Why would you change to large frame commercial alternator or go small frame throttled

[Fuss]

Firstly talking my boat ….
It has as standard 3 half inch pulleys
The belts do not run the water pump.
There is space for 2 alternators and it’s 135 hp.
So for this it makes sense
150a large frame running at 140 degrees C for 1500 hours. And I don’t mean on the outside of the case, that’s 110, I mean inside. Your regulator alt temp sensor measures the case not the insides.

Ok, so if you run the water pump from the pulley then you can change to serpentine for more alternator capacity but in both cases the alternator probably needs throttling back to protect the pump and belts..and maybe also the alt from burnout if it’s one of the common plastic ones. (I have a little experience of burnout way back and I seem to remember it burnt out in the first 1000 hours..it was a plastic one, the sort they put on cars)

So, I imagine that this covers the reasons as a fairly short summary.

[tanglewood]

I think it's pretty simple. Depends on how much output you want, and whether you have the engine power and pulley drive system to power it. There seems to be little downside to having as much power available as practical, where "practical" will vary from boat to boat.

[Bowdrie]

Originally Posted by Fuss

There is space for 2 alternators and it’s 135 hp.

With that you're already ahead of the game.
You have the opportunity to keep the stock little alternator and its drive belt to charge ONLY the starting batteries and add a large frame alternator that has an isolated ground to charge ONLY the house batteries.
Now the engine with its batteries/starter/pre-heat/gages/stop solenoid, can live in its own little world divorced from the rest of the boat.
The big alternator with its isolated ground can interface with a house bank that needs no, (nor wants,) electrical connections, (either pos/neg,) to the engine, (or any external grounds).

[Bowdrie]

Addendum; Keeping the engine and house battery systems totally isolated from each other does require two batt chargers, but that is not a bad thing.
Typical SLA batts for starting and FLA house batts have different plate chemistry, different internal cell resistances. different charge profiles, and different float voltages.

[Wotname]

Originally Posted by Bowdrie

With that you're already ahead of the game.
You have the opportunity to keep the stock little alternator and its drive belt to charge ONLY the starting batteries and add a large frame alternator that has an isolated ground to charge ONLY the house batteries.
Now the engine with its batteries/starter/pre-heat/gages/stop solenoid, can live in its own little world divorced from the rest of the boat.
The big alternator with its isolated ground can interface with a house bank that needs no, (nor wants,) electrical connections, (either pos/neg,) to the engine, (or any external grounds).

What Bowdrie said plus 1000%

[Jammer]

If you have room for a large frame alternator and care about alternator output then you put in a large frame alternator.


Small frame alternators are a compromise for the many boats where there simply isn't enough room for anything else.

[SailingHarmonie]

Originally Posted by Fuss

Firstly talking my boat ….
It has as standard 3 half inch pulleys
The belts do not run the water pump.
There is space for 2 alternators and it’s 135 hp.
So for this it makes sense
150a large frame running at 140 degrees C for 1500 hours. And I don’t mean on the outside of the case, that’s 110, I mean inside. Your regulator alt temp sensor measures the case not the insides.

Ok, so if you run the water pump from the pulley then you can change to serpentine for more alternator capacity but in both cases the alternator probably needs throttling back to protect the pump and belts..and maybe also the alt from burnout if it’s one of the common plastic ones. (I have a little experience of burnout way back and I seem to remember it burnt out in the first 1000 hours..it was a plastic one, the sort they put on cars)

So, I imagine that this covers the reasons as a fairly short summary.

... what is it you are trying to say? I have read this three times, and I still do not get your point. What are the "common plastic ones" you are talking about? Are there plastic alternators? I don't know that I have ever seen one...

[Bowdrie]

Addendum 2.
I felt that I should comment about having an electrically isolated engine and how ABYC protocol fits.
ABYC wants to see a jumper wire between the AC green/ground bus and the boats DC ground bus.
The purpose is to have a low resistance path for AC to the water.
This presupposes that the boats DC system is already connected to the water via the engine>prop shaft and being that the vast majority of boats only have one alternator, and that the engine serves as the "grand central station" for all DC grounding, it's a fair supposition.
If we want the engine to be totally isolated from the house DC system and still adhere to ABYC we'll need other means to connect the house system to the water.
In no particular order we have some choices, I'll list three;
1, Install a "Drivesaver" and use one of those "wiper" arms on the prop shaft.
2, Connect a wire from the DC bus to a keel bolt.
3, Connect a wire from the DC bus to an outside "ground plate", something that comes to mind is one of those "Dynaplates".
However, whether one alternator or several, or one battery or several, and no matter the grounding or bonding scheme, it's important to take whatever steps one can do to not let any electrons, (AC or DC,) escape to cause trouble.

[GordMay]

Dc Negative & Grounding
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