AGM Battery - Very Hot and Sulfur Smell

[VVD]

Mark,

Thank you for your help. I will have a look at how the regulator is wired. An electrician came aboard yesterday and indicated our alternator had an internal regulator (which we didn't know). We for sure have an external Balmar.
We measured the output with the positive probe on the alternator and the negative on the battery negative as well as on the engine. Should we test the resistance of the battery cable to check that the problem is not in the circuit?

We will run some tests on the regulator.

I am not assuming a short or leak but want to rule out any additional problems before we install new batteries.

Thanks again

[colemj]

It is possible that your alternator has an internal regulator, but that would not be in use if the external was hooked up, nor would it fail-over to the internal if the external went bad. Is it a Balmar 6-series alternator? If so, that does have an internal regulator, and you could probably get it back on-line by reconnecting it. That is very easy to do - look in your manual.

Measure the voltage on the battery terminals themselves when the alternator is running. If they are below 14.4V, then the regulator may be OK and the cabling a problem (too small or loose/corroded connection).

Good luck,
Mark

[VVD]

Mark thank you,

I am not sure of the make of our alternator. When measuring the output at the battery terminals themselves we measure 14.2V/ 14.3V. Even before we had this problem, we have never measured more. The regulator is set for them to go to that level and not above. Maybe we need to modify that setting but this rules out a problem in the circuit right?

[CarlF]

Charging most AGM's at high voltages (14.6v) is thought to keep them from sulfating but this is a theory. There's a lot of confusion as to why some AGM's are having early failure. I'd be really surprised if your 14.2v charge rate alone caused the problem.

Going back to your first post, all evidence points to a single bad cell in that battery. If so, it's unlikely that it's your fault but a manufacturing defect. Is your battery stil under warranty? If so, the manufacturer will probably replace it.

Now that the suspect battery is out of the bank, is the bank behaving normally (both charging and capacity)?

Carl

[Paul L]

What brand of AGMs do you have?

[colemj]

Originally Posted by VVD

Mark thank you,

I am not sure of the make of our alternator. When measuring the output at the battery terminals themselves we measure 14.2V/ 14.3V. Even before we had this problem, we have never measured more. The regulator is set for them to go to that level and not above. Maybe we need to modify that setting but this rules out a problem in the circuit right?

If you are measuring 15.5V at the alternator output terminal and 14.2V at the battery terminal when the alternator is running (and at 15.5V), then it suggests there is a voltage drop on the cable connecting the alternator to the batteries.

I would look at the connectors for corrosion or looseness and cable size. What size and length cable and how large of alternator?

Mark

[colemj]

Originally Posted by CarlF

Charging most AGM's at high voltages (14.6v) is thought to keep them from sulfating but this is a theory. There's a lot of confusion as to why some AGM's are having early failure. I'd be really surprised if your 14.2v charge rate alone caused the problem.

Going back to your first post, all evidence points to a single bad cell in that battery. If so, it's unlikely that it's your fault but a manufacturing defect. Is your battery stil under warranty? If so, the manufacturer will probably replace it.

Now that the suspect battery is out of the bank, is the bank behaving normally (both charging and capacity)?

Carl

If I understand him correctly, the rest of the bank is not holding a charge or getting above 12.1V.

Mark

[vientoman]

AGMs really have no place on a boat, see the many posts on them elsewhere IMHO

dave

For safety reasons, in cats that can be lived in after capsize. AGM;s are recommended.

for mono's that sink, it should not matter. ha.

For the sake of the OP, Please disregard the comment about mono's vs Cats.

[VVD]

Hello everybody and thank you for your help.

The alternator was removed, tested and serviced. The voltage it was putting out was oscillating a lot, between 12V and 17/18V. The shop serviced it and it is now presumably much more stable, between 13.8V and 15.5V.

While it is obvious our alternator was troubled, could it alone have caused our batteries to overheat or overcharge? We are puzzled as to how this could have happened without the regulator ringing an alarm or "regulating" the voltage if it was to high (Balmar MC-612)?

The electrician seemed to indicate that it was the jumps in voltage that caused the overheating. Is this a valid explanation?

We will test the regulator further and make sure it is working properly.

Thank you

[btrayfors]

The MC-612 is an excellent voltage regulator. You should NOT be seeing voltage "jumps". Assuming the MC-612 is correctly programmed and correctly wired, including a voltage sense wire to the batteries being charged, the regulator will control the output of the alternator.

Yes, 15.5VDC is quite enough to cause overcharging of AGMs if the charge continues long enough. Most AGMs should be charged at 14.4 to 14.6VDC in the absorption phase.

If you are measuring voltages higher than about 14.6 at the output of the alternator, and if the MC-612 is indeed controlling the alternator's output, that suggests that the voltage sense wire either isn't there or it's not connected properly. The regulator may be incorrectly determining that the battery voltage is too low, and thus raising the output voltage of the alternator.

Another possibility: the temperature sensor(s). The MC-612 can have a temp sensor for the batteries and for the alternator. If either of these sensors is not working properly, that can result in some strange (and sometimes damaging) events.

Be sure there's a good ground cable from the alternator to the batteries....this should be the same size as the main charging cable. Don't depend on the engine ground for the alternator return.

Bill

[btrayfors]

Originally Posted by VVD

The alternator was removed, tested and serviced. The voltage it was putting out was oscillating a lot, between 12V and 17/18V. The shop serviced it and it is now presumably much more stable, between 13.8V and 15.5V.......

How was this measured? With the MC-612? With another external regulator? Are you sure the alternator is set up for external regulation, and that the MC-612 is correctly wired to it?

Bill

[VVD]

Thank you Bill. We had our alternator serviced and it appeared to work properly but today we see it putting out more than 100AMPS on 1400RPM, while it should not put more out than 64AMPS. What could cause this?

[Bash]

On a previous boat I was advised to disable the internal regulation on my alternator if I was using an external regulator. I wonder whether having two competing regulators could have been the source of the voltage spikes?

[smac999]

Originally Posted by goboatingnow

AGMs really have no place on a boat, see the many posts on them elsewhere IMHO

dave

lead acid has no place anywhere. that sh*t is nasty. I go through new jeans every couple weeks.

so many boats I look at have an inch of acid in the battery boxes. and that's if they have boxes... acid in the bilge is probably great for the hull...

[svinshallah]

One quick reminder. The "sulfur smell" you got is hydrogen sulfide gas produced when the sulfate on the plates reacts with hydrogen gas produced from the electrolyte. It's common when you let the plates uncover (dry) and then try to charge the battery. It is poisonous in parts-per-billion levels and is particularly dangerous because it will quickly desensitize your sense of smell. The combination of no sense of smell and the extreme toxicity makes it doubly dangerous.