Help for static power consumption measurement

Hi all, I have to determine the power consumption on a device in different states. I would like to have your inputs about the procedure I have thought:

- Hardcoded the device in a specific mode

- Measure the voltage drop (Vdrop) across a series resistance (Rtest) at batteries output (1.0 or 0.1 Ohm, I'm not sure what is best ???) (Do I must considered cable resistance used to measure??? N.B. I use a HP3456A 6 1/2 digits voltmeters)

- Knowing the batterie voltage (Vbatt), the power drain from batteries is Pstate = Vbatt * Vdrop / Rtest

- Since I use a boost converter to raise the 1.5V from the 2 AA batteries to 3V (voltage at which all the device components works), the current drain by these components is approximatly 2 times less (if I forget the switcher efficiency)?

Don't hesitate if you see major problem and/or have different methode to propose! Thanks in advance for all your input! Fred

Reply to
frb78
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A small series resistor is fine for low power devices - but you need a decent idea of the current drain profile under all circumstances.

A device that may draw 50mA statically may draw 2-3 (or more) amps on startup depending on circuitry - and the power system must still provide sufficient voltage. A series resistor of 1 ohm would be a liability in that case.

I would suggest iterating the sense resistor (which is as good a solution as any for a lab using 6 1/2 digit meters), starting with 0.1 ohm and watching the start transient. Note you have to watch out for the power rating so your sense resistor doesn't burn (or worse, burn

*you*)

Obviously, the largest resistor that does not interfere with the power, the better the measurement (within reason :).

There are other solutions, including magnetically coupled clamps (which are non-inavasive), but they tend to be expensive and often have to be pre-calibrated.

Cheers

PeteS

Reply to
PeteS

But 2AAs in series have already 3V, (when 90% discharged 2V). That will probably be enough to run your device. Is it a PIC? What resistor you use is dependent on the current, for less than 100mA I would take 1R, above 0.1R with fresh batteries or better a bench supply it should be possible to determine the supply current.

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ciao Ban
Bordighera, Italy
Reply to
Ban

In California, it's usually Volts times Amps.

(1) Ask the teacher what the f*ck he's asking for, or (2) Read that chapter of the textbook again.

You Betcha! ;-P

--
The Pig Bladder from Uranus
Reply to
Pig Bladder

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