twin 3.7L alternator conversion question

4

408camaross

New Member
Aug 14, 2010
25
spokane wa
Boat Info
270 sundancer
Engines
twin 470s with 2 brrls 170hp
hey guys im gonna be doin an alternator conversion this winter on the ole sea ray and here is my question. im gonna run 100 amp 1 wire marine alternator, but do i need 1 or 2? im gonna have a total of 4 batteries, 2 house and 2 starting. if i only need 1 how do i get it to charge all 4 batteries? i relize it'll be through the battery switches but still if i have the alternator on the starborad motor, how can i charge the batteries on the port side? here is where it gets kinda tricky, i have a total of 4 battery switches on this thing, and i would like to cut it down to 2 switches. how do i do this while having the alternator(s) charging them all? the only way i can think of is to have 2 alternators, one on each motor with the battery switches set on both while its running?
 
My first question would be why you feel you need a larger alternator? Unless you're adding a heavy load the larger alternator probably won't charge your batteries any faster. Batteries will accept a large charge initially but taper off as they charge. It generally takes a long slow charge to bring a battery up to full charge. You'll notice most battery chargers are 10 amps or less.
 
well these 3.7s dont have an alternator at all, they're a stator/regulator charging system off of the front dampner and since the regulators are about 300 a pop i figured i would just convert over to alternators and get rid of the problematic stator/regulator system for the same price as the alternator conversion kits(which i wont buy ill build my own brakets)
 
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thanks mitch for responding,
ok so i dont have to spend the money on the 100 ampers cool :grin: but there is the question of how should i wire them up? obvisouly the charging wire off of the alternator goes to the starter where the main battery feed is right? but how do i wire up the batteries? should i do house batts on port side and starting batterys on starboard? how do i tell what is the house battery? (the one that doesnt hook to the motor?) cause right now i only have 3 batterys

techmitch said:
The correct way would be to install marine alternators with internal regulators on both engines. 45 amp should be sufficient but but I would probably opt for 60's. As for your battery switches yes, you really only need two (2) 4 position switches. Here is a link.

http://www.westmarine.com/webapp/wc...toreNum=10109&subdeptNum=10548&classNum=10597
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A battery isolator will allow you to charge 2 battery banks from one alternator.It allows you to take the output from the alternator and split it to 2 battery banks.One battery for starting one for charging the house.It's you choice port of starboard.You would need a 4 position switch ( off,1,2 both) with this configuration.You would leave the switch in the # 1 position for starting,(the house is isolated) and you always have the ability to switch to #2 to start if #1 goes down.Both batteries are being charged without moving the selector switch to both. As far as figuring what battery is the house , turn on some accessories (engine off) start disconnecting batteries one at a time until that circuit goes out. BTW Ebay has some great deals on single wire Delco marine alternators.Hope this helps.
 
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the boat is a 1985, and yes we have shore power and on board battery charger, as far as the ac converter i think we do but i am not totally sure, still pretty new to the boat scene but im learning lol. and its on a trailer right now but next spring it will be in a slip.

techmitch said:
What year is your boat? Do you have shore power hook up and an on board ac converter/battery charger? Do you keep it in a slip or on a trailer?
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so what your saying here is then i should run 2 alternators? 1 on each motor and thanks for the heads up about ebay i will definatly check it out.
thanks Jason

sr330daguy said:
A battery isolator will allow you to charge 2 battery banks from one alternator.It allows you to take the output from the alternator and split it to 2 battery banks.One battery for starting one for charging the house.It's you choice port of starboard.You would need a 4 position switch ( off,1,2 both) with this configuration.You would leave the switch in the # 1 position for starting,(the house is isolated) and you always have the ability to switch to #2 to start if #1 goes down.Both batteries are being charged without moving the selector switch to both. As far as figuring what battery is the house , turn on some accessories (engine off) start disconnecting batteries one at a time until that circuit goes out. BTW Ebay has some great deals on single wire Delco marine alternators.Hope this helps.
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ok thank you guys for your help, does anyone have an idea or a diagram of how i should wire this thing with 2 alternators and 2 battery switches rather than the 4 battery switches i have right now?
thanks Jason
 
found this in a search,(youll have to fix it) http://b o a t f i x.com/how/battery4.jpg does this look right to you guys? i have couple other questions? 1 is if i have 2 deep cycle batterys for my house and if my memory serves me correctly, deep cycle batterys need to be mostly drained before recharging right? if so, should i set my batterys up like house+house on port side and starting+starting on starboard side? and, if i start both motors with it set up like this can i leave the battery switch for the house batterys off while the port motor is charging?
 
I had this engine in my first boat. I thought I remember there being a conversion kit so I looked it up. Do a google on Sierra 18-5953-1. Pretty expensive and you'd need two. Just an idea
 
ya ive found these kits before, its rediculous how much they ask for these things, im just gonna make my own alternator brackets, probably 50 bucks in material and then the alternators, probably be into it 300 or so total for both. how did you like the 470? when we took this boat on the sea trial last year it performed flawlessly, got on plane quick, gps said 39.7 mph wide open, and the gph meter was reading between 4.5 and 6.0 gph with both engines running!!! cant wait until next year when this thing is ready to go out on the lake

rondds said:
I had this engine in my first boat. I thought I remember there being a conversion kit so I looked it up. Do a google on Sierra 18-5953-1. Pretty expensive and you'd need two. Just an idea
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boat4sale.jpg


I had a single screw and alpha drive in this boat. Same 2 barrel as yours. Fantastic economy, BUT with 4 people aboard, the boat couldn't get out of its own way. SOmeone told me it is 1/2 of a big block and that it was engineered from the ground up by Merc - not sure how true that is. Wonder why they went with that goofy charging system. They seemed to pretty quickly replace it with the 3.0 liter four so I guess it wasn't all that great (?)
 
our boat also has the alpha 1 drives, really with 4 people it was gutless huh? you think it would have been different had it been a 4 barrel? when we took the sea trial there was 5 of us( dad, me, my 2 uncles, and the owner) 3/4 tank of fuel, and most gear(anchor, lines, life jackets, silverware, etc, etc) so if it did almost 40 with that much weight then i think well be happy with it, besides we didnt get this thing to go fast we got it to enjoy the time on the water lol, and yes the 470 is half of a big block ford 460, they use the head, pistons, and rods, the bellhousing is chevy from what ive read. so i guess its a bitsa motor lol as far as the charging system goes thats what ive been wondering ever since i saw these motors, i remember lookin at them for the first time and askin the guy "wheres the alternators?" lol when he told us that it was a stator charging system, my dad and i at the same time almost said "oh no, thats gotta go" lol. but either way i havent been on the water in almost 10 years so needless to say im getting anxious for next spring lol

rondds said:
boat4sale.jpg

I had a single screw and alpha drive in this boat. Same 2 barrel as yours. Fantastic economy, BUT with 4 people aboard, the boat couldn't get out of its own way. SOmeone told me it is 1/2 of a big block and that it was engineered from the ground up by Merc - not sure how true that is. Wonder why they went with that goofy charging system. They seemed to pretty quickly replace it with the 3.0 liter four so I guess it wasn't all that great (?)
Click to expand...
 
I do think she'd be a better performer with the extra 20hp the 4bbl afforded. But it was fine for our uses. I remember that conversion kit, back in the late 90s, was being sold for less than $200.00 by a guy who advertised in the back of one of those boat brokerage magazines you can pick up in a supermarket. I never did the conversion - the system worked fine. the boat was an '88 - I bought it in 1998 and I sold it in 2002.
 
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