Lloyd's estimate started out strong, with an estimate of 0.4 amp hours
of trickle per day.
But that means 0.4 amps for ONE hour per day

So a 1/8 amp panel at 14 volts (for 3 or 4 hours per day)
would do the job for each battery.

Brian Whatcott Altus OK

On Sun, 23 Nov 2003 08:41:51 -0800, "Lloyd Sumpter"
wrote:

On Sun, 23 Nov 2003 16:06:53 +0000, Hmseconomy wrote:

What's the minimum amps/volts output needed to trickle charge two marine
batteries to keep them up? Can a single small trickle charge panel charge two
batteries at the same time? What's the recommended connection method? Need a
diode to protect against overcharging (even with a minimum output panel?). Any
advice would be appreciated.

I'll start with an assumption that may be wrong, but...Assume a battery loses
50% of its charge in 3 months, and it's about 80AH. That means it loses about .4
AH per day. So it needs about .4 amps CONTINUOUSLY to keep it charged.

Now, since a solar panel only puts out anything about 50% of the time (assume
full sun all day) you would need an 800mA panel. But a "1 Amp" panel only puts
out close to 1 amp in full sun when the sun's directly perpendicular to the
cell, I'd put it a 60-70% "fudge factor" (more if you live in a cloudy area).
This means you need about a 1.3A panel per battery.

Note that most of these "trickle charge" solar panels only put out 200mA or so.

Also, a diode is so that the battery doesn't "backfeed" the panel, not to
prevent overcharging.

Based on this, I'd say you'd be safe with a 2A panel, paralleled to both
batteries (assuming there's no load on the batteries). I've used a 2A panel on
one 4D battery over the summer, and it seemed to work well. I doubt one of these
"trickle charge" panels would be useful for the long term.

Lloyd Sumpter
"Far Cove" Catalina 36

Lloyd's estimate started out strong, with an estimate of 0.4 amp hours
of trickle per day.
But that means 0.4 amps for ONE hour per day

So a 1/8 amp panel at 14 volts (for 3 or 4 hours per day)
would do the job for each battery.

Brian Whatcott Altus OK

On Sun, 23 Nov 2003 08:41:51 -0800, "Lloyd Sumpter"
wrote:

On Sun, 23 Nov 2003 16:06:53 +0000, Hmseconomy wrote:

What's the minimum amps/volts output needed to trickle charge two marine
batteries to keep them up? Can a single small trickle charge panel charge two
batteries at the same time? What's the recommended connection method? Need a
diode to protect against overcharging (even with a minimum output panel?). Any
advice would be appreciated.

I'll start with an assumption that may be wrong, but...Assume a battery loses
50% of its charge in 3 months, and it's about 80AH. That means it loses about .4
AH per day. So it needs about .4 amps CONTINUOUSLY to keep it charged.

Now, since a solar panel only puts out anything about 50% of the time (assume
full sun all day) you would need an 800mA panel. But a "1 Amp" panel only puts
out close to 1 amp in full sun when the sun's directly perpendicular to the
cell, I'd put it a 60-70% "fudge factor" (more if you live in a cloudy area).
This means you need about a 1.3A panel per battery.

Note that most of these "trickle charge" solar panels only put out 200mA or so.

Also, a diode is so that the battery doesn't "backfeed" the panel, not to
prevent overcharging.

Based on this, I'd say you'd be safe with a 2A panel, paralleled to both
batteries (assuming there's no load on the batteries). I've used a 2A panel on
one 4D battery over the summer, and it seemed to work well. I doubt one of these
"trickle charge" panels would be useful for the long term.

Lloyd Sumpter
"Far Cove" Catalina 36

On Sun, 23 Nov 2003 16:06:53 +0000, Hmseconomy wrote:

What's the minimum amps/volts output needed to trickle charge two marine
batteries to keep them up? Can a single small trickle charge panel charge two
batteries at the same time? What's the recommended connection method? Need a
diode to protect against overcharging (even with a minimum output panel?). Any
advice would be appreciated.

I'll start with an assumption that may be wrong, but...Assume a battery loses
50% of its charge in 3 months, and it's about 80AH. That means it loses about .4
AH per day. So it needs about .4 amps CONTINUOUSLY to keep it charged.

Now, since a solar panel only puts out anything about 50% of the time (assume
full sun all day) you would need an 800mA panel. But a "1 Amp" panel only puts
out close to 1 amp in full sun when the sun's directly perpendicular to the
cell, I'd put it a 60-70% "fudge factor" (more if you live in a cloudy area).
This means you need about a 1.3A panel per battery.

Note that most of these "trickle charge" solar panels only put out 200mA or so.

Also, a diode is so that the battery doesn't "backfeed" the panel, not to
prevent overcharging.

Based on this, I'd say you'd be safe with a 2A panel, paralleled to both
batteries (assuming there's no load on the batteries). I've used a 2A panel on
one 4D battery over the summer, and it seemed to work well. I doubt one of these
"trickle charge" panels would be useful for the long term.

Lloyd Sumpter
"Far Cove" Catalina 36

On 23 Nov 2003 16:06:53 GMT, (Hmseconomy) wrote:

What's the minimum amps/volts output needed to trickle charge two marine
batteries to keep them up?

That depends on the size of the marine batteries, the amp-hour rating,
as well as the type of "marine battery"...i.e. starting or deep
cycle.... you have.

Good batteries don't need something to "keep them up", except
occasional use....run the boat.

Can a single small trickle charge panel charge two
batteries at the same time?

Yes, if you use a battery isolator. Lionheart has an isolator between
house and starting battery banks fed from the Windcharger/solar panel
and shaft alternator. The weaker battery has lower voltage and will
get more current through the series diode. The diodes in the
isolator, however, will keep the batteries from discharging each other
at night.

What's the recommended connection method? Need a
diode to protect against overcharging (even with a minimum output panel?). Any
advice would be appreciated.

The series diode in a solar system has nothing to do with protecting
against overcharging. When a solar panel is in the dark, it is NOT an
open circuit. When its charging voltage drops below the battery
voltage connected to it, the battery shoves current through the
darkened solar panel, discharging the battery in the process. The
series diode prevents this.

There IS a charge limiter you can buy to prevent the solar panel from
overcharging (percolating) your battery. It's called a "charge
limiter" or "charge regulator" and is sold by solar companies.


Larry W4CSC

NNNN

On 23 Nov 2003 16:06:53 GMT, (Hmseconomy) wrote:

What's the minimum amps/volts output needed to trickle charge two marine
batteries to keep them up?

That depends on the size of the marine batteries, the amp-hour rating,
as well as the type of "marine battery"...i.e. starting or deep
cycle.... you have.

Good batteries don't need something to "keep them up", except
occasional use....run the boat.

Can a single small trickle charge panel charge two
batteries at the same time?

Yes, if you use a battery isolator. Lionheart has an isolator between
house and starting battery banks fed from the Windcharger/solar panel
and shaft alternator. The weaker battery has lower voltage and will
get more current through the series diode. The diodes in the
isolator, however, will keep the batteries from discharging each other
at night.

What's the recommended connection method? Need a
diode to protect against overcharging (even with a minimum output panel?). Any
advice would be appreciated.

The series diode in a solar system has nothing to do with protecting
against overcharging. When a solar panel is in the dark, it is NOT an
open circuit. When its charging voltage drops below the battery
voltage connected to it, the battery shoves current through the
darkened solar panel, discharging the battery in the process. The
series diode prevents this.

There IS a charge limiter you can buy to prevent the solar panel from
overcharging (percolating) your battery. It's called a "charge
limiter" or "charge regulator" and is sold by solar companies.


Larry W4CSC

NNNN