Small Solar Panel

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capsco

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When I visit my boat, my car can be left unattended for 5/6 weeks, to maintain my battery I would like to use a small solar panel, this would be behind glass so not really efficient, bearing this in mind what size [output] panel should I be looking for?
 
Never measured it on a car, but a BMW motorbike I had seemed to need about 40mA 24hrs a day.
That's an average 1/2watt.
I don't know if that helps much.

I had the bike running off a lab PSU all winter, it would take a few days for the battery to reach full charge at 13.75V, then the current would stabilise at about 40mA.
A car with an alarm might draw a bit more.
My other bike draws less as the ECU is actually properly off when the bike is stopped. That pulls about 25mA, which is presumably the self discharge of the battery.

A 5W panel behind glass and not ideally aligned might be near enough?
 
capsco said:
When I visit my boat, my car can be left unattended for 5/6 weeks, to maintain my battery I would like to use a small solar panel, this would be behind glass so not really efficient, bearing this in mind what size [output] panel should I be looking for?
Click to expand...



You should measure the current flow from the battery to determine what is being used 24/7 - clock, alarm etc. then you will know how much to calculate for the panel.
 
Maplin have 1w panels for a tenner at the moment. I have one under my sprayhood to keep the starter battery up to snuff. I put one on the motorhome dash too, but it is parked in the shade & facing NE so doesn't get nearly enough to keep it alive in the winter, in a better parking place I'm sure it would manage all winter. But I can connect it to a mains lead if I want, so it's not a big deal.
 
VicS said:
Actually 1.5 watts ITYWF

Also 2.4 watts at £25 and 4.8 watts at special offer of £30

http://www.maplin.co.uk/batteries-and-power/solar-and-wind/solar-trickle-chargers
Click to expand...
I bought a pair of £25 ones a couple of years ago went away for couple of months both batteries where flat.

Car COULD of been its electrics, but had left it before and it had SOME life.
Boat battery was disconnected except for solar panel and was flat.

Gave them to an electrician friend, he tested them and did not think there was a diode:confused, just a word of warning...
 
onesea said:
I bought a pair of £25 ones a couple of years ago went away for couple of months both batteries where flat.

Car COULD of been its electrics, but had left it before and it had SOME life.
Boat battery was disconnected except for solar panel and was flat.

Gave them to an electrician friend, he tested them and did not think there was a diode:confused, just a word of warning...
Click to expand...

If a solar panel has been supplied spcifically for battery charging by direct connection to the battery I would expect it to be fitted with a integral diode..

The £25 one in my link does have a diode fitted.
See http://www.maplin.co.uk/solar-powered-12v-2.4w-battery-trickle-charger-223251
 
I seem to recall that VW have solar panels left on the dash to maintain the battery whilst being shipped/awaiting sale. They are 5w and simply plug into the cigarette lighter socket. Guess this means the socket is live all the time and not dependant on the ignition switch.

Edit: I found a reference to them: eHow
 
Last edited:
VicS said:
If a solar panel has been supplied spcifically for battery charging by direct connection to the battery I would expect it to be fitted with a integral diode..

The £25 one in my link does have a diode fitted.
See http://www.maplin.co.uk/solar-powered-12v-2.4w-battery-trickle-charger-223251
Click to expand...

That is what raised alarm bells, they look very similar to what I bought.

When I bought them I thought they had diodes, 3 months on no packaging :confused:
At the time they where the least of my worries, they might of been duds? but they appeared to work until I gave them to an electrician.
 
capsco said:
When I visit my boat, my car can be left unattended for 5/6 weeks, to maintain my battery I would like to use a small solar panel, this would be behind glass so not really efficient, bearing this in mind what size [output] panel should I be looking for?
Click to expand...

from Halfords or Maplin under £20 do the job perfectly and just plugs into the cigar lighter.
 
Some cars have the ciggy lighter socket live all the time. Some only when the ignition is on.

I have one of each!.

If you chop off the ciggy lighter plug and connect to the battery don't forget to put a fuse in the lead.
 
Provided your battery is not on its last legs, 5-6 weeks is nothing, why bother. I left my car for 10 weeks last summer, 6 year old original fit battery, no problems starting on return.
 
Stork_III said:
Provided your battery is not on its last legs, 5-6 weeks is nothing, why bother. I left my car for 10 weeks last summer, 6 year old original fit battery, no problems starting on return.
Click to expand...

OTOH we left SWMBO's and after about 10 days the alarm started going off at random. But it was italian.....
 
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