Battery Voltage Monitor

Just as an adder: That great little digital voltmeter link I gave the link to above earlier - besides being ultra-reliable for the last 5-6 years and inexpensive - did not get neatly built into a panel in the coach on purpose.

I just Velcro'd it to the dash and routed it's long lead back to a 12V receptable in the coach area that was the closest to the cab dash.

I did this so that I was just monitoring voltage on the coach battery terminals ... but for convenient and good-enough simultaneous monitoring of the voltage of both 1), the coach batteries while driving or camped and 2), the RV's 12V system while driving or camped (bearing in mind that this monitored voltage could at times read a bit low versus actual coach battery terminal voltage whenever 12V items in the motorhome were being powered and hence dropping the voltage along the line leading to the coach 12V receptacle where the voltmeter was plugged in).

The most important parts of the 2) reason were: To keep an eye on the main engine alternator's voltage indirectly by watching what was winding up on the RV's 12V system with the engine running, to keep on eye on the condition of the contacts in the inter-connect solenoid between the alternator and the coach batteries, and to keep an eye on whether or not I had turned the coach battery switch back "ON' after refueling the motorhome so that the refrigerator would continue to work while traveling.

So far this dash mounted voltmeter has saved our bacon once ... by indicating why the coach batteries were not getting charged between campsites due to a bad solenoid with corroded/oxidated contacts, and saved our bacon many times ... by indicating that the refrigerator was not working while traveling because the coach batteries had not been reconnected to the coach system after refueling.

Inside i monitor both of my 50A legs with AC Volt & Amp panel meters (similar to others).
I was using a "plug-in" DC volt meter - but changed it to a smaller "panel" meter.



OUTSIDE at my entertainment center i monitor the AC Voltage & DC voltage

Wayne Dohnal wrote:
When charging from a generator it lets you know when it's time to shut the genny off. Somebody with experience can figure this out with the voltmeter/ammeter combo, it's just more work and less accurate.

When charging from solar, voltage is indeed of little practical use, as I've noticed. It varies with load and the charger is adjusting it as temperature changes. Can't say about charging from generator - there hasn't been much need so far - but it should be similar, i.e. very rough way of measuring.

The only time one can estimate the battery SOC by looking at the volt meter, is in absence of loads and charging, and after 20-24 hours rest following the charging.

I use a battery monitor. It provides a voltmeter and ammeter, which many add to their RV with basic low cost meters. What the monitor provides over and above volts and amps is tracking of the approximate number of amp hours that go into and out of the battery. When boondocking, it lets you know how much battery power you've used up. With this info you know whether it safe to continue the consumption rate of if you need to conserve. When charging from a generator it lets you know when it's time to shut the genny off. Somebody with experience can figure this out with the voltmeter/ammeter combo, it's just more work and less accurate. When plugged into shore power a voltmeter is probably all you really need.

Hoped to learn something new about battery monitors here, or whether I even need one ;)...
No such luck, no monitors in the thread...

smkettner wrote:
If the meter says 12.3 or less by all means start the generator.
That covers 12.11 showing 12.2 volts.

Once generator is started let voltage climb over 14 and run one additional hour. Or just run it 2 to 3 hours. That will get you through the night.

Or if you really want a 100% charge run the generator all night because that is how long it takes.

Does it matter if you are 87% or 92% charged? If it does maybe more battery is needed.

Understood. I was thinking in terms of the abs voltage being steady, as in c.v./abs mode. Perhaps your charger has rising voltage throughout the charge? Or perhaps you're referring to rising volts during boost, and then one hour of abs?

This is the weird thing going on with my pm4b... steadily rising voltage, up to the abs set-point, until near full charge, all while amps are tapering... Not exactly the typical 3-stage charging algorithm. What stinks is it's doing a real number on the charge rate because of the lower, slowly rising voltages.

If the meter says 12.3 or less by all means start the generator.
That covers 12.11 showing 12.2 volts.

Once generator is started let voltage climb over 14 and run one additional hour. Or just run it 2 to 3 hours. That will get you through the night.

Or if you really want a 100% charge run the generator all night because that is how long it takes.

Does it matter if you are 87% or 92% charged? If it does maybe more battery is needed.

smkettner wrote:

"The charging source is a fixed voltage. Nothing I do will change that known set point. If I see the battery within .1 of the known voltage I would charge one additional hour and be done"

But how does one 'see' that the battery is within .1v while charging? The remote meter would only display the charging voltage, not the battery's voltage until it was fully charged and no line drop. I'm at a loss as to how you accomplish such a task with a remote meter?

And besides, I am talking about the ability of a remote voltmeter to give an accurate indication of battery S.O.C., which it simply cannot due if it only displays to the 10th of a volt. If the bank is at 12.11v, but the meter says 12.2, this could represent dozens of Ah's needing to be replaced. But for the same time and money, one can install a two decimal place meter and have a much more informed idea of soc. In this case, more data is indeed more information.

pnichols... words mean things...

'digits' are numerical symbols, i.e; numbers

'place' refers to positional notation, i.e; where the decimal is

hence, a four 'digit' meter suggests it simply shows four numbers, whereas a four 'place' meter suggests a reading to within a ten thousandth, i.e; a display range to within the fourth decimal place.

The link you posted shows a four 'digit', 2 'place' meter.

And yes, tens and hundreds are also "places", to the left of the decimal, but to determine the range and usefulness of a voltage meter, it is necessary to make such a distinction. To market a meter as being accurate to the fourth place, would be misleading, in terms of its range of display, seeing as "to the fourth place" is generally understood, within the language of math, to mean "to the fourth decimal place".

That said, I do understand you said "four place", not "fourth place", but in my mind, I reflexly made the distinction between place and digit.

Hope this clarifies things.

jrnymn7 wrote:

smkettner wrote:
I just want to see voltage above 14 at some point in the day. 14.1 or 14.111 does not matter to me.

Even if I had a generator with me I don't see the need for more than one digit.

I'm sure you would agree though, there can be a noticeable difference between charging at 14.1 vabs and 14.19 vabs, especially when running a generator?

And yes, there is little difference between 14.1v and 14.111v, while charging, but there is a significant difference between 12.1v and 12.19v when considering soc. All I'm trying to point out is there are much better alternatives to using a 'single decimal place' volt meter for monitoring battery soc.

The charging source is a fixed voltage. Nothing I do will change that known set point. If I see the battery within .1 of the known voltage I would charge one additional hour and be done. My watch is analog with no second hand.... An hour might be 50 minutes or 70. I am not setting a timer.

More data is not necessarily more information.

There is a place for additional accuracy and I don't see it for managing an RV battery.