Looks very similar to a BM2 battery monitor on eBay for ~ £16.

If unconnected to a battery, the solar panel gives out between 0V (in darkness) and 18-22V in bright sunlight.

There is no reason that the voltage should pulse.

When connected to a battery, the 18-22 V in bright sunlight is 'clipped' by the battery to be between 12-13.8V, this keeps the charging voltage within acceptable limits.

WARNING: If you have a solar charger connected VIA THE CIGAR LIGHTER SOCKET, and you disconnect the battery (or any relevant fuse), this charging voltage is no longer 'clipped' by the battery, and MAY potentially rise to above 15V, (to 22V), 'potentially' damaging vehicle electronics.

So if you intend to disconnect the battery, or unplug fuses, it is a wise precaution to disconnect the solar charger from the cigar lighter socket FIRST.

FWIW, most solar chargers, when used in the latitudes of the UK, seem to give out approximately 1/2 the rated power, not what the manufactures may claim.

A 4W panel, giving 190mA for 6-8 hours, equates to 1.5Ah

In the northern hemisphere, the maximum charging power is obtained when the panel is facing between South East, and South West, ideally South.

If your windscreen is facing North, mount the panel on the side windows, it will make a BIG difference to the effectiveness.

If the solar panel isn't making a noticeable shadow, then it isn't generating a noticeable power !

If you want to see how solar panel generation varies throughout the day, checkout http://www.gridwatch.templar.co.uk/, the red solar generation output for the UK (as well as nuclear, (combined cycle) gas turbine, coal, wind, and power imported from France, Holland, Ireland et al.

I have solar fitted to my Avensis now. The MG doesnt drain a lot as its unlocked in the garage and I have a full sized charger in there if needed. Its a brick garage with metal door so safe enough while I am home with the Avensis in front. Missing driving though.

Solar in car expert
 

I've had solar panels in my cars for 20 years.


In the Rover 75 I have fitted a glass monocrystaline 20Watt panel (£25). I installed this on the rear parcel shelf. In the engine bay lives a cheap PWM solar controller (£15). I use 5amp cable to connect everything.



Small panels are useless excepting on the very sunniest of days.



You must use a charge controller or you risk boiling! the car battery, acid gas will vent and corode your cars engine bay.



With my 20Watt panel I get all year round charging.
Battery never goes flat and always starts well even in winter.

My neighbours car wouldn't start yesterday. In the coming weeks I think many will be caught out!

Bit like asking--how long is a piece of string??---With the car it totally depends on how easy the engine starts.

Won't make any difference really as the output of the alternator is regulated and will remain constant no matter how much you rev the engine.--:shocked:

You'll never boil a battery with a solar charger.---:icon_rolleyes:

True.--99% of the time because of poor maintenance.--:icon_cry: