent's bit of test gear is very good too. 1ohm - even I can work the current out from that.  

Yep, it is. It's basically a volt/ammeter I found on the net that is most likely a panel mount for boats/trucks etc. It appears to be within about 1mA and 1mV accuracy wise, or it exactly as out of calibration as all my other meters LOL.