# I want to be able to read the amps of my solar panels.

#### twister007

Joined Feb 29, 2012
74
I just finished building a 60 amp solar panel voltage controller and I would like to be able to measure the amperage. With the built in volt meter. I can insert a 1 ohm resistor in series but that would waste power and create heat. I have a old 120 v transformer and I was wondering if I removed the winding and passed one output of the voltage controller thru the winding, would I pick up any kind of voltage that would make sense? The controler is pure DC. The volt meter reads down to .01.

Joined Jul 18, 2013
27,002
Use a 0 .1Ω shunt resistor.

#### DickCappels

Joined Aug 21, 2008
9,855
The t transformer only works with AC. If you are using DC, the classic solution it to use a lower value shunt resistor. Instead of 1 ohm you might want to try .01 ohms, or as (I just noticed) 0.1 ohms. I think you get the idea.

#### ElectricSpidey

Joined Dec 2, 2017
2,427
Be sure if you shunt that meter you don't reconnect it as a voltmeter. (Parallel)

Be very sure to reconnect it in series.

Also note, if that meter is an electronic built in meter without an isolated power supply it may not even be possible to rewire as an Ammeter.

Last edited:

Joined Jul 18, 2013
27,002
Be sure if you shunt that meter you don't reconnect it as a voltmeter. (Parallel)
That is the way it is normally done, a volt meter measuring voltage drop across a resistor??

#### ElectricSpidey

Joined Dec 2, 2017
2,427
Yes, but that resistor must be in series with the load, if you just shunt a voltmeter...POOF.

Joined Jul 18, 2013
27,002
I thought that the words "measuring voltage drop across a resistor" imply the indication of a "Shunt Resistor" ?

#### twister007

Joined Feb 29, 2012
74
The t transformer only works with AC. If you are using DC, the classic solution it to use a lower value shunt resistor. Instead of 1 ohm you might want to try .01 ohms, or as (I just noticed) 0.1 ohms. I think you get the idea.
Thanks! A coil around a wire with DC flowing thru it, won't pick up a voltage? How do DC clamp on meters work?

#### twister007

Joined Feb 29, 2012
74
I thought that the words "measuring voltage drop across a resistor" imply the indication of a "Shunt Resistor" ?
This meter is a digital volt meter with an internal resistance of a 100,000 ohms. I can't use a shunt resistor.

#### MisterBill2

Joined Jan 23, 2018
14,677
OK, and if the current that the TS wants to measure is AC, 50 or 60hz, the transformer is avalid concept, but calibration may be a challenge. If the current is DCthen a commercial ammeter shunt is the simple way to go. Not certain what the issue about the high impedance meter is, I have used high resistance digital meters with hundred amp shunts only producing 100 millivolts at 100 amps.
The TS did not provide enough information.

#### MrChips

Joined Oct 2, 2009
28,473
This meter is a digital volt meter with an internal resistance of a 100,000 ohms. I can't use a shunt resistor.
Why not?
Use a 0.1Ω resistor in series between the solar panel and the load.
Measure the voltage across the resistor.
1V reading means 10A current.

#### sghioto

Joined Dec 31, 2017
4,168

#### twister007

Joined Feb 29, 2012
74
Be sure if you shunt that meter you don't reconnect it as a voltmeter. (Parallel)

Be very sure to reconnect it in series.

Also note, if that meter is an electronic built in meter without an isolated power supply it may not even be possible to rewire as an Ammeter.
Thanks, the meter and digital display uses 5 volts from the controller. It a volt meter only.

#### crutschow

Joined Mar 14, 2008
32,031
A coil around a wire with DC flowing thru it, won't pick up a voltage?
Nope.
Only AC current can be picked up that way.
How do DC clamp on meters work?
They typically use a Hall-effect device which generates a voltage in response to a DC magnetic field.

For best accuracy you could use a shunt resistor designed for measuring current such as this 75mV shunt.
It measures 75mV across it with 60A through it (1.25mV per Amp).
You can use any analog or digital DC voltmeter of the appropriate sensitivity to read thus voltage.

You might also consider using a Hall-effect sensor if you want no-contact sensing.

#### twister007

Joined Feb 29, 2012
74
Nope.
Only AC current can be picked up that way.
They typically use a Hall-effect device which generates a voltage in response to a DC magnetic field.

For best accuracy you could use a shunt resistor designed for measuring current such as this 75mV shunt.
It measures 75mV across it with 60A through it (1.25mV per Amp).
You can use any analog or digital DC voltmeter of the appropriate sensitivity to read thus voltage.

You might also consider using a Hall-effect sensor if you want no-contact sensing.
Thanks for saving me a lot of useless experiments! If I made one of the wires from the controller into a coil and put a hall effect sensor in the middle, would that put out a voltage?

#### crutschow

Joined Mar 14, 2008
32,031
If I made one of the wires from the controller into a coil and put a hall effect sensor in the middle, would that put out a voltage?
Depends upon what is going through the wire.

This may also be of interest.
It measures the current, as well as the solar panel voltage and power.

#### twister007

Joined Feb 29, 2012
74
Thanks for the great picture, but I really hate wasting solar power, even a little bit!