Alex_Blackwood
Well-known member
Something else to go wrong when none of it was needed in the first place!
Alternator / engine room fan thermostat
- Thread starter Molteni
- Start date
Ian_Edwards
Well-known member
How on earth do know that " none was needed in the first place"?
You have absolutely no knowledge of the set up on my boat. Or the problems I've had with things getting too hot and failing, resulting in very expensive repair.
The location of these three devices isn't ideal but there's very little I can do about that. They have been added over the years, sqeezed into spaces with poor ventilation.
Adding thermostatically controlled fan, have proved to be reliable and solved the problem.
The forum members may have similar issues, and find that these simple and cheap units may help.
harvey38
Well-known member
What kind of fan do you use?
lynallbel
Active member
How old was the last alternator?
As already mentioned as it is close to the block I reckon you are on a hiding to nothing, Iirc air is 27 times less efficient at heat removal than liquid?
As most modern cars are so power hungry, their alternators are going to be working harder than most marine units.
As already mentioned as it is close to the block I reckon you are on a hiding to nothing, Iirc air is 27 times less efficient at heat removal than liquid?
As most modern cars are so power hungry, their alternators are going to be working harder than most marine units.
Alex_Blackwood
Well-known member
In your case I would have thought that simple switches would do the same job, if the fans are indeed so essential. In the case of the fridge the fan could be controlled by the fridge circuit to come on as required. I just don't think you need to over complicate , but I am not you and I am not criticising your choice, just don't wholly agree. However, I was more pointing at the OP's situation where he has an alternator "Capable of producing 60 amps" which later became a 90 amp alternator. This alternator was seen briefly ? to produce 84 amps, well within FLC . He has two holes in his engine compartment through which the engine draws air. One of these holes has a fan which he wants to switch on, to extract air, once everything is hot. This fan is spinning the wrong way as the engine is sucking air in, so the fan when it does switch on is going to be fighting against the engine suction and adding at least 5amps to his alternator load. The hole without the fan would be just as beneficial! Also as already stated additional complex equipment is only something else to go wrong when , if a fan is considered absolutely essential, a simple switching arrangement would suffice. As I said in my original reply to the OP I think it is overkill. Again as in your case It is his decision for his boat.
geem
Well-known member
Engine extract is a normal provision. We have it on our boat. We have had centrifugal fans that can generate high pressure. They moved a lot of air. We currently have an axial flow fan that moves a surprisingly large amount of air and heat from the engine room. Assuming a good free air inlet there is no conflict between combustion air requirements of the engine and extract ventilation requirements to remove heat. A simple switch is robust and reliable.
Molteni
Member
Finally wired in the extractor fan, which will now draw air in past the alternator.
Much better than the original system where the air was drawn in at the opposite end of the compartment and gave hardly any cooling effect to the alternator.
The concern has always been for the alternator overheating under very heavy load.
Just done a calc for airflow.
The 1400cc engine will need around 1000 litres of air per minute at 1500rpm which is about 37 Cubic feet. The extractor fan is rated at 270 Cubic feet per minute so should now provide significant extra cooling for the alternator.
Much better than the original system where the air was drawn in at the opposite end of the compartment and gave hardly any cooling effect to the alternator.
The concern has always been for the alternator overheating under very heavy load.
Just done a calc for airflow.
The 1400cc engine will need around 1000 litres of air per minute at 1500rpm which is about 37 Cubic feet. The extractor fan is rated at 270 Cubic feet per minute so should now provide significant extra cooling for the alternator.
geem
Well-known member
Is the extractor fan a scroll type fan or axial?
The scroll type fans use lots of power, they rumble a bit but have high performance against any pressure drop. The axial fans move a lot of air with a minimal imposed pressure drop but as soon as you introduce a pressure drop their performance drops substantially. They also have a more high pitched sound.
We converted our engine extract room from a Jabsco scroll type fan to an axial but in the process cut a lot of elements within the system that were causing pressure drop. The axial fans cost about £30 compared to £250 for the Jabsco. By changing the system we still pull as much air out of the engine room at a lower power requirement but with a slight increase in noise level. When the fan fails (which it will do due to the operating temperature) the cost of the replacement is not so eye watering
NormanS
Well-known member
Is the fan an extractor fan? In which case it is fighting against the inward air flow generated by the engine. Or is it bringing in extra cooling air from outside? In which case, the engine room is slightly pressurised, with the result that engine room smells are spread through the boat. Which is it?
harvey38
Well-known member
I run two these -
SEAFLO 12v x 320cfm FLEX MOUNT BILGE MARINE BLOWER (02 series) boat ventilation | eBay
For ten minutes when we shut the engines down, they are vented through the hull overboard to bring the temperature down in the engine room., very effective and quiet.
SEAFLO 12v x 320cfm FLEX MOUNT BILGE MARINE BLOWER (02 series) boat ventilation | eBay
For ten minutes when we shut the engines down, they are vented through the hull overboard to bring the temperature down in the engine room., very effective and quiet.
geem
Well-known member
His post says extractor fan. The previous post says air from outside
NormanS
Well-known member
That's precisely why I'm asking.
Molteni
Member
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Alex_Blackwood
Well-known member
To be accurate, I think, The fan is an extractor taking air from the engine compartment The air inlet to the compartment is via a cockpit locker which has an inlet vent adjacent to the engine control panel. At least hat is what I gleaned from the original posts.
Beaten by 10 sec.!! from that diagram he will recirculate warm air!
Molteni
Member
but rather cooler than before
GHA
Well-known member
Just a little info-
Pity I can't find the data now, but from logging & graphing with ds18b20 thermometers on engine head, exhaust & alternator, the engine & alternator temperatures were always pretty closely matched, with the alternator lagging a little as the engine warmed up.
But,,,,,,,,
That wasn't under full load. 120A alt & lead acid batteries would never be so discharged to accept anything like that for more than a minute or so.
Fan sounds cool idea, but without logging it's hard to know just what's going on .
Pity I can't find the data now, but from logging & graphing with ds18b20 thermometers on engine head, exhaust & alternator, the engine & alternator temperatures were always pretty closely matched, with the alternator lagging a little as the engine warmed up.
But,,,,,,,,
That wasn't under full load. 120A alt & lead acid batteries would never be so discharged to accept anything like that for more than a minute or so.
Fan sounds cool idea, but without logging it's hard to know just what's going on .
Alex_Blackwood
Well-known member
Time will tell! Seriously, I do think you were over worrying the alternator problem. However if what you have done works and you have peace of mind. great! Would be interested to have the results after a reasonably long period of motoring.but rather cooler than before
geem
Well-known member
That not going to work efficiently. You will be recirculating a lot of hot air. You need to extract directly to outside.
Molteni
Member
The new system will be using the large cockpit locker as a "heat sink" so air flowing past the alternator will be cooler than before
PaulRainbow
N/A
But it's still bolted to the 80 degree C engine. How do you imagine that the alternator can be any cooler than that ?