Is it possible to measure AGM voltage during charging?

Did you buy that inexpensive meter you were asking about?

Naio,

When charging, battery voltage will be whatever voltage is being applied to the battery by the charging source... be it rising voltage during bulk/cc, or steady voltage during abs/cv, or constantly changing voltage using solar.

If it's resting voltage you're concerned about, it takes several days for a good surface charge to self dissipate. Yes, you can take a wild @zz guess at how long to run a small load to discharge the surface charge, but a guess is still a guess. This is why I prefer to familiarize myself with my bank, while it's out of service, first, then watch how daily cycling affects things, if any. Sudden changes in bank performance are a definite red flag that something may be amiss, or perhaps it's just a response to temperature, or just a matter of decreased performance, due to being out of service for an extended period of time.

Do as Mex and Landyacht do, and get to know what works best for your agm's, using mfg recommendations as general guidelines, and tweak things from there.

You can also do a Capacity test once or twice a year, to see how the bank is holding up; although you will have to rely solely on voltage readings, throughout, not sg readings. And consider rotating batteries that are in a series and/or parallel configuration, after each C-test, so that the draw is not always off the same battery.

As for using 12v solar panels with a 24v bank... you'll likely need at least three 12v panels in series, to generate sufficient voltage to maintain a charge, if using an mppt controller. Using pwm, you may get away with two 12v panels in series, but it wouldn't take much for the combined panel voltage to drop below the ~ 29v required to sustain a charge.

My idea of fun learning-wise is to charge a battery bank with solar panels connected directly to a bank sans controller. Just a windup timer and an amp hour meter. Correlate -amp hours with time spent through the panels and it doesn't take long to learn the ropes. Fact is when my bank approaches -1400 amp hours I start the gen and set the alarm clock. The 4024 backs off prematurely because it is "smart" but I have another 550-amps online so it doesn't matter much. The weak-syster cell is usually at 1.262 when I walk up and check. It'll settle in at 1.268. The other 23 cells are at 1.270

This is for a 3-day straight run with the 5K window air going day and night and refrigerators and freezers. Because of tropical storms daily gen exercises are not on the program. When my kid was pregnant the temp housekeeper came inside and shreiked. She thought the place was haunted. The cost of fuel for a five hour charge makes my knees wobble. More and more I am using the Lambardini with the 385-amp 50DN Delco alt. It's air-cooled and sounds like a battalion of maracas on steroids.

Kind of amazing how little voltage readings really relates, but combine amps at a certain voltage, and a whole new world is opened up.

Then add in adjusting the voltage to anything one desires, rather than a plug and play resignation, and one can become one, with their battery.

I do goose the voltage after floating for a while just to see, and the amps on my AGM will quickly taper down to 0.1a or less.

If I try and float my AGM under the recommended 13.6v while still loading my 12v system, then nearly every time I look at my battery monitor it says - 0.1a, and then goosing it upto 14.5, the amps required are more, and taper much slower.

That 10 turn potentiometer on my Meanwell just allowed a friend to 'get it' regarding the relationship between amps and voltage on a fully charged battery, and a charging battery.

He now kind of wishes he got a MeanWell like mine rather than a PD9245, as the potentiometer is 'god like' voltage control.

I did give the option of adjustable voltage power supply and a timer, but plug and play was more desirable. The PD9245's setpoints seem to be pretty good for a Lifeline AGM in a mild climate.

Yup. I did so after seeing what happened after 14.4 was discontinued and 13.4 float was employed. The amount of amperage at 13.4. It decreased within 6-minutes. But temperature compensation enters the fray. It's warm here.

If folks would spend time during the charging process and absorb voltage and amperage values, correlating the two values becomes easy. But for ease, nothing equals an amp hour meter, plus factoring amperage and voltage.

Wanna get fancy, measure current with a multimeter after the battery has been floating for a day. The old Trends & Tendencies bit. Float the battery after a guaranteed full charge, let it rest for a day, enable bulk and the amperage should spike then instantly react and rapidly sump to full charge state. A new battery will take "X" amount of amperage to float correctly and if that value changes you'd better find out why. It'll change as the battery ages, but that's a very slight decline and rather linear until failure with the battery occurs, capacity lessened to 80% or less.

A balance between sulfation and plate erosion can be established.This is the definition of truly floating the battery. But chemistry imposes and even an AGM benefits by two-month cycles of top charging. I really do like the periodic goosing with 14.4 volts while monitoring amperage. It's a real BS detector.

Mex, Lifeline says when only 0.5 amps is required to hold 14.4, then revert to float.

page 19:
http://www.lifelinebatteries.com/manual.pdf

Have you decided to end Absorption a bit earlier and go at the high end of the recommended float voltage?

I've been using 0.4a at 14.5v for terminating absorption voltage on my northstar AGM as of late, but there have been a few times where I was a bit late and noticed 0.2a at 14.5.

My Vehicles voltage regulator allows upto 14.9v. My battery monitor has shown +0.0 amps at 14.9v into my AGM at times. It seems to come to a dead stop.

To play orchestra conductor, connect accurate volt and ammeter to the battery. Managing AGM batteries is a matter of knowing when the batteries reach full charge. Without over charging due to too high charging voltage. For example when my Lifeline drops to 1.0 ampere at 14.4 volts it needs to push away from the table and relax with 13.4 floating

The only way to know for sure is by using a battery monitor Victron or Bogart Engineering Trimetric which measure the current going in and coming out.

That's what a portable "smart" battery charger does. Mine, you set it for Standard, Lead Acid or AGM battery & it takes care of the rest. The charger has an LED readout that displays what is going on.

If that is what you are asking.

Measure what?

If you want to know how much charge is in a battery, then you would shut off all charging, put on a 3 amp load for a couple of minutes, then with no loads or charging, get a 'resting voltage'.

If you want to see how many amps are going into each battery, then use a clamp on DC rated amp meter. Home Depot sells one for $89 that is pretty good. You just clamp the meter over the wire, and it will tell you how many amps DC is going through it.

If you are installing a bunch of 12 volt solar panels and hooking them up to a 24 volt voltage controller, then don't worry about the input or output voltage so much. The controller will turn on at anything below 26 volts, and shut off around 27 or 28 volts.

Just match the pairs of 12 volt panels as best you can to their amperage. So if you have a pair of 12 volt 120 watt panels, rated at 7.5 amps, then run ground to the first one, +12 to the second one, and the +24 wire goes to the controller. If you only have space for say a pair of 80 watt panels rated at 4 amps, then run ground to the first one - input, + 12 goes to the second one - input, while + output is 24 volts, and that will go to the controller.

The controller does not care how many amps each wire has on it. It will just turn on when the output wire is less than about 26 volts, if the input voltage is higher than the output voltage. And then shut off when output is near 28 volts +/- 0.5 volts.

I would use #10 wire up to about 15 amps on it. Then if you are going with more amperage, go to larger wire, or run a second line.

You can buy grey #10 wire at Home Depot, UV rated romex, direct burial, and suitable for use on the RV roof. Then run this down the refrigerator vent cover to the controller, then to the batteries.

I made roof mounts from 2" angle aluminum. Cut 6" and drill three holes 3/16" for #10 screws into the roof, and 5/16" hole for a 1/4-20 bolt into the panel. Nylon lock nuts tend to frustrate anyone trying to steal them! Especially if you use tamper resistant round head bolts, with Torx heads.

If you don't already have the panels, this place has great prices on them. SunElec.com You can also check your local Craigslist too.

Good luck!

Fred.