How do I measure total amperage?

[BadAss88GT]

Is there a way I can take my digital multimeter and measure the total draw off the battery of my camper? I'm not real fluent with my tester, this is what I have. Thanks for any help! Dan

[austinado16]

See the area in black where it says DC 10A?  That's where your meter dial would point to.  Then you put your red lead over into the 10A hole that you see there on the left and the black lead stays in the negative hole.

Then you'd disconnect the battery positive cable, and hook the negative lead from your meter to the positive post on the battery.  The positive lead from the meter would then go to the positive battery cable(s) that were hooked to the battery positive post.

Then you'd turn on everything and read the draw of current through the meter.

However......your meter is not set up to read the amount of current your camper could draw with everything that's 12v turned on (including the fridge).  10A isn't very much.  So you could/might damage the meter.

There are other amperage meters available.  Some just clamp around the positive wires at the battery, and then inductively read current draw.  Others, the old school ones, have a trough on the back of the meter and you rest that trough along the wire you are measuring.....and inductively, the meter reads amperage flow.

Hope this answers your question.  If not, print it out and your can wrap fish or line the bird cage with it.

[oreo57]

Well actually, looking at the meter, The green scale is for DC amps to the right ,  but the picture really does'nt show all, is it a clamp on type amp probe or just a VOM.This company makes alot of meters. But Yes Austinado16 is correct, you do want the loop on the hot leg to read amperage draw.

[paspilot]

First take a back of the napkin guess at how much current you're pulling?  What's on?   Light bulbs can take 2A. Just add up what you think you're pulling. If you're greater than 5 or 6A but less than 8A, I would add a 10A fuse in line with the meter- so you don't toast the meter.

Greater than 10A? You can make a shunt. A short length of wire too small to safely carry the current will work for a quick test. You then measure the VOLTAGE drop across the shunt and calculate the current.
http://www.reuk.co.uk/Make-a-Shunt-Resistor.htm
Getting your meter to measure such a small resistance might be an issue. The shunt will warm up, so take the measurement promptly. At 12V this technique works well so long as you don't have mystery resistances from bad connectors.  Where I work, we're doing this a lot lately with a circuit board that takes 100A at 3V. A bit of corrosion on the cable ends is toasting a lot of power supplies. A shunt is out of the question, but the voltage drop and heat on the cable is impressive.

If a shunt seems like too much work, try measuring current at each fuse.  I would guess- but you should do the back of the napkin thing, that most setups have much less than 10A on each fuse. Just set your meter to the 10A setting and wire  to the 10A plug, and put your probes where the fuse ought to be. This has the added benefit of  figuring out what fuse is wired to what.

Have fun,
Carl

[austinado16]

Well actually, looking at the meter, The green scale is for DC amps to the right ,  but the picture really does'nt show all, is it a clamp on type amp probe or just a VOM.This company makes alot of meters. But Yes Austinado16 is correct, you do want the loop on the hot leg to read amperage draw.

Isn't that green zone where you'd messure milli-amps?  Note the mA label down where the red probe is connected in the photo.

[mike4947]

If you just need an immediate draw then I would suggest the clamp on type ammeter in the 50 amp range. To easy to easy to a get a draw that will toast the average 10 amp meter. As in if the converter is charging the battery.
If you wish to continually monitor the draw and check for total used and total charges then permanent monitors like the Link 10/20
or Trimetic will fit the bill. Although a bit more expensive; but very handy for the boondocker who like not to run out of juice in the middle of the night.

[coach]

I like paspilot's approach to measure each circuit via the fuse recepticle, using a VOM like the one shown, then adding them up.

As one who has blown all the fuses in my VOM measuring amps, that 10 or in my case 15A fuse blows quickily (so does the smaller fuse for lower range), expecially hooked up wrong!

I bought something like thisExtech Digital AC/DC Clamp Meter, zero then clamp on wire for reading!

[PattieAM]

Check out Mark Polk's article on RV Converters & Amp Draw (//www.rveducation101.com) as he has great explanations and a great chart of both the 120 volt AC amperage draws and 12-volt DC amperage draws.

You can also find the amperage on the face plates of the various appliances, and if not listed, but wattage is - conversion is Wattage%Volts=Amps.