On Fri, 7 Aug 2015 05:49:39 +0100, Mike Tomlinson wrote:

The PV panel was in a north facing window so not ideal. To get
south
facing wuld require a rather long cable run, proably not far short
of
50m by the time you've gone round things.

Think you're on a loser with that one.

Possibly not as the current is low (1.5 W @ 12 V = 125 mA max) so
volt drop is also low (0.125 V per ohm)

How about putting a smart charger on a timer, so that it runs for only a
couple hours a day and doesn't dry the battery out by running all the
time?

That is an option if a suitable charger can be found. If buying a
charger one may as well try and get something designed to do the job
properly. I suspect that might not be easy.

Build something? Lead Acid are supposed to constant voltage charge
with the volatge set to provide bulk or (frequent) cycle float rates.
reducing the voltage to a level such that the current is very low (
10 mA?) starts me thinking that slight battery changes or even just
temperature change is going to affect the current drmatically. Would
a limited constant curent supply be better and pure DC or pulsed?

Re. preventing the battery from freezing, maybe put it in one of those
polystyrene cool boxes, cut notch(es) in the lid for the cables? This
sort of thing:

http://www.automa.co.za/sites/defaul...ublic/field/im
age/AUT1175_2.jpg

Not easy to retro fit around the battery tray on the genset, there
isn't much clearance from battery to frame/alternator etc. Also with
the garage at -10 C for a week nad near freezing for a month or so
either side I supect everything will get pretty cool insulated or
not. How much warmer would the watt or two from a float charger keep
the battery in such a box?

--
Cheers
Dave.