# FW: Measuring the current draw of a modular

Lahlum-FLR111 Ross ross_lahlum at msmail.wes.mot.com
Mon Mar 10 18:15:05 CET 1997

```OOPS! I just realized after thinking about it that if you have a + supply and a
- supply sharing a ground return, the currents from the two supplies will
cancel out in the ground line.  Doh!  So don't do your current measurement in
the ground return... Sorry if I misled anyone.

Ross
_______________________________________________________________________________
To: Christopher_List at Sonymusic.Com; synth-diy at horus.sara.nl
From: Lahlum-FLR111 Ross on Mon, Mar 10, 1997 1:51 PM
Subject: RE: Measuring the current draw of a modular

Chris,

There are a couple of ways to do this.  The first is what you suggested.
Another way is to get a 0.1 ohm resistor, put it in series with each supply
lead (don't recall how many.. is it one + & one -?), & measure the voltage drop
across it.  Then use ohm's law to calculate the current (I=V/R, or current =
measured voltage/0.1 ohm). Then add up both measured currents.  Another way is
to put the 0.1 ohm resistor in the ground return lead.  Assuming there is only
one gnd return, you'll get all your currents summed up through that branch.
This would also be a fairly safe place to put a current meter in directly if
you don't want to bother with the 0.1 ohm resistor.

Good luck,
Ross

_______________________________________________________________________________
To: synth-diy at horus.sara.nl
From: Christopher_List at Sonymusic.Com on Mon, Mar 10, 1997 1:05 PM
Subject: Measuring the current draw of a modular
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Date: Mon, 10 Mar 1997 13:49:58 -0400
Subject: Measuring the current draw of a modular
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This may seem like a silly question - but how do you guy recommend
measuring the current draw of your modular?

Do you just snip the positive voltage line, strip it and run it through

Is this safe?
I'm scared :).
I don't want to fry a whole mess of chips by turning on only half of the
power supply...

- Thanks,
Chris

```