Another Battery question

[ReggieK]

Hi Folks
What's the panel's advice on best practice for a leisure battery that is rarely used. It is connected up and used only occasionally for cabin lights or nav lights. There is no charge going to it. How often should they be re charged?

 

[VicS]

As frequently as possible, at least every 4 to 6 months if not used, but they should never be left in a discharged or even partly discharged state.

Strongly recommend you investigate the possibility of a small solar panel, 5 or 10 watts depending on the battery capacity, that can be left connected permanently. that solved my problems.

 

[ReggieK]

Thanks for reply VicS
Not being electrical I have looked at posts here re solar panels and mention of putting in fuses and diodes sort of put me off investigating this option. I had thought of rigging a battery charger to shore power, but I would be worried about going away and leaving it charging.
Question was prompted by the death of last battery which eventually would not charge. It was charged only about twice a year and lasted about 3 years. It's a bit of a rigmarole to hang upside down in sail locker to disconnect it and stagger to car ( a good distance as parking here is cr*p) to bring it home. So it tends to get ignored.

 

[IvorClarke]

VicS, Your my first post, so hope it works.
As you mentioned solar panels.
I have two 85 amp hour batteries on my boat, one for dedicated engine starting and the other for everything else.
I would like to fit a solar panel to keep the batteries topped up, but don't know how to size it.
Maplins are selling a solar panel of 12 volts 12 watts for 50 quid which sounds a good deal, I think.
I can rig the two batteries in parallel and that is how I would like to charge them.
Would the Maplins unit be sufficient?
Any help would be most appreciated.
IvorC

 

[VicS]

[ QUOTE ]
mention of putting in fuses and diodes sort of put me off investigating this option.

[/ QUOTE ] Dont be put off.
If a solar panel is supplied for battery charging it should already have a diode fitted, and it should say so in the spec. If it doesn't then look at another!

The simplest solution for the fuse is an in-line fuse holder in the lead going to the +ve battery terminal. Maplin do several waterproof or splashproof ones, one to IP66 standards. A 1 or 2A fuse will be Ok for a 10watt panel but a 500mA or 1A for a 5watt panel.

The biggest problem is finding a suitable deck location for the panel My boat has a sloping cabin front that's just about the right angle and being on a mooring with only a gentle tidal stream it usually gets all the afternoon sun. Plenty of space for a 5watt panel but not for a 10 watt.

 

[VicS]

[ QUOTE ]
my first post, so hope it works.

[/ QUOTE ] Hi and welcome. It works!

I think a 12 watt panel for two 85Ah batteries might be pushing things a bit. Although if you look at the figures and compare what it should deliver in a few hours of decent sunlight with a figure that someone quoted on here recently of 10% self discharge of the battery capacity per month you'll conclude that it will be fine for maintaining charged batteries but not for recharging discharged ones. I don't know where he got the 10% figure from but it sounds reasonable to me.

I'd go for bigger I think for two 85 Ah batteries but I would also be fitting a regulator.

I don't like the idea of leaving two batteries paralleled, but only because if one fails unexpectedly it could discharge the other. A diode splitter would solve that problem but the volts drop imposed would reduce the effectiveness of the solar panel a little bit by shortening the number of hours each day that the panel output could be charging at dawn and dusk but for longer on dull days.
An alternative would be to use the panel to keep the starter battery topped up on the basis that if you can be certain of starting the engine you'll soon have the services battery recharged. Another idea that I rather like is to have separate panels for the two batteries! I might do that rather than parallel two panels to give more output.

I am sure there are regulator/ splitters available that will enable both batteries to be independently charged from one panel, but if the panel is small enough not to require a regulator then its not a big job to make a splitter with a couple of diodes.

What may be a deciding factor is the space available to fit the panels

However, you'll probably now get a lot of different views on the matter!

 

[ReggieK]

I don't think I have a good spot to place a solar panel, I assume they need to be sloping and the only spot would be the front of the cabin. However, all it would need is for a stressed crew member on the foredeck battling with the spinnaker pole to stamp on it. Also the battery is placed in the cockpit locker near the stern. So really the only spot would be on the stern and it would be facing straight up which I assume would not be ideal Though my mooring has the stern facing south west.

 

[Conrad]

Two batts left in parallel create a circuit for each other and will have an element of current flowing and hence eventual discharge.

I opted for the solar panel with regulator then because I visited the vessel reasonably regular I have a simple two way switch so as to flick between the two batts to control which one is on charge, not as great as total automation but half way there.

 

[alan]

Ideally they need to be orthoginal to the sun ............... which means you need to have them movable (azimuth and elevation). But on a boat this is difficult. On a fixed installation (e.g. roof) you would mount them facing south and inclined at roughly your degrees of latitude to the horizontal (i.e. 50 degs N lat , 50 degs to the horizontal); this is a reasonable mid point to allow for the changes in the suns declination during the year or else you would need to move it in elevation during the year to follow the suns apparent movement north and south.

So, most people mount them horizontally on a boat as being a compromise and because it is usually easier; and they will catch some of the sun during the day regardless of which way the boat is heading. From your description I would say at the stern facing straight up is your best bet.

Alan.

 

[shmoo]

I've got one of the Maplins 12W ones. My boat is about to go out on a mooring that will (I think) leave it E-W on one tide and W-E on t'other. If the one looks ok when connected I will get a second and hang one on each side on the guard rails. That way one will always look S. I am currently looking for shackles to go through the 5mm? holes on the maplin unit.

Vertical / horizontal is about evens at this lat. and vertical on the guard rails will (I hope) get less obscured by masts and such and less covered in bird poo.

 

[IvorClarke]

VicS, Thanks for the explanation, also to Conrad for his version of simplicity. I visit my boat regularly as he does, it's just the shifting the batteries home for charging that gives the plastic knee jip. The solar panel will be great for charging each battery - individually !
If it all goes pear shaped, I will be back !!
IvorC

 

[William_H]

A few comments. 2 batteries in paralell should not be a problem it is in fact the same as having a larger battery. If in the unlikely situation you have one die then it will discharge the other but I wouldn't worry.

If you can find the diode in a solar panel. They are often fitted in abox where the wires go in. You can fit another diode. The new diode connects to the same place as the anode of the original diode and you run another wire to the other battery. This means that there is only one diode in the circuit for each battery .

However if you can't make a connection upstream of the original diode then you must add 2 diodes one for each battery. (if you want isolation) If you put the diodes at the battery positive terminal then you don't need a fuse. The diode will stop current flowing from the battery to a fault. The power of the solar panel won't cause a fire.

I have had my solar panel fitted with bungee cord and I have a socket just inside the main entrance. I attach the solar panel to the outside of the boom /mainsail cover when I leave the boat. But always disconnect and put the panel away before sailing. That is after having several damaged when mounted on the cabin top.

The size of a solar panel is totally dependent on space you have and cash you part with. Small will help but bigger 20W will be better.

However to the original poster. A battery charger on shore power should be able to boost your battery in a useful manner. The bigger the better it usefullness depending on the time you can spare at the jetty. One hour at 10 amps would be a very usefull boost if you did it once per month or so. Just make sure you know how much current is going in. The auto types tend to drop to a low current rather quickly and the label that might say 20 amps max is not necesarily what is going in. good lcuk olewill