Battery voltage checking

Poor mans volt checker, (under load)
After dark, with 1 or 2 incadesant lites on, turn on a facuet.
If lite hardly dims, batts in good shape till morning
If lite dims considerably,.....its charge time !

I don't use that method anymore. I know exactly what my LED volt meters should read as I'm headed for bed.
If the one closest to the batteries reads 12.4, I'm in great shape.
If its reading 12.3, I'm good thru the nite (no heat) and solar or Genset
will fix it in the morning.
I don't remember it ever reading 12.2

The other LED voltmeter right at the tv, (sat tv playing) is another story.
This one is reading inverter input under load.
11.5, I'm still in good shape
11.0, still ok, but better think of recharge
10.5, inverter alarms, only happened once under testing.

Johnny G1 wrote:
12.2 and that's as low as I let my batteries get and they have been in the rig since 2003 and are charge by solar all the time.

Says 12.1 here (Table 7 on page 23 of 32)

http://www.trojanbattery.com/pdf/TrojanBattery_UsersGuide.pdf

12.2 and that's as low as I let my batteries get and they have been in the rig since 2003 and are charge by solar all the time.

"And, btw, 12.1V in rested battery corresponds to ~30% full. In other words, 70% discharged. Not good"

Trojan Wet spec is 12.1v = 50%

MEXICOWANDERER wrote:
I would not OWN the rig that does not have proper instrumentation. How EASY it is to see -17 A/H and -1.6 amps which agrees with the expected load, then I turn in for the night. No advanced calculus just before bedtime. X=I/t - L. Read the meter, it's yes or no.

With off-grid it's always some sort of check-up at sundown. For me it's looking at solar controller display where it shows V at the moment, and says that batteries went into Abs stage and then stayed in Float for 4 or 5 hours on that day. My situation is simple, there are no high loads after sunset.

To know "the whole truth", in addition to present-time SOC (approximate as with any counters of this kind), you would need to know your "usual" overnight consumption. Unless you have a little smelly powerhouse that would auto-start every time when voltage drops too low. Or an audio alarm for low voltage - then you go and crank that thing up.

If somebody wants to sleep well and have no idea where their batteries are going to be by the morning (by no means I'm talking about you Mex here), there is a simple "instrument": turn the loads off and crawl under a good down duvet.

OP - beware of $5 China-direct LED voltmeters on Ebay and Amazon. 99% of them is UNBELIEVABLE junk. It would read with 0.3-0.5V error and would change the readings with time as the circuit warms up.
And, btw, 12.1V in rested battery corresponds to ~30% full. In other words, 70% discharged. Not good.

BFL, you certainly are not playing the part of "boob" :)

That is how it is supposed to be done. I would not OWN the rig that does not have proper instrumentation. How EASY it is to see -17 A/H and -1.6 amps which agrees with the expected load, then I turn in for the night. No advanced calculus just before bedtime. X=I/t - L. Read the meter, it's yes or no. There was a gyro gearloose in Willits, CA. that tried to use fuzzy logic algorithm to determine state of charge. He sorta got upset when I returned three of his units for refund and pronounced "Congratulations you have successfully managed to create an entity that manufactures then remembers it's own errors".

I like to cross-check between the volts and the AH counter to see if they "match". EG, if the voltage is too low for the AH you are down, it can mean there is something on you didn't realize. (such as the converter when on inverter--don't ask! :) or an outside light.)

mitch5252 wrote:
I just ordered one of these today - VoltMinder with alarm...



VoltMinder

Hope you are a morning gal, or that alarm can be turned off, else you could get a rude awakening one morning at 0 dark thirty.

A voltage reading is an OBTUSE measure of battery state of charge. Loads have to be off for several minutes, charging has to cease or surface charge has to be eradicated. This is an excellent example of how to make-things-hard.

Looking a cumulative ampere hours gained or lost number is the easy and most accurate way to do things by instrument. No it isn't perfect but compared to voltage in-use guesstimates it's like comparing a micrometer to a ruler when measuring bearing bore sizes. Only if you guess wrong the bearing disintegrates.

For a weekend warrior a voltmeter would be OK anything more serious than that, I would love to be your battery distributor :)

Depends on how much information you want to see.
The Bogart Engineering TM-2030 can be had for $150.00. The Xantrex LinkLite for about $200.00