Power consumption

[Dr.EM]

How would you work out the power consumption of a device? I have designed/built a distortion effect using transistors, but i am worried about how much battery power it may eat :shock: . You see, I have very little idea what I was doing, I just changed components here and there until it sounded good!

I don't know if this is a good sign, but theres a 220mfd cap accross the power rails (9v single) and when you power off the circuit, it can run off of its reserve for a few seconds?

Sorry for the vague post, but I don't know too much about whats going in in there, nothing gets hot though, so I suppose thats good :lol: I could post a schematic, but i'd have to get it onto this computer first...

 

[JimB]

Use your multi-meter to measure the current.

You do have a multi-meter? Dont you?

JimB

 

[Dr.EM]

Oh dear :lol: , they're on the "to buy" list now though honestly! Also need wire strippers...
Thanks anyway, I will do when I get one. Can they all measure current then?

 

[JimB]

Most meters will measure DC volts, AC Volts, DC Current and resistance.
Some will also measure AC Current, but not all.

Then there are the "nice to have" features such as Continuity (a buzzer), Frequency, Diode Test (most resistance ranges wont "turn on" a diode), Hfe (transistor gain), Temperature (with a thermocouple probe).

Read the specifications BEFORE you buy, decide how much you can afford to spend, generally, but not always, the more expensive the meter, the better it is.

JimB

 

[stevez]

You could roughly estimate the amount of power drawn with the information you provided - you said the 220 mfd cap runs it for a few seconds. Capacitor tolerance is likely to be poor but call it 220 mfd. Time the amount of time it runs with a stop watch - that by itself will be crude as well. What you won't know is how far down the discharge curve you'll be when the circuit quits. Assume that 1/3 of the charge is left - or just assume it's all used up. Do the math and you'll have something that represents the order of magnitude. It won't be particularly accurate but it's a place to start. Then when you get your multimeter you can perform more accurate measurements.

You could also see how long it takes to wear out a battery. I don't know how variable battery life can be - as compared to published mah ratings but as with the capacitor method, it will at least define the order of magnitude.

You can get some multimeters for very little money ($10 US, or even less). As has already been stated, you get what you pay for - but a low cost one is better than nothing. From my experience the low cost meters work reasonably well - they just fail mechanically from use or the slightest abuse.