How to install a battery voltmeter

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Benny

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Location: Newport, Tn.
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Topic: How to install a battery voltmeter
Posted: 05 Sep 2018 at 9:01pm

Thanks to everyone for the helpful information

Benny

Ben Herman View Drop Down

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Posted: 04 Sep 2018 at 2:44pm

FWIW, I recently installed on of these (see link below). Tapped into the supply lines inside the fuse panel and duct-taped the voltmeter against the inside of the plexiglass panel facing out, so that I can see it without opening the panel front (because of its size, it's turned 90 degrees but still celarly legible).

https://www.amazon.com/gp/product/B00B689UGA/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

GlueGuy

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Posted: 04 Sep 2018 at 9:46am

The critical issue here is whether the battery is under load or not. If the battery is disconnected from the trailer, and rested for an hour, you can get the best value.

However, you need to ask yourself if you have the patience to do it this way. More likely, you are going to measure the battery "in situ", where the voltages will be lower than open circuit.

More sophisticated charge controllers that I have experience with generally have a "LVD" capability, or Low Voltage Disconnect. They are typically set for 11.5 or 11.6 volts, where they will disconnect the battery from the load to prevent damage. The important thing here is that this is under load. And under load is what will be more likely when you're looking at battery voltage.

But Charlie is right. If you have the time and the patience to disconnect the battery, and give it an hour of rest, then 12 volts is as low as you want to see.

If you don't have the time or the patience to "do the procedure", then you can subtract almost a 1/2 volt from what you're looking for.

bp
2017 R-Pod 179 Hood River
2015 Ford F150 SuperCrew 4WD 3.5L Ecoboost

CharlieM

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Posted: 04 Sep 2018 at 12:07am

Exactly. Camp on.

Charlie
Northern Colorado
OLD: 2013 RP-172, 2010 Honda Pilot 3.5L 4WD
PRESENT: 2014 Camplite 21RBS, 2013 Supercharged Tacoma 4L V6 4WD

poston

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Posted: 03 Sep 2018 at 11:18pm

Originally posted by CharlieM

The critical requirement is knowing the voltage right at the battery terminals with no load or charge after a rest period. If you wire to an internal camper circuit you could get a semi-accurate assessment of the battery terminal voltage if all loads in the camper are off.

I appreciate your analysis. If we don't know what the actual measurement is, we can't know if our estimate is usable information.

--
Jim
Virginia City, Nevada
2016 R-pod 180
2015 Nissan Xterra Pro-4X

CharlieM

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Posted: 03 Sep 2018 at 10:40pm

As I said there are ways to work around the internal wiring but it's not easy. The critical requirement is knowing the voltage right at the battery terminals with no load or charge after a rest period. If you wire to an internal camper circuit you could get a semi-accurate assessment of the battery terminal voltage if all loads in the camper are off. The problem with using internal wiring is the voltage drops between the battery and your measurement point will vary depending on what loads are on that circuit and any other loads that are active. If you make sure that all lights, fans, USB chargers, fridge control boards, thermostats, WH controls, antenna boosters, etc are either off or not on your measurement circuit you might get a good approximation. All that said, there is the real world consideration of "government work requirements" Wink

. Sometimes the "government" doesn't require total precision. With experience you can get by with a internal circuit connection. Camp on.

Charlie
Northern Colorado
OLD: 2013 RP-172, 2010 Honda Pilot 3.5L 4WD
PRESENT: 2014 Camplite 21RBS, 2013 Supercharged Tacoma 4L V6 4WD

poston

podders Helping podders - pHp

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Posted: 03 Sep 2018 at 9:47pm

Originally posted by CharlieM

If you want to permanently install a voltmeter it should be wired right to the battery terminals, not to any internal circuit.

For the purposes of us mere users, does it matter what the exact voltage displayed is? isn't the point that we're trying to find the point at which we should quit discharging the battery and charge it?

If we put the voltmeter in a convenient spot, and we note what the display reads when the true measurement at the battery shows 50%, wouldn't that be "good enough for government work"?

For my purposes, that would be good enough. Maybe it's really 40% discharged, or maybe it's 60%, but I'm not trying set a record for battery longevity, I'm just trying to save money with reasonable effort while enjoying my hobby.

--
Jim
Virginia City, Nevada
2016 R-pod 180
2015 Nissan Xterra Pro-4X

CharlieM

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Posted: 03 Sep 2018 at 9:26pm

A lead acid battery is considered 50% discharged when the open terminal voltage is around 12.0 volts after a rest period. 11 volts is totally discharged and damaging to the battery.

The voltage must be measured right at the battery terminals and after the battery has been "at rest" for about an hour. "At rest" means no load or charge but the residual load of approx 150 ma. found in our campers is close enough. If you want to permanently install a voltmeter it should be wired right to the battery terminals, not to any internal circuit. The internal trailer wiring drop will distort the readings. There are ways to get around this but they require knowing exact loads and circuitry. The voltmeter wiring can be 16-20 AWG since the current draw is minimal.

Charlie
Northern Colorado
OLD: 2013 RP-172, 2010 Honda Pilot 3.5L 4WD
PRESENT: 2014 Camplite 21RBS, 2013 Supercharged Tacoma 4L V6 4WD

GlueGuy

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Posted: 03 Sep 2018 at 8:42pm

The battery depletion level is 50%, and most people consider a lead acid battery at 50% when it's somewhere between 11 and 11.5 volts. IDK if the battery wire at the information panel is the actual 12V line from the battery. If it is, that would be an ideal place to put a volt meter. Depending on the meter, you could have it show the actual voltage when you pushed the battery button, or if it is very low current draw, have it display all the time. I think I would opt for the push the button for status mode.

bp
2017 R-Pod 179 Hood River
2015 Ford F150 SuperCrew 4WD 3.5L Ecoboost

Benny

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Location: Newport, Tn.
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Posted: 03 Sep 2018 at 8:00pm

I can't find the posts now, but it seems like I have read that when the battery reaches a certain voltage, it should be charged, as further usage could damage it.

First question is- what is this voltage.

Next, can a digital battery voltmeter be installed on the pantry wall next to the bath where all the other gauges and switches are on a 179?

If so, can the battery wire from the panel with the 4 red lights be tapped into to power the meter?

There are 5 wires, battery, black, gray, fresh water.and I assume the white is the neutral. Not sure which wire is for the battery.

Will this work, or should I run wires from the converter up the left side of the pantry and out of the wall where the other switches are?

Benny