biggest alternator for 3.0/140?

[madman2021]

i need to know whats the biggest alternator that will fit on my 1986 mercruiser 140 with v-belt setup? i run alot of electronics and 4 batteries. thanks

 

[fishrdan]

Re: biggest alternator for 3.0/140?

I'm running a 1 wire 100 amp Delco (china knock off) alternator from DB electrical . com on my 140HP and it works well.

 

[cr2k]

Re: biggest alternator for 3.0/140?

Only if it is USCG approved.

You can run any size you can bolt to it. Just make sure it is USCG Approved so you don't blow yourself up.

 

[madman2021]

Re: biggest alternator for 3.0/140?

well i guess i should be asking what alternator should i run? i have 2 size 29 starting batteries, and 2 size 24 trolling motor batteries wired up with a solenoid to connect all 4 batteries together when the key is turned on so i can charge the trolling batteries when i run the main motor. for electronics i have a bad azz stereo system, gps, fish finder, lights, 1000 watt power inverter, and the usual boat accesories. im running all this on the stock alternator, but not all at once. since ive done this, the alternator bearings have slowly started to wear out and whine pretty loud now, but still puts out 14.7 volts.

 

[madman2021]

Re: biggest alternator for 3.0/140?

Only if it is USCG approved.

You can run any size you can bolt to it. Just make sure it is USCG Approved so you don't blow yourself up.

why would it blow up if its not uscg approved?

 

[dubs283]

Re: biggest alternator for 3.0/140?

why would it blow up if its not uscg approved?

the alternator won't blow up, but your boat might

if the alternator isn't flash (spark) protected, it will produce a spark which will ignite gasoline fumes in the bilge (if present), thus causing a fire/explosion

the best option for upgrading your current alternator is to bring it to a starter/alternator repair shop and have them either rebuild your current alternator to the specifications you need or trade it towards one that meets your specifications - marine rated of course

i don't see how a greater number of amps will benefit your trolling motor batteries, a low amperage, long time charge is the best for deep cycle batteries - i hope you have a good quality A/C converter/charger for those batteries - i.e. one that "plugs in" to an outlet??

if you tell the rebuilders all the accessories/batteries you need to maintain/charge - they will be able to set up an alternator that will suit your needs

if you are uncertain about a reputable shop in your area, ask friends or fellow boaters to recommend boat repair shops that they trust, they will point you in the right direction

 

[cr2k]

Re: biggest alternator for 3.0/140?

You really need to isolate the batteries too. They will only charge as much as the worst battery the way you say you have they wired.

 

[madman2021]

Re: biggest alternator for 3.0/140?

i have an onboard 1 bank 1.5 amp battery charger hooked up to both trolling motor batteries(split pos and neg into 2). i fish friday saturday and sunday and leave the charger plugged in all week.

as for the solenoid to hook all batteries in conjunction, i used a evinrude 115 starter solenoid with pos signal wire hooked directly to shift interupt switch and neg to battery ground. works nicely and cheap to do.

 

[fishrdan]

Re: biggest alternator for 3.0/140?

i don't see how a greater number of amps will benefit your trolling motor batteries, a low amperage, long time charge is the best for deep cycle batteries

I agree, I wouldn't charge TM batteries at the full output of a 100 amp alternator, too much current. I only charge my TM batteries off the main engine's 100 amp alternator at idle to 1000RPM, where it's putting out a lot less than 100 amps (probably 50 I guess???). If you are going to charge at high RPM, stick with the stock 55 amp alternator, that way you are throwing 20 amps+- at the batteries.