Motorhome advice: How to fit a multi-function battery monitor

To fit a multi-function battery monitor, you will need:

• 50A DC Combo Meter kit model DCM-120100C from elite.element on ebay for £17
• Length of four-core cable (or two twin-core cables, like lighting twin flex) of suitable length to run from the leisure battery area to the monitor location
• Mini-trunking to enclose cables where required in the habitation area. I used Wickes 12x8mm white, self-adhesive mini-trunking at £1.59 per 2m length
• Short length of heavy-duty cable (at least 4mm squared) to connect shunt resistor to leisure battery
• 5A automotive fuse and fuse holder (motor spares shop or ebay)
• Cable clips, cable ties, cable terminals, self-tapping screws
• Electric drill and selection of bits
• Multi-tool with fine wood-cutting blade (or jigsaw, or just chain drill a series of holes for the monitor display)
• File and sandpaper
• Pencil, ruler, screwdrivers, wire cutter, pliers, cable crimping tool or soldering iron and solder.

Why fit a multi-function battery monitor to your motorhome?

Many of the locations we stay at in our 2006 Autocruise Starburst motorhome do not have hook-up, so we depend on a good performance from our leisure battery. I have fitted LED lighting and a second 115Ah leisure battery to double the capacity and we have had no problems with battery capacity to date, despite being off-grid for several consecutive days.

We realised it would be useful to be able to monitor the demand on the battery and have an indication of the remaining capacity available. A search on ebay revealed a wide variety of battery monitoring devices and we opted for a multi-function device for £17. This displays voltage, current consumption, charging current, power and remaining battery capacity in amp hours (or as a percentage of full capacity).

These monitors are available for various maximum current ratings from 30A up to 500A. I selected the 50A model as it uses a separate shunt resistor, which can be mounted close to the leisure battery, avoiding the need to run heavy cables to the monitor’s location. A higher-rating monitor would be required if you have any accessories that have very high power demands (such as inverters with high ratings). The 50A model is fine for our motorhome, though, even with the Eberspächer diesel heating system, which draws over 10A on start-up.

The most important step is to plan the location of the monitor and the shunt resistor (to be located near to the leisure battery) and the route for the cables to connect these two units. This wasn’t too difficult on our motorhome as the ideal location for the monitor’s display was above the existing control panel alongside the habitation door.

The wiring connected to the rear of the monitor can also be concealed behind the removable cover inside the overhead locker behind the instrumentation.Also, the leisure batteries are located in the locker under the nearside settee, which is directly below the selected monitor location, thereby keeping the cable run to a minimum. 

Before starting work, disconnect the leisure battery. I recommend double-checking the wiring to ensure that it is in accordance with the supplied wiring diagram before reconnecting the leisure battery. Also check that the monitor is working correctly. Initially, it should be displaying the leisure battery voltage and the current in amps that is being drawn from it.

The V/W button can be pressed repeatedly to display power (W), working hours (H) or voltage (V). The A/AH button can be pressed repeatedly to display the remaining amp hours (AH), remaining battery percentage (%) or Current (A). The Set button is pressed to turn the display off or on.

It is necessary to initialise the unit by setting the rated capacity of the leisure battery. There are instructions provided in the kit for doing this. It’s probably best to set the unit to around 80% of your battery’s specified Amp hour rating to be realistic on what it can actually provide before the battery is fully drained.

The next step is to ensure that the leisure battery is fully charged and then set the remaining amp hours to match the capacity you entered above. Again, full instructions are provided for this. The unit then uses an internal clock to continuously monitor the amp hours used or replaced through charging so that the remaining battery capacity can be displayed at any time.

There is also the facility for calibrating the voltage and current readings if necessary, using another test meter for comparison. I found that very little adjustment was required except for resetting the zero current reading. We’re now looking forward to seeing how it performs and feel confident it’ll prove to be very useful. 

How to fit a multi-function battery monitor to your motorhome or campervan

1 Disconnect the leisure battery before you do anything else. After planning where to site the monitor box, I looked at the kit, which comprises a green connection block, digital display unit, seven-core ribbon cable and a shunt resistor

2 The wiring diagram for the battery monitor – it’s pretty simple to wire. I started by drilling holes for cable access required in the bottom of the overhead locker and the wooden base of the settee

3 A four-core cable is required to run from the shunt resistor location (by the leisure battery) to the monitor display unit. I used two lengths of flat 6A two-core 0.5mm2 cable. I ran the cables vertically in the corner by the settee and enclosed them in white mini-trunking to give a neat finish

4 The next step was to mark out a rectangular hole of around 73mm by 39mm for mounting the monitor display. I drilled a 4mm hole in each corner of the rectangle before carefully cutting this out using a multi-tool with a fine wood cutting blade. If room, you could use a jigsaw or a small hand keyhole saw. Alternatively, a series of small holes could be drilled around the inside of the rectangle to cut this out. I finished the cut-out using files and sandpaper to achieve a neat aperture of the exact size required

5 The cables from the shunt resistor and the leisure battery were then wired to the connection block using the wiring diagram supplied. NB: If using two identical two-core cables, ensure that you identify which one is for the shunt resistor and which is for the 12V supply from the battery as it will damage the monitor if these are wrong!

6 I then mounted the connection block alongside the rear of the monitor display and connected these together with the short seven-core ribbon cable supplied

7 The shunt resistor was mounted to the side of the battery compartment using self-tapping screws and wired into the negative lead from the battery so that all battery current passes through it (fairly heavy-duty cable of at least 4mm2 is needed). The existing cables from the negative battery terminal were disconnected and reattached to one end of the shunt using a crimped terminal connector. The other end of the shunt was connected to the battery negative terminal. Finally, I connected the four cables from the monitor to the shunt and the leisure battery. The first twin cable wire goes to the shunt resistor (one wire to each end, noting polarity), while the second twin cable is connected to the leisure battery (one to negative, one to positive via a 5A fuse)

8 After reconnecting the batteries, the monitor display showed that the battery voltage was 12.59V and supplying a current of 0.30A

9 When the mains charger was active, the display shows that the battery voltage was 13.15V and was charging at a rate of 4.16A

10 After it had been charged for a while we could see from the display that the battery voltage had risen to 12.81V and had 95.7% of its capacity remaining.

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