Charge driven cooling fan control needed.

[billknny]

Forget everything about controlling a fan from the charging voltage, or anything else around the alternator. It adds a level of complexity and fussiness that is just not at all needed. Do not overthink this.

I'll bet you your engine ALREADY has relays that are activated when the ignition is turned on. If you don't know, hire someone who does.

Just add an extra relay that switches the fan on whenever the ignition is on. Your engine will like the cool air as much as your alternator!

A helpful hint to keep a blower lasting a LOT longer: Use a 24 volt blower on the 12 volt circuit. Yes it will run slower, but it will last two forevers. The ones in my engine room are standard Jabsco squirrel cage blowers that are 25 years old, have 10,000 hours, and two circumnavigations. I have the same model fan running at full rated 24 volts as a galley extraction fan that is lucky if it lasts 500 hours.

Also, remember, if you are blowing air INTO the engine room, it has to get OUT. If the only way out is into the cabin, you and your crew will be a very unhappy campers.

Our engine ignition switch turns on TWO blowers. One blowing in (near the engine air intake) and one up high in the engine room that sucks OUT. Hot air is the enemy of engine performance.

[mlydon]

okay, okay - i’ll run a relay off the regulator off the balmar power circuit, fans will come un whenever I have ignition turned on for simplicity.

While the oil pressure switch idea is nice, they are usually NOrmally Open, reverse of what’s needed. I like the limit switch idea.

GILow was wondering about no current blowers - it’s a ‘67 Columbia 50, has survived 53 years without one so far. Wood sole and interior, so the engine compartment is plenty ‘leaky’ - tons of floor penetrations for plumbing and wiring.

It currently has a yanmar 4jh-hte with manual stop linkage - there are no relays on that engine to ‘double up’ on.
The engine is amidships under the cabin sole, about 5’ behind the mast. I can pull ‘intake air’ from the undersink cabinet in the head, will only have about a 3’ run to the alternator. Exhaust air is another story- it’s about a 20’ run from on top of the engine to the stern, where I have a pair of 3” cowl vents. I was thinking of using a 4” blower to dump air into the cockpit locker/cockpit sole area, where it could naturally circulate back to those vents, rather than run a 3” duct all that distance to one of the cowls, but Just had a second thought, though, that if I had a smoky mess at some point from an oil leak, that would be dumped in there too, mucking up a LOT, so maybe I’d better duct. Those stern cowls also service a westerbeke genset in the lazerette, so I’d prefer to leave them be....maybe just duct to the lazerette........You’ve gotta love design compromises (sigh)

Thanks for all the input so far guys, much appreciated. Keep it coming.

Matt

Ps - there’s a line drawing of the boat here - you can see my duct-run problem....

https://sailboatdata.com/sailboat/columbia-50

[Cpt Pat]

Electrically actuated air conditioner compressor clutch if you want to drive the fan mechanically. Available at any auto parts store.

But since the fan consumes practically no power, and there's no way to over-cool an alternator: why do you need this extra complexity? Just connect the fan to the alternator belt drive or the alternator drive pulley and spin it mechanically instead of electrically.

Or if you really need an electrical switch that closes contact when the engine is running, use your oil pressure warning sender switch. Most make contact to ground (engine chassis) when the engine is running. If it has only one wire then it's that type.

[mlydon]

Pat,
oil pressure warning switches make contact when the pressure is LOW, lighting up warning lights and buzzers. Opens with pressure, turning OFF 12 volt things.

Also, alternators already have mechanical fans built in.....the goal here is to bring cooling air from outside the engine space directly to the alternator intake at the rear of the alternator, requiring forcing air through a duct, most easily handled by in-line electric fans commonly available.
matt

[Cpt Pat]

Originally Posted by mlydon

Pat,
oil pressure warning switches make contact when the pressure is LOW, lighting up warning lights and buzzers. Opens with pressure, turning OFF 12 volt things.

Also, alternators already have mechanical fans built in.....the goal here is to bring cooling air from outside the engine space directly to the alternator intake at the rear of the alternator, requiring forcing air through a duct, most easily handled by in-line electric fans commonly available.
matt

Thanks for the details. And you're right: a relay would be needed to invert the action of the oil pressure sender.

[jkleins]

I had the system you are trying to get too. Big blowers that blew right on the two alternators I had in my last boat. It really works great to keep the output of the alternators up when the batteries are taking it all. I was looking for an automatic solution but ended up just putting two switches with lights by the ignition.
The reason was they were fairly noisy and I wanted to be able to turn them off when I didn’t need them. You usually only need it for a short time as the batteries start to limit the alternator output enough that the temp is not the limiting factor. When idling into an anchorage the blowers were louder then the engine. Then at anchor I could put the output blower on and turn the input off and get some of the heat out of the boat. It was easier to remember then I thought and if I didn’t I could usually see the charge output dropping and it would jog my memory.

Jim

[wsmurdoch]

It is not unusual to have an oil pressure switch with two screws on it. One is the NC contact and the other is the NO contact. One sounds the low oil pressure alarm, and the other turns on the fuel pump. I first learned about them from the installation instruction sheet for my Walbro fuel pump. Since then I have run into them several times. Here is the first one Google found.

https://www.pegasusautoracing.com/pr...BoCHRgQAvD_BwE

Bill

[Reefmagnet]

You can buy voltage controlled or timer relay PCB's off Ebay for a few bucks each. The manufacturing quality is quite good and you can carry spares for the price. Either could be used to achieve your objective.

[slug]

Originally Posted by mlydon

Okay, all you lurking E.E. types...

I want to start a blower to feed fresh air to my alternator, but ONLY when my engine is running (and presumably charging). As I have other charge sources on the boat, I need the circuit to be powered by my ignition.

I’m thinking a relay that closes on ignition switch voltage feeding power to some sort of voltage driven relay to start the blower when voltage climbs above nominal.

In this way, the blower is automatic so I don’t forget it, won’t run if I have a high voltage from solar or battery charger, and also won’t run after shutting down with a high voltage on the bank. As such a blower will only draw a few amps, an acr isn’t really called for.

Does this sound reasonable, and anyone have a source for a ‘voltage switch’ or whatever you would call it?

Matt

Engine room temp peaks after the engine is shut down
Good idea to add a timer circuit that lets the blower run an extra ten minutes after shut down

[Cpt Pat]

Has anyone tried employing a water-cooled alternator? Example: https://oppositelock.kinja.com/water...ors-1686524549

We already have circulated raw water available. All it would require is another small heat exchanger and closed-loop circulation pump. It would alleviate the problem of creating more heated air to expel. It seems (to me) an obvious solution.