full charge voltage ?

[globalworrying]

hello,

I have been a spectator here for about three years, and now I am

ready to ask my first question.

I have a remote cabin that has propane lights, heat, and fridge.

I added a kyocera 80 watt panel, three group 27 100ah agm vrla

sla batteries, a 2000watt harbor freight coleman style inverter

an a 7 amp charge controller from camping world ( it says it can

handle up to 106 watts of solar) I think it is sunforce brand.

this system has been running for approx. three years and seems

to have adequate capacity for what we use it for, which is a few

12v fluorescent lights, an rv waterpump, a tiny microwave, and

watching movies on a 20" tube tv. I went with the sealed batteries

because I wouldn't be there to equalize and other maintenance issues,

however I recently determined the charge controller cuts out at

about 13.2 volts. I thought I learned here that it should be approx.

14.25, is that correct? if so what do you reccomend.

and am I just giving up capacity or sacrificing battery life.

also recently read on here someone said they wouldn't discharge

this type of battery below 12.3 volts? do you agree? and can I

assume that would be resting- not under load?

thanks for you advice.

I really enjoy this forum.


Moved to the proper section.

[zap]

13.2 volts is too low.  Are you measuring the voltage with, what you would consider, an accurate meter?

I would say 14.25 is about the highest you should take an AGM.  The voltage will vary between manufactures because of different chemistry's and you should find the voltage recommended for your batteries AND the voltage will vary with temperature.

To give you and idea...I have a Morningstar controller and it's cutoff voltage will vary from around 14.04 volts @ 75­°F  to 14.23 volts @ 60°F.

If your battery is setting at 13.25 volts once off charge and at rest, then you're not giving up much capacity.  Charging at that voltage may be hurting battery life some but I wouldn't think it would be much IMO.

[Flux]

13.2 is dreadfully low. If you are not there a lot then your setting would be close to the float voltage and for a VRLA would be something like 13.8v. You should be able to find the manufacturers recommended figures.

They don't like too much in the way of equalising but if you have kept them so low it may be worth seeing if the manufacturer suggests an equalising voltage but it will not be as high as 14.25 ( or at least not for long) you don't want them venting.

I really don't know anything about your controller but I am surprised you have managed to keep them running at 13.2v without a lot of loss of capacity, perhaps it is more sophisticated than you think. They do stand that sort of thing better than flooded cells.

Cut off voltage depends too much on the load current and the number of times you discharge them to give much idea.

On load you will see them drop below 12v if you use any significant capacity from them but if after standing for several hours they recover to 12.3 v then you haven't cycled them too deeply. If you stop at 12.3v on load then you aren't using much of their capacity.

[Flux]

Zap makes a good point. I assumed the 13.2v was the controller voltage. If it is battery voltage when standing with no charge then 13.2 is sensible. As I say I don't know what your controller does exactly.

Flux

[zap]

I too assumed the 13.25v was the controller voltage and I believe nearly everyone here would agree that's way too low.

If the batteries haven't been taxed too much they may still possess a decent, if not near full, capacity.

globalworrying, to test the batteries:

After a good full day of charging:

Run the tv for maybe 10/20 minutes.  My tv is a 6 year old 19" Phillips that draws an average of 48 watts. This should be enough time to drain off the batteries surface charge.  Then measure the batteries voltage.

It's probably a little more work but checking each battery separately would be a wise thing to do.

If they show somewhere around 13v, I would say things are fine.  If need be, report back on the battery voltages.

[Airstream]

The Sunforce 11-1890-0 Battery Charge Controller manual operation section in its' entirety:

Green light indicates a full-charged battery. When the battery reaches 14.2 V, the Battery Charge Controller will cutout voltage thereby ensuring no overcharging.

Yellow light indicates a battery that is being charged. When the battery reaches 13 V, the Battery Charge Controller will cut-in and charging.

Are the winky lights working as suggested? Seeing '14.2' being fed to the batteries using a volt meter while the panel is in full sun would settle the question.

Fresh off charging 13.20 plus Volts is a good sign. Like the others have said - a fully charged AGM will produce voltage of 13~V, after sitting overnight or a day or two, as they age that resting voltage number starts to decrease no matter how long it is on float.

Trojan is the first 100AH SLA AGM battery I found on quick Web search, they specify 13.8 - 14.1 daily charge (after usage to get it back up) and Float 13.5V. Note their temperature compensation starts at 80F, if batteries are at 40F their instructions say to ADD 0.672 Volts, so a little higher voltage on charge won't harm cool batteries, especially with only a 100 watt source!

[globalworrying]

thank you for your input.

I think the meter is ok, I checked it with a second

one and get the same readings.

I was taking readings upon arrival with the controller

indicating full charge (not actively charging)

so basically it was resting and at this point I don't

know what the cutout voltage is.

I will try removing the surface charge then watching

as it progresses from charging to full charge.

for some reason it is a good feeling to have the sun

working for you, even when you're not there

don't you think.

thanks

[independent]

http://www.fieldlines.com/story/2003/8/24/20535/6203

I consider this the best bit of info on the net on SLA battery charging.