New Deka batteries not working well...

[biotectureTN]

Hi there. New to the forum, and somewhat new to solar power. Just upgraded my system from a 240w system with a single 33ah battery

I now have two flooded deka 8L16's hooked up in series for a 370ah 12v system. I have 6x60w 12v panels, hope to have a couple more soon

My understanding is that I should have 370ah (or 1 amp for 370 hours???)

My charge controller (Xantrex C60) is telling me that the batteries are fully charged during each day, but then as soon as the sun sets my inverter begins to read only 12.7 volts off the battery... isn't that about as low as I should let it get?

I don't have ANYTHING plugged in when this happens.. just the inverter itself (COBRA 2500w)

shouldn't my batteries maintain a charge after the sun is set for at least a few hours with some low wattage things?

What could be the problem??

[Sunking]

My charge controller (Xantrex C60) is telling me that the batteries are fully charged during each day, but then as soon as the sun sets my inverter begins to read only 12.7 volts off the battery... isn't that about as low as I should let it get? What could be the problem??

There is no problem with the batteries just operator error.

A fully charge Lead Acid Battery at rest will read 12.6 volts when 100% fully charged.

[inetdog]

There is no problem with the batteries just operator error.

A fully charge Lead Acid Battery at rest will read 12.6 volts when 100% fully charged.

And the key is "at rest". If you just left it for three or four hours without any load after you finish charging, it would come down to or close to 12.6 volts on its own. Don't confuse the float voltage, at which the charger will just be replacing current lost to self discharge, to the fully charged and rested voltage.

[biotectureTN]

Ok, I was under the impression that the voltage reading was a direct indication of charge level. I apparently have a lot to learn. Does anyone recommend any resources for better understanding this? If my batteries can read 12.6 when fully charged (though sometimes reading 13.5-14) how can I tell when my battery is low and needs to be allowed to recharge?

[inetdog]

Ok, I was under the impression that the voltage reading was a direct indication of charge level. I apparently have a lot to learn. Does anyone recommend any resources for better understanding this? If my batteries can read 12.6 when fully charged (though sometimes reading 13.5-14) how can I tell when my battery is low and needs to be allowed to recharge?

The exact relationship will vary from battery type to battery type, so that is no hard and fast rule that uses anything except the SG reading on your hydrometer.

A good battery monitor will let you keep track of the number of amp-hours you have drained from the battery bank and the number that you have put back in (with a reduction factor based on charging inefficiency). It has to be properly set up to know the size and current condition of your battery (based on SG) before the results will be very useful.

But if you know the SG of your battery at some point, you can put a known load on the battery, let it run for awhile, and then record what the voltage is at that load and that State of Charge (SOC). The result when you get enough data points will be a rough estimate which you can use between SG measurements.

The battery manufacturer may be able to provide you with curves which show the voltage under load for different SOC values, but it is not likely.
The voltage when you temporarily shut off the load is a better indication than the voltage at the time you stop charging, but neither one is good. The correspondence between voltage under load and SOC is the information that you need to know when to stop draining your batteries. (20% DOD for typical days, 50% for bad weather or emergency use.) I would set the LVCO on the inverter for no lower than the 25% SOC voltage until you learn more. If a "normal" heavy load drops the voltage lower than that while the battery SOC is well above that level, you will have to reconsider.

[russ]

for starters try http://www.hss.doe.gov/nuclearsafety...k/hdbk1084.pdf

[PNjunction]

I now have two flooded deka 8L16's hooked up in series for a 370ah 12v system.

If those East-Penn Deka lead-antimony batteries didn't come with docs, then search for:

0919B (Flooded MonoBloc)

and it will turn up a pdf link for that battery. They say that 12.78 at 77F indicates a full battery for this series. Make sure your C60 controller is set for the voltages they recommend at the bottom of the doc.

Note that inverters if left on without a load still pull some current, so you'll want a way of totally disconnecting it from the battery when not in use - unless the manual says otherwise.