Solar Panel Trickle Charger

I know it is a problem when you have to leave the car unused for long periods (depending on type, a battery loses 1% to 60% a month of its charge). Unfortunately, an unregulated trickle charger (float) charging a car battery is not advised unless a timer is used. And, that is the difficulty, for the timer needs attended to.

"9.3.8. Trickle Charger A trickle charger is typically a cheap, unregulated voltage (C/100) charger used to maintain a battery after it has been fully charged typically costing less than $20 (US). Do NOT use these types of chargers because they can easily overcharge and destroy the wet battery by "boiling" the electrolyte out and dry out the battery or undercharge it. If you have to use a trickle charger, using it on a timer is highly recommended."

(2/3 down the page) Please also take note that this is for charging "after [the battery] has been fully charged".

I'll leave the other query for others to answer.

Boiling a battery with a solar charger inside the car in the uk is about as likely as melting the alternator by recharging a flat battery with it. Almost all the trickle chargers you can buy in the UK are regulated.

A small solar panel sat on the dash won't even make up the normal losses on the average car with the sort of daylight we get at this time of the year. To be of use it would have to be the approximate size of a sunroof and mounted outside.

Yes, I'm aware of this argument. I've long been doubtful how true that is, for trickle charging the car battery requires 50-100 mA (for a 50 Ah model). My shoe-sized bathroom radio is solar powered and works fine, while permanently its photovoltiac panel, only 140 mm x 30 mm, is facing South sitting on the window sill. There is a table of the average sunlight for London I would like to work from -- yes, I'm also aware that the energy conversion efficiency is only 21% or perhaps 25%, its latest figure (reported as a breakthrough a few years ago), if my memory serves me right -- to get to the truth, but at the moment the *internal internet server is down*. I'll try again latter. The table primarily is for solar heating for domestic electricity.

Duncan Wood ( snipped-for-privacy@dmx512.co.uk) gurgled happily, sounding much like they were saying :

actually putting any meaningful charge into the battery with a solar charger in the UK...

Still out of luck! The website I want to check up is this one:

the Rt. there is a column of month by month listing of light energyreceived by a solar panel in kW/m². The lowest is in December. No matter, on the Maplin page where a typical solar panel for charging car battery is show, there is one Solar Panel Kit. From their respective specifications, it is clear that the battery charger is capable outputting

"9.1.3. The optional FLOAT stage is where the charge voltage, depending on the battery type, is reduced to between 13.0 VDC and 13.8 VDC at 80° F (26.7° C), held constant. It can be used indefinitely to maintain a fully charged battery to overcome the natural self-discharge of the battery. The current is reduced to approximately 1% (C/100) or less. Three-stage "smart" chargers usually have the bulk, absorption and float stages. (Please refer to Section 13 for more information about storing batteries and continuous float charging.)"

(The graph for floodedlead-acid, a 50 Ah, shows the 50-100 mA float charging current, bottom Rt.) kit is 5 W of max 390mA @ 16.8V (Panel 300 mm x 200 mm) charger is 1.5 W of 67mA @ 17.5V (Appr. 340 mm x 110mm)

Well my landlord last van used to manage to run a fridge. But then they wheren't inside the van. If meaningfull charge is the difference between your cars last chance of starting being before you get back from holiday versus after you get back then they've got some use, they don't have to supply all the current used to save you a lot of aggro.

On the Rt. there is a column of month by month listing of light energy> received by a solar panel in kW/m². The lowest is in December.>

Which only works when the panels in direct sunlight, the earth & other things that cast a shadow wil get in the way. And the current you need depends on the current the car draws, the self discharge of the battery is negligible. Float chargers regulate the voltage, not the current.

Eh.....Pardon?!

You can get usefull current out of a solar panel. However for any significant amounts of current averaged over 24hours outside of July you need a big solar panel on the roof. The tiny ones acn make the difference between being able to start your car when you've left it at the airport for a fortnight & not being able to, they won't keep the battery in your car topped up if you go to Tenerife for the winter.

Duncan Wood ( snipped-for-privacy@dmx512.co.uk) gurgled happily, sounding much like they were saying :

How long are you going on holiday for...?

The XM started quite happily after being unused for six weeks when I was in the US.

My father used to use one of these on his BMW as it isnt used for 2 weeks at a time - seemed to make very little difference to the charge even mid-summer.

I tried one and my battery is flat after just 3 weeks of non-use - see my post below.

Vin