Solar panel

[Guest]

I just bought a solar panel - 12 v 5 watt

I want to connect it to the battery of my 18' trailer sailer battery to keep it charged when sitting idle. I have no charging facility on the boat, and this might save taking the battery home to charge it.

Someone said that I should have a voltage regulator to prevent overcharging. Could someone please advise?

Also, if I connect a volt meter across the connections in of the solar panel in bright sun (no load) I get 24 v. Is this normal?

Next thing I have to do is to buy a new battery to replace the old, and dead, lead acid one. Any suggestions?

Ray

 

[ccscott49]

You will see that voltage open circuit, but as soon as you connect it, the volatge will drop. You will not need a regulator, for a 5w panel, it may keep up with the natural discharge of your battery. You will need however a diode in the circuit, (if the panel does not have one) to stop the battery discharging through the panel. You can get one from Maplins, quite easily, there must be one of the guys on here who will tell you exactly which doide, but you might like to add the make of panel to your post, some have diodes built in.

 

[Guest]

I agree with all of the previous points. Provided your battery is of reasonable size (Ah) there is no need to provide a regulator.
I have a 5w panel which I use to charge two 17Ah batteries connected in parrallel. (switcheable) The charger maintains the battery at full charge without overcharging resulting in possible gassing.
I would however not rely on the panel replacing all the charge if you have used the battery. I would still take the battery home and charge it up on a mains charger and use the panel as a means of keeping it at peak charge. It is possible to replace the charge by use of the panel alone but it may take quite a few days/weeks to do so. It really depends on how much you take out of the battery and how regular this is.
I also have a trailer sailer (17ft Skipper) which has a depth sounder, log, tiller pilot, GPS, VHF, nav lights and a cabin light. I am careful at what I actually switch on at any one time but the worst case would be a current draw of about 10a (mostly due to the tiller pilot). In theory the 17Ah battery (only one of the two selected at any one time) would last me 1.7 hours but in practice would only last about an hour. The other battery would last the equivelent time. My use of the tiller pilot is for short duration 'hands free sailing' for chart work etc.
I scrounged a couple of gel lead acid batteries (Yuasa) that were going spare from a U.P.S. refurbishment. They are designed not for regular recycling but for ooccassional discharge where they can keep a charge for long periods and then deliver a good current when required. These seem to suit my boat use which is not very regular, perhaps once a month for a long weekend during the summer season. So far they have maintained a good charge for 2 years.
Judging by recent PBO corrispondance a standard leisure or even an automotive lead acid battery would be as good as anything. Just don't allow it to discharge to below its reccomended minimum charge. (average 60%?). Like all lead acid batteries of any kind, they prefere to be kept charged for a long life and if kept at a discharged or partially discharged state for any length of time will shorten its useful life.
One final point, wet lead acids can and do spill acid if tilted to extreme angles. If your boat sails on its ear on a regular basis then consider a spill proof design of battery or go for a gel type. (Maplins stock 17Ah and I think up to 25Ah Yuasa gel batteries).



An Ron Beag

 

[oldharry]

I would go along with most of what Ron has said, except that ordinary car starter batteries are a waste of money in this application. They are designed to give a massive current to the starter motor for around 20 to 30 seconds at most, then to be brought back up to full charge by the cars charging system, which also carries most of the auxiliary loads while the car is running. Because of their design they will not tolerate being left partly discharged, and suffer if they are used for low loads for long periods - which is precisely what you need your boat service battery to do. The battery plates sulphate rapidly reducing the overall capacity of the battery each time it is discharged until it becomes useless. Also because of the design a starter battery's voltage drops away quite rapidly as it discharges, resulting in noticeably dim lights, and potential problems with motorised gadgets like tiller helms which may not tolerate the lower voltage for long. Starter batteries will begin to suffer at 75% charge, which is why you need usually to replace a cars battery when it has gone flat.

The solution lies in either a Traction Battery, or a Leisure battery, the latter being the cheapest option - a 70 - 80 ah leisure battery can often be picked up for around £30 - £40 fro caravan shops. Its design allows deep discharges to around 50% without serious damage, and maintains a higher voltage at the terminals as it discharges - meaning lights stay brighter longer, and tiller helms respond more quickly etc etc.

More expensive 'Traction batteries' do all this and start larger engines too - but at a higher cost. A cheap Leisure battery is usually ok for electric start outboards to round 25hp though.

 

[VicS]

Yes I aree too.

I have a 5w panel connected to a 45AH Leisure battery. If you bought it as a panel for battery charging then I would expect it to have a diode included. Is there a lumpy bit in the lead? If so thats the diode. Don't expect to get the equivalent of 5w ( ie 5/12 amps) from it all the time, that's its theoretical maximum.

It would be a wise precaution to connect it via a fuse.

The two most useful bits of gear I've bought in 24 years, apart from the obvious necessities, are the Autohelm and the solar panel.

 

[ccscott49]

5 1/2 amps from a 5watt panel! I x V = W therefore W/V = I, which is 0.41amps. IMHO

 

[SteveA]

I think he meant 5 twelfths i.e. 0.41!

 

[ccscott49]

Five twelths! bluidy ell' how old is he!

 

[VicS]

Old enough to have learnt fractions, smart enough to still be able to do calculations in them when necessary.

I meant to indicate 5 divided by 12, but as there is no divide sign, ÷, on a computer keyboard the forward slash is used instead. The answer is of course five twelths, 5/12, or about 0.42 if you insist on these new fangled decimals.

Can also still remember how to use logarithms and how to use a slide rule.

No prizes tho' to those who can get a divide sign on their PC. I'll find out in a mo' if it finds its way through the internet & on to the forum.

IT DOES!

<P ID="edit"><FONT SIZE=-1>Edited by VicS on 10/09/2002 20:46 (server time).</FONT></P>

 

[johnsomerhausen]

To find if you solar panel has a diode built in, cover it with thick dark material and connect the negative directly to the battery and the positive to one probe of a multimeter that has a 10 Amps capacity, the other probe going to the positive of the battery. If current passes, there is no diode; if you get practically no reading, there is a diode somewhere in the panel. As far as the fuse that was mentioned in an earlier post, place it on the positive conductor as close to the battery as possible. It's not meant to protect the panel but to prevent a fire in case of a short circuit of the wiring.

john

 

[Guest]

I must say that I am impressed with the helful responses that I have received. Thank you all very much.

Incidentally, is the rule of twelfths still in use. Fractions again, as opposed to the new fangled decimals!!!

The carton says that the solar panel has a built in diode, but I will try the suggestion to test it.

I spoke to a chap in a battery shop, and he suggested that I buy a 26 Ah sealed battery - lead acid with fibreglass mat to hold, support, or whatever, the acid. Quite a neat little battery - but it is made in China. On the other hand, everything seems to be these days, so I presume that it is reasonable quality.

Ray

 

[ccscott49]

Duh.....wots' fractions guv? Me being just a pup. /forums/images/icons/wink.gif
I can't find a divide sign, but I bet theres one somewhere on one of the fonts! But I use the slash aswell!

 

[bedouin]

What sort of "reverse" current would typically flow through a Solar Panel when totally dark? I've heard the argument that it is better not to fit blocking diodes as the power loss they cause during daylight hours is greater than the power lost at night without them.

 

[philip_stevens]

If you fit a Schottky diode, it will only have a forward voltage drop of about 1/4 of a volt. That's .25 volt in EU money.

regards,
Philip

 

[Guest]

Hi

smyth writes

> Incidentally, is the rule of twelfths still in use.

Sure is, and is still taught in the RYA shorebased Coastal Skippers/Yachtmasters course errr..... assuming you are talking about tides here......

1/12th moves in the first hour
2/12th in the second
3/12th in the third
3/12ths in the fourth
2/12ths in the fifth
1/12th in the sixth.

It is a useful way to do a quick estimate on how much water you should see without having to go through the whole tidal curve thingy wotsname. Note the word estimate.

Regards

Fred

Just because you're paranoid doesn't mean they aren't out to get you.

 

[oldharry]

errr - so watts the voltage difference between spring and neap tides....? They both have currents after all.... so how many amps on Chi bar in the third hour of the ebb of a 4.8m tide.

Oh dear!

 

[Guest]

Yes, I was thinking of tides. I was just having a laugh at the use of decimals.

By the way, I did see somether a metric equivalent ot the rule of twelfths, but I can't recall where.

Ray

 

[Guest]

Re: Solar panel: suitable diodes

May I suggest that you employ a "Schottky" diode in line rather than the ordinary silicon rectifier type? You will get a small increase in charging current - but not a lot!
I have just carried out the same exercise myself, for a nominal 5watt panel.
The forward voltage drop quoted for a schottky diode type 1N5819 is 0.5v @ 1amp. Peak holdoff voltage = 40volts.
Similarly rated normal silicon diodes are about 1.1v @ 1amp. Price from Maplin about 10p. Maplin order code is AN07H.
Best of luck, Rod.