Alternator questions (F-L 120 GrandBanks 32)

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Tazling

Veteran Member
Joined
May 17, 2021
Messages
62
Vessel Name
DARXIDE
Vessel Make
Grand Banks 32
1). Alt belt replacement... On my F-L 120 (as other owners may know) to install a new alt belt you have to drain the coolant system (wth were they smoking...) and pull the main coolant hose. This is not a nice feature and I've been considering buying some feet of Fenner power-twist link belt for a quicker repair underway. Has anyone else had any experience using link belt as an alternative to stock rubber fan/alt belts? they are more expensive, but when I consider the messy and inconvenient stock belt replacement they start to look pretty good. There are endorsements and testimonials online from tractor owners, and basically my FL is a tractor engine, so...

2) My alternator just died after a year of service. It looks like this type


with no brand name on it, only a part number 7127-6N

it bothers me that I bought this boat with a dead alternator, replaced it and the battery isolator, and now I have another dead alt.

But there may be a smoking gun here. I am pretty good with load-side 12v (everything from the breaker panel to the various instruments, lights, etc) but frankly, generators and alternators are voodoo to me. I had a marine electrician install the alt and a simple battery isolator from Victron Energy, about 13 months ago. Seems to me it should not have failed so soon.

The smoking gun however, is that both the previous owner and I were sailboat owners dealing with our first motor vessel, and both of us have the ingrained simple sailboat habit of switching batteries to "both" to start the engine, and leaving them ganged while the engine is running to recharge the house battery (i.e. no isolator, just 2 identical batteries and some switches).

I didn't pay much attention when the electrician installed the new parts (there were other issues including a head gasket that I was struggling with at the time). But it has occurred to me now that the battery isolator obviously "isolates" the two battery banks, house and engine; and that maybe that means it's not a good idea to gang them together, defeating the isolator. Could doing this, over time, kill an alternator? Inquiring minds would dearly like to know -- because if this is operator error then the repair path is clear: replace the alt, if necessary also the isolator, and just don't do that again. But if running in Both mode does not account for blowing up an alternator then there may be some hideous, deeper, more complicated wiring problem that I have to figure out. So I'm kinda hoping I just did something ignorant/stupid.

3). The alternator in question has only one electrical connection, the hot lead. As you can see on the web page describing it, it says only one connection is needed (it must be getting its ground via the mounting hardware and engine block). But that seems a bit sketchy to me, especially in a rusty marine environment. Would I be better off with a different brand/model of alternator with two honest connections, plus and minus?

Everything on this boat is soooo much more complicated (and bigger) than my old sailboat, I'm still a bit out of my depth here. Have completed a lot of projects and thought I was winning, but when the alternator died on my way to haulout it was rather disheartening.
 

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Wrt the dead alternators. Are you operating a Battery “1-2-all-off” switch? If so, ensure it is a “make before break” circuit type, otherwise switching while the alternators are on line, could blow their diodes. Just a WAG.
 
Do you have lithium batteries? If so, they could be putting a high charging load on your alternator and over time, burning them up.

David
 
Do you have lithium batteries? If so, they could be putting a high charging load on your alternator and over time, burning them up.

David
Oh if only! nope, conventional flooded lead-acid.
 
Wrt the dead alternators. Are you operating a Battery “1-2-all-off” switch? If so, ensure it is a “make before break” circuit type, otherwise switching while the alternators are on line, could blow their diodes. Just a WAG.
The 1/2/both switch is a certified marine switch of its kind, but I have no idea how to tell if it is MBB... but on the other hand, I never turn that switch when the engine is running. I set it to BOTH, then start the engine, then run, and at end of journey kill the engine and turn the switch back to OFF. So it never gets touched while the engine is running. It's buried under a heavy hatch beneath the afterdeck, so it's easy not to do anything to it by mistake!
 
1). Alt belt replacement... On my F-L 120 (as other owners may know) to install a new alt belt you have to drain the coolant system (wth were they smoking...) and pull the main coolant hose. This is not a nice feature and I've been considering buying some feet of Fenner power-twist link belt for a quicker repair underway. Has anyone else had any experience using link belt as an alternative to stock rubber fan/alt belts? they are more expensive, but when I consider the messy and inconvenient stock belt replacement they start to look pretty good. There are endorsements and testimonials online from tractor owners, and basically my FL is a tractor engine, so...

A common practice with these engines is to leave a spare belt in place, with the coolant hose already though it, so it can be installed without having to disconnect the coolant hose.
 

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I use link belts on certain equipment applications. It’s very good stuff, runs very smooth. I would have no problem running my alternator with it.
 
Also, that thing you’re doing with the battery switch?stop it.
Totally defeating the purpose of the isolator.
The switch should be used for selecting what battery powers the house loads, not what battery to charge.
 
Somewhere there is a thread where they changed the hose configuration to allow an easy belt change. Maybe someone can post a link if you know it.

But given a need to changed antifreeze periodically having a backup belt installed is workable. If only I had thought about that last year when I did mine!
 
2) My alternator just died after a year of service. It looks like this type


with no brand name on it, only a part number 7127-6N
It seems very improbably, but the specs for the alternator you linked say it's 6V. Could that be? Anything else on the label on your alternator? It could explain a lot, but again seems quite improbable
 
Just found this thread. Check the plate on the alternator. It should NOT be 6 volt.
Your entire boat should be 12volt. Remove the alternator and take it to the shop that supplied it and get it checked, tested.
Talk to them about the alternators. It could simply be failing because it is working overtime.
 
Hi folks... iirc there is no info at all on that alternator except the part number. If that part number is for a 6v alternator I'd be very surprised, as it used to put out a solid 13+ vdc at idle and over 14v when running. The one I linked to simply looks a lot like it (same housing) and has a similar part number. but I will try to find some others with the same part number.
 
I use link belts on certain equipment applications. It’s very good stuff, runs very smooth. I would have no problem running my alternator with it.

It seems that "Fenner" is the preferred brand for heavy duty applications but I am not sure how to translate automotive/tractor engine belts into their "industrial" sizes. I'm guessing a 1/2 inch wide V belt should be close enough...?
 
It seems that "Fenner" is the preferred brand for heavy duty applications but I am not sure how to translate automotive/tractor engine belts into their "industrial" sizes. I'm guessing a 1/2 inch wide V belt should be close enough...?
The 1/2 red belt would likely be the choice if you have 1/2 belts now. They take a little effort to put together but when you get the hang of it they aren’t too bad.
 
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