What is the usual or recommended circuit arrangement for incorporating a
solar panel as a backup or trickle charger for motor and/or secondary
batteries? My hope is that a small solar collector would be enough to
keep the batteries charged when the boat is not being used and to charge
the second battery (over a 12-hour period) after using the second
battery to power an auto-steering unit, depth finder, etc., for several
hours during a day's sailing, when the motor isn't being extensively
used and when shore power isn't available. I would also plan on having a
110V-powered battery charger for use when 110 AC was available.

This is a relatively small vessel that will likely be used on cruises of
3-5 days and not for extended blue water cruising, and I don't want to
invest in a large, high power solar collector. (Perhaps 10 watts or so.)
One concern is whether I need a regulator or shutoff device to prevent
overcharging of the batteries if the solar panel is left in a charging
mode for long periods. What's necessary for providing an appropriate
charging time, level, etc., or is it not that critical?

Thanks for any suggestions.

Jim

Jim:

A 10 watt solar panel is only good for maintaining a charge on your
batteries, not recharging in a short time. A 10 watt panel doesn't need a
controller. A rule of thumb is that if the charging current is less than 2%
of the amphour capacity of your batteries, then you don't need a charger.
For even a single group 27 battery you will be below this threshold for a 10
watt panel.

As you note, for a 3-4 day cruise it isn't worth installing a big solar
array to keep your batteries charged up. It would take 100-200 watts to
begin to keep up with refrigeration and other demands of extended cruising.

I would first install a high output alternator and a good regulator- Balmar
sells a package for $600 which will keep you going on a limited cruise
duration. You may have to run your engine for an hour or two each day, but
for occaisional use, it's ok.

David

David&Joan wrote:
Jim:

A 10 watt solar panel is only good for maintaining a charge on your
batteries, not recharging in a short time. A 10 watt panel doesn't need a
controller. A rule of thumb is that if the charging current is less than 2%
of the amphour capacity of your batteries, then you don't need a charger.
For even a single group 27 battery you will be below this threshold for a 10
watt panel.

As you note, for a 3-4 day cruise it isn't worth installing a big solar
array to keep your batteries charged up. It would take 100-200 watts to
begin to keep up with refrigeration and other demands of extended cruising.

I would first install a high output alternator and a good regulator- Balmar
sells a package for $600 which will keep you going on a limited cruise
duration. You may have to run your engine for an hour or two each day, but
for occaisional use, it's ok.

David


Thanks for the suggestions. This is a small (26-ft) boat with a 50 hp
outboard, but I plan to use it for bay and coastal cruising, on trips
normally less than 5 days or so. The boat will not have refrigeration,
AC, hot-plates, windlass, etc., but I would be using the second battery
to power the autosteering unit, depth finder, GPS chartplotter, VHF
radio, lights, etc., and possibly radar. Also, I would like to use the
solar panel in trickle charge mode to keep the batteries charged when
the boat is not being used.

Jim

Jim,
You should work out an "energy budget," conservatively estimating your usage.
Although your boat gear (autopilot, VHF,GPS, etc) might seem to be the worst,
their usage will likely be limited, and often used while your engine is running.
Creature comforts can be much worse, especially if you hang out for extended
periods at an anchorage (like a rainy day) while the kids watch videos, you
listen to the ball game, and someone forgets to turn off a light.

BTW, your Bigfoot has a 10 amp alternator, so it will easily keep up with usage
while running, but it will take a long time charge a depleted battery. If this
is really an issue for you, the best bet might be a small, portable generator,
which could be had for under $500 and might have other uses.




"Jim Cate" wrote in message
...


David&Joan wrote:
Jim:

A 10 watt solar panel is only good for maintaining a charge on your
batteries, not recharging in a short time. A 10 watt panel doesn't need a
controller. A rule of thumb is that if the charging current is less than 2%
of the amphour capacity of your batteries, then you don't need a charger.
For even a single group 27 battery you will be below this threshold for a 10
watt panel.

As you note, for a 3-4 day cruise it isn't worth installing a big solar
array to keep your batteries charged up. It would take 100-200 watts to
begin to keep up with refrigeration and other demands of extended cruising.

I would first install a high output alternator and a good regulator- Balmar
sells a package for $600 which will keep you going on a limited cruise
duration. You may have to run your engine for an hour or two each day, but
for occaisional use, it's ok.

David


Thanks for the suggestions. This is a small (26-ft) boat with a 50 hp
outboard, but I plan to use it for bay and coastal cruising, on trips
normally less than 5 days or so. The boat will not have refrigeration,
AC, hot-plates, windlass, etc., but I would be using the second battery
to power the autosteering unit, depth finder, GPS chartplotter, VHF
radio, lights, etc., and possibly radar. Also, I would like to use the
solar panel in trickle charge mode to keep the batteries charged when
the boat is not being used.

Jim

Jim:

Ah, I now understand that you have an outboard engine and no refrigeration,
etc. As Jeff noted, the O/B alternator should keep up with all of your DC
needs while running. Then all you have to consider is what you use while at
anchor. This should be fairly small- cabin lights, radio and anchor light.
This will total about 20-30 amphours per day for several hours of cabin
lights and the anchor light all night.

This much power usage can be replaced with a single 100 watt solar panel on
a good sunny day. You could wire this panel into your boat's electrical
system through a cigarette lighter outlet without a controller if you are
careful to unplug it after you are done cruising and are back at the dock.

And some of your usage will be replaced by the O/B alternator if you move
from anchorage to anchorage. You might get by with as little as a 50 watt
solar panel if you start with fully charged batteries and are only out for
2-3 days at a time.

If that is your usage pattern, it might be cheaper still to install two 6v
golf cart batteries to add 220 amphours of capacity to bring you up to 300
amphours or so. With this much capacity, and your limited usage, you
wouldn't need to recharge at all for 4-5 days. Batteries are cheaper than
solar panels or generators if you can recharge them back at the dock.

David

Adding battery capacity is usually appropriate for cruisers, but perhaps not in
Jim's case. The 150 pounds of added weight will cost him over a knot of speed.
The speed under power is dependent on keeping the weight to a minimum.

The solar panel option is useful, but as I pointed out, sometimes when you need
it the most, it isn't there. I'm thinking of the times I've been stuck "below"
on a rainy day with electronic toys for entertainment.

Whatever solution is found, Jim should take care that he always has a charged
starting battery, since pull-starting the 50HP Bigfoot might not work.



"David&Joan" wrote in message
news:ydtpc.49104$Z%5.26023@okepread01...
Jim:

Ah, I now understand that you have an outboard engine and no refrigeration,
etc. As Jeff noted, the O/B alternator should keep up with all of your DC
needs while running. Then all you have to consider is what you use while at
anchor. This should be fairly small- cabin lights, radio and anchor light.
This will total about 20-30 amphours per day for several hours of cabin
lights and the anchor light all night.

This much power usage can be replaced with a single 100 watt solar panel on
a good sunny day. You could wire this panel into your boat's electrical
system through a cigarette lighter outlet without a controller if you are
careful to unplug it after you are done cruising and are back at the dock.

And some of your usage will be replaced by the O/B alternator if you move
from anchorage to anchorage. You might get by with as little as a 50 watt
solar panel if you start with fully charged batteries and are only out for
2-3 days at a time.

If that is your usage pattern, it might be cheaper still to install two 6v
golf cart batteries to add 220 amphours of capacity to bring you up to 300
amphours or so. With this much capacity, and your limited usage, you
wouldn't need to recharge at all for 4-5 days. Batteries are cheaper than
solar panels or generators if you can recharge them back at the dock.

David

In article ,
Jim Cate wrote:

David&Joan wrote:
Jim:

A 10 watt solar panel is only good for maintaining a charge on your
batteries, not recharging in a short time. A 10 watt panel doesn't need a
controller. A rule of thumb is that if the charging current is less than 2%
of the amphour capacity of your batteries, then you don't need a charger.
For even a single group 27 battery you will be below this threshold for a 10
watt panel.

As you note, for a 3-4 day cruise it isn't worth installing a big solar
array to keep your batteries charged up. It would take 100-200 watts to
begin to keep up with refrigeration and other demands of extended cruising.

I would first install a high output alternator and a good regulator- Balmar
sells a package for $600 which will keep you going on a limited cruise
duration. You may have to run your engine for an hour or two each day, but
for occaisional use, it's ok.

David


Thanks for the suggestions. This is a small (26-ft) boat with a 50 hp
outboard, but I plan to use it for bay and coastal cruising, on trips
normally less than 5 days or so. The boat will not have refrigeration,
AC, hot-plates, windlass, etc., but I would be using the second battery
to power the autosteering unit, depth finder, GPS chartplotter, VHF
radio, lights, etc., and possibly radar. Also, I would like to use the
solar panel in trickle charge mode to keep the batteries charged when
the boat is not being used.

Jim


We just got a 11 watt panel for about the same purposes. From others'
experience, it'll be enough to top the batteries up during the week
(possibly 50-60 amp hours), or if we blow battery management while
cruising, give us enough charge to start the diesel after a few hours'
exposure with everything else off (aka belts and suspenders).

The 1-2 peak amps shouldn't hurt a fully charged battery and I'm hoping
that being better charged more of the time will keep the batteries
healthier.

A good alternator and regulator would be nice to have, but are probably
tough to put on an outboard. We could mount them on our diesel, but for
various reasons I opted for solar first. One of them was the cheap
Walmart charger: though it seemed to work to spec, it didn't charge at a
much higher rate than our current alternator.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

I wouldn't worry about a regulator for a 10 watt solar panel, however you
without a regulator, you should have a diode to prevent the panel from
discharging the batteries when the sun goes down.. If you end up with more
than one panel, you need a diode between panels to prevent problems if one
panel get shaded while the other has full sun. Just bare in mind that each
diode will drop the panel voltage about a half volt.

I'm running two 56 watt panels and a Windbugger wind gen. Neither has a
regulator.. However I'm charging a 800 amp/hr battery bank..

(Just as a side note. Once while working on the DC circuit, I turned off all
batteries but noticed that the frig was still running. Turns out I had
neglected to turn off the solar panels and they were running the frig
directly.)

Steve
s/v Good Intentions