CO2 Detector Going Off

[hockeybill]

Hi all ... We are in our second summer with our 2008 42DS. Love the boat and really enjoying cruising the Chesapeake. We are having an issue periodically with the.CO2 detector going off in the middle of the night or when we are away from the boat. Perfect example ... arrive at a transient slip around 4 PM today. Hot 95 degree day and once settled we turn the A/C on. 11 PM rolls around and the boat CO2 detector above the control panel starts going off. No idea why. If it was left over engine fumes from a leak in the exhaust, it should have gone off earlier. Even so, I have gotten into the habit of leaving the key on for about 20-30 seconds after I press the button to turn the engine off to let the blower pull the hot air out of the engine compartment. What could be generating CO2 (A/C, refrigerator, etc) ... or be causing this to give a false alarm? Thanks in advance for any advice.

[hockeybill]

Clarification ... carbon monoxide detector, not carbon dioxide.

[Charlie-Bravo]

Doesn't sound good ..... as a first move, I would buy another detector, place it by your original one, see if they both go off more or less at the same time, in an effort to see if it is a dodgy alarm. If they do, then I would suspect exhaust , diesel heater, oven problems, fully vent the boat including the bilge, and don't rest until you find the cause, 
Sure others will know of a good list of causes.

CB

[alenka]

Venting batteries will trigger Carbon monoxide alarms.  Are you charging the batteries from shore power at the times it goes off?

Ours would go off at 3 in the morning when on shore power. Never when being charged from the engine or at sociable hours.

[Syrah]

We have a CO monitor in our 42ds. It always reads zero. I agree that the first thing to check is the instrument itself.

[Syrah]

Some other thoughts (I was an oil industry Chemist in the first decade of my career): CO comes from the partial oxidation of carbon-containing compounds; it forms when there is not enough oxygen to produce carbon dioxide (CO2).

On a yacht, the top sources of CO would be the fuel for the engine, generator, diesel heater, oven/stove, etc. ie. Anything that uses a carbon based fuel.

I would also think there would be a possibility that it could come from the carbon contained in the plastic insulation of wires, particularly if that wire was overheating. It would likely be a low oxidation regime. With your sensor mounted above the control panel, I’d be flipping it down and looking for any visible signs of components overheating behind that panel.

(I still think it’s just as likely that the test equipment could be the faulty component)

[MalcolmP]

Worth checking that your batteries are not being overcharged and gassing as hydrogen had been reported to trigger CO monitors hawkequip.com/hydrogen-gas-false-readings-carbon-monoxide-alarm/

[hockeybill]

Thanks to all for your responses. Consensus view is that I am overcharging the batteries and the sensor is picking up hydrogen sulfide.battery  Charger off tonight and we will see.

[alenka]

Let us know the result.

After my initial false alarms one of our house batteries died a week or so later, but by the time we had worked that out, it had dragged the other two down and they failed very shortly afterwards.

Annoyingly, I had asked the yard to drop test the batteries before we launched and they said they were fine... Which I suspect means they merely checked them on the panel voltage meter and not under load with appropriate device.

Good Luck with your search for the source.

[Mistroma]

Yes, it is very well documented that carbon monoxide (CO) detectors are sensitive to hydrogen from overcharging batteries. I don't think that cross sensitivity with hydrogen sulfide is a problem for common CO detectors. You would smell hydrogen sulfide but be oblivious to hydrogen.

It would be useful to know where your sensor is located. I assume it is built into the unit in the panel beside the chart table and that's quite far from the domestic battery bank.

I found that the underside of the panel covering the battery box was badly dis-coloured on my 42DS. Just lift the berth cushions and then the panel along the bottom. You will probably see signs of vapour on the underside if the batteries have been gassing a lot for a long time.

I actually fitted forced ventilation to my battery compartment and the fan only goes to full power when voltage is high enough for gassing. I installed a lower sealed lid and also fitted straps to act as hinges and can easily prop up the cushions and panel to work on the batteries, water-sep. and mains charger. Quite a useful, simple and cheap modification.

I would be a bit surprised if hydrogen was reaching the main saloon as it tends to move upwards and dissipates quickly. It is unlikely to travel along spaces behind panels and fittings as there are 2 bulkheads in the way. Holes are mostly quite low down. The most direct route involves passing through the aft. cabin, aft. head and then into the main saloon. I would expect most would escape upwards.

[alenka]

My battery bank is located under the aft cabin berth and the sensor was in the galley when it went off. It is normally in the aft cabin. (I would hate to be sleeping in there whilst under passage (on engine) and the crew kill me off!).  The velcro holding it in place had given up so it had been put on the counter in the galley pending refitting.

It was our first night onboard following winter lay up so I guess the batteries were hungry even after 3 hours of engine. 

[Syrah]

Jul 5, 2020 12:08:48 GMT Mistroma said:

I would be a bit surprised if hydrogen was reaching the main saloon as it tends to move upwards and dissipates quickly. It is unlikely to travel along spaces behind panels and fittings as there are 2 bulkheads in the way. Holes are mostly quite low down. The most direct route involves passing through the aft. cabin, aft. head and then into the main saloon. I would expect most would escape upwards.

The location of your sensor seemed to be too far away from batteries for it to drift there, but if the aircon is running when this happens, where does it draw fresh air from? Is there a cabin outlet vent directed towards the sensor.

[Don Reaves]

Jul 4, 2020 3:09:53 GMT hockeybill said:

Hi all ... We are in our second summer with our 2008 42DS. Love the boat and really enjoying cruising the Chesapeake. We are having an issue periodically with the.CO detector going off in the middle of the night or when we are away from the boat. Perfect example ... arrive at a transient slip around 4 PM today. Hot 95 degree day and once settled we turn the A/C on. 11 PM rolls around and the boat CO detector above the control panel starts going off. No idea why. If it was left over engine fumes from a leak in the exhaust, it should have gone off earlier. Even so, I have gotten into the habit of leaving the key on for about 20-30 seconds after I press the button to turn the engine off to let the blower pull the hot air out of the engine compartment. What could be generating CO (A/C, refrigerator, etc) ... or be causing this to give a false alarm? Thanks in advance for any advice.

I have had a similar problem since replacing my CO detector this spring. I had installed a home unit, but this morning some renewal paperwork from my insurance company indicated I should install marine-grade CO detectors instead. I've ordered two of these, which I'll install the next time I get to my boat.

Are you using a marine-grade CO detector? The marketing information indicates that they are more accurate (i.e. fewer false alarms), and I'm hoping this will solve my problem.