How much input current does a charger need?

[asm2750]

Hello everyone, I was wondering, I dont feel like lugging around a large Lead battery or a car with me when I need to charge batteries, I am thinking about just hooking solar cells to a charger since, I live in vegas most of the time and its sunny most of the year. I know a charger, (lets make the GP Triton an example) needs 12 volts, which is possible with just a few solar cells put into series. The only problem is how much current do I need to put in solar cells with a voltage over 3V mostly gives about 100 to 150 mA? Also I'll probably be chargeing a battery with a 750 to 1500mAh capacity so I dont know if the current requirements change or not.

[hul]

charger input current = (charging voltage x charging current) / (charger efficiency x input voltage)

example:
charging 10 NiMh cells at 2A (guessing about 16V while charging)
80% charger efficiency
12V input voltage

charger input current = (16V x 2A) / (0.8 x 12V) = 3.33A

You need quite a solar panel for this. I think it would be better to have a smallish buffer battery between panel and charger and reduce the size of the panel. The charger would probably be happier with the cleaner supply as well.

Hans

[asm2750]

I could hook up a diode and a small 12V battery to a small 12W solar array. Do I still have to get a lead acid battery or is there a substution out there?

[jeffs555]

It is all a matter of how fast you want to charge your batteries. For 1500mah batteries, you could charge them for an hour at 1.5 amps or ten hours at 150ma. A 12 watt 12volt solar panel would supply about 1 amp, and factoring in the charger efficiency, it would take at least 2 hours to charge a 1500mah battery. Not a very practical field charger.

[asm2750]

Yeah I see what you mean, I really dont feel like setting up an array of about 20 to 60 cells depending on which cell I buy. I'll do a simulation, on multisim and see if I can get away with various cells combined, but that might not be possible.