Solar Trickle Charge - Myth or Fact?

[Wind Chime]

I would think that when it comes to electricity and electric storage the facts would be black and white, but I get some different options and need guidance from the group.

We have two group-24 (deep cycle) batteries onboard that are connected using a West Marine combiner-50 (in place of the A-B-Both switch), they are charged using shore power on a A/C 3-stage charger. This whole systems works great, never short on power on the hook even when running the TV on the 300 watt inverter.

We also use one small 5-watt solar panel that hooks directly into the cigarette lighter (no inline voltage regulator) that tops up the batteries a small amount while on the hook or at the marine when not in use during the summer.

To help keep the batteries conditioned during the winter, I pull them and the 3-stage charger off the boat and leave them charging on float all winter in the garage This works great - the batteries always get a hi-volt charge during the summer and last long. I try not to discharge less that 50% to reduce lead sulfate. (learned this at a West Marine battery seminar).


Here’s the question:
I was told by a marine electrician that if you have a solar panel with no inline voltage regulator, the panel will charge during the daylight hours and then discharge overnight. Is this true?

Thanks!!

[Steve K]

The 5w panel I have says it has a discharge protection circuit. Some kind of diode or resistor or something that prevents discharge (not expert at this so not sure what it is). However, I keep my 5w panel installed all the time, never have a problem. (Three group 24 deep cycles no controller, direct connection). Been doing this for 10 years and two of my batteries are every bit of ten years old and work like new. (super high quality gel cells cost $374 each when new) The Walmart special only lasts a few years, if well cared for. (which is my other one and even these will last up to five years on my boat. Have replaced these cheap ones in as little as three though).

SK

[Russ]

Good question about those small solar chargers.
I would like to keep one out all winter to keep batteries from draining. Would rather not pull batteries out, they are hard to get to.

My concern is

1) Will it over charge and cook the battery
2) Will it drain the battery (question above) such as when it gets covered in snow and can't charge.

[Obelix]

I used a 10W panel for the same purpose, but it came with it's own small regulator. Your marine electrician is correct, that if you don't use a protective circuit, the panel will discharge the battery. The protective circuit on a small panel could be as simple as a diode to block reverse current, but it will also cause a small voltage reduction during the charging phase.

Obelix

[Stevenhigbee]

Hook up an ammeter between the battery and the solar panel, and see if any current is flowing out of the battery while the panel is covered. That's the way to find out if it is happening with YOUR setup. And now that you mention the possibilty, I think I'm going to run the test on my own setup.

[Ammiraglio]

I have a small solar panel, about 1ft by 1ft, connected directly to the battery, to keep it topped off. Before the solar panel I destroyed a battery every year or every other year (I am really bad at maintenance, especially winterization). With the solar panel, the battery has happily survived four winters and it is still going strong. If needed I can dig out the technical info.

[padge]

Most smaller solar panels should have a blocking diode fitted

the larger panels 100W+ designed for running other equipment may not and would need a charge regulator anyway.

The rule of thumb is don't constantly charge the battery at more than 3%
So a 100Ah battery can handle 3amps without damage

A 5W panel will only produce approx .4 amps - no risk of boiling your battery.
This current is into a flat battery , as the battery approaches full the current drops to almost zero.

I have a 12W panel charging my 180Ah battery when fully charged it is drawing <20mA ( replacing internal battery losses).

[mastreb]

It is true that keeping a solar panel connected will discharge a battery if its dark. However, all it takes is a diode to solve this problem and if your 5W panel was sold as a battery maintainer, it will have the necessary diode in place to prevent this.

[Three Gypsies]

In 2013 while we were on our 8 month cruise , I connected a small panel to the deep cycle battery on our travel trailer . When we got home the battery was fully charged and in good condition .

It kept the battery fully charged but didn't boil away the water .

The panel I used was about .5 amp at 12vdc

[ronacarme]

A 5 watt solar plate (with built-in blocking diode) continuously connected to the original house battery in my old 1988 Mac D, kept that battery fully charged
, in the boat, thru Michigan summers and winters, from when new (1988) till I sold the boat in 2000. The outboard was a manual start 8, so battery use was minimal, limited to occaisional VHF, FM, and running lights(rare) use. The plate and original battery went with the D when it sold.
I have used a similar 5 watt plate on my present Mac X from 2000 till now. The X uses the house battery also for motor (9.9 Honda) starting. I have replaced the battery once, maybe 5 years ago.
This, in my opinion is the easiest and best way to long house battery life.
Ron

[Three Gypsies]

Our Dinghy is completely solar powered .
We have a 'wheelchair' battery being charged
by a 12 watt or 1 amp solar cell .

The boat's motor is a 28 lb thrust Minn-Kota

The boat is good for about 5 miles @ 3mph
and is usually recharged by the next day
if ran all the way down.

If not ran all the way down , it stays topped off .

Although the range of 5 miles has never been a problem ,
I am putting a little bit larger panel on it this year . Just
to stay ahead of running the battery down.

[vizwhiz]

I like that idea!

[Boblee]

Most panels have a blocking diode which will stop reverse flow, as for boiling the battery I wouldn't connect any size panel without a regulator even with wet cell batteries and certainly not with eg calcium types.
Our's usually has a small panel on it off season and it plugs into an Anderson plug where the larger ones do then goes through the regulator into the system, checked the batteries with the 7 stage charger yesterday after 8 weeks and they were all good.

[kevinnem]

my knowlage of electrical is a bit limited, but in case it has been clearly stated, a diode is a "one way value" of the electrical world, it lets electricity flow only one direction. if it is used on a dc source, it stops the flow from reversing. and in AC it does what is called rectification, letting only only 1/2 the wave through ( though use in sets it basically converts ac to dc). Because of this ability in the DC world to stop reverse flow , it is often called a blocking diode.

Your manual might say if it has one, .. do you have any details on make/model?

[BOAT]

It is true that keeping a solar panel connected will discharge a battery if its dark. However, all it takes is a diode to solve this problem and if your 5W panel was sold as a battery maintainer, it will have the necessary diode in place to prevent this.

Gee, If I send a lot of power to a solar panel will sunlight come out of it?