Overheated battery - any ideas?

[LittleSister]

I was investigating a lack of puff from the engine battery and was shocked to find that it appears to have partly melted its case, burning (or so it looks) through the sail tie that was wrapped round it, and leaving a clear impression of the fabric in the plastic case of the battery, which now bulges at the top and the sides. I guess we were lucky not to have a full blown fire or split battery case.

The label on the battery says if it gets hot stop charging it, but of course it lives in a fairly inaccessible place out of sight and one wouldn't know in normal use. We never smelt any burning. The battery is a sealed type 'Red Flash'. The other (domestic) battery does not seem to have suffered, though as it weighs a ton I haven't lifted it out yet.

Any ideas what would cause this degree of overheating? Presumably something to do with overcharging due to fault on alternator voltage regulator, or a short inside the battery? The engine battery is charged by the alternator, and the domestic battery is charged when a voltage sensitive relay cuts in (at least in theory - I don't have much confidence in the wiring skills of the previous owner).

Also, could this overheating cause a noxious, sewerage farm type smell? We've been suffering with a mysterious pong that we thought was coming from the heads, but have been unable to find anything wrong with the plumbing. The batteries live in a compartment behind the heads, and when the pong appeared we had been doing quite a bit of motoring, so perhaps the two things are related.

 

[l'escargot]

[ QUOTE ]
...Also, could this overheating cause a noxious, sewerage farm type smell? We've been suffering with a mysterious pong that we thought was coming from the heads, but have been unable to find anything wrong with the plumbing. The batteries live in a compartment behind the heads, and when the pong appeared we had been doing quite a bit of motoring, so perhaps the two things are related.

[/ QUOTE ]
It is quite normal to get a "rotten eggs" smell from the toilet when it is first used after it has stood for more than a few days - this is caused by bacteria in the "clean" seawater intake pipe when it is flushed the first time. This should however disappear after the first few flushes. If it remains it may well be the battery.

 

[roly_voya]

Rotton eggs is sulpher, yes can be decaying vegitation in the inlet loo pipe but in this case I think it will be reduction of the sulphuric acid in the battery as the electrolite boils off. In this case its a starved gell so there is not much water in there and it will boil of very quickly. The only way to have spotted the fault would be that there was an unusually large charge current when the cell shorted. Some battery monitors have a temp sensor linked in but usually only on on the house bank so that doesn't help. If it's any consolation they do not usually catch fire. The best safely device to prevent future problems is to fit a domestic smoke alarm above the batteries but one of the type designed for kitchens that senses heat rather than smoke.

Replacement - From the description of the house battery it sounds like it is a deep cycle flooded bank, if so is ther a fast charge/seperate regulator or other multi-step charger attached? If the answer is yes this was the cause of the problem. Gell cells have a different charge characturistic with a lower max voltage tollerence (14.4 instead of 14.8) so you can mix the two types on the same charger. If you do you either boil the gell sells by charging them on the flooded rate as you did or the flooded cells die from sulphation because the wont fully charge on the gell cycle. When replacing the start battery make sure its the same type as the house bank. I would advise staying with flooded cells unless you have a very good reason to change as they are half the price and last twice as long in cycle use (little difference except cost for start batt). If you PM me with a list of the components and settings I can confirm if this is likely to have been the problem or get a qual;ified marine electricion to look at it.

 

[SwedishLass]

I boiled a battery in a similar set up. Engine and house charging separated using a vsr. Alternator regulator had blown due to accidental switching of the isolator.
The alternator had been pumping out 17 volts and as the start battery is the first in line it got the bulk of the overcharge, sounds & smells like cause is similar. I use a couple of leisure batteries, more than enough to start engine, just enough for the house but space is limited. I now have a voltmeter situated where it can be seen. Anything over 14.5 and I worry.

 

[trouville]

same hear.On my Hillyard motoring all day.By very good luck i stopped to anchor on a sand bank miles out at sea there were dozens of boats already.

Once the engine was off i lifted a locker for something & saw a battery boiling to melting point!It was a wonder the gas hadent exploded.

I had two alternators then i just took the fan belt off.Could have been very bad

Later in port i dropped the offending battery and alternator overboard & replaced it with a dynamo!I kept an alternator but fitted a magnetic clutch

 

[whipper_snapper]

As others have said, the classic 'rotten eggs' smell is hydrogen sulphide. This is produced both by a battery in pain and by anaerobic growth in the heads plumbing. When it is from the heads, in my experience, you get a blast of smell when you pump after it has been unused for a while, and it is unmistakable where it comes from - it hits you as you make the 1st few strokes.

An overheating battery produces a constant stream as it charges, so it should not be hard to distinguish them.

From what you say, I would be 100% confident that it is the battery that is responsible for the pong.

You should be aware that it is quite toxic and should avoid prolonged exposure. Although it rarely kills anyone because it smells so foul!

 

[pampas]

wet cell batterys will charge on the lower setting for matt cell batterys, In 9 years of this regime I have never had to top up any of my batterys, Just changed the start one, lasted 10 years the others are 5 &7 years old. So Mr Sterling is right.

 

[Bilgediver]

Although it rarely kills anyone because it smells so foul!
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Unfortunately this is not true.......Yes it smells foul and yes yes it does kill so is treated with respect where it might be encountered.

Unfortunately when H2S is encountered it deadens the nerves in the nose so the longer you expose yourself to it the less you smell it. Therefore a good idea to get out from a noxious compartment and vent it before enjoying prolonged exposure fixing the problem. Mind you it is not normally encountered in dangerous concentrations on boats but you never know.......Too many hard boiled eggs for breakfast might tip the balance..

/forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif

 

[LittleSister]

Thanks for all the analysis and suggestions.

Roly-Voya, the engine battery is (or was!) a DMS Technologies Red Flash 1100 "lead acid battery" "non-spillable". I'm not clear whether that's a gel battery or not. The domestic battery is a Lifeline AGM (I think 105ah), which I guess is something like gel, as it says can be used on its side or upside down. These were at the time the previous owner fitted them (about 2 or 3 years ago) the recommended 'upgrade' batteries for the S100 electrics system from Merlin Equipment of Poole. (I rang them today, but haven't yet been able to speak to their technical person. I notice that they no longer advertise the Red Flash batteries, and now recommend special starting batteries from Lifeline and another manufacturer I've forgotten the name of.)

The batteries are charged by a 40W alternator without, as far as I can see, any fast/multi-stage charger or external voltage regulator. The engine charges the engine battery, and a voltage sensitive relay is supposed to cut in the domestic battery when the voltage rises to (I think) 12.7 volts.

There is a battery monitor (BEP DCM600) in the boat but it is not wired up (it's on my list but hadn't got to the top!). As far as i can see from a brochure I inherited with the boat this won't measure battery temperature, but I don't have full details or a wiring diagram for it.

Having had trouble starting a couple of times a few days ago, I checked using a multi-meter and found that the engine battery was showing only 10.2 volts (no load). (At this time I hadn't seen the damage (only top of battery is fully visible) but did think I hadn't previously noticed the top of the battery was convex!). On starting the engine (using the domestic battery) I found that the voltage across the engine battery rose to 14.7 volts, and if I manually switched in the domestic battery again it fell to 14.2 volts.

I don't know if any of that means anything to you in terms of judging whether it was likely to be overcharging. If it wasn't that what else might be the cause? I'd like to avoid having the same thing again (though the boat had been fine for the one month previous that we've had it in use.

You say to get the same type of batteries for engine and domestic. So, given that I have a seemingly perfect AGM domestic battery I should get the same (i.e. AGM) for the replacement engine battery? If so would you advise against using as a temporary measure an old Varta B17 Blue Dynamic (I think it's not gel) I have lying around?

At least I've now got the mystery 'toilet smell' solved! I'll warn the bank about the impending damage for a new battery!

 

[LittleSister]

Update:

Problem solved - It turned out to have been an internal short of one cell in the engine battery.

The person I eventually spoke to at Merlin Power-Store (who had supplied the batteries and other electrical gear to the previous owner) was very knowledgeable and helpful, and immediately had it diagnosed over the phone as either failed alternator regulator or internal short in battery, and as soon as I told her the voltage readings I had obtained (see earlier posts) said "There's nothing wrong with your regulator, it's an internal short in the battery" (which in turn was causing alternator regulator to go bananas).

She was insistent that there wasn't an issue with charging voltages for the batteries in question, and that these were perfectly capable and happy with the higher charge level for liquid type batteries. When I wondered aloud whether I should get a fancy multi-stage regulator (which might have been a sale for them) she said "You don't need one".

As she predicted the system worked fine again with a replacement battery. I'm temporarily using an old Varta battery I had lying around, but this is too big for the available space, so I'm planning to buy another AGM type from Merlin.

I mentioned that I had a battery monitor (supplied by them) fitted in the boat, but that it wasn't wired up, and I didn't have a wiring diagram. I was amazed when she was able to tell me off the top of her head which of the eight terminals should connect to what! She also directed me to where on their web-site I could download a full wiring diagram and owners' manual.

Many thanks to all you Forumites for your help, and to Vicky at Merlin Power-Store for great service and advice.

 

[ShipsWoofy]

[ QUOTE ]
So Mr Sterling is right.

[/ QUOTE ]

Mr Sterling is always bloody right, he will shout it down the telephone at you if you disagree. Such a shame as I might have bought his kit otherwise. /forums/images/graemlins/mad.gif