Need some battery advice!

[Powerstroke2000]

I'm currently having had an issue with my Interstate 12V (dual) batteries in my Arctic Fox camper, in that after 3 days of boon docking, my fridge stopped working, thus realizing I must be below 6 volts of power (was told the fridge needs 6V to run while on propane). After the 3 days we where back on the road, so the truck charged the batteries to the point where the fridge would run fine, and after that we stopped where we would have shore power for the few nights prior to heading home.

I did pull my batteries and put them in my garage on a piece of carpet and my 4 stage charger started out showing 25% power in the battery, and within a half hour it was up to 100%. I'm unsure if this is a true 100%, or if the charger has been fooled in some way, as it didn't take long to get to where it should have been. I say this, as I put this same charger on my wife's car, where she was having no battery issue, but when I put it on it showed her battery at 50% and it took overnight and into the late morning before 100% showed. My charger breaks down the sulfation process, but whether the battery is at a true 100% I don't know on this camper battery. I have another 12V interstate (currently in the camper which I'll change out with the charged one) and see how long that one takes as well. I think these batteries are about 5+ years old, but we're thinking of perhaps going to a motorhome, so I don't know if it's worth spending the $$ to change them out, or if a full charge and maintenance through the winter (if it didn't sell) is worth it?

[KX5002]

Q: What do engineers use for birth control?

A: Their personality!
Badum tsssss

[MEXICOWANDERER]

Yeah but coming from an "engineer" it is way out of line. Stuff like that turns people off. The best argument is an informative counterpoint.

[KX5002]

For the record... I was not insulted... I thought it was pretty funny

[westend]

MEXICOWANDERER wrote:
Just My Opinion-

The following really damaged the validity of the remainder of the post.

Not being a psychologist or psychiatrist, I'll pass on evaluating your sanity

There is NEVER a reason to publicly insult someone on a tech or information forum. Disagree(?) counter something with pure facts minus disparaging personal comments.

Mex,
The member he quoted and answered had, "Am I nuts ?" at the end of his post. It invites a diagnosis.

[MEXICOWANDERER]

" The problem with paralleling different capacity batteries is that the discharge curve isn't linear. Once you draw a certain amount of power, the smaller of the batteries can become a load on the larger. It will work, but you don't get the capacity increase you might think you are getting. Your actual capacity will be close to two of the small batteries in parallel rather than the sum of the two"

The larger accumulator will augment the voltage of the smaller if the chemistry and construction are twins. Do an amp hour test to verify this. The results of which will be indisputable. The science can be compared to adding a smaller shock absorber in tandem with a larger unit.

Different chemistries are another animal. A shorted cell is the antagonist in a paralleled configuration. Thus 9 batteries with open cells can be paralleled with a remaining "good" battery with no ill-effect on the good battery. But the nine must not have a quiescent self discharge rate higher than the good battery.

This is not an esoteric subject. Identification of a shorted cell can be done with incidental specific gravity measurement or time-elapse voltage degradation of isolated batteries (meaning out of circuit).

[MEXICOWANDERER]

Just My Opinion-

The following really damaged the validity of the remainder of the post.

Not being a psychologist or psychiatrist, I'll pass on evaluating your sanity

There is NEVER a reason to publicly insult someone on a tech or information forum. Disagree(?) counter something with pure facts minus disparaging personal comments.

[OldSmokey]

jplante4 wrote:

KX5002 wrote:
Why wouldn't you parallel 12 volt batteries?

I found this curious as well. If you don't parallel the batteries, how do you wire them? Is one just a cold standby?

Nothing curious, you just don't have two 12 volt batteries in the first place.

FLA batteries come in 2,4,6,8 and 12 volts and of capacities up to many thousands of Amp/hrs as you need.

Standard practice ( in the professional solar arena ) is to establish the required capacity first, then select cells to fit the desired voltage requirement.

for example: say you need 600 Amp/hr capacity and a voltage of 12 volts. you have several solutions:

1. a single 12V battery of 600 A/hr
2. two 6V 600 A/hr batteries
3. six 2 volt 600 A/hr cells

most often the choice of battery is determined by cost, load and expected lifespan. quite often it is actually more cost effective to use smaller voltage cells than one big multiple cell battery.
it all depends on the intended use.


I will be posting a battery/solar design tutorial soon to cover the issues I see here on the RV forums. there seem to be an increasing number of posts regarding solar/batteries, and too many conflicting answers..

[RJsfishin]

Well the battery knowitalls are at it again.

If everyone would just read and listen to the info and advice of BLF13,
the battery world would be a better place.
Any post that says not to parallel 12v batteries, should be deleted immedieately !

As far as paralleling batteries of different capacity, that also works perfectly, as the system charge and discharge rates are controlled by voltage, not amp capacity.
When it come to batteries, there is probably dam little that BLF13 has not done, tested, and proven from vast hands on experience. Just believe it !!

[jkwilson]

Double posted

[jkwilson]

BFL13 wrote:

jkwilson wrote:

BFL13 wrote:
"You don't want to connect batteries of different capacity or condition in parallel."

Yes to condition, no to capacity. No problem paralleling different capacity batteries. They charge and discharge in proportion. They maintain the same voltage and SOC.

The charger tuned to stop at 1a per battery would stop at 2a on the pair.

The problem with paralleling different capacity batteries is that the discharge curve isn't linear. Once you draw a certain amount of power, the smaller of the batteries can become a load on the larger. It will work, but you don't get the capacity increase you might think you are getting. Your actual capacity will be close to two of the small batteries in parallel rather than the sum of the two.

My Trimetric shows otherwise, but I am off camping so will not be able to continue this for now. Maybe some others can chime in.

Actually adding the two gets you more than their total, in effect, because of Peukert, but they still remain proportionate.

I wouldn't disagree that they can play nicely together, but for the average user two identical* batteries are less prone to pitfalls. Often a smaller battery uses different plate geometry which can affect internal resistance when new and the rate at which the battery ages.

*The differences in batteries off the same production line can be pretty profound. I used to spend days measuring internal resistances of hundreds of commercial batteries to assemble a stand-in for a large high voltage battery bank before we thought to specify internal resistance when we purchased.

[BFL13]

jkwilson wrote:

BFL13 wrote:
"You don't want to connect batteries of different capacity or condition in parallel."

Yes to condition, no to capacity. No problem paralleling different capacity batteries. They charge and discharge in proportion. They maintain the same voltage and SOC.

The charger tuned to stop at 1a per battery would stop at 2a on the pair.

The problem with paralleling different capacity batteries is that the discharge curve isn't linear. Once you draw a certain amount of power, the smaller of the batteries can become a load on the larger. It will work, but you don't get the capacity increase you might think you are getting. Your actual capacity will be close to two of the small batteries in parallel rather than the sum of the two.

My Trimetric shows otherwise, but I am off camping so will not be able to continue this for now. Maybe some others can chime in.

Actually adding the two gets you more than their total, in effect, because of Peukert, but they still remain proportionate.

[jkwilson]

BFL13 wrote:
"You don't want to connect batteries of different capacity or condition in parallel."

Yes to condition, no to capacity. No problem paralleling different capacity batteries. They charge and discharge in proportion. They maintain the same voltage and SOC.

The charger tuned to stop at 1a per battery would stop at 2a on the pair.

The problem with paralleling different capacity batteries is that the discharge curve isn't linear. Once you draw a certain amount of power, the smaller of the batteries can become a load on the larger. It will work, but you don't get the capacity increase you might think you are getting. Your actual capacity will be close to two of the small batteries in parallel rather than the sum of the two.

[TomG2]

mbopp wrote:
That's the problem with 12V batteries in parallel - a bad cell in one battery will drag the good battery down. I'd have them both load tested.

Wouldn't there be a similar problem with one bad cell in a pair of 6V's in series? In fact, once the bad cell is located, he could proceed with just the good 12V battery. Can't do that with a pair of Sixes.

[BFL13]

"You don't want to connect batteries of different capacity or condition in parallel."

Yes to condition, no to capacity. No problem paralleling different capacity batteries. They charge and discharge in proportion. They maintain the same voltage and SOC.

The charger tuned to stop at 1a per battery would stop at 2a on the pair.