How do I measure voltage drop?

[tsenfw 10+ year member]

Ok, this is going to sound stupid but, how do I measure voltage drop correctly?

DMM at the battery or amp? What is the EXACT procedure? I know it sounds elementary but I would like to be sure before attempting again. I don't want to fry my DMM or die.

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[IgnoreMe 5,000+ posts]

Ok, this is going to sound stupid but, how do I measure voltage drop correctly?
DMM at the battery or amp? What is the EXACT procedure? I know it sounds elementary but I would like to be sure before attempting again. I don't want to fry my DMM or die.

lol, you wont die.

just put one lead in the ground and one lead in the power terminals on your amplifier. and set your dmm to read DC voltage (a V with a - - above it). play a test tone, or a song that has a steady bassline. and read the voltage. tone/bass has to be long enough for your dmm to actually read and give you a figure (usually takes about half a second to 1 second, which is why a song with drums wont really work because its to quick for the dmm)

this isnt really a voltage drop test, but this is how you test what kind of voltage is going to your amp. voltage drop tests are usually done between two points, and used for diagnosis (for example, you want to check what kind of voltage drop you get between your battery terminal and your battery post. 1 terminal on the battery post, 1 on the terminal, crank the engine, and read the drop)

 

[scottiej 10+ year member]

If you're testing the 12v input voltage, you will need to use DCV not ACV.

 

[IgnoreMe 5,000+ posts]

If you're testing the 12v input voltage, you will need to use DCV not ACV.

lol, what the **** did i put that for.

yes scottiej is right. you need to read Dc voltage //content.invisioncic.com/y282845/emoticons/banghead.gif.8606515f668c74f6de0281deb475b6fd.gif

post edited.

 

[tsenfw 10+ year member]

lol, you wont die.

You'd be surprised, car batteries are pretty dangerous.

Thanks for all the advice. So let me make sure I have this right.

1.) I can just put the probes on the amp power and ground input terminals to see what voltage is going to the amp.

2.) To measure the voltage drop I can put the probes on the battery positive and negative, note the voltage. Then turn on the car and measure the same thing for the drop? (Does this result from the draw from the amp?)

This is all done on the DC voltage setting correct?

 

[n2audio 5,000+ posts]

You'd be surprised, car batteries are pretty dangerous.

500A would kill you in an instant, but at a couple million ohms you'll only see a few millionths of an amp

you have a better chance of being hurt by the acid than by electrical forces

 

[helotaxi 5,000+ posts]

The hazard won't be to you directly getting electrocuted. The hazard lies in the possibility of the battery or whatever you short it out with going thermal. If you disconnect the ground wire from the battery before doing any wiring work, the risk is reduced to almost zero. No danger when using a DMM.

 

[IgnoreMe 5,000+ posts]

You'd be surprised, car batteries are pretty dangerous.
Thanks for all the advice. So let me make sure I have this right.

1.) I can just put the probes on the amp power and ground input terminals to see what voltage is going to the amp.

2.) To measure the voltage drop I can put the probes on the battery positive and negative, note the voltage. Then turn on the car and measure the same thing for the drop? (Does this result from the draw from the amp?)

This is all done on the DC voltage setting correct?

batteries arent dangerous.current is a dangerous thing, but with the amount of resistance you have in the body, you can touch both the negative and pos. of the battery and hold them and be fine. at 12V with a resistance of 2 million ohms you are looking at .000006 amps.

now if you are disconnecting wires here and there, then yes the battery starts to get dangerous, and as helotaxi pointed out, disconnecting the ground will almost guarantee your safety. but the beautiful thing about voltage is, that you hook up in parallel to it, not series, which means you never even have to disconnect anything, just probe.

now here's my question, what voltage drop are you trying to read?

1) what your voltage is when you are playing bass heavy material?

- play a track thats bass heavy that has consistent bass lines, probe the +/- terminals and read your voltage when it holds steady. then compare to what it was reading before anything started playing.

2) if you are dropping voltage somewhere on the power line?

a) same method, but no music. get a reading from the battery, then get a reading at the amp, and subtract to see your voltage drop

or

b) if you have alligator clips and some speaker wire, one probe on positive teminal on amp, then 1 probe attached to some wire, and then the wire ran to the positive terminal on the battery. the value is your voltage drop.

but yes, everything is measured in DC, the only thing thats measured in AC voltage is the outputs on the amplifier (speaker terminals)

 

[btdickey99 5,000+ posts]

If you're testing the 12v input voltage, you will need to use DCV not ACV.

or just simply use a voltage drop tester!!!!//content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[btdickey99 5,000+ posts]

hey, with a ruler.

 

[IgnoreMe 5,000+ posts]

nvm, i see. its a joke.