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

Bob_Vaughn
Explorer
Feb 01, 2015
The things I have bought on evil bay and amazon turned out to be a 6 to 8 week wait go get it....I think not....
DrewE
Explorer II
Jan 31, 2015
tenbear wrote:
I don't think an analog voltmeter is what you want for battery monitoring. You are really looking for voltage changes in the 12.0 to 14v range. A tenth of a volt is important. That may be hard to see on an analog meter.

I know some people use them but IMHO, a digital meter is better for this task.

If you want an analog meter, you can always hook up a 5V meter in series with a 10V zener diode or some more sophisticated voltage reference and create a 10-15V analog meter to get better precision in the readings. The meter scale would have to be recalibrated and redrawn, of course.
tenbear
Explorer
Jan 31, 2015
I don't think an analog voltmeter is what you want for battery monitoring. You are really looking for voltage changes in the 12.0 to 14v range. A tenth of a volt is important. That may be hard to see on an analog meter.

I know some people use them but IMHO, a digital meter is better for this task.
Bob_Vaughn
Explorer
Jan 31, 2015
I have an analog volt meter which I do not think would hold up to the vibration of going down the road in our rv....
teddyu
Explorer
Jan 31, 2015
I installed a self-powered voltmeter (under $5) that monitors the auxiliary (coach) battery buss. It’s mounted in the dashboard above the Generator run-hour meter and is connected to an auxiliary (coach) battery terminal on the BCC battery isolator solenoid through a 1A fuse. This allows for continuous monitoring while driving.

By monitoring the auxiliary battery buss:
One, with the engine and shore power/generator OFF – I know the charge condition of the coach batteries. Two, with the engine ON – I know the charge condition of the coach/chassis batteries, the functionally of the BIRD, and the output of the engine alternator. And three, with shore power/generator ON – I know the charge condition of the coach/chassis batteries, functionally of the BIRD, and output of power converter.

I bought (from Jennyear on eBay) a self-powered Green 3~30V (12V) Mini Digital DC LED Battery Voltmeter and bezels (items 130875885643 & 140940500425).
tenbear
Explorer
Jan 31, 2015
Bob Vaughn wrote:
Apparently Radio Shack does not sell this type of digital display. I am not a big fan of buying things on line because if it has to be sent back then the advantage is gone. Plus many times the shipping to my home is more than cost of the item then if it has to be returned that makes the cost more than driving to a local store and pick up an item....

You can buy a digital voltmeter on eBay for under $5.

I have had good luck doing this, but if it is not as you expected I have been able to get a new one without returning the old one. Just buy from sellers with good ratings and don't rate the seller until you are satisfied.

At that price you can just throw it away if all else fails.
Bob_Vaughn
Explorer
Jan 31, 2015
Apparently Radio Shack does not sell this type of digital display. I am not a big fan of buying things on line because if it has to be sent back then the advantage is gone. Plus many times the shipping to my home is more than cost of the item then if it has to be returned that makes the cost more than driving to a local store and pick up an item....
ewarnerusa
Nomad
Jan 28, 2015
Fixed Sight Training wrote:
I used a voltmeter that just plugged into the 12 v cigarette lighter. It was pretty accurate when checked with my multi meter. No drilling or wiring and I can pull it out and check other RVs or cars with it.

I have one of those and I also like it. I have decided to go down a different route for a couple reasons. (1) I already have this voltmeter that has been sitting in the tool box for a year or so and I'm motivated to install it. I think it will be more "pro" looking. (2) The 12V outlet that I've used for the plug-in voltmeter is on the same circuit as the propane detector and radio. This winter I decided to pull that fuse to reduce the parasitic draws while the TT is parked in the driveway for the winter. I have found that when my solar panels get buried under the snow, my battery voltage starts to fall behind after a few days and I'll have to plug the TT in and let the converter charge them back up to 100%. This winter I pulled that fuse and notice an improvement in maintaining battery voltage during this scenario. But to check the voltage I have that plug in meter in a different 12V outlet that is less convenient to check. It is in my pass-through storage area where my solar controller and inverter are installed. So this motivated me to come up with something better and leads back to my reason (1)! :)

As an update, I wired up the voltmeter last night to verify that I get a good 12V reading. I picked some "favorite" wire nut junctions that I confirmed with my multimeter will give me an always-hot 12V reading and wired the voltmeter directly to them. I was initially disappointed because the voltmeter consistently read 0.2V lower than what my multimeter read. My other plug-in voltmeter at the other location confirmed the multimeter reading. I went back to the amazon listing for the voltmeter and read in the reviews that the reading can be calibrated by turning a potentiometer on the rear of the unit. I confirmed that this is the case and I adjusted to voltage reading so it was the same as the multimeter reading. I'll update again when the project is finished.
Fixed_Sight_Tra
Explorer
Jan 28, 2015
I used a voltmeter that just plugged into the 12 v cigarette lighter. It was pretty accurate when checked with my multi meter. No drilling or wiring and I can pull it out and check other RVs or cars with it.
Jack_Kay
Explorer
Jan 28, 2015
I installed a 12v meter under our dinnet and tied it into the power plug. I didn't have a need for a switch as I rarely dry camp.