Gas Alarm - worth it?

[CharlesM]

Hello All

I wonder (stupid statement) if anyone has any opinions regarding Gas alarms.

Now I feel they are a worthwhile piece of kit, but not sure about their practicality.

My mate has one on his Moody, and it goes off at odd times, when there seems to be no indication of a gas leak. Now I am aware these detectors do not only detect propan & butane, but solvents and the like as well. Anyway, he tends to switch it off, which to my mind means one might as well save cash and not install it in the first place.

Is there a solutio0n to these finikey gas alarms?

In another thread someone said the consume a lot of power. Does one keep it on all the time while on board?

Finaly, does anyone have the £39.95 12/240v gas alarm advertised by Compass, and is it any good?

Thanks
Charles

ps - maybe in a few months I will be able to post posts without the question mark, but maybe even answer some - heres hoping. hehe

 

[iangrant]

Charles

For what it is worth, mine has gone off twice for (apparently) no reason, once at 0200 hrs with SWMBO on board. (She was out on deck quicker than you could say oh bollox). The other time it was singing to itself when I went down the the boat one evening. The gas was turned off at the bottle!

Anyway I'd rather it was that way than the other and it didn't go off when it should. I test mine now and again and get my gas system pressure tested one a year.

Keep on asking and I'm sure you'll get answers,

Ian

 

[tome]

[ QUOTE ]
get my gas system pressure tested one a year

[/ QUOTE ]

I just bet you do, and no wonder she was out on deck faster than a robbers dog. That was before the alarum went off!

 

[tome]

Gas alarms are a bit of a double edged sword on a boat. The detector needs to be mounted low to be effective, but they are very susceptible to moisture so the ideal place to mount one for gas detection (bilges) provides the worst environment.

We have one beneath the cooker but the sensor has just gone faulty so the system is disconnected. I'll replace the sensor, but have meantime fitted an inline leak-detector at the gas bottle.

 

[iangrant]

Doh, you have to be so careful what you say on here, I meant:

The gas system installed on the vessel is fully pressure tested with the correct, calibrated equipment operated by a qualified technician who is registered and authorized to issue a CORGI (marine derivative) certificate.

We will have no mention of getting any ladies gas tight thanks.

Ian

 

[jerryat]

Hi tome!

I had the same problem as you and others and had the damned thing going off at random too. I traced the cause to one of the cleaning liquid bottles stowed under the cooker, the ingredients of which were evidently enough to trigger the sensor.
I cured the problem by buying a different sensor that can be varied for sensitivity by adjusting a screw (potentiometer?). I set it to go off when a gas cigarette lighter flicked open (but obviously not lit) and held near the sensor for a few seconds just set it off. No problems since, and I check the system the same way a couple of times a year.

Just an idea!

Cheers Jerry

 

[tome]

Hi Jerry

Sounds like a good solution - do you recall what the sensor was and where you bought it?

 

[itsonlymoney]

I'm in the Gas trade and your right certain solvents will set them off. My hand held gas leak tester is affected by "gas leak spray" which is a real pain sometimes. As previously stated better to have it go off every now and then than not at all. If you are mounting a detecter remember that Butane / Propane gas is heavier than air and therefore any escaped gas will drop to the lowest level ie bilges, so it could be critical where you mount it.
Ian

 

[Hardley]

Mine has been on the boat for 14 years and still working OK.
I would not sail on a boat that did not have one fitted.
Have run mine for up to 10 days, without switching off, very little drain on battery.
Must be fitted as low as possible.
Self tests every time it is switched on, but I do occasional check with gas lighter.
Mine went off when cooker developed a leak and when I was laying Trackmark in the cockpit.
Spend the money, it might save your life and boat.

 

[CharlesM]

so is one gets an alarm, should you go for single or multiple sensors. Also, what about solenoid switches or only audable alarm?

Cheers
Charles

 

[iangrant]

Mine is a single sensor, like Tomes, under the cooker, the most likely place for a gas leak. You may want one in the bilge but as has been said they are sensitive little wotsits.

Solenoid switches are mandatory in the States I believe, but not in Europe. I rely on turning off at the bottle anyway.

Ian

 

[jerryat]

Hi Itsonlymoney and tome!!

My sensor is sited about one inch above the floor of the bilge and as near to the underside of the cooker as it will go (about 6 inches away) so is in the ideal place as we never get any water at all in the bilge.

Tome, I'm away from home at the moment but back in a few days. I'll see if I can dig out the sensor receipt (it's been a few years since I bought it!) and post the info you're after on this thread or advise you otherwise. I do remember it being quite pricey relative to the cost of the alarm itself and it may be that someone else on the forum will be able to offer a cheap(er) supplier.

Cheers Jerry

 

[bluedragon]

I just bought a Pilot Mini gas alarm (about to be fitted). This had the lowest standby current draw I could find and seems to have a good reputation. I have a long keel / deep bilge, so water, gas, screws, anything, seems to run downhill to one point just forward of the engine. So whilst keeping it above normal bilge water level, that's where I'll try the sensor. By the way, a gas alarm saved a friend's boat...it was flooding and the gas alarm went off, acting as a bilge water sensor! I don't know if they all do that, but an interesting side benefit.

 

[BobOwen]

Do bear in mind that human "gas" sets them off too......:>)

 

[Matrosen]

We have a solenoid fitted in the gas locker so that there is only gas in the boat when the cooker is on. I have also fitted a pressure gauge between the bottle and the solenoid so that I can check that the solenoid is shutting correctly. Yes, the gauge could go wrong as well, but then it's time to give up and go to the pub.

 

[pappaecho]

Gas alarms have two functions, one of which is not documented. They firstly detect gas, and generally pretty well. Secondly they have low voltage thresholds, which vary from make to make. In any event they will sound off if the voltage drops below a certain voltage. This not usually documented, or if so in small print so small only lawyers can read it. I found this out by chance, as my beer cooler (fridge) had run the service battery down to below 9 volts last year. Off went the alarm!
Much time spent like headless chickens trying to find the gas leak. Since then have observed several false alarms at the Folly in Cowes, and have in each case found a depleted battery. I suspect therefore that low battery voltages are the source of most false alarms. I think that the makers could do more to indicate the voltage at which the alarm will sound, when the threshold low voltage is reached.
For another 10p they could add another LED indicating low voltage

 

[ongolo]

It is not to say, that the alarm goes off when the battery voltage goes low. This depends if the sensor circuit is biased to positive or negative rail.

I have designed andbuilt my alarm system and have one sensor for explosive gases and one for CO (carbon monixide) detection. The latter because I plan to install a solid fuel stove.

The only sensors I have found all need a 5Volt 100mA heating current, so that is about 2.5Ah per day or equivalent to a 20W bulb bunring for 1.5 hours.

It is very easy to built a gas detector, all it needs is a 741 op amp , a few resistors and diodes, a 7805 voltage regulator and a simple printed circuit board that you can draw by hand.

The advantage of building it your slef is that you can leave the electronics in a dry place and only keep the sensor for explosive gases below the stove. The other CO sensor should be in a saloon or cabin/bunk area.

In my case I integrated low voltge, over voltage, water in diesel and gas alarms and connected them via different audible alarms. Gas alarms are really horrid sounding as the most severe, next is water in diesel, not as irritating and voltage alarms rater mildly noticeable.

My philosophy is, If I designed it and built it in the first place, I can repair it again as well


regards ongolo

 

[Becky]

When we bought Cornish Maid, the cooker didn't have fail-safe gas rings, so I fitted a gas alarm. It had 2 sensors, one placed below the cooker, the other in the engine room. When we had been to a dinner in Cowes, with a guest staying with us, on returning to the boat, the alarm was singing away. Strangely, I was the one left to go below to sort it out! HWMBO and our guest stayed on deck. It was the blower heater which had failed to start that was the fault, and the sensor in the engine room had been set off.
BUT, sadly chivalry is dead on CM : /forums/images/graemlins/frown.gif /forums/images/graemlins/frown.gif /forums/images/graemlins/frown.gif

 

[CharlesM]

Hey Ongolo

Could you supply us with the design? It might be an interesting project to build one.

Charles

 

[ongolo]

Charles, yes I could and I will,

It shall include the cct diagramm, and even a layout of a number of boards. Etching is done best with a staedtler lumo colour red 317, it must be the red, the others are not acid fast. Etching is done best with a mixture of hydrochloric acid and peroxide. Dont leave that smoking mixture inside or near tools and machines. It make steel rust a mile away. For drilling a little dremel tool with discarded dentist drill will do. or 1.2mm ordinary drill running at 10000 rpm or more.

I have also designed a single univiersal board that can be:

overvoltage
undervoltage
water in diesel
gas detector
hamcom modem
and there was something else which I forgot

Depending on some straps one inserts or ommittes all based on 741 op am.

However, when I am deisgning for myself, I dont take notes, "bacause I know", then some of the more complicated things, I look at later and swear I have never seen it before. That universal board works, has a strapping list for each application even. But there may be a bug some where that I fixed but not recorded.

The alarm boards are much more straight forward and consist of 3 different small printed circuit boards, maybe it is four. If you PM your email address and can read .dwg or .dxf files you can attempt it. If not just say and I sort something out. I have a number of free cad programms.

If you have a machine with sound cards, I can let you have sw to convert your pc to an oscilloscope, which is handy to do the testing. I have a real oscilloscope and cannot vouch how well the sw works, but frequency seems to be limited to about 20Kz which is sufficient for testing an gas alarm.

However, at present, time wise, I cannot spend much time on anything but the boat. I will have the time to send you the drawings, but no description, you have to puzzle it out. Or what would also work, we had a site where we posted technical thing on yahoo groups. then anybody can down load, but as long as the description is not complete, I am reluctant to publish anything.

I have a list a mile long of boat projects which I want to publishj eventually, that is making good anchors, traditional blocks, a sterntube that is oil filled, and the whole boat design for an amatuer, a new way of lofting. And electronics.

One day, it will be in PBO. In the meantime I will pass it on to forumites. But hurry, in about 2 weeks I am off the net.

regards ongolo