Overheating Battery Issues

[Amnesia II]

This has me scratching my head!

On my Catalina 42 I have a 790 ah battery bank. The temp sensor is located on one of those bateries..so an overheating issue will only be notified if THAT battery overheats.

Infact that is what did happen...the batt with the sensor on it dropped a cell and overheated and I was notified by the Prosine display.

That was lucky, I thought, so I took that dead batt out of service and all was well. then a few weeks later a batt with the sensor on it overheated again!! I took that out of service and carried on

So, I've arrived in Australia and for the 3rd time the batt with temp sensor overheats and I'm thinking this is too much of a coincidence...something funny is going on!!!

The first two overheatings occurred at sea on my Pacific crossing, batteries being charged by the engine driven 200amp alternator.
The third overheating occurred on Bundaberg marina while on shore power and through my onboard battery charger.

The 79AH AGM's were installed 2008 and of high quality so is it just that it's their time to fail? Or is something funny going on with my electrical system?

[Cheechako]

it is a litle wierd that only the battery you put the sensor on went bad... 3 times... what are the odds? Also wierd that 3 batteries would fail prematurely. Over charging? Maybe the batt manufacturer is having a bad batch..?

[foggysail]

Are your batteries 79 or 790 amphour rated? Sure, if they are only 79 amphour rated and your charging with a 200 ampere alternator you must have a temperature sensor that reduces the charge rate as a function of the battery's temperature.

Others who are more up on this most likely will reply.

Foggy

[westwinds]

Probably a short somewhere in the electrical system, but everything should be fused to prevent this. Unlikely to be a shorted cell on all the batteries that "failed" Maybe one cell, but too much of a coincidence for more than one battery to fail this way. Did the batteries feel hot? Might be the temperature sensor is at fault. These batteries can take a tremendous amount of charge current, but not sure what would happen if the voltage regulator failed with the battery fully charged, but then more than one battery would be affected if in parallel and overcharging took place.

[Ike]

AGM batteries are temperature and charging voltage sensitive. I would suspect overcharging. Check the voltage output of the alternator. If it is more than 14.5 volts your are cooking the battery. Most AGMs require a charging voltage between 14.1 and 14.4 volts. Unfortunately many alternators put out more than that and need to voltage regulated for AGMs and Gel cells.

[phorvati]

I am not sure about overheating. Ive had AGMs (420AH) since 2009. I regularly get high voltage, 15-16V, sometimes from solar/wind, sometimes from alternator. In 3 years they never felt warm to the touch. On a sunny windy day, i would come home, link 10 would show +20AH, +30Ah, on few occasions +40AH, meaning i covered last night's use plus another 40AH. Voltage would be at 15V, 16V, and batteries feel cool to the touch.
AGMs have very small internal resistance in comparison to lead acid. Small internal resistance means no internal losses, and no heating. Mine don't sit in those plastic boxes.
When you get an alarm did battery feel hot to the touch? It would be nice to know how hot the battery is.

[Ike]

If your read the owners manuals and talk to the battery manufacturers they will all tell you not to exceed 14.4 volts and to use a temperature regulated charger. They will also tell you the quickest way to kill an AGM or Gel is overcharging and/or overheating. I have never used these batteries, I use old fashioned wet cells, but I have talked to the manufacturers and many users and invariably the ones that died were due to overcharging.

That does not mean that the temp sensor isn't faulty. It might be. But I would check charging voltage first.

[sailorchic34]

I would load test the "Dead" batteries first. Three batteries that show overheating but only the ones with the sensor on... well to me I would look at the temp sensor first before tossing the batteries.

Of course it could be that all the AGM are cooked. They get really annoyed with over voltage. Why I too use wet cells. More forgiving if something else goes south

[noelex 77]

Welcome to the forum
As sailorchic says check the temp independently. You can feel a hot battery, but an IR thermometer is a great bit of gear to have on any boat.
Check the charging voltage with a mulitmeter and make sure it fits in with battery specs.

If your boat batteries are wired incorrectly as 90% of boats are (with both the + and - leads to battery switch coming from the same battery) then that battery receives a higher charge than the other batteries. This battery will be first one to overheat if your charging voltages are too high.

[sailinglegend]

I was going to buy an alternator battery temperature sensor for my Lifelines but the supplier said not to bother because they just don't overheat - unless there is a fault - and I have 5 in my house bank so where to put it?

My shorepower charger has a battery temp sensor but that has been disconnected because it tries to put more volts on the battery to get them up to 25 deg C!!!!!!!

I would agree you should have them in warm climates - but not necessarily with AGMs.

[GordMay]

Greetings and welcome aboard the CF, Amnesia II.

[noelex 77]

Originally Posted by sailinglegend

I was going to buy an alternator battery temperature sensor for my Lifelines but the supplier said not to bother because they just don't overheat - unless there is a fault - and I have 5 in my house bank so where to put it?

My shorepower charger has a battery temp sensor but that has been disconnected because it tries to put more volts on the battery to get them up to 25 deg C!!!!!!!

I would agree you should have them in warm climates - but not necessarily with AGMs.

I think you are misunderstanding how the temperature sensors work.The temperature sensors on all regulators (alternator, solar, battery charger and wind) generally serve two important functions.

1. They adjust the charging voltage based on the battery temperature. All manufacturers recommend charging set points be adjusted for temperature.
Even if the battery does not heat up during charging variations in ambient temperature should result in a variation in charging voltage.

2. If a fault develops in the battery (like an internal short) and the battery heats up to a dangerous temperature the charging will be disconnected.

The latter function unfortunately will only work with the battery to which the sensor is attached, but if you can sandwich the sensor between two batteries, you can get reasonable protection for both.

The temperature sensor is still valuable even if no heating of the battery occurred during normal charging.

[FlyingCloud1937]

Originally Posted by noelex 77

I think you are misunderstanding how the temperature sensors work.The temperature sensors on all regulators (alternator, solar, battery charger and wind) generally serve two important functions.

1. They adjust the charging voltage based on the battery temperature. All manufacturers recommend charging set points be adjusted for temperature.
Even if the battery does not heat up during charging variations in ambient temperature should result in a variation in charging voltage.

2. If a fault develops in the battery (like an internal short) and the battery heats up to a dangerous temperature the charging will be disconnected.

The latter function unfortunately will only work with the battery to which the sensor is attached, but if you can sandwich the sensor between two batteries, you can get reasonable protection for both.

The temperature sensor is still valuable even if no heating of the battery occurred during normal charging.

Don't forget a temp censor for the alternator, especially for charging AGM's and Lith, it will save the alternator from burning up. FLA's also need a alternator temp sensor, when you have a large bank in ratio to the size of the alt.

lloyd

[Cheechako]

Originally Posted by sailorchic34

I would load test the "Dead" batteries first. Three batteries that show overheating but only the ones with the sensor on... well to me I would look at the temp sensor first before tossing the batteries.

Of course it could be that all the AGM are cooked. They get really annoyed with over voltage. Why I too use wet cells. More forgiving if something else goes south

Wow... good point... I assumed he knows the batteries are bad... not just indicating overheating!

[witzgall]

+1 on the wiring issue. Do you have the positive and negative leads going to the same battery? If so, then there is your likely problem, or at least there is one problem. The positive cable need to be on one end of the string, and the negative at the furtest _ terminal at the other end of the string.

Chris