View Full Version : Looking for Ammeter

SteveRich

10-25-2008, 06:09 PM

I am looking for an inexpensive source for an 0-75 AMP ammeter

I understand there are 2 types and "shunt" type and a "CT"( current transformer) type. I perfer the CT type either analog or digital but small and cheap is necessary.

I have a clamp on for testing by I'd like to install one in my car to moitor the operation of my dry cell.

Thanks, Steve

BoyntonStu

10-25-2008, 08:15 PM

I am looking for an inexpensive source for an 0-75 AMP ammeter

I understand there are 2 types and "shunt" type and a "CT"( current transformer) type. I perfer the CT type either analog or digital but small and cheap is necessary.

I have a clamp on for testing by I'd like to install one in my car to moitor the operation of my dry cell.

Thanks, Steve

My digital "Ammeter" cost $3.50

Go to Harbor Freight and but their cheapest multimeter.

Next, go to Home Depot or Lowes and buy 1 foot of #10 solid copper wire.

Cut the test probes off the meter and replace them with alligator clips.

Run the current to your cell through the #10 wire.

Use the alligator clips to connect to the wire itself 12" apart (not to any other connection point or the reading will be false).

Turn on your meter to the 200 mV scale.

Your meter will read current directly.

IOW If your meter reads 7 mV the current is 7 Amps. +- 3%

I hope that this helps.

BoyntonStu

P.S. If I get the chance, I will upload a photo of my setup.

I use 2 multimeters, one for Volts and the other for Amps.

$6.00 is cheap enough for a pair of dedicated digital built-in meters.

SteveRich

10-25-2008, 10:21 PM

Thanks,

This is a terrific idea. As is mentioned I'm looking for 0-75 Amps. I wonder if th "Shunt" of 12 inches of 10 gage wire will handle it(75 amps). Maybe I could find a CT of the right size to do the same thing with a current transformer.

Steve

BoyntonStu

10-25-2008, 11:15 PM

Thanks,

This is a terrific idea. As is mentioned I'm looking for 0-75 Amps. I wonder if th "Shunt" of 12 inches of 10 gage wire will handle it(75 amps). Maybe I could find a CT of the right size to do the same thing with a current transformer.

Steve

Steve,

#10 wire is very convenient to calibrate because it has a resistance of 0.001 ohm per foot and therefore 0.001 Volt means 1 Amp.

This is a simple solution to safely increase the shunt capability.

Use N #10 wires in parallel and measure only one wire; multiply the reading by N.

BoyntonStu

PS If you passed 100 Amps through a single #10 wire the power dissipated would be (I^2 x R) 100 x 100 x .001 or only 10 Watts. A little heat, but not much. A night light is typically 7.5 Watts.

If you have ever seen a 10 Watt resistor, its leads were way smaller than #10 wire.

IronBear

10-27-2008, 12:55 PM

You mostly find Romex in 12 gauge spec, but if you are lucky you might find some scrap Romex cable that is 10 gauge grade.

That will cover you cheaply.

HHO King

01-26-2009, 09:34 PM

Here's a 0-100 amp digital gauge. http://www.extremehho.com

I have also used the cheap square ones on ebay and found them to be accurate.

cully

01-27-2009, 03:45 AM

i think you will find the "CT" as in Current Transformer only works on AC

I am looking for an inexpensive source for an 0-75 AMP ammeter

I understand there are 2 types and "shunt" type and a "CT"( current transformer) type. I perfer the CT type either analog or digital but small and cheap is necessary.

I have a clamp on for testing by I'd like to install one in my car to moitor the operation of my dry cell.

Thanks, Steve