Why charge at only 12v and not higher?

[Cosmos]

Hi everyone,

I've just joined the site and thoroughly enjoying reading the various posts.

I've bought 40 5x5 2.6Wp and really looking forward to building my first solar panel. Previously I couldn't understand why some panels are rated 12v and others 18v, but after studying this forum I can now see that 12v panels are for charging 12v batteries without using a charge controller. Had a quick look on eBay and the MPPT controllers seem cheap enough so why bother with 12v when 18v can be used, which is surely a better set-up? Anyway, my main question is this: Why can't a 12v battery be charged at a higher voltage, say 13-15v or even higher, as the battery would charge much quicker. When I worked in a garage, many years ago, we used to charge 12v car batteries, using a charger/starter device, at 25-30v. Everything was fine as long as we didn't leave them charging for too long, otherwise they would be cooked instead of charged! All this is probably making some of you cringe from top to toe!

Anyway, if someone could answer my question I'd be very grateful.

[SeanB]

Generally charging with a higher voltage is to get charge into a dead flat battery with high internal resistance. Not good to do that to a battery every day, as it will only survive around a dozen or so cycles of that before dying. Charging a flat battery in a car with that will get it started, though you will have reduced the life of the battery a lot in doing so. In a solar charge system you match the voltage and current to what is going to give best battery life instead, as the battery cost is one of the highest costs of the system.

[Cosmos]

Hi SeanB,

Sorry for not replying sooner, but the site didn't send me a reply reminder.

Thanks for clearing all that up for me, everything is understood now. I'll be extremely careful when solar charging my battery in the shed. Will have to construct my own solar panel first though!