Charging a 12v battery with Solar panel..

[barrymons]

Hey all..

I have a solar panel dont have the time to give u guys the specs but when i come off work tonight i will post it..
I want to use the solar panel to charge a 12v car battery during the day and use the battery during the night. This is for camping purposes.
If anybody can shed some light on this subject to help it would be greatly appreciated..
The solar panel got 40 small cells...

Thanx :roll:

 

[barrymons]

The Specs for the solar panel is this:

Rated Power : 30 Watts
Open circuit voltage: 21.6
Short circuit current: 2.05 amps
Series fuse: 4 amps
Fire Rating: Class C

Rated Voltage: 16.0v
Rated Current: 1.9 amps
Maximum System open Circuit voltage: 600 volts
Bypass Diode: 8 amps

Thanx for a great forum

 

[chemelec]

Here is a Very Simple Circuit, but it works.

**broken link removed**

 

[Nigel Goodwin]

Here is a Very Simple Circuit, but it works.

**broken link removed**

Love the simplicity of it, it's rather like the old Triumph motorbikes, except they just used a high wattage stud mounted zener on a heatsink between the fork legs.

However, I don't see as it's required? - he specified a car battery, and the maximum output of that cell isn't going to over charge a car battery.

 

[Oznog]

2 amps on a fully charged car battery is "sort of" significant. It it's done for just a camping trip it's not significant. If you planned to use it like this for months on end then the overcharge would be less acceptable.

The solar panel may or may not already have a blocking diode installed. It is likely that it has one, in which case this is a very simple matter of hooking the panel onto the car battery, or really virutally any live point on the 12v wiring such as the cigarette lighter (if it's the type that stays connected with the key off). Preferrably add a fuse, not because the panel produces dangerous amounts of current, but if the wiring is damaged the battery can supply a dangerous amount of current through a short.

 

[Nigel Goodwin]

2 amps on a fully charged car battery is "sort of" significant. It it's done for just a camping trip it's not significant. If you planned to use it like this for months on end then the overcharge would be less acceptable.

You've got to bear in mind a couple of things, for a start it's unlikely to provide 2A for very long per day (if ever!) - secondly (of course) it only works during daylight hours. The average during any 24 hour period is going to be a pretty low trickle charge.

 

[barrymons]

Thanx For..

Thanx for the input guys..
So u suggest i put a diode on the solar panel to prevent the battery giving power back to the solar panel.. I'm going to put about 6 fluorecent 8watt lights on the batterysay i run all 6 of them for a period lets say 8 hours will the solar panel be enuff to recharge the battery once the sun starts to shine?

Thanx

 

[Nigel Goodwin]

Re: Thanx For..

Thanx for the input guys..
So u suggest i put a diode on the solar panel to prevent the battery giving power back to the solar panel.. I'm going to put about 6 fluorecent 8watt lights on the batterysay i run all 6 of them for a period lets say 8 hours will the solar panel be enuff to recharge the battery once the sun starts to shine?

Just do the sums!. The absolutely maximum the panel can charge is 24W 12V x 2A, and it's unlikely to be that high (although you don't have your location filled in, so we've no idea how much sun you might get?). Your six 8W lights consume 6 x 8 = 48W - TWICE the absolute maximum of the panel.

Please note, this assumes 100% efficiency! - which you obviously can't get, I would expect the lights to consume nearer 60W than 48W. I would also expect you to be VERY lucky to average 1A during 8 hours of good light.

So, 8 hours of night lights = 480Watt hours, 8 hours of charging = 96Watt hours - strikes me as a 'slight' shortfall?.

For a start I would suggest you get your panel and battery out, connect an ammeter between them, and monitor the current you get every 5 or 10 minutes throughout the day, making a note of the conditions at the time - you can draw a graph from this, and work out the amount of charge you can expect.

Be prepared to be VERY disappointed!.

 

[barrymons]

By the way i live in south Africa

I did put it in the sun this morning an d i have put a voltmeter on it

DONT NOW IF IT MATTERS BUT THE VOLTAGE WAS between 21v and 20.5v didnt put an ammeter on it though.
Can i connect the panel straight onto the battery?

 

[Nigel Goodwin]

By the way i live in south Africa

I did put it in the sun this morning an d i have put a voltmeter on it

DONT NOW IF IT MATTERS BUT THE VOLTAGE WAS between 21v and 20.5v didnt put an ammeter on it though.
Can i connect the panel straight onto the battery?

Yes, make sure it's the right way round though!.

Many of these panels already have a reverse protection diode, so you may not need to add one.

So connect the panel, through an ammeter, to the battery and see what current readings you get, the off-load voltage isn't of much interest (as long as it's considerably higher than the battery).

I'm presuming it's VERY sunny where you are?, how long per day do you get bright sun?.

 

[barrymons]

in summer all day round except when it rains
in winter there is alomost every day a bit of sun except when cold fronts come through here...

 

[zevon8]

As stated above, you can directly connect the solar panel to the battery, provided it has a built-in diode. The diode will prevent reverse flow into the panel when the panel voltage is lower than the battery ( night, clouds, etc ) that can cause heating in the panel, possibly damaging it.

One thing that would be much better would be to use a deep cycle battery, such as those sold for marine use, or RV's or golf carts, etc. These are designed to provide steady output and not be damaged by deep discharging, something likely to happen in your application.

Where I work we use deep cycle golf cart batteries on solar powered trailers that run until the batteries are flat. Then they are recharged, the solar panel is mostly to extend the run time of the batteries. These batteries regularily last for 5 to 7 or more years with minimal maintanence, where as a regular car battery fails this experience in less than a six months The cost of one deep cycle marine ( 350 AH @ 25 A ) battery is about US$100 , not much more than a standard car battery, but lasts at least 5 time longer.