Another goofy battery problem

[Mesquito]

OK we are at the campground, plug in to shore power -everything works. The next day interior lights start going out. Check the battery and one cell is boiling, voltage is 21. Everything checked out before we left - battery was good. Everything else works great but we have no lights. Any ideas? Disconnected battery to be safe. Help!

[donn]

Converter dead killing the battery in the process.

[LadyWindrider]

Agree, converter in overcharge and won't drop out. Only other explanation, bad cell in the battery. Now I don't understand why the lights would be going out if you have 21 volts, but to be safe, disconnect the battery. Insulate the positive terminal, or just disconnect the ground lead (negative), only. Wait one hour and check the battery voltage. Make a note, should be rather high, 14 volts or so. Check again in 12 hours or so, if less than 10 volts, bad cell. Also check the voltage at the battery terminals. Don't hook back up, just check from positive to negative, and see if down around 14 volts or so. If not fried converter.

[Mesquito]

Thanks guys. If the converter fan runs 24/7 would that be an indication it is bad or is that normal?

[LadyWindrider]

The fan runs when the converter gets hot. After it cools down, it should shut off. How long it runs depends on the load on the converter, and the temp in the trailer. I would immediately disconnect the negative off that battery if you haven't. The converter will run the trailer, average load. Besides, that only takes a little time, not $$$$. Wait a few minutes, and check voltage between positive wire on battery, and dangling ground wire. If the voltage comes back to around 14 volts, probably a bad battery. If it stays at 21 volts, then the converter is bad, and it may be too late to save your battery, in which case, now you have to buy both. Just my 2 cents, but your camper and $$$$.

[Dave_Monica]

The converter fan running 100% of the time would be bad and a sure sign that not all is right.

Dave

[TURBS]

If you have a wfco brand converter
I would suggest not replacing it with another wfco.
If its under warranty pay the little bit extra for a progressive dynamics with charge wizard.

Wfco id short for junk

[dnaraG_1M]

Originally Posted by windrider

The fan runs when the converter gets hot. After it cools down, it should shut off. How long it runs depends on the load on the converter, and the temp in the trailer. I would immediately disconnect the negative off that battery if you haven't. The converter will run the trailer, average load. Besides, that only takes a little time, not $$$$. Wait a few minutes, and check voltage between positive wire on battery, and dangling ground wire. If the voltage comes back to around 14 volts, probably a bad battery. If it stays at 21 volts, then the converter is bad, and it may be too late to save your battery, in which case, now you have to buy both. Just my 2 cents, but your camper and $$$$.

Just curious. What sort of fault in the battery could cause
a terminal voltage of 21VDC? (Assuming a voltage-limited
charger - which a good one should be.)

A shorted cell should - as bitter experience shows - produce
a LOWER terminal voltage. An open cell would produce a
terminal voltage of 0VDC. A sulphated battery producing
a lower max current output.

I don't see a battery fault mechanism that would produce
21VDC. The only way that I can see 21VDC on the terminals
is if the charger was at fault, allowing too high a charge voltage.
Yes?

His statement that the battery was boiling would seem
to confirm that, right?

cheers,
johnd

[LadyWindrider]

A shorted cell would cause increased current flow, thus tricking the charger in to thinking it needed to produce more current and voltage to charge the battery faster. Thus the converter would produce a high voltage and wait for the voltage to drop before it started to reduce current. That would explain the fan running all the time, producing high current constantly. It is all in the electronic brains of the converter.

[dnaraG_1M]

Originally Posted by windrider

A shorted cell would cause increased current flow, thus tricking the charger in to thinking it needed to produce more current and voltage to charge the battery faster. Thus the converter would produce a high voltage and wait for the voltage to drop before it started to reduce current. That would explain the fan running all the time, producing high current constantly. It is all in the electronic brains of the converter.

Only if it was brain-dead enough to produce too high a voltage.
A good quality charger is BOTH current and voltage limited.
And not tricked so easily. Agreed that a shorted cell that
lowers the internal impedance and terminal voltage of the
battery can confuse SOME chargers. A truly "smart" charger
will switch off the charge current regularly and measure
the terminal voltage. Finding terminal voltage too low (shorted
cell) would cause the charger to quit and light a fault indicator......


But sounds more likely (to me) that the pass transistor in
the charger was stuck in in it's lowest impedance mode,
causing the max voltage the charger can produce to be
output. This can happen due to several single point failure
modes - shorted pass transistor, defective voltage sense
circuit, other failure points depending on type of
charger - linear or switching mode. Have experienced all
of these kind of failures at one time or another............

Still a very good reason to suspect the charger; the smell
of fish hangs heavily in the air. Unfortunately, the boiling
may well mean that the battery is toast, regardless of
original fault. Ouch.

cheers,
johnd

[LadyWindrider]

From post #10, "A good quality charger is BOTH current and voltage limited.
And not tricked so easily."

And when did you ever see a "good quality" charger in a camper. Sorry, not wanting to start a war. It could be either, but disconnecting the battery is cheap, fast, and easy, and will tell a lot. And neither of us know what converter or battery the OP has.

[dnaraG_1M]

Originally Posted by windrider

From post #10, "A good quality charger is BOTH current and voltage limited.
And not tricked so easily."

And when did you ever see a "good quality" charger in a camper.
You didn't listen to the salesman???
Seriously, I get the idea that some of the third
party replacements may be, at least, close to
good quality. OEM stuff? Yeah OK.

Sorry, not wanting to start a war. It could be either, but disconnecting the battery is cheap, fast, and easy, and will tell a lot. And neither of us know what converter or battery the OP has.
Nope, we don't.
And I hope that he doesn't connect a fresh battery
to a questionable charger, thinking the problem
is solved. Seems a lot more likely
the charger is the primary culprit.....

Cheers,
johnd