Solar panel electrics

[A1Sailor]

I am considering purchasing a small solar panel to trickle charge while my Sadler 25 is unattended on a mooring. Boat has two 12volt batteries; one for engine start, one for domestics, with independent on-off isolator switches. Another switch to link the batteries if required.
There is a Volvo-Penta sensing charging distributer between the alternator and the two batteries. I think this charges them separately according to their state of charge. I wouldn't want to do any harm...
There is an electrical socket in the cockpit to plug in an autohelm for the tiller.
The plan:
- small solar panel, without regulator, which can be plugged in to the cockpit socket
- domestic battery left turned on, with "autohelm" power switch left turned on at control panel.

Questions:
- will the above work?
- What is the recommended maximum rating for unregulated solar charging? It is related to battery capacity, I think.
- will a 20W solar panel to trickle charge at ~1.5amps be OK unregulated? Not sure how big the battery is, only bought the boat last weekend, but it won't be more than 100aH.
I could, I suppose, purchase a bigger panel and a regulator - but not keen to run new cabling/drill holes on my new boat just yet! All I want to do is to be able to reliably start the engine, using a full domestic battery should the engine start one be low.

Would appreciate others' experience. Thanks, A1

 

[noelex]

A solar panel to maintain he battery is a good one. Your idea may or may not charge the start battery as well depending on the type of charge distribution you have. Is it a VSR or diode splitter.
If it doesn't combine them you can leave the combiner switch on.

20w is a bit high without a regulator for your battery size. You can often fit a regulator in a small waterproof box attached to the panel.

Finally make sure there is nothing powered, or draing the battery when the main battery switch is and autohelm cb are on (other than bilge pumps)

 

[wotayottie]

I am considering purchasing a small solar panel to trickle charge while my Sadler 25 is unattended on a mooring. Boat has two 12volt batteries; one for engine start, one for domestics, with independent on-off isolator switches. Another switch to link the batteries if required.
There is a Volvo-Penta sensing charging distributer between the alternator and the two batteries. I think this charges them separately according to their state of charge. I wouldn't want to do any harm...
There is an electrical socket in the cockpit to plug in an autohelm for the tiller.
The plan:
- small solar panel, without regulator, which can be plugged in to the cockpit socket
- domestic battery left turned on, with "autohelm" power switch left turned on at control panel.

Questions:
- will the above work?
- What is the recommended maximum rating for unregulated solar charging? It is related to battery capacity, I think. The vcoltage on an unregulated panel can quite easily go over 16v and cause gassing of the battery
- will a 20W solar panel to trickle charge at ~1.5amps be OK unregulated? Not sure how big the battery is, only bought the boat last weekend, but it won't be more than 100aH.
I could, I suppose, purchase a bigger panel and a regulator - but not keen to run new cabling/drill holes on my new boat just yet! All I want to do is to be able to reliably start the engine, using a full domestic battery should the engine start one be low.

Would appreciate others' experience. Thanks, A1

I have a 35 watt solar panel that keeps 3x110ah batteries charged when the boat is at its mooring. Not sufficient power to make much of a difference when the boat is in use ( I rarely see more than 2amps) but OK for maintenance. I use a solar panel regulator which is a small box, the size of a ciggy packet for ex smokers a\nd easy to install. Like you I use a cockpit socket.

I would be nervous of leaving a 20w panel unregulated into just one battery of maybe 110aH and possible quite a bit less..

 

[A1Sailor]

Is it a VSR or diode splitter.

It is a metal box with wires sticking out of it! I'll get more info when at the boat tomorrow if I remember. The various switches are set up such that it should be impossible to drain both batteries; unless the one to link them is "on". Good tip, though, to ensure that I don't leave stuff turned on - thanks.
Other option I have is to have a longer cable from the solar panel and plug it into the cigarette lighter type socket inside the boat. A regulator could then be inside also, between the panel and plug. A higher rated panel, with regulator, might be best - although locating a physically bigger panel would be less convenient.
When sailing, I'd typically have on the VHF, Lowrance chartplotter, autohelm bi-data speed/depth and autohelm1000. No fridge! I can do the sums myself - but I guess the total draw might be ~4amps, depending on how hard the autohelm is working.
A panel on the coachroof and cable led into the cabin, with regulator, might offer best flexibility.

 

[vyv_cox]

The usual ratio of unregulated solar panel to battery size is 10%, i.e. 10 watts of panel to 100 Ah of battery. I have left my camper van for several months in Greece with this ratio on both starter and domestic batteries, without problems. However, Maplins do regulators at very low cost if you decided to go for a bigger, and far more useful, panel. The topic has appeared many times so a search may pay off.

Cigarette plugs and sockets are pretty poor things, unreliable for long periods at anchor. Something better would improve the chances of it remaining connected. I use Dri-plugs but there are many cheaper options.

 

[GrahamM376]

You could forget whatever distribution control you have at the moment and just connect the panel via a couple of 5 amp shotky diodes and fuses direct to the batteries.

 

[lw395]

You could forget whatever distribution control you have at the moment and just connect the panel via a couple of 5 amp shotky diodes and fuses direct to the batteries.

I think I would do that.
The wires could be led out under a locker lid, no need to drill holes if it's only for on the mooring.
Then you know the electrics can be properly isolated and you will not risk something flattening the batteries.

 

[rogerthebodger]

Been discussed before http://www.ybw.com/forums/showthread.php?t=307625

 

[VicS]

Another vote in favour of a panel and a pair of Schottky diodes connecting it directly to the batteries

But the o/c voltage of the solar panel ( ie the EMF of the cells themselve) is so large ( 20 volts odd) that the drop across ordinary silicon diodes should be no great problem.

Whichever, put fuses in the connections to the batteries.

FWIW I find a 5 watt panel more than enough to keep a 60Ah battery fully charged.

 

[A1Sailor]

An update

Thanks everybody! I know I could have searched through endless posts - but much more fun to start thread 10062.b on the subject. "Apologies"...
Thanks Vyv for pointing out the "10% rule" about ratio of panel/battery size when deciding whether or not to regulate.
Revised plan:
A cable, with appropriate fuse(s) direct from the domestic battery to a Dri-Plug socket somewhere; perhaps under the sprayhood. I'll run it externally before drilling holes...
A regulator either between the battery and the Dri-Plug socket, or externally between the Solar Panel and the Dri-Plug plug!
I know that starting the engine will discharge the engine start battery, but hopefully this will be recovered after running the engine for 15-20mins; will it? If it doesn't, a fully (solar) charged domestic battery will be available - I am in Scotland, with it's endless supply of natural resources and freshly printed £100 notes!
With the boat on a mooring, and since I know how to sail (on/off the mooring), there should be no need to run the engine much - although it is supposedly good for it to be run now and again...
From my Laser, pictured at Lee-on-Solent:

to "Whirligig" pictured at Loch Tarbert, Jura:

with an outboard and a charging coil I fitted under the flywheel to:
Merrymaker II

via "Second Star" pictured off Oronsay:

I'm just "enjoying the pleasure of boat ownership again"...

 

[ghostlymoron]

I am considering purchasing a small solar panel to trickle charge while my Sadler 25 is unattended on a mooring. Boat has two 12volt batteries; one for engine start, one for domestics, with independent on-off isolator switches. Another switch to link the batteries if required.
There is a Volvo-Penta sensing charging distributer between the alternator and the two batteries. I think this charges them separately according to their state of charge. I wouldn't want to do any harm...
There is an electrical socket in the cockpit to plug in an autohelm for the tiller.
The plan:
- small solar panel, without regulator, which can be plugged in to the cockpit socket
- domestic battery left turned on, with "autohelm" power switch left turned on at control panel.

Questions:
- will the above work?
- What is the recommended maximum rating for unregulated solar charging? It is related to battery capacity, I think.
- will a 20W solar panel to trickle charge at ~1.5amps be OK unregulated? Not sure how big the battery is, only bought the boat last weekend, but it won't be more than 100aH.
I could, I suppose, purchase a bigger panel and a regulator - but not keen to run new cabling/drill holes on my new boat just yet! All I want to do is to be able to reliably start the engine, using a full domestic battery should the engine start one be low.

Would appreciate others' experience. Thanks, A1

With solar regulars available for about a tenner, it's foolish not to include one in your setup. I would only solar charge the 'house' battery as the 'start' battery will be recharged within minutes of the engine starting. In an emergency you can 'hotwire' your house battery or, better still, incorporate a changeover emergency switch.