Battery always at 13v a bad thing?

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Battery always at 13v a bad thing?

Postby Camp4Life » Mon Aug 14, 2017 10:12 pm

I've installed a roof-mounted solar setup with a Coleman PWM charge controller. I find that during the day my battery sits at 13.6-14.5 volts depending on sunshine, and stays that way all day. A couple hours after sundown it sits at 13 volts. At this point (No power from the panel) I tried turning on a few LED lights and ran the water pump for about 10 seconds. Then, with the lights still on, the battery read 12.8 volts. When I turn the lights off it goes back to 13 volts.

By morning the battery is 12.8-12.9 volts and then it goes back to 13.6-14.5 while the sun is up.

Is this bad for my battery? It's an 85Ah deep cycle, group 24.

I do plan to eventually swap out the controller for a proper MPPT one, but I was hoping to keep using this one for the rest of the summer.

Any suggestions/input would be appreciated

:beer:
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Re: Battery always at 13v a bad thing?

Postby Dale M. » Tue Aug 15, 2017 7:45 am

Do load test on battery.... From the voltage fluctuation you describe I would not be alarming.... Its normal for battery to change voltage a bit from its float voltage (really hot off charger) to its normal idle voltage (off "charge" for a while)... If really concerned drag it down to auto parts store and have it load tested... Or turn on whatever would be your normal night usage of lighting and for several hours and observe battery voltage.... If it stabilizes around 12 .8 ans stays there for 2-3 hours with just some LED lights on, it probably not a problem...

Might want to go to top of electrical page and read sticky "Battery FAQ" to have better understanding on voltage fluctuations between charge states and usage...

http://www.batteryfaq.org/

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Re: Battery always at 13v a bad thing?

Postby tony.latham » Tue Aug 15, 2017 8:02 am

I suspect it is just fine. What are you measuring your voltage with?

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Re: Battery always at 13v a bad thing?

Postby MtnDon » Tue Aug 15, 2017 8:25 am

Not a problem. Every solar system with lead acid batteries has the same thing happen as the day passes. For example, our cabin is solar powered and uses golf cart batteries. Most of the year the cabin is unused. The solar system is up and running full time. Every day the charge controller goes through a short bulk charge then switches to absorb according to it's program. The batteries then sit in float till the sun goes down.

Those golf cart batteries were installed July 2009. The plates still look like new and the batteries still perform well.


What is the voltage output of your solar panel? I doubt an MPPT controller will offer much advantage considering the cost if the panels are what are usually sold as "12 volt" panels.
Our 6x12 deep vee nose cargo trailer camper conversion... viewtopic.php?f=42&t=58336

We have a small off grid cabin we built ourselves in the NM mountains; small PV solar system; 624 watts PV, Outback CC & inverter/charger ... http://countryplans.com/smf/index.php?topic=2335.0
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Re: Battery always at 13v a bad thing?

Postby Camp4Life » Tue Aug 15, 2017 8:49 am

Dale: Thanks, I'll try leaving some lights on for a few hours when the sun is setting and see what happens afterwards.

Tony: I forget the brand of multimeter I bought, but it was $99 so it's not a cheapie.

Don: Straight from the panels is usually about 17.5 volts, but in full mid-day sunshine I get 21 volts going into the controller.
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Re: Battery always at 13v a bad thing?

Postby Trebor English » Tue Aug 15, 2017 11:46 am

The battery stays full. When the PWM charges in constant current, bulk, mode it is turned on and the panel and battery are tied together. The battery voltage and panel voltage match. The 17.5 and 20 mean the controller thinks the battery is full and the panel to battery switch is off.

When the battery is almost full the controller turns the switch on and off rapidly to keep the battery at 14.4 volts or so. The voltmeter reading on the panel will be less than 20 and a digital meter might be erratic. An analog meter might be more useful.

A "proper MPPT" controller will do exactly what your PWM controller is doing, keep the battery full without over charging. It will also help keep your wallet from overfilling.

Keep an eye on water consumption. Mine uses 30 to 40 ml per cell per month. Watch for a change.
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Re: Battery always at 13v a bad thing?

Postby John61CT » Tue Aug 15, 2017 3:47 pm

Likely whatever is showing batt voltage just isn't accurate.

If that's a lead battery.

Get a known good DMM on it isolated after 24 hrs resting.
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Re: Battery always at 13v a bad thing?

Postby Camp4Life » Wed Aug 16, 2017 8:54 am

Thanks, I'll keep an eye on the water level. It is a flooded deep cycle battery.

My digital multimeter is very accurate, and the whole reason why I spent more money on a good one was for better quality. It's only a month old.

I turned on 6 lights at around 6 PM and left them on until 11 PM (Sunset is 9:45). With all lights on at 11 PM, battery across the terminals showed 12.6. Turned all the lights off and waited a few minutes to retest, and showed 12.75v. This morning heading out to work I checked again. Sky was bright but no sunshine yet, showed 12.8v. I think tonight I will leave one of my LED lights on all night and see what happens. Maybe having a constant load on it will keep it below 13v when the sun is down. But I'm not sure if this slight discharge/recharge daily will be bad for the battery.

I've done tons of reading on different solar setups, and batteries, but this is my first actual setup.
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Re: Battery always at 13v a bad thing?

Postby John61CT » Wed Aug 16, 2017 10:15 am

Then don't fret, no harm, maybe your battery is just in extraordinarily healthy condition.

Those little drops and resting bounce back is 100% normal.
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Re: Battery always at 13v a bad thing?

Postby Tigris99 » Wed Aug 16, 2017 11:36 am

Actuall6 all this the op is referring to is normal for these batteries. 12v charging systems, automotive or otherwise.

14.2v during charging is quite normal. Batteries being at or above 13V after fully charging from the vehicle is completely normal.

12V is nominal voltage, storage voltage. Run a DMM across batteries at the store. All right about 12V. After full charging my batteries are always right about 13V.

If you get above 14V after charger is disconnected then its time to worry about your charge controller.

There is absolutely NOTHING wrong with your current system. Ive been dealing with 12v systems most of my life between boats, Im an auto tech by trade, and so on. ~13V is literally normal full charge voltage. Thats why all electrical components used for 12v systems are actually rated for 15V because charging load voltage can hit close to that.

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Re: Battery always at 13v a bad thing?

Postby Camp4Life » Thu Aug 17, 2017 8:33 am

Thanks Tigris, makes me feel better knowing 13 is normal! After the sunshine yesterday, the battery is still sitting steady at 12.95v.

John, good to know. I'll be leaving my outdoor LED light on fulltime from now on while it's parked in my driveway. It doesn't seem to be much of a drain so I'll see what the battery is like in the morning before the sun comes up. And the battery is new as of this spring :thumbsup:
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