Solar panel trickle charge to battery. Could battery overcharge?

[trialanderror]

Hi all,  I was informed that when off grid over the winter, a good way to keep the auto bilge pump functioning would be to use a solar panel to trickle charge the battery.  I am not 100% sure if this is what the guy said to me.  Assuming this is possible, I wish to know (1)  if a very small solar panel (12V, 4.5W) linked to the battery via crocodile clips would suffice?; (2) is there a recommended solar panel wattage considered appropriate for trickle charging the battery over winter, if above version is not appropriate; (3) could such a  trickle charge  solar panel  overcharge the battery with no escape for potential gas build-up in the battery?

As a newbie, these are the first of many naïve questions that I may ask - hopefully, once you have jettisoned your world weary sagely countenance, you might take pity upon this pathetic wretch and offer a modicum of advice.  Thank you in advance for reading this. 

[WotEver]

1. No, it would be extremely unlikely to even cover the battery’s self-discharge, let alone pump use. It’s way too small. 
 

2. 120W might do it but there are lots of variables, like how often the pump runs and how many sunny days we get. Unfortunately the pump probably runs more often when it’s raining which is also the time you’ll get nothing from solar. 
 

3. No. 

[trialanderror]

Hi Wotever,

 

Thank you for that sound advice, just what I needed.  Can I take it that auto bilge pumps are designed where winter shore power is available  & not for several months off grid?

[WotEver]

4 minutes ago, trialanderror said:

Hi Wotever,

 

Thank you for that sound advice, just what I needed.  Can I take it that auto bilge pumps are designed where winter shore power is available  & not for several months off grid?

Not at all. But Solar is essential if you’re off-grid and leaving the boat unattended. Obviously if you’re visiting the boat often then you can simply run the engine to keep the battery charged. 

[Sea Dog]

Does your bilge pump operate frequently or even at all?  My bilge, for example, under a trad stern and with a Volvo stern seal, is always bone dry so no power whatsoever is drawn by the bilge pump. This is a completely different scenario to a cruiser stern with a leaky deck and a drippy stern gland, possibly even a well deck up forward draining through the boat to the stern bilge. The load is key here as @WotEver touched on above.

[Tony Brooks]

Having a cruiser stern with leaky deck boards, very poor self draining set-up and a non-leaking conventional gland over 20 years I have found that even after several days of horrendous rain the bilge water collected between winter visits at four to six week intervals has never got above the engine  beds. I refuse to have an automatic bilge pump because of the ever present danger of a switch fault ruining the batteries. This was true even when a deck board under water drain pipe started leaking. Based on this I would suggest that the OP either has a stern gland problem or a battery/electrical problem.  If the OP intends to abandon the boat for the winter months then  things are a bit different but doing that without 40W plus of solar or shore line charging is asking for a short battery life because nothing is making up for any self discharge.

[doratheexplorer]

17 minutes ago, Sea Dog said:

Does your bilge pump operate frequently or even at all?  My bilge, for example, under a trad stern and with a Volvo stern seal, is always bone dry so no power whatsoever is drawn by the bilge pump. This is a completely different scenario to a cruiser stern with a leaky deck and a drippy stern gland, possibly even a well deck up forward draining through the boat to the stern bilge. The load is key here as @WotEver touched on above.

 

Have you been spying on my boat?

[Sea Dog]

8 minutes ago, doratheexplorer said:

 

Have you been spying on my boat?

Couldn't help but notice the water lapping over the top of your button. I've left you my dustpan - they make quite good bailers, particularly for the last inch or so! 

 

[Detling]

I have an auto pump in a bucket under the stern gland and in normally never runs but is there for belt and braces. I have a 10 watt panel on my starter (always on) and I replaced my starter last yea,r the old one was dated 2008 so I don't think you will damage your battery by overcharge with such a small panel.