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Old 04-06-2016, 11:26   #1
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How high can I safely charge 12 V batts?

When batts are down to 12V, they are basically "empty".
Charger/inverter/regulator bring them up to around 13.2 to 13.4V.

I have solar panels that I can set to higher than that. I tested them on an old battery and can get up to 16V. Silly I know, but it started me thinking.

How high can my house batteries be charge safely (14V, 14.5V)? And what advantage do I get when they get that high?

I have 6 AGM 100AH (8G31DT) gel house bank and a second bank of 2 Marine Deep Cycle (24DC-1) for cranking my engines (catamaran).
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Old 04-06-2016, 16:33   #2
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Re: How high can I safely charge 12 V batts?

I would look at the manufacturers data for these specific batteries. http://www.mkbattery.com/images/8G31DT.pdf
http://www.eastpennmanufacturing.com...chure-0273.pdf

It will tell you the max voltage for a fully charged battery and float charge. Any other answers will not be very accurate and may reduce the working life of your batteries.
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Old 04-06-2016, 16:42   #3
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Re: How high can I safely charge 12 V batts?

Suggest you read this: Charging Information For Lead Acid Batteries – Battery University

To put it briefly: You can safely charge a LA battery with voltages up to about 14.5 for some time if you monitor them carefully. That doesn't mean that you can "charge your batteries that high" (as in get them to a point where they have a voltage of 14.5) it just means that you can push charge into the batteries using that voltage.

No matter how long or how high a voltage you push into a battery, it will never provide more than about 13.5V after you disconnect the charging source.
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Old 04-06-2016, 22:26   #4
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Re: How high can I safely charge 12 V batts?

This guy really had something to say about FLA batteries:

His blog really has some good information on charging, and it's DEFINITELY worth reading.

https://handybobsolar.wordpress.com/...d-up-so-angry/

The RV battery charging puzzle has great info.
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Old 04-06-2016, 22:45   #5
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Re: How high can I safely charge 12 V batts?

There's applied charging voltage... and then there's the max voltage at rest for the batteries.

You must apply higher voltage to the battery than what it can hold at rest (no load and not being charged) in order to charge it.

There is a chart of "TVG" ( Temperature, Voltage, Gassing) applicable for any lead acid battery. At a certain voltage at a certain temperature the battery will begin gassing when its fully charged.
http://www.tekrispower.com/pdfs/xant...20Charging.pdf
Its a bad idea to ever get in the gassing range for a gelled electrolyte battery.

At rest a common "12 volt" flooded lead acid battery (most automotive and "deep cycle marine" and similar) is considered to be full between 13.5 and 13.8 volts.
6 volt nominal (golf cart batteries and similar) flooded lead acid batteries would be 6.75 to 6.9 volts at rest when full.

****************

We typically use simple charger systems that are set assuming the battery temperature will be appx 75 F.
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Old 05-06-2016, 08:52   #6
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Re: How high can I safely charge 12 V batts?

Think a correction/clarification may be needed. Lead acid batteries can have a charger attached in the 13's for extended periods without damage. This is the "float" voltage.

If disconnected from loads and charging, lead acid will drop to 12.7 or 12.8. This is fully charged. Will only stay higher if a charging source is attached.

12.1 volts (at rest - no loads or charging) is considered 50% charged. Letting lead acid batteries go below 12.1 (at rest) shortens their lives considerably.

Many of today's chargers have a lead attached to the battery that senses battery temperature and adjusts their output.

In any case, putting 16 volts into a battery for very long will fry it. Need a charge controller to bring the voltage down to an acceptable range.

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Old 05-06-2016, 11:47   #7
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Re: How high can I safely charge 12 V batts?

I believe I may have just had the same issue and the problem was that the MPPT charger needs to be connected to the batteries first. The charger will then detect whether it is a 12v or 24v system. Then it is connected to the solar panel. If you do it the other way around, it will default to the 24v system settings and you will overcharge your batteries

Without knowing more this may be an answer or it may leave you non the wiser!
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Old 05-06-2016, 17:54   #8
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Re: How high can I safely charge 12 V batts?

we use agm batteries and run the solar regulator on 14.3volt /trying for an average 13.8 full charge in the batteries / sometimes continuing on after sailing all day in the tropics it was necessary to turn on several appliances to drop the battery voltage slightly to start the sonar as the battery voltage was just out of it's operating range / the led nav lights, gps and ais all worked fine/ we have asked the advice from an electronics nerd along the lines of a resister on the power to sonar wire his answer was naaaaah! / just turn the fan on or run the tv . there is a little bit more planning necessary for all climate situations
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Old 05-06-2016, 17:59   #9
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Re: How high can I safely charge 12 V batts?

A 12v FLA battery should not get more than 14.7 bulk charge. a Gel cell should take a 13.7 to 14 volt charge as ii will gas some what, with more and the gel will hold the bubble down next to the plate where it formed. causing that section of the plate to sulfate. After charging a battery to full, when disconnected from the charger and with no load on it it will read over 13 volts if the battery is in good condition. this is because of "residual" charge .... an excess of electrons floating in the electrolyte. This will bleed off in an hour or two, you could also take a 3 to 5 amp load on the battery for 15 or 20 minutes and recheck the state of charge. it should be around 12.6 to 12.8. If you have some big batteries Like 8D"s then the charge would be around 12.7 to 12.9 the same will be there with 4 or more 6 volt batteries wired in series and parallel, to make one bank.

As has been mentioned charging with too high a voltage and/or over charging will shorten a batteries Life dramatically.

A solar panel rated for a 12 volt system puts out 17 to 24 volts, and like wise a 24 volt system's panel will put out 28 to 36 volts. It's not necessarily the Amps that cause a battery to "cook" it's the speed that the amps are delivered. Not to mention Gassing has caused EXPLOSIONS, in confined spaces. Gassing is also caused when a battery is discharged too low and recharged. If you're adding water....distilled only....once a month you need more Amp/Hr s in the bank or charge it mote often. I have 500 amp/hrs and only add water once every 4 to 5 months. I get 5 to 7 years out of the house Before I start loosing amp/hrs and my cranking batt is almost 10 years old.

Charge controllers are worth there weight.
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Old 05-06-2016, 18:10   #10
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Re: How high can I safely charge 12 V batts?

Fyi, victron energy mppt controllers recommend a 16.2V set point for equalization of LA batts.. pretty high bUT can't be damaging much if that'S a default setting. I don't think you want to equalize too often as excessive equalizing can shorten life, but a few times a year can help keep the plates from sulfication.
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Old 05-06-2016, 18:35   #11
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Re: How high can I safely charge 12 V batts?

Quote:
Originally Posted by tinkrman69 View Post
A solar panel rated for a 12 volt system puts out 17 to 24 volts, and like wise a 24 volt system's panel will put out 28 to 36 volts. It's not necessarily the Amps that cause a battery to "cook" it's the speed that the amps are delivered. ...
I have 500 amp/hrs and only add water once every 4 to 5 months. I get 5 to 7 years out of the house Before I start loosing amp/hrs and my cranking batt is almost 10 years old.
Sigh! Here we go yet again.

"It's not necessarily the Amps that cause a battery to "cook" it's the speed that the amps are delivered"

That has to be the most crazy of the many inaccurate statements I have ever seen here on the subject. An Amp is an instantaneous measure of the speed at which energy is delivered. There is no such thing as "speed that the amps are delivered".


"
amp/hrs" - No it"s Amp Hrs. i.e. "Amps multiplied by Hours", not "Amps divided by hours"
Once again. Please see:
Amps v Amp hours v Amps/Hr
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Old 06-06-2016, 06:53   #12
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Re: How high can I safely charge 12 V batts?

You know the really amazing thing about lead-acid batteries? Even with so much misinformation out there, they still mostly do their job pretty well, and last pretty long. Given some of the things I've read, I'm amazed that more people don't kill their batteries in a matter of months. But even if you really mistreat them, they still seem to last a few years at least.
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Old 06-06-2016, 07:53   #13
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Re: How high can I safely charge 12 V batts?

Do study the difference between the different types of battery. It is part of the answer, and, although answers here might help, you ought to go further. The best info DOES come from the manufacturer - and is usually available on line. If it is not, they all seem to have people to answer technical emails.
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Old 06-06-2016, 07:54   #14
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Re: How high can I safely charge 12 V batts?

...and stop emptying your batteries!
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Old 06-06-2016, 12:13   #15
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Re: How high can I safely charge 12 V batts?

Quote:
Originally Posted by zstine View Post
Fyi, victron energy mppt controllers recommend a 16.2V set point for equalization of LA batts.. pretty high bUT can't be damaging much if that'S a default setting. I don't think you want to equalize too often as excessive equalizing can shorten life, but a few times a year can help keep the plates from sulfication.
This is true for FLA batteries, but... The OP has AGM batteries which should never be equalized. It will kill them.
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