I am constantly surprised

[Chief Engineer]

at some of the gadgets and gizmos that some owners or mechanics(?) put on engines.

Just today I worked on an Atomic 4 that had a huge Electric Fuel Pump (for diesel fuel only) mounted on the side of the engine. It also had a solenoid fuel shutoff mounted at the tank. It had the normal oil pressure switch that powered up the fuel pump.

I wonder who sold the previous owner that "Bill of goods"

Earlier this season I had a call for "loss of power" on a Yanmar 1gm.
The guy had someone put an engine driven reefer compressor and a 100 amp alternator on it.

The mechanic(?) put a switch on the alternator to "take it off line" when he needed full power.

I can't even begin to think how somebody could do this and sleep at night.

Attention on deck....the ranting light has been extinguished

[delmarrey]

I see you haven't been around boats long.

Just kidding, of course. I'm sure we all have some stories!..............._/)

[Chief Engineer]

I arrive at a boat....to troubleshoot performance problem....gas or diesel...the owner has gotten opinions from others or reading and puts in this additive...then that....then too mush stabil....then some dri-gas...yeah, lets put some acetone in there....you sample the fuel and it smells like solvent...all of this has made it ways thru the fuel system...injectors or carb. I gently tell my customers that this is NOT the way to go. Sometimes, it gets 'spensive.

BTW anytime I work on a diesel and I see cans of ether on board I take them off....I tell the owner that that stuff has NO place on a diesel boat.
Maybe to clean tools....maybe

Cleaning tools with ether? Boy that would be a great way to go out in a ball of fire!

[cooper]

HEY l switch my alternator off when running. (moving) my 7.5 thumpin hp of raw power and thrust turns positivly wimpy when l nicely ask it to consider allowing me to draw off 3.5 hp for my 35 amp alternater. It displays its complete contempt for me by throwing out a cloud of black smoke and gloom, with an even bigger slick of carbon on the water, acting like a huge finger pointing to at best "a polluter of monumental proportions", or at worst "an engine abuser".........So we now have a deal,I supply it with a never ending bowser of engine oil and dont ask it to do two tasks at once, and it (ocassionally) runs : )

[Alan Wheeler]

You need to see what is taking the current then Coops. Switching the Alternator off when it is charging can blow the alternator. If the Alt is drawing a heavy load like that, then a battery must be fair sucking it.

Alan,

The usual way to "shut off" an alternator when full engine power is needed is to shut off the field current. It then becomes just a spinning piece of metal. If you disconnect the OUTPUT lines, that's when you blow the diodes.

Cooper's situation is a good one where this is a practical and accepted approach. If the current consumer is the batteries being charged, he'd be stuck with a 3.5 hp engine until they were topped up. Turning the field current off solves his problem.

Bill

[cooper]

Bill you got it in one......The field current is indeed what is being shut off. I got an old bosch aletrnator and took out the inbuilt voltage regulator and brush housing and put back in an even older brush only housing with terminals. This l then hooked up to a solid state regulator with ther "Master Switch" on the field. Works very well....and compared to the power that was coming out of the previous "dynastart" .........Hi wheels..the problem most of the time is when the alternator is first switched on, for a short period of time it tries to pump nearly its full 35 amps. The poor old engine just cant cope with that and a propeller and goes into over fueling (lots of smoke). Bringing the engine revs down then no longers supplies enough power and the whole situation gets worse. l found all this out before l could switch off the alternator........On the day that l relaunched the boat....or should l say ...middle of ther night....chugg chugg straight out into the channel....engine dies....no sails on board ....l could turn the engine over and it would start but the minute the revs reached high enough for the alternator to kick in.........There is a photo around somewhere with me sitting on the jetty afterwards with a beer in my paw......and a very stressed look..cheers

[cal40john]

I can believe all of it except the 3.5 HP. 35 amp x 14.2 volts =497 watts x 1 hp/746 watts = .66 HP / .8 (80% efficient, I think most are much better) = 0.8 HP, not 3.5 HP.

That is, unless I've missed something important.

I have a friend who put a 100 amp Balmar on an Atomic 4. he shortly afterwards added a regulator that had a delay before energizing the field. That made it much easier to start.

Regulators short the field to turn off the alternator. If you leave it open you will still generate some electricity.

John



John

[cooper]

Is your engine large enough?
For example, if you are driving your alternator with a diesel engine, and assuming adequate flywheel mass and a 3:1 engine drive pulley to alternator pulley ratio, a high efficiency, high current, 12V alternator will require about 1 hp per 30 amps of output power + about 1-2 hp for engine operating/muffling loads . Given the age of the alternator l reckon another 1/2 a HP could disapear !! I LUV THEORY.......: )

[Alan Wheeler]

There is also the frictional loss int he drive belt as well to add into that figure.
Yep using the feild to turn the Alternator on and off is the right way. Not many do that, in fact, some simply use the ignition switch which is real bad. So top marks for doing this correctly.