Hello all,
I have been reading all these messages about charging batteries with solar panels, but what I have found works really
well is a switchmode regulated power supply of about 40 amps capacity. When this is plugged into a generator of 700 watts, it putts out full current (40 A). The acceptance rate of a deep cycle battery depends on the voltage. At 14.5 volts, which is what I charge at, the current on a nearly empty deep cycle battery can be 30-40 amps. This heats it up, but as long as it stays cool enough to touch, its no prob.
So to charge a deep cycle battery, I leave it at 14.5 and slowly the current will drop off, until it effectively stops < 0.5 A.
So the charge might go a little like this
1st hour 25 A
2nd hour 15 A
3rd hour 10 A
4th hour 5A
5th hour 2 A
But you get the point. What I am trying to show is that in the first two hours you can put in about 40A. So really, you only need a gennie running two hours a day, if youre only using a 12 V fridge. A car alternator idleing will not charge at this rate, as they are rated at about engine 2000 rpm. This is cruising speed on highway revs.
So what I do, on the occasions where a friend brings a fridge along, is maintain his car with my charging equipment.
A generator from bunnings is about $100 and a switchmode 40A power supply is $350 or so. I got
mine much cheaper. But the point is that this costs much less then solar panels, and has many other uses, like running an electric chainsaw, and charging batteries all around the home etc. And is a lot quicker, but noisier...
By the way, you should occasionally balance the cells in a deep cycle by charging the battery up at 14.5 V till current stops, and then turn up the power supply to 15.5 V to get the sulphuric acid really boiling and disassociating hydrogen gas. This will equilise the specific gravity of the sulphuric acid. This takes about 1-2 hours, and then your battery will hold charge significantly longer. Ie. it will be closer to advertised capacity ie. 70 Ah
Also you have to make sure that you never leave a partially discharged lead acid battery sit even for a few days as you will get lead sulphate crystallising on the lead plates, and lose battery capacity. So if you run lights at night, ideally the battery should be put on charge before going to sleep. Not always possible though...
Cheers