Battery Voltage Question

[Bigbear]

I have been running my system for about 30 days now, and all seems well.  The Morningstar says full in the morning, after running power for an evening and early morning.  The voltage says 12.2 or 12.3, is this too low?  After a few hrs of sun, the voltage is back up to 12.7 to 12.9, with very little load on the system most of the day.  Thanks, BEAR

[Volvo farmer]

What are your batteries? That does seem a little low, though not too bad. In an ideal circumstance, I'd think you should be getting up over 14V for an hour or two each day while charging. I get mine up to about 29V for two hours on a daily basis (14.5V for a 12 volt system) and they're at 24.8 or 25V right before the sun comes up. Does that Morningstar do a three-stage charge? What voltages do you have it set at?

[Bigbear]

I have noticed the voltage over 13 volts during the day, full sun and getting about 29 amps input from the 4 - 130 Kyocera panels.  My batteries are, 8 Watchdog batteries, 140 amphrs.  I have the Morningstar set to 3-stage charge.  I guess it seems that if the Morningstar reads 12.2 or 12.3 the LED light would read half charge, but I'm still quite new to this stuff.  Any help is appreciated.

[AbyssUnderground]

Am I right in thinking 29 Amps is a little low for such a large battery bank?

[Flux]

Voltage seems low to me at 13v on charge at 30A for a significant time, even if it has dropped to float mode it seems low.

I presume you have no means of measuring the current directly into the battery, so you will have to look to see if the controller is operating or still delivering full current to the battery. If it is in bulk mode and you only have 13v then it seems as though your batteries need more charge. If in the absorbtion phase you should see at least 14v. If it has gone to float mode then I would expect about 13.6v

Ideally you need an ammeter between the controller and the battery then it becomes obvious what is happening. If you have over 10A into the batteries and they are only at 13v they are in trouble or need more charging.

If you have been in this state for a month the batteries almost certainly need to be got up to 14v or more for a while.

Do you have an independent check on the voltage or are you taking the volts from the controller.

Flux

[Bigbear]

I am taking the readings from the Morningstar.  I checked the specific gravity and they all read in the upper green level.  When I run the 7000 generator, (couple times a week) it also powers a 40 amp Xantrex 40+ charger and that does bring it up to 14 volts.  It starts with 40 amps, and eventually drops back to 5.  Do I need to run the Xantrex a little more often or longer.  BEAR

[Flux]

It seems as though you are using a bit more than the panels can supply.

Seems as though the Morningstar is reading volts ok, it would still be wise to try and see what voltages it is set for. The Xantrex seems able to bring the volts right up.

Keep an eye on the sg with your hydrometer, that is your best guide. When the readings start to fall or become different from cell to cell then is the time to equalise with the xantrex.

I hadn't realised you had a back up, as long as you use this regularly you should be fine.

Flux

[Bigbear]

Sorry I didn't add the xantrex in.  It's been overcast and rain today, maybe I should run the gas genny for a couple hrs tonight.  I know it's hard to tell, but what would you guess the gas genny run time to be for my battery bank, that is, not below 12.3, using the Xantrex.  You say that maybe my panels are not putting in enough, I wondered that too, but I was going on what the Morningstar tells me, and it says the batteries are full, but only shows 12.3 (before daylight) and maybe a 20 watt light running.  I wonder if it hits 12.1 or 12.2 it will show half full?  Before adding battery #7 and 8 a week ago, it would show 12.2 volts and the half full light would come on.  I added the extra batteries and within a couple days, it said full at 12.2.  I just don't want to trash my batteries, from my lack of experience.  You guys are all great.  BEAR

[Volvo farmer]

One thing I've been doing if I'm worried about batteries not being full is run the generator in the morning for an hour or so. I can charge at about 75A @ 24V and this does almost all the bulk charging. Then the solar takes over and will get the batteries up to absorbtion voltage much earlier in the day. My MX60 is factory set to hold the voltage at 14.4 for two hours, then if there are no loads, it switches into float at 13.4 or so for the rest of the afternoon. It really helps to keep the sulfate off the plates if you can hold the voltage at over 14V for a while every day. If you run your batteries in a cycle where you don't get them fully charged on a regular basis, their life will be shorter.

I think you perhaps have too much battery for your solar. I have an 800Ahr bank of L16s at 24V and 680W of solar and I think I have too much battery for my configuration. Actually the batteries are fine, I just need more solar... or wind. It takes a lot more power to get that last ten percent in there than it does to charge up from 60% to 90%, the charging process becomes more inefficient the fuller the battery gets.

 

[SamoaPower]

I agree that it sounds like you are using somewhat more from the batteries than you are replacing from the solar alone. It's good that you are running the backup periodically.

I wouldn't put too much faith in LED state-of-charge (SOC) indicators on the controller. There are two types of voltage measurements that are useful in maintaining batteries. The resting voltage, taken after the surface charge has been removed and with no load or charge, is an indicator of SOC. Readings of 12.7 to 12.9 would be indicative of a full charge under these conditions. Hydrometer readings are even better.

Secondly, voltage measurement under charge will tell you something about the charge algorithm being used, namely, the set points of the controller. At the end of the bulk phase or during the absorption phase, it should be up to about 14.2-14.4 volts and should remain there for some time after reaching that point. After the absorption phase, it should switch to the float phase at 13.2-13.5 volts and should remain there as long as you have charge current available.

I have two rules-of-thumb that I find useful for batteries. One, is that I need charge sources capable of 5 to 10% of the battery capacity to bring them up in a reasonable time (daily). That would mean 55 to 110 amps for your 1120 Ah bank. The other is that I don't want to go more than 48 hours without the bank being brought up to full charge. The longer they remain in a partial charge state, the more of the sulphate converts to the hard-to-remove variety. The effect accumulates.

Chronic undercharge is the real battery killer.

[altosack]

Hello BEAR,

Run, don't walk, run and get yourself a state-of-charge meter. You will kill your batteries without knowing what they are doing and how much you are using. It may seem like an unnecessary chunk of change, but you will save money by not having to replace your battery bank. Don't be penny wise and pound foolish. If you are just playing around to learn about RE, fine (although I would still get one even then), but if it's your prime mover and gets drawn from every day, do not go without it; you will learn and understand so much more about your system.

I use a Trimetric TM-2020 by Bogart Engineering, Inc. and always recommend that, although you can also get an E-meter or a Xantrex. The Trimetric is the cheapest and the best (IMHO). It costs about $160 with a shunt, but this is a lot less than a battery bank, and it provides endless entertainment for a information junkie.

Yeah, I know advice is cheaper than a SOC meter !

Best of Luck,

Dave

[Bigbear]

Wow, thanks for all the replys and help, and I agree, more battery than solar.  Last night we run the generator for about 4 hrs, and after the regular night and early morning usage, the voltage was at 12.5 when I left for work this morning.  We live about 1/2 mile off the grid, so this is our only means of power, and depend on it every day.  I have been looking at the state-of-charge meters, and was in question as to which one to get.  I'm in this thing so deep now, even a couple hundred bucks will more than offset the cost of a new battery bank.  I was leaning toward the E-meter only because it costs the most and seemed to have the most features, but any hands on advice would be appreciated.  I will look at the Trimetric again today, man, I can spend several hrs. a day researching all that is needed to make this work. Running the generator more often seems like the best path to take for now, as the solar panel budget is low.  I do have an AirX wind generator, but no wind right now, too many trees, and not high enough. BEAR

[ghurd]

Jerry sells blades to make the AirX 'work'.

Sounds like they may be a good investment with the days getting shorter.

G-

[altosack]

You really can't go wrong with an E-meter, either, but it is more expensive and most of the extra features are more useful for an electric car, which is what it's best at. The TriMetric is purpose-built for a home power system, and has everything you need.

The only thing I would like to have that it doesn't is a way to change the how long your battery has to stay at the voltage cut-off and current cut-off before it decides that you battery is full (it's hard-wired at 20 seconds; I think it should be higher). As far as I know, no other meter does that, either. If you're interested in the esoterica of battery metering, check out the document on the Bogart Eng. web site: http://www.bogartengineering.com/UsingTriMetMaintain.pdf

Best Regards,

Dave

[Bigbear]

OK, I ordered the Trimetric 2020, should be here Friday.  I run the generator again last night and this morning, we had 12.4 volts just after shutting down the lights and TV.  Should I be putting more amps into this bank?  My Xantrex 40+ puts in 40, can I buy another one, and run both from the generator, and put in 80 amps, or would this cause problems.  BEAR

[AbyssUnderground]

That would depend on how powerful your generator is.

[Bigbear]

The generator is a 7000 watt DeWalt, 50 amp 120, 25 amp 240, electric start, that I normally use for the charger, seems overkill, but my smaller generators are not pure sine wave, and the charger seems to do better.  I would like to use the smaller 1875 watt coleman, better fuel economy, but not sure it's enough.  BEAR