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Old 01-08-2005, 15:51   #1
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Need Help with a Charging Voltage Mystery

What would cause excessiveely high charging voltages?

Starting my engine last week, for the first time in over a year, I noticed that the terminal voltage on the starter batteries was over 18 volts. After attempting to adjust the external regulator and being unable to do so, I decided to replace the regulator. In the process, I found a broken ground wire connection (alternator to engine block) and replaced it.

I also replaced my aging Gel house-bank batteries with four new Deka 6 volt 'deep cycle' Gel batteries, wired in series/parallel, to produce 12 V and 360AH capacity.

Since I was also in the process of replacing my alternator and external regulator for the starter batteries, (I have two alternators and two regulators, one each for the separate battery banks) I couldn't start the engine to charge the new batteries, so I initially used an external (automotive-type) charger and, yesterday, hooked up the Xantrex AC to DC, 3-stage charger that I recently installed.

The mystery: terminal voltage at the new batteries - with either charger - now is 18-20 volts!!. The Xantrex charger is voltage-regulated (supposedly) at either 13.5V or "bulk/absorption/float" voltages, not to exceed 14.7V. Despite that limitation, voltage at the battery terminals was approximately 20 volts and the battery was gassing. I shut the charger down immediately and the terminal voltage fell to approximately 10 volts within an hour.
The new batteries appear to be "dead".

One other piece to the puzzle: when using the automotive charger the other day, I inadvertently switched it (kicked the switch) to 75 amps charge rate - and didn't discover that until 2-3 hours later, at which time the battery terminal voltage was 18.3V.

I've checked the ground cables and can't find a 'short'.

What would account for the runaway charging voltage? What can I do to remedy it? Did the 75 amp/unregulated output from the autocharger "fry" the batteries?
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Old 01-08-2005, 19:10   #2
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Please provide info

Are there any diode isolators between the charging sources and the batteries? Do BOTH batery banks and both alternators appear to be "charging" at 18 V? WHAT exactly are you using to verify the voltage (what meter, what mode, like ac plus dc).

If your new batteries did not expel electrolyte all over the place then it is unlikely that they are fried, yet tell me about any electrolyte loss.

I am very suspicious of just how you are making the voltage measurements because the Xantrex chargers, in general, are not capable of outputing 18V.
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Old 01-08-2005, 19:23   #3
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My first thought was to get hold of an alternative meter and make sure that the numbers you report are correct. However, if the batteries are boiling dry this would indicate tha the system is not working properly.
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Old 01-08-2005, 19:50   #4
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I'd make certain I have the batteries wired together correctly. You want two sets of two of the 6 volt batteries in series, then you want to tie those batteries together in parellel. It sounds like you have one of the 6 volt batteries tied to the twelve volt series.

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Old 01-08-2005, 21:07   #5
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Orrr, just to throw a curve ball, I presume your charger IS 12V, not 24V. I presume you do have a 12V system, not a 24V system you have fitted 12V batteries to. Just a thought, cause otherwise, you have a strange situation.
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Old 02-08-2005, 12:04   #6
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Good questions.

Answers:

The batteries did not expel any liquid electrolyte, but did smell like acid when charging. (burned my nose and eyes slightly)

They're wired as two pairs in series, then parallelled at the pos and neg terminals/cables.

I also suspect my meter, which is a digital TrueValue Hdwe $49 job, set on DCV, 0-20 volt range. My "good" VOM disappeared during the move from my house to the boat.

Initial, pre-installation terminal voltages of the new individual batteries were in the range of 6.8 - 7.5 V, so the batteries and the meter were presumed to be OK.

There are no isolators or combiners in the setup; there is a Link 10 shunt in the ground cable setup, but the Link isn't connected as yet.

It's a 12V system, not 24 or 32.

Rick, yes, both battery banks seemed to be charging at 18+V. That's what initially prompted me to replace the alternator-regulator and to replace the starter bank alternator (which was my spare) with the recently rebuilt OEM, 51 amp Motorola alt. After the changeout, the alternator output voltage for starter bank (with the 'new' Alt and regulator) was showing 18+, which was when I discovered and replaced the broken ground wire from the alt ' -' plug to the engine block.

All cable in the system is over-sized; 1/0 & 2/0and is less than 2 years old.

With the system off at the master breakers for the last 30 hours or so, terminal voltage at the house bank is 11.3V.

One other fact inadvertently omitted from my original post:
After I installed the replacement alternator and regulator, I accidentally attached the wire from the AC tap on the alt to the wrong connection on the electric tach. That caused the wire (and the engine harness green/grd wire) to BURN UP!
However, the two battery banks and charging systems are completely separate, with only an actuator circuit at the ignition switch (which was unaffected) in common. I can parallel the two banks by means of a permanently installed, switched cable between the two battery master switches.

The "overcharge" condition existed before I made that wiring error.
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Old 02-08-2005, 12:20   #7
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While your voltmeter may (incidentally ) be inaccurate, you still shouldn’t have significant outgassing, and ‘dead’ batteries.
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Old 02-08-2005, 20:11   #8
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Mystery (partly) solved:

3 more VOM's later, it appears that mine was crying wolf.
All the others show 13-14 volts when mine measured (!) 18.5.

So, that explains the "overcharging" indications that started the whole mess, but it doesn't explain why the batteries were gassing when hooked up to the external charger, or why the terminal voltage was so low this AM.

'Running the 3-stage Xantrex charger all day today to see if the batteries can hold a charge overnight. If not, it looks like I've fried them and will need replacements.
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Old 02-08-2005, 20:28   #9
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Observe carefully

When charging observe carefully the terminal voltage of the batteries as well as the amount of gassing. I'm thinking that the gassing is minimal (not vigorous) when charging at acceptance voltages near 14.4V. You will not recover those batteries if you do not exceed 14.2 V (unless the battery temperatures are above 90 deg F).

Observe EACH cell for fairly uniform gassing. If two cells in a 6 Volt battery are gassing vigorously and the other cell not then you may have a bad battery. If this is the case after a few hours the two cells gassing will have their electroylite levels rise until it looks like it will overflow. If so, terminate charging.

If your batteries are merely sadly needing a recovery charge (as I suspect) then they will take a long time to charge until gassing becomes vigorous. Do not be afraid to gas the batteries as long as the electrolye does not threaten to overflow or rise to the top.
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Old 03-08-2005, 07:04   #10
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And just to add to Ricks thread, anhinga, you metioned you thought the batteries were gassing because it hurt your eyes and nose. Yep, any charging battery will do that. So don't use that as an evaluation. Any (OK) charging battery will bubble away slightly. I won't or should say, can't add anymore to Ricks informative post.
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Old 18-01-2011, 12:13   #11
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...If your batteries are merely sadly needing a recovery charge (as I suspect) then they will take a long time to charge until gassing becomes vigorous. Do not be afraid to gas the batteries as long as the electrolye does not threaten to overflow or rise to the top.
Is this true of AGM or Gel cells? Should I be worried about a little gassing in trying to recover an AGM battery? How much gassing is too much with an AGM during this process?
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Old 18-01-2011, 17:04   #12
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Greetings and welcome aboard the CF, Opie.

No.
Yes.
Any amount of gassing that "vents".
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Old 18-01-2011, 18:21   #13
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Greetings and welcome aboard the CF, Opie.
Quote:
Is this true of AGM or Gel cells?
Quote:
Originally Posted by GordMay View Post
No.
Quote:
Should I be worried about a little gassing in trying to recover an AGM battery?
Quote:
Originally Posted by GordMay View Post
Yes.
Quote:
How much gassing is too much with an AGM during this process?
Quote:
Originally Posted by GordMay View Post
Any amount of gassing that "vents".
Thanks GordMay!

I have been searching quite extensively looking through posts here on the topic and found some additional posts by Rick that he had had success in bringing back AGM batteries from the dead using a strong equalization process of raising the voltage upwards to 20 volts with a current based on a 2%-7% of the batteries total amp hour capacity. He didn't mention from what I could find, about what to do with gassing AGM type cells and if a little was expected and needed in order to reclaim the AGM batteries capacity.

The post above from Rick mentions what is possible gassing wise with a wet cell but I wondered if there was anymore clarification for AGM type batteries?
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