An Alternator Question

[eianm]

I want to put a larger alternator on my 1991 H42- I believe the factory original is 55amp- I have been offered a brand new
MODEL NO; 42785
12 volt 105 amp
Series: 19S1
Part no: 3675256PX -Cummins Genuine Alternator is suitable for Cummins B330 of 370hp marine diesels.
QUESTION- is this a good upgrade ? I can see no reason why it wouldn't be suitable, I realize I will have to be careful and also change the voltage regulator-any knowledgeable advice will be appreciated.
Eianm

 

[Bob 04 H260]

What will you use for a belt to drive a new alternator ? A single V-belt will be overloaded driving an alternator above 80 amps, lots of dust and a short life. You can change to new pulleys to allow use of double belts or a flat 1" belt. Pulley conversion kits are available for many engines. Double belts can have issues matching the two belts so both run with the same tension. Get a flat belt kit if available.

An external regulator allows the engine to run a bit after starting before ramping up the alternator output, easier on the belt and the engine.

A bigger alternator (140 Amps) was a good investment for us, we use a 1" flat belt to drive it.
Bob

 

[Benny17441]

What are your recharging needs? The batteries have a maximum acceptance rate which diminishes in direct proportion to their state of charge. Depending on the size of the bank and the average % of discharge your 55A alternator could be more than adequate. Them large alternators are ideal for cruisers running refrigeration with large battery banks.

 

[Maine Sail]

The Delco 19SI is a large frame alt and would most likely require a custom made mounting bracket as the off sets and foot mounts are different.. Most sailboat aux engines use small case alts in the factory location...

 

[eianm]

thanks all- particularly Maine sail- that's what I was worried about!

 

[Paul Cossman]

P42 alternator upgrade

Eian,

As you know, my P42 is only a couple of hull numbers off from yours. In 1993 I installed a higher-output amp small-case alternator using the factory mounts and a normal single belt. Unfortunately I'm far from my boat, so I don't know either the make or exact output of the alternator. When it's cool the alternator puts out about 110 amps, then drops to about 80 when it gets hot (in the tropics). I think it is a 110, but it could be a 120 amp unit. Anyway, it's functioned perfectly for 20 years w/o problems. I may have changed the belt once or twice in all those years. Externally voltage regulated, of course.

I also have a 130 amp alternator, large case, that runs off my 5 hp Kubota generator. It puts out more like 100 amps when hot, and requires two belts. I have found that belts are generally so finely measured that the (very hard-to-find) matching sets are not required. However, I think the 4JH2-TE doesn't permit such a large alternator to fit, and if you change the mounting angle and add a second pulley I think the Yanmar is subject to damage. (I remember seeing Yanmar literature warning against doing so).

My experience: get the largest small-case alternator you can that fits and uses a single belt. Mine charged my boat for a couple years of full time cruising before I went to the Kubota.

 

[Rick D]

Re: P42 alternator upgrade

So, Paul: you are only the second person I know who installed a DC genset. Still happy with it? Would you do it again? No probs with the 120 volts through the inverter? It always seemed to me a pretty slick way to go for our typical consumption (unless a lot of air conditioning needs).

 

[Paul Cossman]

P42 DC genset

So, Paul: you are only the second person I know who installed a DC genset. Still happy with it? Would you do it again? No probs with the 120 volts through the inverter? It always seemed to me a pretty slick way to go for our typical consumption (unless a lot of air conditioning needs).

Hi Rick,

After the installation of two full-sized solar panels, the DC genset is the best thing I've ever done for the electrical system. It puts out about 85 amps at 2500 RPM burning about a pint of diesel/hour. No more light loads on the engine for power generation. VERY easy to maintain, and about 2,000 hours on it so far. No repairs. I also mounted a scuba compressor there, and the 5 HP will run one or the other with a change of belts. (However, the compressor has been problematic, and I would not do that part of it again).

No problem with the inverter usage at all. We never use much AC at all, not having air conditioning or anything like that. It works great. I'm a big fan. If I were to do it again, I might use the Kubota 6 HP and upgrade to an even larger alternator. But that's unnecessary.

Paul.