Camper Trailers Tech Tips

Watt's Up Meter




watt's up

Watt's Up power meter

A Watt's Up is a portable meter that measures current, voltage & time. From those measurements it calculates peak current in Amps, peak power in Watts, minimum voltage in Volts, power in Watts, energy in Watt hours and charge in Amp hours. For a camper trailer owner it is a handy device to connect inline as an instant readout to the power usage of different 12volt appliances & accessories or the state of charge of your battery at rest. 

It is especially useful to measure the power consumption of your 12volt fridge over time, say for a 24 hour period, as the fridge cycles on & off to maintain a set temperature. The Watt's Up can also be used to monitor the output of your solar panel over the course of a day.

The Watt's Up meter will handle 50 Amps continuously & up to 100 Amps peak at 60 Volts, so is well suited for a number of tasks around the camper trailer & vehicle.



top left displays Amps  

 top right displays Volts

bottom left five data logs  

 bottom right displays Watts

the display

After startup there are three values continuously displayed on the screen showing instant readouts -
Amps displayed on the top left
Volts displayed on the top right 
Watts displayed on the bottom right

The bottom left of the panel has five data logs shown in sequence every two second which will be recorded until the Watt's Up is removed. They include Ah, Wh, Ap, Vm & Wp. This data is not saved when the Watt's Up is disconnected from the power source.
Ah displays the total charge in Amp hours delivered to the load since power was applied to the Watt's Up. It is measured on the load side.
Wh displays the total energy delivered to the load in Watt hours since power was applied to the Watt's Up meter. This is measured on the load side.
Ap displays peak Amps as the maximum current drawn on the load side.
Vm displays the minimum voltage or “droop” measured on the source side.
Wp displays Peak Watts as the maximum power drawn on the load side.

setting it up

My Watt's Up meter sits on a small jiffy box with some double sided tape. The jiffy box measures 130 x 68 x 44mm - Jaycar catalogue number HB6013. I then fitted an Anderson & fused 15amp Narva cigarette plug on the source end & an Anderson & cigarette socket on the load end as these are the only connections we use. Each wire of the Watt's Up connects to two other wires, one off the cigarette fitting & one off the Anderson, safely secured using single screw insulated connectors. If we used T plugs or Hella/Merit plugs & sockets I could of incorporated these into the jiffy box as well.

source wiring diagram load

The source end goes towards where the power is. For example towards the battery if you are measuring an accessory or towards a solar panel if you are measuring the solar input to the battery. In other words this is the in end.

The load end goes towards the accessory you are measuring or towards the battery if you are measuring the solar input to the battery. 

As the positive post of the cigarette plug is 12volt live when the Anderson is connected, I found amongst my "handy bits & pieces that might come in handy one day tin' a tent pole end cap that fits perfectly. This will save the internal fuse of the plug blowing if the positive post accidently earths.

cigarette plug cap state of charge chart screw insulated connector

uses for the watt's up

A few ideas for uses of the Watt's Up meter around the vehicle & camper.

battery state of charge

The state of charge of a camper's 12volt battery can measured by connecting the cigarette lighter plug or Anderson from the source end of the Watt's Up meter to the battery & reading the Amps.

The best time to do this is when the battery has been at rest for at least a couple of hours or more with no load or charge. The voltage readout will show the percentage of the battery capacity via the chart above.


battery state of charge



alternator charge

You can check the vehicle's alternator output in Amps by plugging the Watt's Up source end into the Anderson at your towbar when the motor is running.

Plugging it in before starting the vehicle of a morning will show the state of charge of the battery.

  alternator charge

solar panel output

Plug the Watt's Up source end into the Anderson from the solar panel & then the load end into the Anderson to the battery. You will get an instant readout of what the panel is producing in Amps, Volts & Watts.

Alternately you can leave it there to see what the total is at the end of the day via the readout of the five data logs. Don't forget to write down this data as it will disappear when the Watt's Up meter is disconnected.

  solar input

fridge power consumption

To gain a better understanding to the power consumption of our Engel fridge, I connected the Watt's Up source end to the cigarette socket on the camper & the fridge's plug into the load socket in the jiffy box. I can see instantly what the fridge is drawing via the three continuous readouts of Amps, Volts & Watts.

Leaving the Watt's Up in place for 24 hours will show what the fridge draws over that time cycling at a particular setting via the five data logs. Before removing the meter you need to write down the values, as these values will disappear once the Watt's Up is disconnected. 

  fridge instant readout

more reading

Watt's Up user manual watts_up_manual.pdf
Watt's Up simulator


Article by Rob



march 2013