replacement alternator

Don12364 · Jun 28, 2010

It's a big subject and there is plenty to study on this site and the main issues you need to consider are listed below:-

First question is whether your batteries can accommodate a charge rate of 100 amps.
Conventional 'Valve Regulated Lead Acid' cells can usually accept C/4. i.e. a 200 Amp hour house bank can accept 50 amps.
Many 'Gel Cells' can accept C/2 so a 200 Ah bank can accept 100 A.
'AGMs' can often take even more.

However that is only the beginning. The above are only generalisations and ONLY apply to the bulk charge phases. i.e. up to 75% fully charged.

Then you need to be sure your drive belt can carry the extra horsepower as many people with 100 A chargers have found they shred their belts - so a twin belt/pulley system may be needed.

Again it all depends upon the sophistication of your charger and whether it can sense the battery's needs and control this level of current.

High charging currents 'work' the batteries harder so shorten their lives and are thus only to be used with care.

Once again do some calculations to discover whether your charge time will be materially shortened as the 'acceptance' phase following the 'bulk' phase seems to take for ever and this is the same regardless of your charger. So saving a couple of hours of bulk phase charging may not be worth the hassle, particularly if you run your engine for longish periods anyway.

Lastly alternators mainly come in two mounting styles and several frame sizes so make sure you know which fitting you need and whether there is sufficient room to get it into the engine box.

Unless you know exactly what you are doing I suggest reading Mainsail's postings and Stu Jackson's. And, having wised up and learned to speak the language, then seek advice from your local marine electrical company.

So really the answer to your question is a very limited 'yes'.

Sorry to be a Jonah but these are issues we all have to face at some time.

Bill Roosa · Jun 28, 2010

Donalex should have said

"will" require twin belts. If you can't do twin belts don't even bother going over 60ish amps on the alternator. Even with a 400 AH bank it is debatable whether the 1 hour (1.2 hours vs 2.2 hours) you save going from 50% charged to 80% charged even matters as you will still need to spend 4 hours topping off the batteries. When was the last time you ran the motor for an hour just to charge the batteries? If you are running the motor to get home then the bats will get some charge but you are going to put her on the charger when you get to the slip so what is the point?
High output alternators are not the solution to most folks electrical problems. Bigger battery banks are. For the weekend sailor my advice is to buy more AH and leave the stock alternator on.

Lee Coller · Jun 28, 2010

Bill Roosa said:
"will" require twin belts. If you can't do twin belts don't even bother going over 60ish amps on the alternator. Even with a 400 AH bank it is debatable whether the 1 hour (1.2 hours vs 2.2 hours) you save going from 50% charged to 80% charged even matters as you will still need to spend 4 hours topping off the batteries. When was the last time you ran the motor for an hour just to charge the batteries? If you are running the motor to get home then the bats will get some charge but you are going to put her on the charger when you get to the slip so what is the point?
High output alternators are not the solution to most folks electrical problems. Bigger battery banks are. For the weekend sailor my advice is to buy more AH and leave the stock alternator on.

I've had no problems with my 100 amp Balmar with a single belt, over 700 hours of engine time, many hours charging on the hook.

From the Balmar site:

The second factor in determining proper alternator fit requires matching the alternator's output to the width of the engine's drive belt. If your engine uses a single 3/8" (or metric equivalent) belt, the largest recommended alternator will be 80 amps. A single 1/2" (or metric equivalent) belt can support up to 110 amps of alternator output. Dual 3/8" or larger belts can support up to 200 amps of alternator output. Any alternator loads in excess of 200 amps will require dual 1/2" or larger belts.

Don12364 · Jun 29, 2010

Francis said:
Thanks, Donalex. It all makes sense.
The bank is more like in the 400-amp size (gel), so 100 amps alt. should not be a problem.
Not sure what you mean by: "...it all depends upon the sophistication of your charger and whether it can sense the battery's needs and control this level of current" since the alternator charges the batteries without the help of a charger. Please clarify.
Do you know where I can find the postings of Mainsail and Stu Jackson on this topic?

Hi,
Nowadays mains powered chargers do their work in several stages to suit the 'Bulk', Absorption', 'Float' and 'Equalize' requirements of different types of battery construction. To achieve this the charger designers assume the charger is left on during the whole of the charging cycle.
Alternators DO need controllers or regulators (I used 'charger' by mistake, though it does the same job - apologies) because they otherwise would never achieve 100% charge without danger of severe overcharging. The problem is that the engine is unlikely to be run continuously for the duration of the charge. Many 'smart' alternator controllers make an attempt at emulating the various phases necessary but the vital part is they must not overcharge; so this normally leads to undercharging.

Simply buying a new alternator does not gain the benefits of a decent charge controller. They are rated for the maximum capacity of the alternator so, if you have one, make sure it can handle 100 amps. Indeed, if your boat does not have one of these already then the biggest improvement to your battery charging might be to buy one.

High rate mains chargers usually include battery temperature monitoring and adjust their charge rates accordingly. With a 100 amp capability one really needs this temperature monitoring on the alternator's regulator also.
This, together with the previous paragraph, was behind my remark about the sophistication of your charger etc.

Like I said it is a big subject - and it has been worked over endlessly on this site over the years.

To locate contributions from the two Gents mentioned use the search facility on this site using either their user names or by using 'battery' as a search keyword. You will get hours of happy reading. Also look for Stu on the Catalina Owners site.

These guys have made it a lifetime's study; and - most importantly - no crap or bullshit.

kavakava · Nov 28, 2010

We have the same engine and installed a single belt larger alternator, about 110 amps. We bought the Powerline alternator from e-Marine with a seperate smart regulator. Our house bank is six 6 volt wet cell batteries, and this setup works well.

reraft · Nov 30, 2010

I just want to throw in my 2 cents worth & tell you that we are currently cruising Mexico & installed an electromaax 160 amp alternator on out 376 & it performns perfectly. check out their website - electromaax.com . we have a yanmar 3jh2 - installed the 160 amp alternator - smart regulator & converted to serpentine belt pulley system - all supplied by electromaax. we have two 4d agm house batteries & a start battery. the system has been trouble free.no shredding belts - no black dust.
check it out - should be worth your while.
Rick sv hotel california

Vinny · Dec 1, 2010

reraft said:
I just want to throw in my 2 cents worth & tell you that we are currently cruising Mexico & installed an electromaax 160 amp alternator on out 376 & it performns perfectly. check out their website - electromaax.com . we have a yanmar 3jh2 - installed the 160 amp alternator - smart regulator & converted to serpentine belt pulley system - all supplied by electromaax. we have two 4d agm house batteries & a start battery. the system has been trouble free.no shredding belts - no black dust.
check it out - should be worth your while.
Rick sv hotel california

The serpentine belt makes all the difference in the world. It's all about contact surface area and nothing else. The serpentine system wraps the belt around more surface area on each pulley.

John T1594 · Dec 1, 2010

What about the wiring harness? Will the original 55 amp wiring handle the higher alternator output?

Vinny · Dec 4, 2010

John T1594 said:
What about the wiring harness? Will the original 55 amp wiring handle the higher alternator output?

The new Alternator will need a new smart voltage regulator and that will wire directly to the battery 1-2-Both switch or be wired in by some other system. My preference is to by pass the combo switch and wire the regulator directly to the house bank B+ and then use an Echo charger for the start battery.

If you are asking this you may need to seek additional help. I'm not trying to be rude but just make sure you understand the system you are working with. Under sizing the wire will result in an insurance claim that will most likely be denied.

Bill Roosa · Dec 4, 2010

Wiring harnesses

The regulator harness should be OK as that came with the regulator. The only other wire is the high amp output (and ground if it has a dedicated ground return) from the alternator. That would need to be sized for the max amperage of the alternator. Note that most systems wire the alternator output to the starter high amp 12 volt + input which runs back to the batteries or maybe just the starter battery and then there is a connecting buss (with switch or isolator no doubt) that connects the two batteries together. all these wire need to be sized to accept the higher amps. Don't forget the engine ground if that is the return path from the batteries to the starter/alternator. did I mention the 3-way and any other switches that will see the high amps should also be of sufficient amp capacity to handle the new current.......... there are a lot of wire that get involved and without knowing your set up it is difficult to be specific.
Do you have a diagram?
Did I mention to include a new fuse?

Vinny · Dec 5, 2010

Bill Roosa said:
The regulator harness should be OK as that came with the regulator. The only other wire is the high amp output (and ground if it has a dedicated ground return) from the alternator. That would need to be sized for the max amperage of the alternator. Note that most systems wire the alternator output to the starter high amp 12 volt + input which runs back to the batteries or maybe just the starter battery and then there is a connecting buss (with switch or isolator no doubt) that connects the two batteries together. all these wire need to be sized to accept the higher amps. Don't forget the engine ground if that is the return path from the batteries to the starter/alternator. did I mention the 3-way and any other switches that will see the high amps should also be of sufficient amp capacity to handle the new current.......... there are a lot of wire that get involved and without knowing your set up it is difficult to be specific.
Do you have a diagram?
Did I mention to include a new fuse?

Bill,

The Balmar Regulator has an ample wire. I'm not sure of the other brands. The regulator wire to the battery is ample as well. The one from the regulator to the alternator is ample as well. The ground to the engine should be OK as it is because if it can take the starter draw which out ranks the alternator.

Bill Roosa · Dec 5, 2010

wiring harnesses

I should point out that the regulator harness never has any high currents in it. It is for the control of the alternator rotor coil. All it does it turns the rotor coil on and off rapidly to control the alternator output.
Also the starter wiring is intended for VERY LOW DUTY use. It will not support a starter running for hours at a time and should never have to. The alternator output is, however, just that kind of current. Your starter source and ground wires MAY be up to the task but I'd do the math and make sure for nothing more than my peace of mind.
FWIW