Alternator Bypass?

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Sandy

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Thinking about recent alternator issues posted here , I have an at least hypothetical question for those that know a lot more about alternators and boat electrical systems.

On a boat with twin I/B or I/O 's, if one was well at sea and experienced what was clearly an alternator problem, maybe shorted or bad diodes on one engine, could there be a reasonable and safe way of bypassing the bad alternator and using the good alternator on the other engine via the battery switch(es) on BOTH to power the ignition of the down engine (keeping other load-draws to minimum)?

If that was possible how would you go about that?

I would guess it that could be done and if engines were reasonably synched that one good, say, common 70 amp alt could easily supply way more than required current for just the ignition demand for both engines at normal cruise RPM.
 
To be positive ,remove the wire from the alt. and tape it. Put both battery switches to ALL,BOTH .Then start the bad engine first, then the good one. This way you wont surge the alt with the good motor running.
 
Thanks , alien. Sounds reasonable and too simple.

Have you by any chance ever tried this? Or know someone who has done so on a spark ignition engine? It does seem to potentially be a far better solution than ...trying... to get back substantial distance on battery-powered ignition alone, particularly with the min. voltage requirements of the MPI injected engines' ECMs. Your way maintains battery charge too as long as optional loads are not excessive.

I presume you mean remove and insulate all wires from the back of the alt. .
The (Crusader) 70A Delco alt (I replaced with same a few years ago & just checked) has a 2 conductor female plug and a stud for a ring terminal , and another female plug that was not used in service.
 
The alternator is pretty much independent of the ignition system, and the engine will run just fine without it as long as the battery stays charged; be it from the other engine, solar, genset, whatever. I once ran an old Chrysler on a pair of 6v dry cells.

I'd disconnect all the wires to the bad unit as Alien suggests, and keep "house" loads to a minimum.
 
I have had to cobble a new fuel system to 1 motor at the canyon once.Was a very creative solution using all the fuel lines and fittings, making a "T" in the good engines fuel line to the carb to go over to the bad ones carb. Managed to get to planning speed on a 31 Bertram ,that was all 1 puel pump could provide for 2 motors.Beat trolling in from 106 miles.
 
I have had to cobble a new fuel system to 1 motor at the canyon once.Was a very creative solution using all the fuel lines and fittings, making a "T" in the good engines fuel line to the carb to go over to the bad ones carb. Managed to get to planning speed on a 31 Bertram ,that was all 1 puel pump could provide for 2 motors.Beat trolling in from 106 miles.
 
If you have a generator you could simply run your battery charger on the dead engines side that would keep it running. You could start it with the emergency start parallel switch. In my boat I have a constant duty remote combine switch (made by BlueSea), the center position is off, up is a momentary on for parallel start and down holds the solinoid on.
It starts to get hairy when you have electronic shift throttles, but my system is a KE4 made by Morse/ Teleflex and each side taps power from 2 different power sources. I have the standby aux power attached to my house battery bank the primary for each side is the start battery bank for each motor.
It could also be done with a pair of battery jumpers between the 2 start batteries if you really had to wing it.
Bill
 
To be positive ,remove the wire from the alt. and tape it. Put both battery switches to ALL,BOTH .Then start the bad engine first, then the good one. This way you wont surge the alt with the good motor running

I did this about a month ago for 6 hrs with no issues the stbd alternator volts where a little higher.
 
To be positive ,remove the wire from the alt. and tape it. Put both battery switches to ALL,BOTH .Then start the bad engine first, then the good one. This way you wont surge the alt with the good motor running

I did this about a month ago for 6 hrs with no issues the stbd alternator volts where a little higher.
 
Thanks very much, all!
Glad I asked as I was afraid I was missing something and it seemed wise to confirm safe procedure "pre-need."

BillyIII- No genny or emergency combiner relay or electronic controls on this boat, but it would be simple enough to just set both the main engine battery switches to Both after isolating a bad alt ...& burn rubber for Dodge. Obviously the battery negs and engine grounds all need to be tied together as mine are & is generally customary anyway.

One of the reasons I brought this up now is a few days ago I noticed in spite of normal gauge temps and no noticeable odor, my port RW pump had leaked and left a dried salty crust over much of the front of my Crusaders, including the alternator.

Quickly replaced the pump with an on-hand new spare. And, after /brushing wiping off as much of the dried salt as I could , I gave it all several applications of bottle-sprayed diluted Salt-Away and wiping away more salt crust and careful rinsing, repeating still.

Everything works fine & I will spray the alternator liberally with WD-40, but know from past RW pump seal leak failures, delayed but clearly-related alternator problems can pop up.

Thanks again.
 
It does also occur to me if the alternator bushing bearing (seized) were to become the culprit, all of the above is moot . The hinged alternator is the only tensioner for the non-serpentine belt, so even a smaller belt bypassing the alt would not likely work. Hmmm, besides the spare new belt mounted inside the crank-mount RW pump bracket, I do also have onboard an emergency spare belt made up of all removable links, so, maybe at slow rpms....?
 
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