On 13/02/2012 14:10, The Natural Philosopher wrote:
David wrote:
On 12/02/2012 18:31, M.Joshi wrote:
Hello all,

I'm thinking of connecting a 12V 10W solar panel permanently to my
vehicle battery as I am not using it very often.

The battery keeps going flat in the cold weather.

What I wanted to know is if others have done this and whether there is a
danger of damage leaving the panel connected when starting the car?

The panel I am thinking of purchasing off eBay has a protection diode
built-in.





I use a 4.8 watt solar panel in a car with a 90Ah battery that is not
started very often (can be 6 weeks). But then the car is driven for at
least 2 hours, often more like 7.

It works fine, and before starting the engine, I turn it over for 5
seconds on the starter to get the oil circulated before starting.

It sits attached to the front screen with suction cups at an angle of
about 35 degrees with the car facing south.

Never a problem.

wont be if you start the car every 6 weeks.

hats enough to fully charge the battery if you run it more than half an
hour.

David

I'm not sure what you are saying, but the solar panel is not used to
charge from flat, but to maintain a charged battery.

David

On 14/02/2012 10:42, David wrote:
On 13/02/2012 17:09, js.b1 wrote:
On Feb 13, 2:59 pm, Martin
wrote:
I happen to have a nominally 8W PV panel to hand. Today on a relatively
overcast afternoon 7/8 cloud it managed a no load terminal voltage of
20v and a much more disappointing short circuit current of under 10mA.
If you are *very* lucky it might deliver 3mA into a 12v load (40mW).

Thank you for some very useful info.
I assume polycrystalline, mono should do a bit better in overcast.

My 4.8 (claimed) solar panel is in series with a mA meter and I look
whenever I am near the car.

On a day like today, completely overcast, between 11 am and 3 pm, the mA
meter reads between 10 mA and 25 mA.

On a sunny day, in winter, it can go as high as 170 mA.

In summer, it can go over 250 mA.

David

Typo: 4.8 watt (claimed)

On 13/02/2012 12:04, David wrote:
On 12/02/2012 18:31, M.Joshi wrote:
Hello all,

I'm thinking of connecting a 12V 10W solar panel permanently to my
vehicle battery as I am not using it very often.

The battery keeps going flat in the cold weather.

What I wanted to know is if others have done this and whether there is a
danger of damage leaving the panel connected when starting the car?

The panel I am thinking of purchasing off eBay has a protection diode
built-in.





I use a 4.8 watt solar panel in a car with a 90Ah battery that is not
started very often (can be 6 weeks). But then the car is driven for at
least 2 hours, often more like 7.

It works fine, and before starting the engine, I turn it over for 5
seconds on the starter to get the oil circulated before starting.

It sits attached to the front screen with suction cups at an angle of
about 35 degrees with the car facing south.

Never a problem.

David

Sorry, forgot to add, always disconnect before starting the car.

David

On Feb 14, 10:24*am, RobertL wrote:
On Feb 12, 8:39*pm, The Natural Philosopher
wrote:

M.Joshi wrote:
Hello all,

I'm thinking of connecting a 12V 10W solar panel permanently to my
vehicle battery as I am not using it very often.

The battery keeps going flat in the cold weather.

You will have noticed that weather is cold because , by and large the
sun doesn't come out much, or *for long, and its a bit weak when it
does, so exactly what do you hope to achieve by this ridiculous exercise
in *naïveté?

What an abrasive and sarcastic reply to a very reasonable request for
advice.

Robert

Really? I'd call it insulting. Perhaps I'm a bit too simple for
this group.

In article ,
David wrote:
My 4.8 (claimed) solar panel is in series with a mA meter and I look
whenever I am near the car.

On a day like today, completely overcast, between 11 am and 3 pm, the mA
meter reads between 10 mA and 25 mA.

That, of course would barely cover the quiescent draw on a modern car. And
not at all when dark.

On a sunny day, in winter, it can go as high as 170 mA.

In summer, it can go over 250 mA.

Sadly, there's less drain from the starter etc in the summer - and a lead
acid also works rather better when warm.

I suppose it might just make a slight difference - but worth the effort?

--


Dave Plowman London SW
To e-mail, change noise into sound.

In article , The Natural Philosopher wrote:

If you really think a solar panel in winter is going to be cheaper than
an occasional boost from a normal charger, feel free to waste our money.

Nobody uses a solar panel to charge[1] a battery because it's cheaper, they
use it because it's less hassle than running a mains cable to wherever they
want something charged.

[1] or at least "reduce rate of discharge"

RobertL wrote:
On Feb 12, 8:39 pm, The Natural Philosopher
wrote:
M.Joshi wrote:
Hello all,
I'm thinking of connecting a 12V 10W solar panel permanently to my
vehicle battery as I am not using it very often.
The battery keeps going flat in the cold weather.
You will have noticed that weather is cold because , by and large the
sun doesn't come out much, or for long, and its a bit weak when it
does, so exactly what do you hope to achieve by this ridiculous exercise
in naïveté?


What an abrasive and sarcastic reply to a very reasonable request for
advice.


And that advice was to consider the question .

On 14/02/2012 11:26, Dave Plowman (News) wrote:
In ,
wrote:
My 4.8 (claimed) solar panel is in series with a mA meter and I look
whenever I am near the car.

On a day like today, completely overcast, between 11 am and 3 pm, the mA
meter reads between 10 mA and 25 mA.

That, of course would barely cover the quiescent draw on a modern car. And
not at all when dark.

Of course, but it is better than nothing.
I have not bothered to check what the car draws whilst 'asleep'.


On a sunny day, in winter, it can go as high as 170 mA.

In summer, it can go over 250 mA.

Sadly, there's less drain from the starter etc in the summer - and a lead
acid also works rather better when warm.

I suppose it might just make a slight difference - but worth the effort?


Well, I have been doing this for a number of years now, and I've not had
a problem starting a car (this and previous cars, when we used to have
three) that had not been started for quite a while.

This engine takes some turning over, too. Even the solenoid on the
starter draws over 6.5 amps.

Apparently, the alternator on the 118i auto is rated at 160 amps, I do
not know what it is on the 335d.

David

harry writes:

On Feb 12, 11:40=A0pm, Andy Dingley wrote:
On Feb 12, 6:31=A0pm, M.Joshi wrote:

The panel I am thinking of purchasing off eBay has a protection diode
built-in.

I bought one of Maplins - it cost me a car battery. =A0The supposed
diode was more of a didn't.


The PV cells are themselves diodes.

But I think they are sometimes rather _leaky_ diodes.
Which might cause problems if a car is stored over a long dark northern
winter, though not when there's plenty of light.

--
Windmill, Use t m i l l
J.R.R. Tolkien:- @ O n e t e l . c o m
All that is gold does not glister / Not all who wander are lost

On 14/02/2012 10:24, RobertL wrote:
On Feb 12, 8:39 pm, The Natural
wrote:
M.Joshi wrote:
Hello all,

I'm thinking of connecting a 12V 10W solar panel permanently to my
vehicle battery as I am not using it very often.

The battery keeps going flat in the cold weather.

You will have noticed that weather is cold because , by and large the
sun doesn't come out much, or for long, and its a bit weak when it
does, so exactly what do you hope to achieve by this ridiculous exercise
in naïveté?

What an abrasive and sarcastic reply to a very reasonable request for
advice.

Perhaps, but it *is* exactly on the mark.

We are up to the eyeballs in solar powered radar triggered warning signs
round here on dangerous bends that fail with monotonous regularity in
mid winter at the first sign of a hard frost.

--
Regards,
Martin Brown

Martin Brown writes:

The OP would be much better off buying a mains powered battery charger
instead. That at least will do the job of making the car start!

But if you plan to leave a car in a long-term airport car park for a
month, you may need to do all you can to improve the chances of
starting the car on your return - largest PV panel you can fit in the
car, parking so the panel faces south, etc.

Not that it would help much in winter (when you are more likely to have
planned a trip to warmer climes :-( ).

The only time I found an off grid application (greenhouse watering
system) where a solar PV could be almost competitive it was still easily
beaten by two lead acid batteries swapped as and when needed.

They're good for ultra-low-power applications such as simple pocket
calculators, parking ticket machines (provided they aren't heavily
used, so that the average battery drain is low), temporary traffic
light systems where there's a need to periodically send a short burst
of signal, just a few milliwatts of RF power for a few milliseconds,
from a remote transmitter to a traffic light (where the receiver can be
powered by the AC mains or by a small petrol generator), and so on.
Those uses don't require large batteries which won't be sufficiently
charged in winter.

Other than that, IMHO the only half-sensible use for solar power in the
UK is to provide hot water heating via tubes on the roof (which still
will require additional gas or electric heating to make up energy
shortfalls in winter or in a bad summer).
A useful addition to, but not a replacement for traditional methods.
And you need a fair-sized roof.

Saudi Arabia may well benefit from some kind of solar energy, but not
us.

It's a shame that the people who have actually experimented with solar
panels and know the small and irregular amount of power they generate
don't seem to be the ones making the decisions.
As the public become more aware of PV limitations there may be an
equally irrational backlash against any use of solar power.

Energy from space would be terrific, if there was only a *practical*
way of getting gigawatts of power safely down to earth.

Not any time soon.



--
Windmill, Use t m i l l
J.R.R. Tolkien:- @ O n e t e l . c o m
All that is gold does not glister / Not all who wander are lost