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Open Roads Forum  >  Tech Issues

 > Another AGM conditioning question

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time2roll

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Posted: 03/06/18 03:01pm Link  |  Quote  |  Print  |  Notify Moderator

Naio wrote:

Okay Max, will do. Starting was around 1.8 volts or something.
An overly discharged lead-acid battery, including AGM, will have very high internal resistance as the electrolyte is almost pure water. As the sulfate ions move back into the electrolyte solution the resistance drops and current flows faster and faster. Once you get above 11 or 12 volts the battery should start to act more normal.

6.8 volts? Keep charging. 5 to 10 amps is plenty. Just let it charge several hours until you get the voltage up to 14.5 then keep a steady voltage until amps drop below 1.

Watch the battery temperature. If battery is shorted it will get hot.


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BFL13

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Posted: 03/06/18 03:05pm Link  |  Quote  |  Print  |  Notify Moderator

Ok then amps going up on a near dead battery is normal. As the battery comes back from near dead, it can accept more and more amps with the charger voltage as set.

Eventually the battery gets back to "normal" and accepts max charger amps for a while, and then amps taper as usual until the battery is full.

If that is what you have going, then IMO (subject to what Mex might say) set the charger to 14.4ish and let the amps climb as long as the battery does not get hot. Amps should only climb to the charger's max amps anyway with a "current limited" charger.

I don't know how that charger works for max amps, so Mex might have to say how that is.

Expect this to take a very long time if the battery will indeed recover.


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Naio

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Posted: 03/06/18 03:31pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks you guys!!!!


3/4 timing in a DIY van conversion. Backroads, mountains, boondocking, sometimes big cities for a change of pace.


Naio

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Posted: 03/06/18 03:35pm Link  |  Quote  |  Print  |  Notify Moderator

Oh, phooey. Mex says in p.m. that the low voltage means it has an internal short and is dead dead dead. I had a ceiling light switch go bad while the van was in storage, that's what killed it. Thanks, all of you, for your help.

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Posted: 03/06/18 03:43pm Link  |  Quote  |  Print  |  Notify Moderator

While MEX is probably right I would still charge 24 hours in a safe place and see what goes.

MEXICOWANDERER

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Posted: 03/06/18 04:30pm Link  |  Quote  |  Print  |  Notify Moderator

Not with the amperage continuing to rise and voltage half of what it should be.

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Posted: 03/06/18 05:20pm Link  |  Quote  |  Print  |  Notify Moderator

MEXICOWANDERER wrote:

Not with the amperage continuing to rise and voltage half of what it should be.


Just so we know for next time, with the battery not getting hot (how hot--wrt to touching it?)

--how can you distinguish between

A. this bad situation with amps rising and voltage at that, and

B. the safe situation with a very low battery where amps rise at first and then then battery acts normally?

MEXICOWANDERER

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Posted: 03/06/18 06:32pm Link  |  Quote  |  Print  |  Notify Moderator

This info wasn't published...time spent charging =+ total amp hour capacity. I know of no lead acid battery that has recovered successfully from a 50% cell voltage that had spent time utterly and totally depleted. 0.00 volts, then a rebound to 50% voltage after extensive charging attempts.

With something like a Megawatt, current limiting through a light bulb (amperage throttle) is the only safeguard that would prevent runaway. A 25 watt bulb would limit current to two amperes and change.

Hasn't had a heartbeat in a half hour would be an appropriate analogy as to why mouth-to-mouth would be futile.

Sometimes it's best to yell "Uncle" and settle for a low battery cutout.

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Posted: 03/06/18 06:51pm Link  |  Quote  |  Print  |  Notify Moderator

The example I saw with a really low battery bank (two 6s) still had enough volts to allow the smart charger to operate. That meant the battery was over 4 or 6 volts whatever the charger spec on that is.

( If lower voltage at first, you need a non-smart charger (like jumper cables) to get past 4-6 volts first, then cut in the smart charger and it will do its routine.)

The smart charger (a Vector A model) was set at 14.6 and battery voltage slowly climbed while amps did too, until it got to the "mid-voltages" when things went to "normal" and the batteries did ok after that.

Still not sure how you can tell it is not going to work (unless the battery gets hot) unless you try it. ?????

time2roll

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Posted: 03/06/18 07:25pm Link  |  Quote  |  Print  |  Notify Moderator

Well if the battery has been getting 10 amps for 24 hours then there is no reason to go another 24 hours.

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