solar advice

[Johnboy2004]

hello i am buying the 15w solar panel as detailed below from maplins. they are out of
charge controllers, .... if i connect the solar panel to the battery without the charge controller , will it damage the battery?

if i only connect it to the battery for a few hours at a time would that be ok? and would it save the battery from damage?

thanks


The 15W output makes the BatterySAVER PRO 15W an ideal choice for charging a variety of small 12V appliances. Helping to run lights, refrigerators, TVs, VCRs, heaters, stereos and microwave ovens, the BatterySAVER PRO 15W is a great choice for use on boats, motor-homes or caravans. Panel Dimensions: 33cm x 96.5cm
· Constant solar charge for larger battery needs
· Installs in seconds
· Maintenance free
· Weather/rust/shock/UV-resistant frame
· Works even under low light conditions
· Built-in discharge protection
· Battery clamps
· 3m (10ft) of 16 gauge wire


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[maxi]

15w solar panels are very very unlikely to cause any damage to a battery of 75ah or upwards, even when permanantly connected, as mine has been for the past 5 years. Unless you are in the Med or similar. None of our Summers have been enough to cause a problem. Save the money and don't bother with a regulator.

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[waterrat365]

I have a 15 watt panel on a 85 AH battery, and a 32W panel on a 240 AH battery, no regulators, for the past three years. No problems at all. I don't use a diode because the diode eats more current than the panels would lose at night. BTW, I sail mostly weekends except for the entire month of July, when I go from NJ to Martha's Vineyard, running and anchor lights, GPS, instruements, radio, VHF, autopilot. I generally check the water level monthly. Happy sailing, Cliff Moore, S/V PELORUS, USA.

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[William_H]

Expect a current of less than 1 amp for about 3/4 of the day time. So it should be no problem with any reasonable sized battery. It probably wouldn't hurt a small car battery. For mounting I have settled on attaching 2 bungee elastic cords on one side and 2 saddles on the other to lash the panel to the boom cover. A pair of banana plugs connects into the switch panel. My panels have all been smaller than yours around 5 watts. I have tried on a 21 footer mounting on the front hatch cover but it was susceptible to damage from spinnacher poles etc. I take mine off and stow now when sailing. I am on number 5 panel in 20 years from damage and corrosion. They are an excellent power source for a boat with no motor (occasional outboard) on a swing mooring. regards ole will

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[Johnboy2004]

hi thanks for the info , very helpful.... these forums are an excellent resource, for information....

my battery is an 85 ah battery...

would a 15w panel be able to fully charge it?

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[steve_cronin]

I have a spare controller.....

...as my two 55watt panels run from a shared one but I'm not going to send it to you. WhY? Because like the others have said you don't need it.

Your 15watt (& that's in bright Med. style sunlight) is really a trickle charger which will counteract natural discharge and maybe give you a little increase in charge over this. Over a sunny week on the south coast of England you might get up to full capacity if the battery is healthy and no draw is connected to it. But in poorer light conditions, little more than maintenance of present charge state or at best 85% (say) would be experienced. Don't forget that as the battery's voltage rises so the flow from the panel reduces and nothing or negative charge is given over-night.

Steve Cronin



<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[jerryat]

Hi Maxi,

100% agree. With natural discharge and the inherent inefficiencies of solar panels (I have two) it's very doubtful that an 85ah battery would get 100% charged even in the Med. and it definitely won't get damaged by over-charging.

Very useful bits of kit though.

Good sailing!

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[Johnboy2004]

hi folks
got the solar panel........15 watt.......... at 7.30 this evening with a little sun out
i tested the output from the panel.......i was getting 22 volts from it,,, using multimeter to measure the voltage


i took your advice and didnt get the charge monitor thingy........

i have a 12 volt pc fan that i am going to use to keep the cabin ventilated,
the panel will be very useful for that alright,,,,,,

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[john_morris_uk]

Remember 22 volts into your volt meter (high impedence and very low load) will not be 22 volts into your battery. Try monitoring the battery voltage with it connected and see what it says. For the batteries to be charging at any meaningfuly rate it should be reading at least 13.8 volts or so.

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[jkim1]

Put the money towards a Rutland wind charger. I have had a couple of solar panels and the 16 watt one would only light a 2,2 watt light bulb when pointed at the sun, on a sunny hazy day, they are so fragile when you consider that a jibstick or a shackle can ruin them. The only successful one I had was one made out of single cells fitted on a square of perspex sheet and fitted under the forehatch. Some people do swear by them but if you actually measure the output they are very poor value for money. They are also half the price in the USA. Thats maybe why the retailers are so keen on selling them. And of course they dont work at night. I have seen some big ones on a proper "roll over bar" that were out of the way and looked good but I was looking at a lot of money there. If you want to run a fridge you are looking at a very large solar panel or a medium sized wind generator. or a gas fridge. But thats another nightmare isnt it.

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[Gunfleet]

22volts

Also solar panels have higher voltage than in their working life when they are first put into service, so expect the 22 volts to drop over the next few weeks. It won't mean there's anything wrong.

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[Johnboy2004]

Re: 22volts

hi
i have the solar panel connected directed to the battery
with the multimeter connected , to the battery i am reading 12.69 volts.,

this is going up slowly, after 20mins it went to 12.70 volts,


in relation to a wind generator , my boat is 21 foot, arnt wind generators large?



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[Gunfleet]

Re: 22volts

Hi John,
I'm no electrician, but I know a bit about what I'm looking at with photoelectric cells because I spent ages researching before I bought one. If you've connected your multimeter across the cell while it's connected to the battery, all you're doing is measuring the potential difference on the battery, in your case 12.7 volts. If you measure in SERIES with the photoelectric cell, you'll be measuring the amps (power it's producing). I bought a 30W one and connected it via a digital controller (because it's my intention to get a second) and that measured the voltage produced by the cell/panel... 18 volts to begin with dropping to just under 14. That drop took a few weeks and the cell manufacturers assured me it's normal. On a bright sunny day, by the way, I can count on 1 or 1.2 amps for however long I'm able to keep the cell pointed straight at the sun. Say 10 amps per day on clear sunny days. During the winter the output is very little.

My only comment about wind generators on a 20 ft boat is that there used to be a very small (about 19/20 ft) cat moored near me with one when the kids were small and they used to call it 'the inventor's boat'. You have been warned! ;-)

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[sundance]

Yes, but it will take longer to do so. But, since you are not using a controller, you should use a blocking diode to stop current drain-back at night. You will have a small voltage drop as a result but with an open circuit voltage of 22 volts you need not even think about that -especially in UK/Ireland where there no serious heat factor to bring the voltage further down.

Cheers

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[sundance]

Possibly - over time! The correct design criteria on this is based on a factor of 1 to 10, ie if your battery is 100 ampere hours, your solar panel should be no more than 10 watts. So, in your case, with an 85 ampere-hour battery, your solar panel should be no more than 8.50 watts.



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