2.4W solar trickle charge to batteries over 10 months absence?

[Amari]

Amari will be on the hard at Yat Marine, Marmaris, Turkey unused for 10 months from November 2008. She has 90ah batteries x4, each 3 years old. Not having been at that marina before I'm uncertain of the facilities. To maintain the batteries the choices seem to be:
-Get boat guardian to charge via shore power monthly, if within reach
-Take out batteries and put in care of yard for recharging-?dodgy reliability
-Maplins currently have 2.4W solar panels, stated to be suitable for battery trickle charging, reduced from £29.99 to £9.99. Stated to be waterproof but ''charging when raining not advised''.
Would the panels (presumably one per battery or could the lead be split so that two would do?) function if placed inside the saloon against a window or hatch?
Grateful for forumites suggestions /forums/images/graemlins/confused.gif

 

[pappaecho]

I have a 15 watt Solar panel which charges 4 batteries about 400 amp hours in total, in the UK with a simple controller which limits the charge over 14 volts.
I also have an ex Maplin smaller solar panel for trickle charging car batteries and it is useless. I know that Turkish sunshine hours are many more than the UK, but with a controller you should not have a problem - better to have more charge and dump it than not enough to keep the batteries up

 

[lw395]

It depends on the health of your batteries. I have here an oldish 75ah battery, ex telecomms standy equipment. It takes only about 7mA to keep it at float voltage once charged.
2.4W at 12V is 200mA, so even allowing for efficiency and night hours, one of these panels should be quite useful.
Some batteries however develop a much higher self-discharge rate when a few years old, despite being absolutely fine in other respects.
A couple of the maplin jobs looks like 20quid well spent, but that doesn't mean a dearer option won't suit you better.
A mate of mine uses a small panel inside a portlight (S facing) and finds it makes a significant difference.
Its worth making sure there are no other drains on the battery, such as heater circuit, navtex, radio memory, as the standy loads can add up.
10 months is a long time though.
HTH.

 

[Amari]

Many thanks pappaecho & HTH. If I used the solar trickle I assume I would first disconnect the batteries completely so as to avoid occult drain.

 

[Norman_E]

PM sent.

 

[William_H]

The calculation for current to expect from a solar panel are incorrect. Sol;ar panels are rated in watts as max voltage times max current.
Max voltage is usually 20 volts or a little less so can only expect 120ma max from a 2.4 watt panel. This will be a lot less if behind a window and less when not directly facing the sun.

Re original post I would suggest if you want to use these particular panels that you get 4 panels one for each battery. I hope you have enough S facing windows or are willing to mount them outside.

There is no certainty that 2.4 watt panel will keep your batteries alive but this size should be of some use. Bigger would be better.

If you wan to share batteries from one panel then it is best to use diodes for isolation. ie one diode for each battery pos of panel to all the diode anodes. (tail of arrow or opposite end to band) Each diode cathode goes to a battery pos with all negatives connected together.
You may get better current form schotky diodes with lower volt drop but this is not usually necessary.

If you are feeding 4 batteries from one solar panel then you could have a panel up to 70 watts without having a regulator.

Finally I use a 2 watt solar panel on about 10AH of NiCad batteries and it will recharge the batteries over a few weeks. But that is in Oz summer sun. I mount the solar panel on the top of the boom /mainsail cover.
So it is up to you how much you spend and what you risk outside to the thieves
good luck olewill

 

[Amari]

Many thanks for that William. Norman has suggested that I get a liveaboard from the marina to supervise the battery maintenance and that seems a good compromise

 

[lw395]

Olewill, your point is correct, I had put the alleged 120mA vs 200mA as part of the 'efficiciency' of running a 12v battery from a 20(?) volt panel.
So if you take 120mA then you might allow
25% for night hours and non ideal illumination early and late in the day
80% for window transmission
80% for angle of window?
Giving about 19mA average.
If this overcomes the self discharge, it will help hugely, or at least it will stop the batteries flattening as much as without, so I stand by my 20quid well spent comment.
However 10 months of neglect is a long time, so I think getting someone to take a look a few times will pay dividends.
Don't forget the self discharge can be a lot bigger than the random example I have measured, and with diode sharing one battery which drops in volts will prevent another from getting much charge.
I don't know the particular panels so whether they would be up to a winter outdoors is not known to me. So south facing windows or hatches could be at a premium.
A simple approach like this can make a big difference, to achieve much more the costs escalate and the panels start to take over the boat sometimes!

 

[Heckler]

guardianage in greece around lefkas is about £800 PA quoted last week. If about the same in Turkey then get a big panel 40 watts, good make such as Solaris £300 and a regulator £ 20ish. You will save a load on guardiannage, still have solar charging for the future and save ending up with shagged batteries, its a no brainer from where I'm standing.
Stu