[sdiy] Measuring current use of a module?

[Tim Parkhurst]

Hey Bret,

Are you sure your voltmeter doesn't have an ampere (A or mA) setting? Most
modern meters do. Basically, you'll use the meter in the Amps (or milliAmps)
setting, and just remember that you put the meter IN SERIES with the power
supply lines to read the current draw. Here's an ASCII schematic that I'm
sure everyone will easily understand ;)

POWER SUPPLY                                              MODULE
               +V out ---------------Meter----------+V in

               GND ---------------------------------GND

               -V out -------------------------------V in


Note the difference now for measuring voltage (shown below). To measure
voltage, you set the meter to a Volts setting, and put it in across the
power and ground (you're basically putting the meter in parallel with the
supply to the module). 


POWER SUPPLY                                              MODULE
               +V out ------------------------------+V in ----------------
 
Meter
               GND ---------------------------------GND ------------------

               -V out -------------------------------V in


One note of caution: DON'T try to measure the current capability of a power
supply by simply setting the meter to Amps and putting it across the power
and ground lines. This is a common mistake and it will usually draw too much
current from the supply. To measure the current, you have to have some sort
of load (like the module shown above) and put the meter (set to amps) in
series with the load. You can measure the current capability of a supply by
using a low value (usually less than 50 ohms), HIGH WATTAGE resistor and
(again) putting the meter in series with the load. However, I wouldn't
recommend trying this unless you know what you are doing.


Have a good one,

Tim (low wattage) Servo

*****************************************************

> -----Original Message-----
> From: Bret Truchan [mailto:clone45 at hotmail.com]
> Sent: Friday, April 09, 2004 2:20 PM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] Measuring current use of a module?
> 
> Hello!
> 
> Sorry for yet another trivial electronics question.  I'm such the eternal
> newbie!!  How would one measure the total current used by a module?  My
> module uses +12 volts and -12 volts for an op-amp, and feeds the +12 volts
> into a 5 volt regulator to power a microcontroller.  I would like to know
> what the total current requirements for the module is.  Is there an easy
way
> to measure it?  Or, would a better approach be to sum up the current
> requirements of the individual chips?  Do the inputs and outputs have any
> effect on the current consumption?  I have a volt meter, but not an
ammeter.
> 
> It's obviously for a dual-spiraling neural waveform multiplier module.
> (kidding, of course)
> 
> Thanks a ton.
> - Bret
> 
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