Here is a problem I hope can be solved. I want to keep my starter battery topped up over winter while the bus is stored for a few weeks, in order to maintain charge to keep the security system live and so it will start when I collect it. The security system would be the only drain (the manufacturer keeps the energy consumption secret however). So, if I could get a solar panel outside in the winter weather, what size/output would it need to be? Also, if the bus was in a barn with even less light entering, what size/output then? Is there an answer or do I need to leave it to go flat in storage and just have to make sure the storage is as secure as possible? Thank you all.
if you connect an amp meter between the positive terminal on the battery, and the positive battery lead, that will tell you the system idle current draw on the battery... you'll then know what sort of solar panel you will need!! Other option is a mains hook-up and a wired in 12v charger
Solar panels really only work outdoors in sunshine and generally bright weather. If your bus is in a barn you would need to put the panel outside on a long wire. I just looked on ebay and there were suitable 10 watt monocrystalline panels with blocking diode for £23.95 Thats a bit under 1 amp on a clear skies summer day at midday and less at all other times. You should get one with a diode because in dim conditions solar panels leak charge faster than they generate it. Amorphous cells leak most current and need the most light to get going as a result. These are often sold by the likes of Maplins. Avoid.
I have electric trickle charges on my bike ,lawnmower and camper... something like this http://www.ebay.co.uk/itm/12v-Trickle-Battery-Charger-Electric-Winter-Car-Motorcycle-Quad-Mower-Leisure-/271098400930?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item3f1eb950a2
Solar panels good enough to do the job are expensive. Cheap ones rarely live up to their spec. especially in winter when daylight is lower in both intensity and duration. For a few weeks storage you could remove/disconnect the battery. For "security" how about a mechanical solution, like removing a critical component?
If you have the means ($) I would invest in a solar charger, however with any charger there is always the danger of overcharging, so please make sure your battery needs it, and to remove, or turn off the charger once you have charged it to the recommended limit. Rumor has it they now make chargers that automatically cut off when your battery is 100% charged. I only have an older charger that you have to keep an eye on.
I have an Optimate charger (also known as Accumate) Originally designed for stored motorcycles. It's on a 7 day plug timer and comes on once a week for 12 hours, it automatically senses the battery's level of charge and switches off when done. It also has a 'de-sulphate' mode which can actually re-juvenate tired batteries. I've been using them for many many years and have never had any issues. Mains is the way to go. My storage company were very helpful and don't even charge as the usage is so minimal.
