How do I wire up a volt and ammeter?

[86mud]

I bought one of these the other day so I could measure the amount of amps that my waeco fridge draws.

12V RED LED AMP Dual Digital Volt Meter Gauge Voltmeter Ammeter FOR CAR Motor | eBay (http://www.ebay.com.au/itm/12V-Red-LED-Amp-Dual-Digital-Volt-Meter-Gauge-Voltmeter-Ammeter-for-Car-Motor-/291819193475?hash=item43f1c78483:g:IuQAAOSwtnpXiIp f)

There 3 pins on the back: +ve, -ve and one marked "O". Where does the O get attached to?

Thanks heaps

[PhilipA]

The wiring diagram is on the ebay page further down.
It is interesting that the + is not in line but parallel.
Regards Philip A

[l00kin4]

Just to be crystal clear with that, you need to disconnect the -ve connection from your fridge and connect to the O on the meter.

For ammeter you need the current to flow through it.

David

[AK83]

The O wire seems to connect to the -ve terminal of the DC load you're measuring.

So that if you had some device(eg. a fridge) you'd connect the +ve to the positive as shown, but the -ve(earth) connection of the device(fridge) would wire up to the central(or O) connector on the ammeter.

OOPS! l00kin4 beat me to it: too slow, and too distracted by kids this arvo.

[86mud]

Thanks heaps for the input

Before I posted this thread, I connected my "O" terminal on the meter to the -ve terminal on my distribution block that is connected directly to my 2 x 120amp secondary batteries.

Will this give me a correct reading? I thought this would then show me what the current draw is on all accessories connected to the secondary batteries (80L waeco, water pump and lights)

Thnaks

[l00kin4]

Thanks heaps for the input

Before I posted this thread, I connected my "O" terminal on the meter to the -ve terminal on my distribution block that is connected directly to my 2 x 120amp secondary batteries.

Will this give me a correct reading? I thought this would then show me what the current draw is on all accessories connected to the secondary batteries (80L waeco, water pump and lights)

Thnaks



If you have both the "O" and the -ve on the meter connected to -ve on the batteries, whether via distribution block or not, it won't give you what you want.
To measure the current draw of your fridge you need to have the -ve on the meter connected to your distribution block and the -ve of your fridge connected to the "O" This will have the current for the fridge flowing through the meter. This is what you need to measure current. Same will apply for anything else you want to measure the current draw for.
If you are going to start measuring larger loads you need to be careful not to exceed the 10A rating of the meter and I would say be conservative and stay well below that.
Hope that makes sense.
David

[drivesafe]

Hi Andrew, and first off, there is no such thing as "+ve" or "-ve" in automotive wiring diagrams.

Those symbols are Electronic's Schematic Diagram symbols. +ve mean a voltage above 0v or EARTH, and -ve means a voltage below 0v or EARTH and if your vehicle has any voltages below 0v, you have a major problem.

Next, and PhilipA this will answer query about the all the positive ( + ) being in parallel.

The meter has a SHUNT fitted between the NEGATIVE ( - ) input and the NEGATIVE output ( "O" or the middle terminal ) and the current readings are sourced from this SHUNT, as David posted.

This is known as a Low Side Current Monitor.

Andrew, the diagram is quite straightforward, just follow the wiring setup and you will be fine.

The setup requires the battery positive ( + ) to be connected to the ( + ) terminal on your meter and also to the positive ( + ) terminal on the socket.

The Battery negative ( - ) connects to the ( - ) terminal on the meter.

The Centre terminal on the meter connects to the negative ( - ) terminal on your socket.

Job done.

[86mud]

Thanks all for your advice. Forum is always a great source of knowledge!

[drivesafe]

Hi again Andrew. I should have asked how you intend to use this meter and I don't mean the obvious.

Being an LED display, your meter may draw quite a bit of power just to run the LEDs, and most meters like this have a push-button on them so that the display is only on when you want to read it.

If you have a multi meter, you might want to measure the power consumption of the meter.

If you are driving your vehicle everyday then there should be a problem.

But if you intend leaving it unused for a few days at a time, then you might consider fitting a 10 amp ( or higher ) switch in the positive lead running from the battery to the meter and the fridge, so you can turn it off while not in use.

[86mud]

Thanks Drive safe

I wired up the meter this morning as per the instructions given in this thread.

I'll monitor it for consumption draw during the week as the truck will probably not be used.

With the compressor running, the 80 litre Waeco (set at -7) draws about 2.65A, with the compressor off, runs at 0.05A

Cheers

[drivesafe]

Hi Andrew, the 0.05A is the output current and will only be what your fridge's electronics is drawing while the motor is off.

However, your meter could be drawing a lot more current just to power the LEDs, so you will need to measure the current on the input to the meter.

If you have a multi meter, it will have the ability to measure low amps, and you might be very surprised at how much the meter itself draws, and the meter's own power consumption could flatten your battery in a very short time, like in a couple of days of not using your vehicle.