[sdiy] Measuring current use of a module?

[Bret Truchan]

Thanks for of your responses!!

I put a 10 ohm resistor in series with my +12 volt line, and another one in 
series with my -12 volt line.  I then put the module under the most stress 
possible (both LEDs on, all outputs active, etc).  I measured the voltage 
drops across the resistors and here's what I found:

Voltage drop across the +12 volt line: 346 millivolt
Voltage drop across the -12 volt line:  42 millivolt

This makes sense, since the +12 volts is feeding a regulator, which in turn 
feeds most of the circuitry.

Whipping out a little OHMs law gives me:

Calculate Current given 10 ohms resistance and 346 millivolts:
=================================================
V = I x R
.346 = I x 10
I = .0346 Amps = 34.6 milliamps


Calculate Current given 10 ohms resistance and 42 millivolts:
=================================================
V = I x R
.042 = I x 10
I = .0042 Amps = 4.2 milliamps


Total milliamps: 38.8
Using Scott Gravenhorst's 20% rule (add 20% to it, just in case..)

Total milliamps, plus fudging:
38.8 + (.2 * 38.8) =  46.56

I'll round up to 50 milliamps.
If I look at the current ratings of Doepfer gear, it looks like I'm in the 
ballpark.

Thanks everyone!  I learn something new every day.  I just tend to learn a 
lot of things out of order. :-)
- Bret

_________________________________________________________________
Free up your inbox with MSN Hotmail Extra Storage! Multiple plans available. 
http://join.msn.com/?pgmarket=en-us&page=hotmail/es2&ST=1/go/onm00200362ave/direct/01/