acceptance charging rate AGM batteries

Hi MrWizard,

Thanks for sharing your results.

About 2 p.m. the sun broke through the clouds. I was not at the RV to see the charging numbers, but I am pretty sure they were significant.

load was 2.83 amps during the day. (Fantastic fan and fridge valve).

5:20 p.m.

Solar showing 13.5 volts and 3.5 amps.

Started generator because RV was too hot for my tastes.

Charging at between 4 and 6 amps.

Really I can't complain about the solar system I have. I really expected to see 20 to 30 amps of charging.

I'll be running the generator again for supper time. Tomorrow I won't run the generator for breakfast and I'll post the results.

Over night use 8pm to 8am was 98 ampHrs...no Fans no TV
Just lights and the PC .. Fridge etc..

Start generator and charge rate was 57.x amps into batteries
This does not include the various 12v loads also being supplied via converter and solar
Right now three hours later 13.5 amps charge rate, 14.10 volts

Before sunrise it was down 83 ampHrs and showing 12.8v with a 2 amp load

I would have ordered the French toast, but it would take to long to get here
So we had Jimmy Deans meat lovers breakfast bowl,
Two minutes in the MW per bowl

load of 3.2 amps throughout testing.

voltage with no solar 12.5/12.6 volts

start generator to cook breakfast

charging rate 69 amps

after 5 minutes 60 amps plus 1 amp from solar

after 15 minutes 48 amps plus 1 amp from solar

voltage 13.2 just after run

voltage 12.8 one hour later with 1 amp from solar (totally overcast gray day)

voltage 12.8 after 2 hours with 3.2 amps from solar

Started engine 16 amps @ 13.7 volts from the alternator circuits.

Anyone for french toast?

I'll start the generator to do this (I was going to invert)--and see what the rate of charge is. I'll time it--and measure the rate again when I shut down the generator.

Next I'll start the engine and see if the alternator wishes to send significant amps to the house bank.

Mr. Wizard your statements appear to make a lot of sense.

getting back to Mexi's 20% rule at SOC less than 70%
and what Landyacht has been saying about a 'stout' charge to wake his up

i think i get the 'gist' of 'why'

its because these batteries are NOT flooded, the electrolyte cannot be shaken/mixed/stirred/de-stratified

the chemical migration of the electrons in the electrolyte
needs the strong current to reverse the process and return the electrons back into the deeper ? layers of electrolyte in the glass matting
they migrate out of the liquid into the plate to go thru the wire to the other plate, put they must be forced back into the liquid

analogy: think of it like driving air bubbles thru a sponge
or osmosis when filtering water

we can't do an SG check, we can't add distilled water, we can't do a bubbling over charge to stir the electrolyte
what we must do is 'trends and tendencies' and stay on top of keeping them fully recharged as often as possible
try to stay away from doing 50~90's, especially when your a full timer
like you and me

Hi pnichols,

I have two charging paths that I have manual control over. I went for very high amperage continuous duty solenoids which I have manual control over. My problem was fuses failing, so I switched to 50 amp automatic circuit breakers.

I do monitor voltage at the dash and at the house bank.

The specific gravity of the telecoms is 1.3 and the voltage is correspondingly higher. My starter battery is now 7 years old and is a Marine from Walmart. It's voltage is lower of course and the charging circuit sees that first.

When all my batteries were wally world marines I saw lots of charge flowing to the house batteries. That simply no longer happens unless I have a large load on the house--or if I have run them a long ways down.

pnichols wrote:
Don,

My Ford E450's 130 amp alternator every once in awhile spikes to over 60 amps (I saw 70 amps, once) when I run my two paralled ,12 volt 115 AH Group 31 Fullriver AGM coach batteries down too much. I monitor the Fullriver batteries while going down the road with a voltmeter and ammeter for them that I mounted on the cab dash.

I also have a voltmeter on the dash for the engine battery/alternator system. When this voltmeter does not closely match the coach batteries' voltmeter, I know that the alternator-to-coach-battery automatic interconnect solenoid is bad. This has happened twice to me, now, in 10 years. I hate arriving at a campsite to find that the coach batteries haven't been topped up by the alternator!

I prefer to keep an eye on things in order keep surprises to a minimum.

Hi Westend,

Actually they are surplus acid rather than starved acid.

The Victron is a nice piece of kit.

I really would rather not have an amp-hour counter.

I am noticing some trends about charging at low rate solar vs high rate shore power or generator power, but it is too early to start posting about it.

Don, your starved cells may require more "cradle rocking" than more typical AGM jars. To that, I have no knowledge. In typical AGM charging, pushing high amperage is going to make the AGM healthy and robust since it recovers from a discharged state quickly and will tolerate the high amp charge. Member Landyacht has noticed and confirmed the same.
The Mfg information for my East Penn telecom/medical batteries stated that there was no high amperage threshold as long as temperatures were maintained within reason. Testing was performed at high charge rate for an extended period and capacity was not reduced nor battery damaged.

Your question appears to be pointed towards the efficiency of charging, i.e. at what point of acceptance rate can I limit charging? I'm guessing that the understanding of this point is desirable to fit in with the powering of loads while charging. The only suggestion I could make is to buy an adequate battery monitor. I use a Victron and it will include the Peukert effect to more accurately display capacity and charging levels (although I don't pay much attention to it). Getting a high amperage shunt shouldn't be a problem for the level of power you're drawing.

Don,

My Ford E450's 130 amp alternator every once in awhile spikes to over 60 amps (I saw 70 amps, once) when I run my two paralled 12 volt 115 AH Group 31 Fullriver AGM coach batteries down too much. I monitor the Fullriver batteries while going down the road with a voltmeter and ammeter for them that I mounted on the cab dash.

I also have a voltmeter on the dash for the engine battery/alternator system. When this voltmeter does not closely match the coach batteries' voltmeter, I know that the alternator-to-coach-battery automatic interconnect solenoid is bad. This has happened twice to me, now, in 10 years. I hate arriving at a campsite to find that the coach batteries haven't been topped up by the alternator!

I prefer to keep an eye on things in order keep surprises to a minimum.