Carbon monoxide going off - possible causes?

[Grumpydev]

So the last few days the carbon monoxide alarm has been going off on my boat at night (Sealine S34) - I haven't been at the boat, only noticed via the security camera, and it had stopped by morning but then started again that night.

I was there all day yesterday, with heating on etc. from about 9am to 5pm and not a peep out of it (or any effects from co poisoning in myself), but noticed there was a reed diffuser right next to it, so thought it might be that, or maybe the unit was faulty. I fitted a second detector in the bedroom, can't be too safe, locked it all up and left, but then it went off again about 9pm that night (just the old one), so assumed it must just be a faulty unit, but then checking at 8am this morning the new one is also going off and reporting carbon monoxide issues.

The engines haven't been run for 2.5 weeks, the gas heating was on yesterday for a few hours (checked exhaust was working fine) but was switched off several hours before leaving, and prior to that hadn't been switched on for 4-5 days before the alarm started sounding.

The gas system is switched off, and hasn't been used since 3rd march.

The only things "on" on the boat is the battery charger, the sockets to run a small oil filled radiator, and the two fridges because we left food there.

The one that went off first is in the galley on the port side, the one that went off second is in the front cabin on the sb side.

Does anyone know what might be causing it? I'd read that dying batteries can emit carbon monoxide, but I spent 3-4 hours in the engine room yesterday doing jobs and there was no sign of "fizzing" or excess heat (or any ill effects for me, but I obviously had the hatch open). I can't think how an oil filled radiator could cause it. Could the galley fridge somehow be emitting either CO or some kind of gas that's fooling the detectors? Although I'm not sure why that would only manifest in the evening.

I'm pretty stumped, but obviously can't risk staying at the boat until we get to the bottom of it, which we're meant to be doing next weekend, so any thoughts would be greatly appreciated.

 

[MoodySabre]

The only time mine has gone off was when the batteries were cooking. I never leave the charger on these days.

 

[jdc]

+1 for batteries. CO alarms are very sensitive to Hydrogen, and just as for MoodySabre above, the only time I have had the CO alarm go off was outgassing from a boiling battery. Switch off the battery charger is my advice, and feel the batteries to see if one is hot - I found one really very hot which I very carefully (no spark!) disconnected and then threw out, and all was well thereafter. Ventilate well!

 

[Grumpydev]

Thanks both, the battery charger is on so hopefully its "just" that and I can isolate / replace.

 

[mikegunn]

+1 for battery problem. The alarm is sensing fumes from a battery that is suffering a cell failure. I experienced a similar problem a couple of years ago and thought I had faulty alarms. Further exploration revealed a battery that was too hot to touch!! I presume that the alarms were sensing hydrogen gas. DO NOT TOUCH ANY SWITCHES IN THE BOAT TO PREVENT ARCING. Isolate the shore power from outside the boat and allow the batteries to cool down and their location ventilate any accumulation of gas. Only then will it be safe to investigate further. When batteries explode they make one hell of a bang!
Mike

 

[Momac]

My guess would be its the bow thruster battery which is faulty .
Battery gas is a rotten egg smell which you may notice.
In the meantime switch the battery charger off immediately. The duff battery may be hot so , as said, let it cool down before removing it .

 

[Grumpydev]

I was just about to leave, having turned off the charger and checked all the engine bay batteries, and I just thought I didn't check the bow thruster battery!

Not entirely sure where it is, I'm guessing under the bed somewhere

 

[Grumpydev]

That was it! Still pretty warm to the touch, even after several hours without charging - I thought the heads was a bit smelly yesterday, but must have been this.



Any recommendations on a replacement? I guess it needs to be pretty heavy duty given how much umph the bow thruster uses.

 

[mikegunn]

Glad you’ve found the culprit without further incident. Out of interest, what’s the voltage across the terminals? If you’ve found the battery to be of adequate size in the past I would recommend going for the same capacity but substituting it with a gel type. Then you can forget about having to check its cells for water loss. Particularly useful if it’s in an out of the way place such as under- bunk.
Mike

 

[Alex_Blackwood]

That was it! Still pretty warm to the touch, even after several hours without charging - I thought the heads was a bit smelly yesterday, but must have been this.

View attachment 174053View attachment 174054

Any recommendations on a replacement? I guess it needs to be pretty heavy duty given how much umph the bow thruster uses.

That is a Flooded Lead Acid Battery which needs the cell electrolyte level maintained with Distilled or De-Ionised water. Given that you were unsure of its location I bet it is bone dry!! It is marked 85UKG. I reckon it is 85 ahr. I would suspect that that Paul R. would recommend an AGM replacement. What is the power rating of your thruster?
MG just beat me!

 

[Boater Sam]

Be very careful! And be aware that Hydrogen Sulphide ( H2S ) from a 'cooking' battery will set a CO alarm off.
H2S is an insipid poisonous gas, slight exposure can dull the olfactory nerves so that you don't smell the bad eggs smell after a while. It is also cumulative in your body and toxic.

 

[Momac]

The bow thruster is only used with the engine running so doesn't need a huge Ah capacity . But it does need to be an engine starter battery.
It must fit in the box and have the correct terminals for ease of fitting.

The QL guidance for the BP600 is 100Ah but not sure a 100Ah battery will fit in the battery box?



https://www.moegster.no/QL BP800.pdf

I have a 60Ah sealed starter battery and it works fine. But the suggestion of a gel battery is good.

 

[westernman]

The bow thruster is only used with the engine running so doesn't need a huge Ah capacity . But it does need to be an engine starter battery.
It must fit in the box and have the correct terminals for ease of fitting.

The QL guidance for the BP600 is 100Ah but not sure a 100Ah battery will fit in the battery box?
View attachment 174055


https://www.moegster.no/QL BP800.pdf

I have a 60Ah sealed starter battery and it works fine. But the suggestion of a gel battery is good.

Indeed a normal starter battery would be much better than a leisure battery.
The higher the "Cold Cranking Amps" (CCA) the better.

 

[Grumpydev]

Thanks folks, I've only had the boat a few weeks so still getting to know it. I've no idea if the current capacity is sufficient, but I suspect the battery is quite old so I assume it served its purpose. My main concern is making sure whatever I replace it with fits in the box, as getting this one out of the box was a bit of a sod!

 

[Grumpydev]

Potentially stupid question - I've isolated those battery cables with the isolator at the foot of the bed, am I OK to use the inverter and charger with these cables disconnected? Main reason I'm asking is I measured the old battery, but stupidly didn't measure the box - may as well wait to see whether I can get a larger aH battery in there (the height was main issue getting it out, think it still had some wiggle room otherwise)

 

[PaulRainbow]

Potentially stupid question - I've isolated those battery cables with the isolator at the foot of the bed, am I OK to use the inverter and charger with these cables disconnected? Main reason I'm asking is I measured the old battery, but stupidly didn't measure the box - may as well wait to see whether I can get a larger aH battery in there (the height was main issue getting it out, think it still had some wiggle room otherwise)

Fit one of the same size, but go for AGM. With respect to post #9, gel is a very expensive option compared to AGM, which still has the important feature of not needing to be topped up.

 

[westernman]

Potentially stupid question - I've isolated those battery cables with the isolator at the foot of the bed, am I OK to use the inverter and charger with these cables disconnected? Main reason I'm asking is I measured the old battery, but stupidly didn't measure the box - may as well wait to see whether I can get a larger aH battery in there (the height was main issue getting it out, think it still had some wiggle room otherwise)

For windlass it is CCA which is more important than Ah.

 

[PaulRainbow]

Indeed a normal starter battery would be much better than a leisure battery.
The higher the "Cold Cranking Amps" (CCA) the better.

"Leisure" and "Marine" batteries are starter batteries, with a bit of extra cell support (if you are lucky).

The ones to avoid for bow thruster and windlass use are true deep cycle batteries.

 

[mikegunn]

Go with Paul R’s suggestion. A more considered response than mine.
Mike

 

[Grumpydev]

I have a procharge ultra battery charger, which has different settings for AGM and sealed lead acid (which all my engine room batteries are) - won't it cause issues if I just change the bow thruster battery to AGM?