3 month battery question

[Bigbear]

Well, we have been off grid for 3 months now, but I still have a couple questions.  The batteries are charged by the solar panels or the generator, and the indoor and outdoor meters show them as full.  They start out in the evening after the charging has stopped at about 12.9, and quickly fall to about 12.5 or 6.  We use them about 2 or 3 hours in the evening, and again about the same in the morning.  When I leave for work they are down to about 12.4 or sometimes 12.3.  When the wife is using the very small hair dryer, on low, no more than 2 to 4 minutes, they sometimes pull down to 12.2, but then come right back up to 12.3 or 4.  Our consumption is a very small TV (15 AC watts), and one or sometimes 2 at a time lights of 13 watts AC.  I do have a 12 volt well pump that pumps water for the shower, stool, doing dishes, etc, not sure on the watts, Shurflo 2088 series.  We may also charge a cell phone now and then.  Am I pulling the batteries down to far or am I worried about nothing, I have never saw the batteries at 12.1, always 12.2 for a couple minutes, usually settle in at 12.3 to 12.5.  Please help ease and old mans mind.  Thanks, BEAR

[AbyssUnderground]

It looks like you are pulling the batteries down to around 50% so you are stressing them a bit. It would probably help to double your battery capacity. You might have to add in more solar to compensate for the extra capacity too unless you intend to run the generator more.

[Titantornado]

Though, he does say he only sees 12.2 while there is a load applied (the hair dryer) And settles back to 12.4 (No load, right?)  Disconnect battery loads for an accurate voltage reading, or far better, take a hydrometer reading.

Sounds like you're operating just within safe operation limits to me.

[AbyssUnderground]

I never know whether to take the reading under load or off load with that table so I play it safe and do it under load.

[wpowokal]

Bear, read here some,

http://www.sandia.gov/pv/docs/BattIntro.htm

But don,t get bogged down on voltage, it's an indicator only, very dependant on load/no load.

A good quality hydromiter is the only way to tell the true state of charge of a battery, and having said that those readings even have to be taken with a grain of salt.

Voltage and specific gravity readings will change with battery age, so that's another complication. The only bottom line IMHO is if you run them too low on charge for too long you will murder them.

Battery failure is the main reason most people give up on renewable energy. Simply floating lead acid batteries indefinatly will destroy them, they need some cycling to keep them healthy, but then any cycling reduces their life, so its all a jugling act, part of the fun of going off grid.

I like to run my batteries hot my 24v system is frequently at 32V doing a gentle boil, now if I was pushing large currents through them relative to their amphour capacity I would damage them but I dont. They get around 5% of amphour capacity when boiling, they were estimated at 13 years old when I received them and I have been using them for 4+ years, last capacity test showed them at basically full capacity, depends how one interpruts the information.

So just enjoy the experience and come along for the ride.

allan down under

[altosack]

Hello Bear,

From what you say, it sounds like you don't have a battery meter (not a voltmeter, a State of Charge meter). Yes, it costs about $150-160 with the shunt (TriMetric 2020), but it will save that in premature battery failures and peace-of-mind over the years.

Having said that, I disagree with a previous poster that said you are drawing down to 50%. It sounds more like 75-80% or so, with voltage dips due to temporary heavy loads and sustained lighter loads. In the absense of a battery meter (or a hydrometer), the next best thing is to make sure all loads are off overnight (even the inverter, if possible), and take a voltage reading first thing in the morning before anything is turned on; this should be a true reading. From what you say, I would expect it to be about 12.4-12.5 volts in that condition, which is fine.

Dave

[Ungrounded Lightning Rod]

I'm with altosack on this.  Sounds like you're probably doing fine.

The initial drop from 12.9 is eating off the surface charge from the charging.  It would happen even with no load in a somewhat longer time.

Sounds like the only big unknown in your consumption (and the only large one that's on for a long time) is your well.  The pump rating won't give you the consumption since the load varies depending on the pressure the pump is working against - which depends on how far it's lifting the water and what your tank pressure is set at.

[Bigbear]

Dave, the readings are from my Morning Star Prostar 30, and the remote in the cabin which is a TriMetric battery monitor.  The morning readings right before going to work are about 12.3 or 12.4, usually 12.4, and that is with everything off except the inverter (Exeltech 1100), Aims transfer switch and the inhouse LP gas and carbon monxide sniffer that plugs into the wall.  I checked yesterday and today, readings after 1 hour it creeps back up to 12.5.  I checked some of the batteries this morning and they read 1.23 to 1.25, but I did not check each and every cell, just a couple cells from 4 different batteries.  The fluid level never seems to go down, seems like the Morning Star has been doing a monthly equalization, noticed the voltage up over 15 volts.  When I run the generator, the transfer switch throws generator power to the house and the generator also runs a Xantrex True Charge 40, which charges the batteries up very quickly.  Thanks for all the responses, I feel like everything is OK, I guess it's just hard for me to believe every thing is working fine on the first try.  Thanks, BEAR

[Volvo farmer]

I think you're fine too. Keep in mind, that voltage chart is suppposed to me measured with no load and after several hours of rest. Any load at all will result in a lower battery voltage.

We've also been off grid for only a few months. I have a 24V system and my voltages are always 24.8-25.2 right before the sun comes up. I've got an MX60 and I'm often out of absorb and into float by noon or early afternoon. So I know I'm not using more power than I'm making. We use maybe 50-60 Ahr overnight on 1000 Ahr worth of battery. There's no way I'm hurting these things.

The trimetric will tell you how many Ahr you used since the batteries were last fully charged. One way to figure out where you're at is to compare that number in the early morning, to the rated Ahr of your battery bank, if you're less than 40 percent and the batteries get to float every day, I think you're fine.