How to measure mA draw?

Connect to a 12 V source and measure the current. BTW, piezo devices don't draw much.

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The usual connection for current measurement (and 120mA should be fine with your multimeter, as most of them seem to support that much) is to connect your meter in series with the device.

Without the meter, you have two connections like this:

(+) ------ (+)piezo horn(-) ------ (-)

I've labeled the polarity of the horn above and the remaining (+) is the plus side of your 12V battery and the (-) is the other side.

To test the current draw, insert your meter this way:

(+) ------ (+)meter(-) ------ (+)piezo horn(-) ------ (-)

or else this way:

(+) ------ (+)piezo horn(-) ------ (+)meter(-) ------ (-)

And make sure you connect up the leads to the A or ampere connections and set the meter to measure current with the range appropriate for

120mA, at least. (There may be smaller ranges and you don't want to injure the unit, so make sure the range you use supports at least 120mA or more.) Also, verify the meter's polarity as well as the horn's.

Jon

The multimeter needs to be in series with the siren.

One lead of the siren to the positive 12 volt source. The other lead of the siren to one lead of the multimeter. The other lead of the multimeter to the negative 12 volt source.

Make sure the multimeter is set up for measurement of current. If it is digital, it will not matter which multimeter lead (black or red) goes to the negative 12 volt source. With an analog meter, it does matter and it should be the black lead.

When measuring unkown values, it is good practice to begin your measurement at the highest range on the meter, which in this case may be

20 amperes. A piezoelectric siren will probably not show any indication when the meter is on the 20 ampere scale. You can move to more sensitive current ranges until you get a decent reading. The idea is to avoid damaging the meter by passing too much current through it on any particular range.

Chuck

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And never ever ever connect it to a voltage source when in current measuring mode, the meter is basically a short circuit. Just replaced a fuse in my meter yesterday. :-(

Well.... that's right! Though the OP may not know what you mean.

To the OP, Anthony means don't connect your meter, when switched into current measuring mode, directly across the 12V terminals of the battery. Make sure you have your horn or other current limiting load inserted in series with it, as well. That's because without the load added in series, there is very little to otherwise limit the current flowing and the result is that your meter looks about like a wire to the battery and a LOT of current starts to flow, with the result that your meter will either be damaged or else will pop a protective fuse.

If you've ever made the mistake of touching a jumper cable across the two terminals of your car battery, you will be able to understand the result we're talking about here.

Jon

Or ohms modes.

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For some reason that doesn't seem to bother my old Micronta. I'm not sure how they do that though. My first meters sure didn't like you doing that. :-O Usually the application of 120VAC in Ohms mode is what did most of them in.

Hi, AB. If you're concerned about the alarm electrical load, have your burglar alarm drive a small relay. If you put a back-biased diode across the relay coil, you should be able to turn on a relay that can switch several amps with no problem.

Look for a 5V relay with a coil whose resistance is greater than 42 ohms. Here's one from Radio Shack that will do the job:

5VDC/1A SPDT Micro Relay $4.49 USD Model/Catalog #: : 275-240

This relay can switch up to 1 amp.

Cheers Chris

Thanks to all for the great info. I feel confident going forward now.