I have a 1997 Monk 36 with the Cummins 6BT5.9M 220 engine. I'm switching
to six golf cart batteries for the house bank and wonder if the stock
alternator is big enough for this application.

Does anyone out there know how many amps that alternator is likely to
crank out?

Capt Jeff
"Adirondack"

Why not ask Cummins?

My guess is, while it will of course charge them, it just won't charge them very fast if you have drained them down to 50% capacity.

Tamaroak wrote:
I have a 1997 Monk 36 with the Cummins 6BT5.9M 220 engine. I'm switching
to six golf cart batteries for the house bank and wonder if the stock
alternator is big enough for this application.

Does anyone out there know how many amps that alternator is likely to
crank out?

Capt Jeff
"Adirondack"

Cummins might have rigged that engine with any of several alternators
when it was installed.

You will need to check the info plate on the alternator.

The basic premise for calculating alternator size is 4:1. Your
alternator output in amps should be at least 1/4 the amp hour capacity
of the battery bank it is being asked to charge.

There are two good reasons why you don't just run out and slap on the
biggest alternator that will fit on your engine's bracket. First is the
drive belt capacity; a very high output alternator will snap drive
belts like cheap rubber bands. You can always go to a larger pulley for
the belt, but if you do that you run the risk of plowing headlong into
the second good reason for not simply slapping on the highest output
alternator you can lay hands on:
waterpump side load. Engines with a coolant circulation pump driven by
a belt shared in common with the alternator can experience too much
side load on the pulley when the larger belt is tightened up (and that
can lead to premature failure of the waterpump).

Should you decide to go for a monster alternator, one of the better
approaches is to add an additional crankshaft pulley of sufficient size
and drive the alternatior with a dedicated belt.
Some of the boaters who go this route will actually mount the
alternator on a custom bracket near the engine rather than on the
original bracket.

Like this? http://www.foleyengines.com/TechTips/TechTip22.html

Regards,
Harry

wrote:
Tamaroak wrote:
I have a 1997 Monk 36 with the Cummins 6BT5.9M 220 engine. I'm switching
to six golf cart batteries for the house bank and wonder if the stock
alternator is big enough for this application.

Does anyone out there know how many amps that alternator is likely to
crank out?

Capt Jeff
"Adirondack"

Cummins might have rigged that engine with any of several alternators
when it was installed.

You will need to check the info plate on the alternator.

The basic premise for calculating alternator size is 4:1. Your
alternator output in amps should be at least 1/4 the amp hour capacity
of the battery bank it is being asked to charge.

There are two good reasons why you don't just run out and slap on the
biggest alternator that will fit on your engine's bracket. First is the
drive belt capacity; a very high output alternator will snap drive
belts like cheap rubber bands. You can always go to a larger pulley for
the belt, but if you do that you run the risk of plowing headlong into
the second good reason for not simply slapping on the highest output
alternator you can lay hands on:
waterpump side load. Engines with a coolant circulation pump driven by
a belt shared in common with the alternator can experience too much
side load on the pulley when the larger belt is tightened up (and that
can lead to premature failure of the waterpump).

Should you decide to go for a monster alternator, one of the better
approaches is to add an additional crankshaft pulley of sufficient size
and drive the alternatior with a dedicated belt.
Some of the boaters who go this route will actually mount the
alternator on a custom bracket near the engine rather than on the
original bracket.

HarryV wrote:
Like this? http://www.foleyengines.com/TechTips/TechTip22.html

Regards,
Harry

Yes, that or something essentially the same would work very well as a
remote alternator mount.




wrote:
Tamaroak wrote:
I have a 1997 Monk 36 with the Cummins 6BT5.9M 220 engine. I'm switching
to six golf cart batteries for the house bank and wonder if the stock
alternator is big enough for this application.

Does anyone out there know how many amps that alternator is likely to
crank out?

Capt Jeff
"Adirondack"

Cummins might have rigged that engine with any of several alternators
when it was installed.

You will need to check the info plate on the alternator.

The basic premise for calculating alternator size is 4:1. Your
alternator output in amps should be at least 1/4 the amp hour capacity
of the battery bank it is being asked to charge.

There are two good reasons why you don't just run out and slap on the
biggest alternator that will fit on your engine's bracket. First is the
drive belt capacity; a very high output alternator will snap drive
belts like cheap rubber bands. You can always go to a larger pulley for
the belt, but if you do that you run the risk of plowing headlong into
the second good reason for not simply slapping on the highest output
alternator you can lay hands on:
waterpump side load. Engines with a coolant circulation pump driven by
a belt shared in common with the alternator can experience too much
side load on the pulley when the larger belt is tightened up (and that
can lead to premature failure of the waterpump).

Should you decide to go for a monster alternator, one of the better
approaches is to add an additional crankshaft pulley of sufficient size
and drive the alternatior with a dedicated belt.
Some of the boaters who go this route will actually mount the
alternator on a custom bracket near the engine rather than on the
original bracket.

Tamaroak wrote:
I have a 1997 Monk 36 with the Cummins 6BT5.9M 220 engine. I'm switching
to six golf cart batteries for the house bank and wonder if the stock
alternator is big enough for this application.

Does anyone out there know how many amps that alternator is likely to
crank out?

Capt Jeff
"Adirondack"

It helps to know what Alternator you have.
Motorola/prestolite/leece-niville , delco, Bosch,
part # (O.E or Cummins.

Amp size?

Give us some specs.

wrote:
Tamaroak wrote:

I have a 1997 Monk 36 with the Cummins 6BT5.9M 220 engine. I'm switching
to six golf cart batteries for the house bank and wonder if the stock
alternator is big enough for this application.

Does anyone out there know how many amps that alternator is likely to
crank out?

Capt Jeff
"Adirondack"


Cummins might have rigged that engine with any of several alternators
when it was installed.

You will need to check the info plate on the alternator.

The basic premise for calculating alternator size is 4:1. Your
alternator output in amps should be at least 1/4 the amp hour capacity
of the battery bank it is being asked to charge.

....

Actually, I've heard that it doesn't make sense to go larger the 1/4
of the capacity, since that's the highest charge rate you would want
with regular lead-acid batteries.

My own experience is that 4 Trojan t105s (425-450 Amp-hours) will
accept a little over 100 Amps when down 50%, but are down to 85-90
Amps for much of the charge cycle. For six of these batteries, you
could charge at up to 150 Amps, which I'm guessing is bigger than any
stock alternator. At this size, you would probably want a good mount
with dual belts, etc. (I get by with a simple mount, but I do go
through belts.)

On the other hand, a 100 Amp alternator will "handle" the bank, it
just will take a bit longer to charge. In fact, if your plans were to
power the boat daily for several hours, you might find that even a
60 Amp alternator keeps the bank charged. The only problem comes
when you hang out for a week or so and have to run the engine every
day for 90 minutes to charge up - in this case for the last 30 minutes
of each run you'd be cursing the fact that you didn't get the "full
size" alternator.

Newer Cummins engines use small frame Delco alternators. Those with the
air-heater start assist feature (again all new ones) have 105A alternators.
If you have twin engines, two 105A alternators is plenty to charge the bank
of golf carts below from 40% charge to 80% in 2 hours. If you have only a
single engine more time will be required but it's still within reason and
will work.

However, there are two problems he 1) the Delco alternators have internal
regulators designed for charging starting batteries and when used with deep
cycles will charge them pathetically slowly, and 2) 105 A from a small frame
actually pretty hard to achieve reliably in continuous operation. The
solution to the first problem is to take the alternator out and wire for
external regulator. Any alternator shop can do this for an hours labor.
Then you need to purchase an external regulator. I like the Balmars because
they are highly adjustable but many companies make them. With an external
alternator on you can charge at any rate up to 105A which solves problem one
but you'll then run into the second problem: a small frame alternator
producing 105A is on the edge of heat failure from day one and will likely
fail in under a day (I've seen them do it). Basically, 105A is marketing
and it will produce 105A with full field current for short periods of time
before burning out so they aren't lying but it'll over heat within minutes.

What I do is get an external adjustable regulator and tune the charging rate
such that the alternators don't go over 200 to 225F. At full field
producing 105A, they'll hit 350F very quickly. If you set the field to
produce no more than 200 to 225F in most installations, you'll be charging
at around 70A and they will run at that level all day.

So the short answer is that your alternators can be made to charge that
battery bank efficiently but you'll need an external regulator and you'll
need to ensure that the alternators are not charging at much more than 70A
to, at the outside, 80A each. In such a config, they will work well. It's
more money and more hassle but installing larger alternators is another
solution and you can get alternators of over 200A each but they cost real
money. Its up to you on whether you want to run the stock alternators
carefully tuned or buy an industrial 200A alternator and run that way.

--jrh


"Tamaroak" wrote in message
news
I have a 1997 Monk 36 with the Cummins 6BT5.9M 220 engine. I'm switching to
six golf cart batteries for the house bank and wonder if the stock
alternator is big enough for this application.

Does anyone out there know how many amps that alternator is likely to
crank out?

Capt Jeff
"Adirondack"

On 15 May 2006 07:50:23 -0700, in message
. com
" wrote:

The basic premise for calculating alternator size is 4:1. Your
alternator output in amps should be at least 1/4 the amp hour capacity
of the battery bank it is being asked to charge.

I have read this in all sorts of places but haven't seen a good
explanation for the why of it, other than the common sense notion that
it would be nice to get from 50% to 75% in not too much more than an
hour. I agree that it seems like a sensibly balanced rule of thumb.
I'm not sure I see why charging a 400 AH bank at 50 A would be a bad
idea. Maybe something about not running the alternator full out for
hours on end?

65 A into 200 AH seems to be working for me....

Ryk

Ryk wrote:
On 15 May 2006 07:50:23 -0700, in message
. com
" wrote:

The basic premise for calculating alternator size is 4:1. Your
alternator output in amps should be at least 1/4 the amp hour capacity
of the battery bank it is being asked to charge.

I have read this in all sorts of places but haven't seen a good
explanation for the why of it, other than the common sense notion that
it would be nice to get from 50% to 75% in not too much more than an
hour. I agree that it seems like a sensibly balanced rule of thumb.
I'm not sure I see why charging a 400 AH bank at 50 A would be a bad
idea. Maybe something about not running the alternator full out for
hours on end?

65 A into 200 AH seems to be working for me....


The thing is, you're not throwing a constant 65a into a 200AH battery.
When the typical integral regulated alternator kicks in, the voltage
setting is usually in the 13.8-14.2 amp. range. Higher on modern
vehicles. The Alt. is forced to throw a full amp load in the Battery,
but as it charges, the voltage will remain the same on the alt. output,
however the amperage will decrease down to say 7-10 amps. The more
fully charged the battery, the less amps it takes to maintain it at the
set voltage.
Ryk