"Glenn Ashmore" wrote in message
...
I will be pumping over 200 amps for as long as an hour every day while
cruising. I had to go back and look at some of your previous posts to
figure out why you are thinking the way you are. Then I found the post
about having a 0-75 MPH speedo and realized that you are a hot rod ski
boater with no idea of how a cruising boat works.

A typical 35' to 50' cruising boat with a well balanced electrical
system will have anywhere from 350 to 1200 amp hours of battery bank and
will regularly draw it from 75% to 50% to keep the charging cycle in the
bulk current range. They will have an alternator capable of outputting
20 to 25% of the bank's capacity per hour and run it once or twice a day
for up to an hour at as close to full capacity as possible. That is
what those fancy three stage regulators with temperature sensors and
recombinant caps are for.

As an example, my boat will have a pretty heavy duty system but it is
not as large as some in that size range and not all that much larger
than most. It is 800 amp hours in four L16HC batteries charged by a 250
amp brushless Niehoff fire truck alternator with an external three stage
regulator and external rectifier. The energy budget calls for charging
and making water for 45 minutes to an hour every day while cruising.
Should a guest unknowingly turn the master battery switch during that
time I could be out about $1,000. In this situation, which is not
unusual for a cruiser, a $25 investment in a Zap Stop is a no brainer.

The single most common reason for failures in cruising boat alternators
is load dump spikes with bearing failures a distant second. OTOH, a ski
boat with only a cranking battery, no master battery switch and a stock
60 amp alternator would never have to worry.

Ed Price wrote:

Very illuminating, Glenn. Now I understand why your posts have trouble
answering a question and often ramble off into an insulting lecture. You are
obviously distracted by the rigors of searching previous postings looking
for clues about the poster's lifestyle and recreational habits.

I find it truly hilarious that you have concluded that I am a "hot rod ski
boater." Based on that profound logic, I suppose that having a DVM with a
1200 VAC range makes you an electrician? You are becoming a pretentious
twit.

One of the first things I did when you started lecturing me was to visit
your little sailboat construction site. Actually, for an unpleasant person,
you do nice work. If I lived near you, I would be happy to see you complete
the project and sail over the horizon.

But I am learning some interesting things about you and your cutter. I
always thought that sailors chose sail because they liked the "off the grid"
lifestyle. They wanted to get out there with the lee scuppers sloshing green
water, close to nature and in touch with the long heritage of men against
the sea. At least that's what they always said when I offered them a tow off
a sand bar. They liked to look down on "stink-potters" just the way you
casually insult small powerboat owners.

You seem to have some really hearty electrical needs. Yeah, I guess I'm
really out of touch with the average cruising sailor. I mean, on a 31-foot
twin engine cruiser I had, once I shut down the engines, my electrical load
was only an anchor light, a couple of 12 VDC cabin lights, sometimes a
half-amp radio, a minute or so of rare bilge pump operation, a 30-second
burst of the toilet macerator pump, and a rare burst of the freshwater
pressure pump. Then, I had a 50-foot down-east style diesel trawler. It was
more primitive, without an electric head (see how long ago that was?), but I
did have a big battery bank, because starting the diesel (GM 6-71) was a
tough load. And, it was pretty leaky, with two Rule 1200 GPH pumps
disturbingly active. I guess your way of sailing must include microwave
ovens and color TV's and full-time radar and autohelm.

I'm not criticizing your choices, just trying to account for your electrical
budget. Now, you said you had 800 amp-hours batteries, and you plan to use
about 65% of that capacity in one day. That's 520 amp-hours, and with 12
VDC, that's 6240 watt-hours. Averaged out evenly, that's equivalent to a
continuous 23 amp drain. And then, to put that charge back in one hour, that
implies a charging current of 520 amps. But since your alternator has a
capacity of 250 amps, you will need to run the charge for two hours. If not,
then you will hit full discharge on maybe the third or fourth day. But aside
from the schedule, what is your projected load budget?

Meanwhile, curb your imagination. I'm presently doing a restoration on a
14-foot steel displacement hull vessel with a rated 36 HP gasoline engine.
As you can imagine, hull speed is quite a bit less than 75 MPH. Maybe if I
had your battery pack, I could get it to plane for a couple of minutes!


Ed

The reason for the 800 amp hour bank is that I will have two large
computers, a 3000 watt inverter, SSB radio and a rather powerful
autopilot. All of which will eat a fair number of amps. I have
estimated my daily energy budget underway to be between 180 and about
225 amp hours.

Two other factors determined the bank size. The first is that deep
cycle batteries should never ne discharged below 50% to preserve their
useful life. That limits my usable power to 400 amps. The second is
that I would like to keep engine time to a minimum. All the systems
that use engine power, charging, watermaking and refrigeration are
designed to restore themselves in one hour of engine time per day.

Up to about 75-80% charge, deep cycle batteries can accept a charge
current of up to 25% of their capacity. As they approach full charge
the rate has to be reduced substantially. That sets an upper limit for
daily charging at about 80%. The result is a net usable capacity of 30%
or about 240 amp hours.

As I said, You set the tone of the conversation.


--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com