" wrote in news:9a05e729-1a6f-
:

I was able to load up the
alternator with a bunch of stuff hooked to the inverter and some fans
etc and had perfect throttle control and was getting ~100 amps out of
the thing in either fast idle or in gear and pushing against the dock
lines... Smoke free and purring smoothly. Then, it started its
hunting again and when I removed all the loads and let it sit a while
it didn't get any better. Hmmmm... What is going on? It has neve

ASk Skip what happens when you go charging huge banks of batteries with
a standard alternator made to feed current to the starting battery for a
few minutes. I got quite an education when he brought back his fried
alternator and I took him to the electric shop.

A 100A alternator will NOT put out 100A! It will put out 100A for a FEW
MINUTES, then must be cut back to prevent its heat destruction....and I
didn't know that, myself.

http://www.delcoremy.com/pdfs/servic...acy/1G-262.pdf
Here's the kind of alternator they put on the sailboats. Oh, it puts
out 50A or 70A in INTERMITTENT SERVICE....like recharging the starting
battery. This is the kind of 70A alternator boaters are sold and are
buying.

Cheap alternators are NOT battery chargers, I found out.

http://www.delcoremy.com/pdfs/servic...ent/1G-500.pdf
THIS is the kind of alternator made to charge the house monsters. It
can put out tremendous current for long periods of time....AND IT HAS
LOAD DUMP PROTECTION FOR WHEN IT OVERHEATS the little alternators do
not.

Of course, it isn't $69, even from the discount store.

I've also found out things about ENGINE SPEED, which DIRECTLY relates to
ALTERNATOR FAN SPEED and ALTERNATOR TEMPERATURE....the real criminal.

Oh, sure, my alternator puts out 110A at dead idle. BUT, the FAN
turning so slow ISN'T COOLING THE COILS! Very few ever mention what
this heavy, continuous, idle charging does to ALTERNATOR COOLING in the
hot engine room under the ladder!

I felt really bad when Skip brought back his new alternator that I had a
hand in him buying, its coils cooked.

Boaters are fascinated by impressive-looking EXTERNAL voltage regulators
that are perceived as the holy grail of alternator charging. Does the
fancy expensive alternator have an internal thermocouple INSIDE the
alternator it's controlling so it doesn't melt the stator coils?

No, it doesn't.....not that I've seen. That would require more wires
than they have on them. However, on this heavy duty alternator with
load dump protection, the INTERNAL regulator DOES monitor the core
temperature it's firmly attached to....and shuts down the alternator
until it cools off under overstress...charging those big monsters you
killed last night.

There's lots of great manuals to read and information on alternators on:
http://www.delcoremy.com/manuals.aspx#alternators
http://www.delcoremy.com/Technical.aspx

I especially like the idea of "remote sensing" with alternators like
this monster:
http://www.delcoremy.com/pdfs/Fleet_Issue6.pdf
It's regulator runs off a separate line on the battery bank
terminal....not the other end of the high current cabling and its
voltage drop.

From reading these and lots of other alternator manufacturer
information, I think boaters, particularly sailboaters trying to be on-
the-cheap, are making a mistake charging massive house batteries at low
idle speeds just fast enough to get output from the alternators. This
point produces the most internal heat in alternators NOT designed for
continuous duty use. Without a load dumping circuit to protect them,
we're simply cooking them until they fail. When charging the beasts, a
LOT of the heat cooking the alternators could be reduced by running all
the bilge vent fans, continuously, during charging, reducing the
temperature of the air going INTO the alternator. I can see a benefit
to ducting some OUTSIDE air from some place that won't spray the
alternator with seawater to the air intake of the alternator improving
cooling even further. It would only have to be a length of the same
hose the bilge vent fans use with its open end right near the back end
of the alternator away from the drive belt and easily doable. The vent
fans' suction would pull air through the duct so the alternator could
catch it.

This post just caught my eye as we're all talking about idling the
damned diesel so slow it will coke up....ruining the alternator if the
house batteries are dead....THEN SEEING HOW MUCH EXTRA CURRENT WE COULD
DRAG OUT OF THE POOR, HOT THING AT THE SAME TIME!

UNLOAD THE SYSTEM DURING CHARGING! YOU'RE COOKIN' IT! Ask Skip!

"Larry" wrote:

A 100A alternator will NOT put out 100A! It will put out 100A for a
FEW
MINUTES, then must be cut back to prevent its heat
destruction....and I
didn't know that, myself.

If you buy a real alternator, not a boat toy, you won't have a
problem.

If the alternator has "hot" rating, not a "cold" rating, then it will
carry nameplate rating.

Marine electrical devices are rated for a 50C ambient, not 40C for
land based installations.

These days, the above will limit you to Leece-Neville or some Delco
models.

The rest are basically toys.


As a former L-N design engineer, yes, my reply is biased, but
truthful.

Lew

On Mar 26, 5:46 pm, Larry wrote:
... A 100A alternator will NOT put out 100A! It will put out 100A for a FEW
MINUTES, then must be cut back to prevent its heat destruction....and I
didn't know that, myself. ...

I'm sure you're right. On the advise of a rather eccentric, but I
think very competent EE (Gary Pacey of Outback Marine) we installed
oversized alternators and then down-rated them. At least in theory
they are supposed to be able to run continuously around 100 amps. At
any rate, I've used them to charge my ~500ah bank of AGM's for years
and they've handled it well. Underway that means they run full out
for ~15 minutes a couple of times a day. At anchor the solar panels
do most of the work and I the alternators much less of a workout.

-- Tom.

On Thu, 27 Mar 2008 12:08:40 -0700 (PDT), "
wrote:

On Mar 26, 5:46 pm, Larry wrote:
... A 100A alternator will NOT put out 100A! It will put out 100A for a FEW
MINUTES, then must be cut back to prevent its heat destruction....and I
didn't know that, myself. ...

I'm sure you're right. On the advise of a rather eccentric, but I
think very competent EE (Gary Pacey of Outback Marine) we installed
oversized alternators and then down-rated them. At least in theory
they are supposed to be able to run continuously around 100 amps. At
any rate, I've used them to charge my ~500ah bank of AGM's for years
and they've handled it well. Underway that means they run full out
for ~15 minutes a couple of times a day. At anchor the solar panels
do most of the work and I the alternators much less of a workout.

I seem to recall that for best battery life you should charge it at
the 20 hour rate. You have a 2000 AH starting battery? [Ten times the
size of the one on Cat's biggest bulldozer]. Charging a 25 AH battery
at the fifteen minute rate has to be a poor idea.

Casady

On Mar 27, 11:04 am, (Richard Casady)
wrote:
I seem to recall that for best battery life you should charge it at
the 20 hour rate. You have a 2000 AH starting battery? [Ten times the
size of the one on Cat's biggest bulldozer]. Charging a 25 AH battery
at the fifteen minute rate has to be a poor idea.

Sorry, I wasn't clear. The batteries absorption rate drops below the
alternators full output at about the 15 min mark if the batteries have
been deeply discharged. I dont' stop charging at that point, I just
stop asking as much from the alternators. These are AGMs and have
unusually high absorption rates. I do not use a separate starting and
house bank. I have a small reserve battery for emergency starting but
otherwise use a 2x8D Lifeline bank for all of my electrical needs.

-- Tom.

"Richard Casady" wrote:

I seem to recall that for best battery life you should charge it at
the 20 hour rate. You have a 2000 AH starting battery? [Ten times
the
size of the one on Cat's biggest bulldozer]. Charging a 25 AH
battery
at the fifteen minute rate has to be a poor idea.


Rule of thumb given to me by an old time Trojan application engineer:

Recharge rate = 15% of total connected AH rating of bank.

Based on 2000AH bank, it will accept a 300A recharge rate without
complaint.

Every 100AH consumed requires 125AH replacement.

Yes you can play games with the above, but it will come back to bite
you.

Wet cell battery technology hasn't changed much in the past 100 years,
it is a very mature product.

Lew