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.

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 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?


Why not connect it to a micro-ammeter. At least you will be able to see
something happening.

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

Which clearly shows thinking is something best left to people who know
how to do it.

First, what is the parasitic drain of the car?
By that I mean the Engine ECU, Alarm, Radio, etc. It should be 30mA,
but some cars can be a bit higher.

Second, will the panel be enough in overcast winter?
30mA sounds little but over 24hrs totals 8.64 watt at 12V. In overcast
winter your 10W panel may produce only 2W for a few hours a day. The
car windscreen reduces light, the angle of the panel and coverage
provided by the car reduces light further. So you might get just 4-5W
on the worst days which means a shortfall.

A 10W panel is not cheap, a 15W panel is getting quite costly.
If you have a high parasitic drain such that the car battery goes flat
in 2wks, they can be useful when parking at airports or for tipping
the balance back towards tolerable.

Would be better to connect the battery to something like a CTEK smart
battery charger / maintainer. They are about £45 for the multi-LED
version. They can be left connected outside (waterproof), but require
an equally waterproof mains connection - so best put in a shed or
garage with the battery.

On 12/02/2012 20:39, 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?

Increase the profits of people who sell useless solar PV kit.

At the moment up in North Yorkshire I am surrounded by solar powered
"please go round the bend" signs that wreck their batteries at this time
of year. This is exactly the time when they are needed, but alas the
cold dank dark days at sub zero leaves them dead in the water and on
frosty mornings people inexplicably fail to negotiate the bends.

Some people even manage to do it in midsummer too:

http://www.gazettelive.co.uk/news/te...4229-26963106/

The snazzy bend signs are usually working in the summer when there is no
frost and plenty of sun.

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?

Why not connect it to a micro-ammeter. At least you will be able to see
something happening.

Be fair - in ambient light in winter it might just provide enough to
null out the base load of the car during daytime.

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

Which clearly shows thinking is something best left to people who know
how to do it.

You do need to pay some attention if your PV array is capable of
charging the battery at a decent rate, but for something as pathetic as
this it could stay connected forever and never be able to damage the
main car battery by overcharging. You have to make sure it cannot leak
current back through the PV panel in the dark. The protection diode
should prevent this but do check. It isn't even remotely cost effective.

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!

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.

--
Regards,
Martin Brown

In message , M. Joshi
writes

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.




The diode is to prevent the battery discharging back through the solar
panel when output falls below 12v

I had one similar from Maplins for the caravan - complete waste of time.
Gave 17v in bright sunlight but dropped to about 7v in any shade.
Failed to keep the battery charged with only the alarm to cope with.
--
hugh

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.




As others said, I wouldn't consider it. I tried using a similar sized
panel to maintain a car type battery running small lights in a stables
once. I had a clear view of sky, and carefully mounted it at the optimum
angle, and it still only gave a small fraction of the theoretical output
most of the time. Built in trickle charger is a much better bet.

On 12/02/2012 21:02, js.b1 wrote:

30mA sounds little but over 24hrs totals 8.64 watt at 12V. In overcast
winter your 10W panel may produce only 2W for a few hours a day. The
car windscreen reduces light, the angle of the panel and coverage
provided by the car reduces light further. So you might get just 4-5W
on the worst days which means a shortfall.


Eh? 30mA at 12v is 0.36 watts - whether for an hour or a week! Over a 24
hour period it is 8.64 watt-HOURS *not* watts.

So, assuming 30mA to be the drain, the question is whether or nor a 10w
panel can produce enough watts for enough hours to produce 8.64
watt-hours in a 24 hour period. If it could produce 2 watts for 5 hours,
that should be enough.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

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'd be inclined to connect the panel via a 2A fuse.

I had one of these panels for years on my old motorhome and it did its
job. The output is zero on an overcast day though.

Bill

On Feb 12, 9:51*pm, Roger Mills wrote:
Eh? 30mA at 12v is 0.36 watts - whether for an hour or a week! Over a 24
hour period it is 8.64 watt-HOURS *not* watts.

Oops, typo, obviously.

So, assuming 30mA to be the drain, the question is whether or nor a 10w
panel can produce enough watts for enough hours to produce 8.64
watt-hours in a 24 hour period. If it could produce 2 watts for 5 hours,
that should be enough.

It comes down to where it is sited.
A combination of car location re house shadowing, solar transit,
located in front or rear window, angle of panel etc.

A monochromatic panel would outperform polycrystalline under overcast
skies.

js.b1 wrote:

Second, will the panel be enough in overcast winter?
30mA sounds little but over 24hrs totals 8.64 watt at 12V.
You can't express it like that. Do you mean 8.64 watts for an hour? If
so it doesn't sound as if it would be difficult for the panel to at
least help the situation significantly.

As I said in a previous post I used one of these for years and it kept
the battery in good nick right through the winter. Although it was
physically big; could have been 20W I suppose. It failed eventually; a
bad contact that I couldn't resolder.

Bill

On Sun, 12 Feb 2012 18:31:48 +0000, M.Joshi
wrote:

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

Yep; I did it for years, as I'd just bought a new battery for my car
but wasn't using it much (at all).
It kept the battery up to snuff until last winter, when -18degC killed
it.

and whether there is a
danger of damage leaving the panel connected when starting the car?

I couldn't tell you that, I always disconnect first. Offhand, I doubt
it.

On Sun, 12 Feb 2012 20:39:44 +0000, The Natural Philosopher
wrote:

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?

Because it works, you arse.
Once again, we see TNP pontificating about something he knows **** all
about, never having tried it.

On Sun, 12 Feb 2012 21:30:43 +0000, Martin Brown
wrote:

You do need to pay some attention if your PV array is capable of
charging the battery at a decent rate, but for something as pathetic as
this it could stay connected forever and never be able to damage the
main car battery by overcharging. You have to make sure it cannot leak
current back through the PV panel in the dark. The protection diode
should prevent this but do check. It isn't even remotely cost effective.

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!

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.

Yet another know-nothing arsehole.

On Feb 12, 10:17*pm, Bill Wright wrote:
Do you mean 8.64 watts for an hour?

Obviously, 0.03 Amps x 12 Volts x 24 hrs = 8.64 Whours.

If so it doesn't sound as if it would be difficult for the
panel to at least help the situation significantly.

Oh it will help.

Just realise where you locate it will make a big difference.
If you stick it on the dashboard with the solar transit entirely
behind the car you are not going to get much direct sun :-))

On Feb 12, 6:31*pm, 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. The supposed
diode was more of a didn't.

On Feb 12, 11:40*pm, Andy Dingley wrote:
On Feb 12, 6:31*pm, 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. *The supposed
diode was more of a didn't.


The PV cells are themselves diodes.

On 13/02/2012 08:24, harry wrote:
On Feb 12, 11:40 pm, Andy wrote:
On Feb 12, 6:31 pm, 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. The supposed
diode was more of a didn't.

The PV cells are themselves diodes.

Yes. But leaky ones - left to its own devices a PV array connected
across a battery without a charge controller or a protection diode will
discharge the battery at a rate that may be comparable to the charge it
can put in during the daytime at this dark dismal time of year.

A crude basic PV and diode combo won't do much by way of charging the
nominally 12v lead acid battery until its terminal voltage reaches 14v
or so. This condition may not be met at all in diffuse winter light.

A Schottky diode in series is a wise precaution as is a low voltage
automotive fuse to avoid serious embarrassment in the event of a short.

They are penny items at Maplin
http://www.maplin.co.uk/1a-schottky-...6354&u=mapauto

Thin connection wire becomes red hot rather quickly with the current
that a 12v car battery can supply.

The OP would be better off with a mains powered battery charger.

The other point worth making in a DIY group is that since silicon is
expensive and mirrors are cheap if you want to get the most out of a PV
array and can afford the space a pair of mirrors will help. Simplest
configuration is \_/ - half a hexagon with the PV array at the bottom.
No good on a roof, but useful in smaller devices. It does tend to cook
the PV and some yellowing of the plastic may occur if you overdo it.

More sophisticated non focussing flux concentrators use truncated
parabolas with the focus of each at the opposite edge of the array. In
this configuration it is possible to prove that any light that enters
the front aperture will eventually hit the PV cells.

It gives a gain of around 3-10x in diffuse light depending on the
geometry. The technique originates from HEP bulk scintillator designs.
An article with some design details online at:

http://home.iitk.ac.in/~aradhya/cpc.pdf

Not checked in detail all the way through but it looks about right.

--
Regards,
Martin Brown

In article ,
M.Joshi wrote:
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?

Absolutely no danger of damage because it doesn't produce enough output to
do so. Or charge the battery either. The quoted output only happens in the
Sahara at midday.

--
*Failure is not an option. It's bundled with your software.

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

Thanks for all your replies so far. I have considered pulse chargers such as the CTek and others however, I don't have a mains socket outside near the front driveway. I would have to have a trailing mains lead from the front door and that wouldn't be ideal for a long-term solution. The CTek ones are also quite costly too.

I read many positive reviews about using a solar charger to keep a car battery trickle charged and prevent it from going flat due to long periods of not being used.

There are some good reviews for the Maplin's solar charger but it is only a few watts.

Another one I saw on Amazon/eBay looks like a folding briefcase and is about 4W.

I decided to look at a 10W panel as I assumed this would produce an adequate output with reduced sunlight in winter.

After reading some of the replies to my original post, I'm not so sure now?

At present the battery is completely flat. Is it likely that leaving a solar panel connected for a few weeks would restore the charge? The solar panel would be placed inside the windscreen or rear window.

I probably intend to also connect a desulphator to the battery with the solar panel.

wrote:
On Sun, 12 Feb 2012 18:31:48 +0000, M.Joshi
wrote:

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

Yep; I did it for years, as I'd just bought a new battery for my car
but wasn't using it much (at all).
It kept the battery up to snuff until last winter, when -18degC killed
it.

Do you know if it was actually better than not doing anything?

--
Chris Green

On 12/02/2012 22:10, js.b1 wrote:
On Feb 12, 9:51 pm, Roger wrote:
Eh? 30mA at 12v is 0.36 watts - whether for an hour or a week! Over a 24
hour period it is 8.64 watt-HOURS *not* watts.

Oops, typo, obviously.


Hopefully! Perish the thought that you don't know the difference between
a watt and a watt-hour!
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

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

On Mon, 13 Feb 2012 11:03:17 +0000, wrote:

Yep; I did it for years, as I'd just bought a new battery for my car
but wasn't using it much (at all).
It kept the battery up to snuff until last winter, when -18degC killed
it.

Do you know if it was actually better than not doing anything?

I should clarify it was a polycrystalline 15W panel, mounted inside
the windscreen facing south. Charge rates varied from 30mA to 170mA,
depending on time of year.

The car lay unused for four years and it was in a position where
coupling up a charger would have been impractical. It had to be
started and moved from time to time and the battery was a pita to get
in and out, so the solar panel kept the battery up for all that time.
When the car went back into service the battery was as good as I
expected it to be. Certainly if I'd done nothing it would have been
utterly shagged. A self-discharged battery that's left to lie idle is
a write-off; the solar panel avoids that.
On re-entering service the alternator turned its toes up and I had
difficulty finding another one, so for a couple of months I was
trickle-charging the battery in-situ every night. Now, solar panel or
not, the battery was four years old at this point so I wasn't
expecting miracles. The death blow came during a period of intense
cold, when even with a tubular heater under the battery tray, the
engine bay was cold enough to adversely affect the battery. One night
I forgot to put the heater in - and the battery had definitely lost a
lot of capacity. It became obvious over the next few days that it was
on borrowed time. I replaced the battery in the spring and kept the
old one on an Aldidl charger - it continues to show a healthy charge
even now, but I wouldn't trust it for winter use. It'll do as a
standby/emergency boost battery for now.

The upshot of all this is - I would recommend a decent sized solar
panel for a car that's idle for at least a while; whether anyone wants
to use it for years is up to them. For a few weeks or months I see no
downside.

On 12/02/2012 6:31 PM, 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.


These are very popular with Boat owners ... get them cheap on line.
It is such a low trickle charge, there is no risk

js.b1 wrote:
On Feb 12, 9:51 pm, Roger Mills wrote:
Eh? 30mA at 12v is 0.36 watts - whether for an hour or a week! Over a 24
hour period it is 8.64 watt-HOURS *not* watts.

Oops, typo, obviously.

So, assuming 30mA to be the drain, the question is whether or nor a 10w
panel can produce enough watts for enough hours to produce 8.64
watt-hours in a 24 hour period. If it could produce 2 watts for 5 hours,
that should be enough.

It comes down to where it is sited.

Yeah. Kenya is a good place at this time of year.

wrote:
On Sun, 12 Feb 2012 20:39:44 +0000, The Natural Philosopher
wrote:

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?

Because it works, you arse.

Only in bright sunlight.


Once again, we see TNP pontificating about something he knows **** all
about, never having tried it.

Beats lying and pretending that I have tho.


The insolation figures for the country are well known and widely available.

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.

But don't encourage others to waste theirs.

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

In article ,
M.Joshi wrote:
At present the battery is completely flat. Is it likely that leaving a
solar panel connected for a few weeks would restore the charge? The
solar panel would be placed inside the windscreen or rear window.

If the battery is completely flat it might well be scrap.

I probably intend to also connect a desulphator to the battery with the
solar panel.

What's that? A high voltage low current charge - say about 30 volts or so
- will sometimes get a flat battery back to some usefulness. But not if
it's been flat for some time.

--
*If you think nobody cares about you, try missing a couple of payments *

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

On Feb 13, 10:29*am, M.Joshi wrote:
I decided to look at a 10W panel as I assumed this would
produce an adequate output with reduced sunlight in winter.

Not to charge from flat.
Remove the battery from the car, get a battery charger from Ebay / 2nd-
hand shop (£5-10), then charge until about 75-80%.

After reading some of the replies to my original post, I'm not so sure
now?

I just skimmed through and noticed the assumption the car remains
connected to the battery - so the solar panel has to handle the
parasitic drain of the car clock, car radio, car ECU, car alarm, car
immobiliser etc.

If you disconnect the car from the battery the solar panel need only
keep the battery topped up. That is viable. Some here might be able to
tell you the self-discharge of a lead acid battery, and thus whether
you could get away with a 5W panel.

On Ebay & Online there is a simple battery connector where you unscrew
a knurled plug from it to disconnect the battery. No idea how reliable
they are, but it would make disconnect the car from the battery
somewhat spanner-free.

M.Joshi wrote:

At present the battery is completely flat. Is it likely that leaving a
solar panel connected for a few weeks would restore the charge?
No.

Bill

On 13/02/2012 10:29, M.Joshi wrote:
Thanks for all your replies so far. I have considered pulse chargers
such as the CTek and others however, I don't have a mains socket outside
near the front driveway. I would have to have a trailing mains lead
from the front door and that wouldn't be ideal for a long-term solution.
The CTek ones are also quite costly too.

I read many positive reviews about using a solar charger to keep a car
battery trickle charged and prevent it from going flat due to long
periods of not being used.

There are some good reviews for the Maplin's solar charger but it is
only a few watts.

Another one I saw on Amazon/eBay looks like a folding briefcase and is
about 4W.

I decided to look at a 10W panel as I assumed this would produce an
adequate output with reduced sunlight in winter.

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).

So it will add about 18mAh of charge per 6 hour day at this time of
year. The self discharge rate for a lead acid car battery is likely to
be a lot more than that (especially when you include any continuously
powered car electronics like clocks or alarms). On a perfect sunny
winters day it might give 0.4A for 5 hours so 2Ah on a good day.

Starting from a battery that is fully charged the handful of decent
sunny winters days might be just about enough to replace losses due to
self discharge, but it is never going to recharge a flat battery in
winter unless we have fluke weather or the Earths axis shifts!

In midsummer when it can maybe deliver more like 0.6A and 6Ah per 10
hour day of charge then it stands a sporting chance of working. It would
still take the best part of a week even under the most favourable
conditions to get the battery charged back up to 40Ah.

For comparison the cheapest and nastiest 5A/12volt car battery charger
will recharge a battery from flat in about half a day elapsed time.

After reading some of the replies to my original post, I'm not so sure
now?

At present the battery is completely flat. Is it likely that leaving a
solar panel connected for a few weeks would restore the charge? The
solar panel would be placed inside the windscreen or rear window.

Not a chance at this time of year. Complete waste of money.

I probably intend to also connect a desulphator to the battery with the
solar panel.

You really would be a lot better off with a cheap and cheerful mains
powered battery charger. Amazon has one that looks suitable:

http://www.amazon.co.uk/Ferm-BCM1018...2611&sr =1-13

I expect there are cheaper ones still if you look around.

A solar panel might just possibly stop your unused car battery going
completely flat in winter or at least delay it somewhat, but it is
expensive and no substitute for a mains powered battery charger.

--
Regards,
Martin Brown

M.Joshi wrote:
Thanks for all your replies so far. I have considered pulse chargers
such as the CTek and others however, I don't have a mains socket outside
near the front driveway. I would have to have a trailing mains lead
from the front door and that wouldn't be ideal for a long-term solution.
The CTek ones are also quite costly too.

I read many positive reviews about using a solar charger to keep a car
battery trickle charged and prevent it from going flat due to long
periods of not being used.

There are some good reviews for the Maplin's solar charger but it is
only a few watts.

Another one I saw on Amazon/eBay looks like a folding briefcase and is
about 4W.

Absurdly useless.

I decided to look at a 10W panel as I assumed this would produce an
adequate output with reduced sunlight in winter.

Still not big enough IMO.

After reading some of the replies to my original post, I'm not so sure
now?

FWIW, I use a 50W panel to keep the battery on my tractor topped up. I have
a solar charge controller to avoid overcharging. It takes about three days
to charge the battery (110AH) from 40% discharge then the controller
switches to trickle charging.

On Feb 13, 2:59*pm, Martin Brown
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.

Huge wrote:
On 2012-02-13, Steve Firth wrote:
M.Joshi wrote:
Thanks for all your replies so far. I have considered pulse chargers
such as the CTek and others however, I don't have a mains socket outside
near the front driveway. I would have to have a trailing mains lead
from the front door and that wouldn't be ideal for a long-term solution.
The CTek ones are also quite costly too.

I read many positive reviews about using a solar charger to keep a car
battery trickle charged and prevent it from going flat due to long
periods of not being used.

There are some good reviews for the Maplin's solar charger but it is
only a few watts.

Another one I saw on Amazon/eBay looks like a folding briefcase and is
about 4W.

Absurdly useless.

I decided to look at a 10W panel as I assumed this would produce an
adequate output with reduced sunlight in winter.

Still not big enough IMO.

After reading some of the replies to my original post, I'm not so sure
now?

FWIW, I use a 50W panel to keep the battery on my tractor topped up. I have
a solar charge controller to avoid overcharging. It takes about three days
to charge the battery (110AH) from 40% discharge then the controller
switches to trickle charging.

Is not your tractor somewhere considerably sunnier than hereabouts?

Oh yes, forgot to mention that. The solar panel averages 3A on a
south-facing roof. We do have cloud, snow, fog etc but only up to March.
After that it starts to get warm again. Even in winter we can have long
sunny periods. November was 20-25C, only turned wet and rainy in December.

On 12/02/12 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.




This regulator is too powerful,
there may be a smaller version somewhere.

http://www.maplin.co.uk/dual-16a-sol...fygifaodawybhg

Dual 16A Solar Charge Regulator

and disconnect the battery from the car as someone has said.

[g]

On Feb 12, 10:17*pm, Bill Wright wrote:
js.b1 wrote:
Second, will the panel be enough in overcast winter?
30mA sounds little but over 24hrs totals 8.64 watt at 12V.

You can't express it like that. Do you mean 8.64 watts for an hour? If
so it doesn't sound as if it would be difficult for the panel to at
least help the situation significantly.

As I said in a previous post I used one of these for years and it kept
the battery in good nick right through the winter. Although it was
physically big; could have been 20W I suppose. It failed eventually; a
bad contact that I couldn't resolder.

Bill

Soldering is a magic art best left to professionals.

thirty-six wrote:
On Feb 12, 10:17 pm, Bill Wright wrote:
js.b1 wrote:
Second, will the panel be enough in overcast winter?
30mA sounds little but over 24hrs totals 8.64 watt at 12V.
You can't express it like that. Do you mean 8.64 watts for an hour? If
so it doesn't sound as if it would be difficult for the panel to at
least help the situation significantly.

As I said in a previous post I used one of these for years and it kept
the battery in good nick right through the winter. Although it was
physically big; could have been 20W I suppose. It failed eventually; a
bad contact that I couldn't resolder.

Bill

Soldering is a magic art best left to professionals.
The problem was that the terminal was between two sheets of glass, so
was inaccessible.

Bill
(still soldering on)

On Feb 14, 3:15*am, Bill Wright wrote:
thirty-six wrote:
On Feb 12, 10:17 pm, Bill Wright wrote:
js.b1 wrote:
Second, will the panel be enough in overcast winter?
30mA sounds little but over 24hrs totals 8.64 watt at 12V.
You can't express it like that. Do you mean 8.64 watts for an hour? If
so it doesn't sound as if it would be difficult for the panel to at
least help the situation significantly.

As I said in a previous post I used one of these for years and it kept
the battery in good nick right through the winter. Although it was
physically big; could have been 20W I suppose. It failed eventually; a
bad contact that I couldn't resolder.

Bill

Soldering is a magic art best left to professionals.

The problem was that the terminal was between two sheets of glass, so
was inaccessible.

Bill
(still soldering on)

Harry the hammer says not.

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

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