Solar Panel Voltage

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oakleyb

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Just purchased a new 4.8watt solar pannel from Maplins but not sure if the below is correct

1, Put pannel in the sun and measured voltage which was above 20
2, Measured voltage over terminals which was 12.64, when pannel connected watched the voltage rise steadily. Voltage rose to 13.5 volts
3, Will this overcharge battery
4, Am i ok to leave connected

thanks, i've never really understood electrics
 
Thats spot on the money on every point.
Unless you have an exceptionally small battery then you can ceratinly leave it connected all the time.
 
sounds good, you can put 10% of the battery capacity in with a solar without damage.
so, your panel is at best 0.4A that means you can wire it up to a 4Ah or more battery for ever.
if it does not have a blocking diode the battery will discharge overnight through the panel. i've never seen a panel without a diode.

check the voltage in the morning with leaving the panel on all night and again leaving it off all night. if it drops a lot more overnight with the panel on, say 0.1V, you don't have a diode on the panel and you need to disconnect it overnight, or fit a diode.
they sell those in Maplins too, dead cheap easy to fit, one way the panel will charge your battery, the other way it won't !
 
[ QUOTE ]
if it does not have a blocking diode the battery will discharge overnight

[/ QUOTE ] Maplin sell it for battery charging so you would expect it to have a blocking diode.
If you read the description on the website surprise, surprise they say it has a blocking diode!
 
I have a 10W "monocrystalline" panel connected to a mini-sized car battery. Word was that it should be OK without any regulator etc.
This last sunny week it has been pushing the battery up to nearly 16 volts. It is only putting about 100 mA into it and there doesn't seem to be noticable gassing so presume it's OK. Not sure how my sounder and GPS will like the volts though. If I turn the nav lights on it soon goes down to less than 13 but don't want to waste those lovely amps!
 
I just got one of these BUT WATCH OUT because for some bizzare reason there is no in line fuse connected to lead. LAst year I had a fire on board after a short circuit from a solar panel without a fuse. I was Lucky as we were on board that night. Dread to think what might have happened had we not been or worse still asleep. (Happened at 10pm).

I have learnt my lesson.

Regards Nick

Nick
 
Anything connected to the battery should have a fuse rated to protect the wiring and fitted as close to the battery as possible.

I would not however expect to see one supplied with the panel. Great if it was though.
 
Simon your mention of .4 amp from 4.8 watt solar panel is a bit misleading. Solar panels are rated in watts by multiplying the max voltage by the max current. So you must use 20volts not 12 so 4.8 watts at 20v is .28 amp. not .4 amp. olewill
 
[ QUOTE ]
Solar panels are rated in watts by multiplying the max voltage by the max current

[/ QUOTE ] I thought they were rated at 16 volts so on that basis 4.8watts is 0.3 amps (Your arithmetic is wrong as well!)

But its all pretty academic since Trio is in the Solent not WA so not often likely to see the maximum output.
 
[ QUOTE ]
Anything connected to the battery should have a fuse rated to protect the wiring and fitted as close to the battery as possible.

I would not however expect to see one supplied with the panel. Great if it was though.

[/ QUOTE ]

I've just bought & fitted the 10w Maplin solar panel and that comes with fuse
 
[ QUOTE ]
10w Maplin solar panel and that comes with fuse

[/ QUOTE ] That's good. They don't specifically say it does in the description on the website. It's included in the expression "all necessary cable, connectors and instructions" I suppose.
Those with cigarette lighter plugs (like the 4.8watt one) probably have a fused plug but if fitted in a boat that will most likely be chopped off and discarded.
 
Actually they are not all 16v nor 20v; depends on the make of panel. If you look at the specs for a panel you should find a maximum voltage quoted (not the open circuit voltage) and this the volts that you use for the calculation.
Also in practice you will find that you are lucky if you get 60% of this maximum wattage for two or three hours a day, unless you are going to install a system to continuously point your panel at the sun (azimuth and elevation); so I think that in the U.K. there is very little chance of overcharging the batteries even with a larger panel.

Alan.
 
[ QUOTE ]
Actually they are not all 16v nor 20v; depends on the make of panel

[/ QUOTE ] Yes I know really but all the ones I have looked up have been at around 15 or 16 volts. I have not seen one quoted at 20V though.
 
Charge? Very optimistic.

We usually multiply a panel's max Amp output by a number of hours to find one day's AmpHours output. This number is about 6h in Athens in the summer, so I think 3h is rather on the optimistic side for the English winter.

This panel claims 0,260A max output. Multiplied by 3hours gives 0,78 Amphours per day or 23.4 Amphours per month.

A lead-acid battery has an internal consumption of about 10% of its capacity per month. Putting all these together we see that if all goes well this panel can only equal the discharge rate of a battery bank up to 234 Ah. And this should be expected or else these guys who install these big ugly panels to charge their batteries would look really silly...
 
Yeah, you're correct most are around there. Kyocera 130W are 17.6 volts load voltage and 20 volts open circuit. I think Ole'Wills main point is that dividing the watts by 12v gives completely the wrong impression ......... by about 40% !!

Alan.
 
Thanks for the warning! I just wired it into the burglar alarm circuit so it is connected all the time. I'll have to do some deep thinking to figure out what rating of fuse to use - presumably 1 amp should handle 10w. The wire should handle at least 5a but a fault could be a high-resistance "short" and 10w could start a fire.
 
[ QUOTE ]
figure out what rating of fuse to use

[/ QUOTE ] The purpose of the fuse is to protect the wire going to the solar panel from the large current that could flow from the battery in the event of the wire being damaged and shorted. The wire can handle the maximun current that the solar panel can produce so there is no risk from that end.
Therefore the fuse goes at the battery end of the wire.
It obviously needs to be able to withstand the maximum outpt from the panel so a 1amp fuse should do fine. If the wiring is 5amp (0.5mm²) then it can safely be upto a 5amp fuse. So 1, 2, 3 or 5 the choice is yours really.

Hopefully your burglar alarm circuit is already fused and if that fuse is 5 amp or less that would be adequate on its own.
 
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