I wanted to install a digital LCD volt meter with LED backlight display that I bought off amazon. I'm familiar and comfortable with 12V electrical and I have decided to just tie into a 12V connection from behind the existing control center (where the tank/battery gauges are, water pump switch, water heater switch, etc.). I'm going to mount the volt meter above the control center. While the LED backlight would draw very little juice, I figured I'd want a way to switch it off to avoid any unnecessary parasitic loads. My plan is to wire up a switch that will turn the volt meter display on and off. I snooped around with my multimeter and there are many different wires carrying the 12V signal to choose from. My plan was to pick a favorite and tie the switch into it, then hook the meter to the switch. Anyone have any comments or suggestions for my idea? Thanks.

It will be a lot better than the standard idiot lights.

What you suggest would generally work fine and be simple enough. You would be measuring the voltage at your control center, which may not be exactly the voltage at the battery.If your voltmeter has separate power and sense lines, you can get a more accurate reading of the battery voltage by connecting the sense lines directly to the battery connections (with an appropriate small fuse in the positive line) and just switching the power line on and off for the meter. The meter itself doesn't use much power at so circuit capacity for powering it shouldn't be a big concern.The sense lines don't need to be heavy wire from an electrical point of view; they don't carry any appreciable current at all, only a few microamps. They should, of course, be heavy enough to be avoid breaking mechanically.

I would leave the backlight on. Probably just a couple milliamps and far less than even the propane detector. Consider mounting out of the way so it does not stare at you when watching tv or trying to sleep etc. Can always add a momentary button switch later.

I recognize that I'd be measuring the voltage at the control center versus actual voltage across the battery posts. But I'm ok with that discrepancy. The amazon seller says the LED backlight draws 9 milliamps. That is practically nothing. I'll ponder the switch.... It is always something I can add later.Thanks for the input so for everyone.

DrewE wrote:What you suggest would generally work fine and be simple enough. You would be measuring the voltage at your control center, which may not be exactly the voltage at the battery... To OP, I installed a volt meter I bought off Amazon, in the very rear of my 28 1/2' TT, 30 feet from my two batteries. I tapped a small always hot wire inside the hood of the stove and mounted the volt meter in the kitchen. I then tested the voltage at the batteries with a handheld volt meter, and I got the exact same reading, to two decimal points, as my meter in the rear of the coach was displaying! Accurate to the hundreth is close enough for me! So personally, I would not worry at all about where you pick up 12V in your RV for the meter. My volt meter is on 24/7, not switched, but it's an LED, so I don't worry about the very minor parasitic draw.

I want to install a 12V digital volt meter | Good Sam Community

CA_Traveler
Explorer III
Jan 26, 2015
It will be a lot better than the standard idiot lights.
DrewE
Explorer II
Jan 26, 2015
What you suggest would generally work fine and be simple enough. You would be measuring the voltage at your control center, which may not be exactly the voltage at the battery.

If your voltmeter has separate power and sense lines, you can get a more accurate reading of the battery voltage by connecting the sense lines directly to the battery connections (with an appropriate small fuse in the positive line) and just switching the power line on and off for the meter. The meter itself doesn't use much power at so circuit capacity for powering it shouldn't be a big concern.

The sense lines don't need to be heavy wire from an electrical point of view; they don't carry any appreciable current at all, only a few microamps. They should, of course, be heavy enough to be avoid breaking mechanically.
time2roll
Nomad
Jan 26, 2015
I would leave the backlight on. Probably just a couple milliamps and far less than even the propane detector. Consider mounting out of the way so it does not stare at you when watching tv or trying to sleep etc. Can always add a momentary button switch later.
ewarnerusa
Nomad
Jan 26, 2015
I recognize that I'd be measuring the voltage at the control center versus actual voltage across the battery posts. But I'm ok with that discrepancy.

The amazon seller says the LED backlight draws 9 milliamps. That is practically nothing. I'll ponder the switch.... It is always something I can add later.

Thanks for the input so for everyone.
crcr
Explorer
Jan 26, 2015
DrewE wrote:
What you suggest would generally work fine and be simple enough. You would be measuring the voltage at your control center, which may not be exactly the voltage at the battery...

To OP, I installed a volt meter I bought off Amazon, in the very rear of my 28 1/2' TT, 30 feet from my two batteries. I tapped a small always hot wire inside the hood of the stove and mounted the volt meter in the kitchen. I then tested the voltage at the batteries with a handheld volt meter, and I got the exact same reading, to two decimal points, as my meter in the rear of the coach was displaying! Accurate to the hundreth is close enough for me!

So personally, I would not worry at all about where you pick up 12V in your RV for the meter. My volt meter is on 24/7, not switched, but it's an LED, so I don't worry about the very minor parasitic draw.
RoyB
Explorer II
Jan 26, 2015
Hey Ed - I made up a three digital meter battery bank monitor panel for my off-road popup setup and believe me when I say I had a very bright 'night' light... Lit up the whole area... I used one of those three gang specialty switch assy (Lowes) and routed my wiring to the main battery switch using PVC flexible conduit...

I had to install a ON-OFF small toggle switch for each panel...

Roy Ken
tenbear
Explorer
Jan 27, 2015
When I installed a voltmeter I used a SPDT switch to switch the meter to read either the battery voltage or the converter voltage. The switch has a center off position.

For the converter voltage I chose to tap into the wire to the propane detector. It draws a constant low current and is on a fuse with nothing else. For the battery voltage I went directly to the battery.

There is definitely a difference between the two, especially when the converter is in boost mode and the battery is low.
64thunderbolt
Explorer II
Jan 27, 2015
had a friend cut the stainless faceplate and the momentay switch and Vmeter frem ebay. Total cost was less than $12.
audio1der
Explorer
Jan 27, 2015
Momentary switch is what I would do as well. Then you have draw only when you want to check the voltage and minimize your parasitic draw.
Alternatively, a battery disconnect switch may not be a bad idea for when in storage or between trips.
tenbear
Explorer
Jan 27, 2015
audio1der wrote:
Momentary switch is what I would do as well. Then you have draw only when you want to check the voltage and minimize your parasitic draw.
Alternatively, a battery disconnect switch may not be a bad idea for when in storage or between trips.

I originally had a momentary switch on my voltmeter but I replaced it. I didn't like holding the switch on when I wanted to watch the meter.

The parasitic drain of the meter is very low. If you don't want to watch the meter, just turn it off.