12v Solar panels to keep 6volt charged

[tim2]

I have a question about using a 12Volt solar panel to keep sealed 6V7a lead acid battery charged.
The Specs of Solar panel is 12VDC
wattes 1.5W
VOC(open circuit volt)
Max output 120 mA

Specs of battery 6V 7Ah
Standby use 6.75-6.90V
Cyclic Use 7.2-7.6 V 2a max
This is going to power a Power slave flash and D380 camera thecamera will have 4aa batterys in it.
Can anyone see a problem arising from using this and a solution to problem.

 

[steve-o]

That's a good idea. I'm hoping to maybe use a solar panel too. Hopefully someone else has some ideas about how to use one.

 

[Hill Hopper]

Tim, I got your e-mail, and I'm not really up on chargers/solar panels. Jon, Arch, or Tinhorn can probibly help though.

 

[Jon5ja]

Tim and I talked a bit off line about this -- I don't think it'll hurt anything to just hook the 12V panel to the 6V battery (with a blocking diode if the panel doesn't already have one built in to keep it from running down the battery at night)... after all, it's really a 22 volt panel that's already being lugged down to charge a 12V battery.

The only thing I'd have any trepidation about would be the (potentially) 7.6 volts on the battery when you've got it topped off. I don't reallly think it would hurt the camera, but I'm not positive, and I'd sure hate to give anyone advice that cost them $150.

Is anyone else out there running a solar panel on a lead-acid battery, powering a D-380? Or maybe just running a D-380 on that high a voltage?

 

[GPo]

Jon,
Your saying that a 12 V solar panel charger will only top off a 6 Volt supply to 7.6 volts ? So there's no danger of it charging up to 10 or 12 volts ?

GPo

 

[GPo]

Further to this, Some of these solar panels are mini's, only 3" x 6" and 1 to 2 watts, they say 3,6,9,12 volts but in the specs it says 3 volt @ 150 mA, is this enough? Some others are 12 volt, 5 watt at 170mA, that sounds like it would work to keep up a 7Ah lead cell. I guess one would have to test the mA output in direct sunlight and in the shade, because under a tree there would be little direct sunlight. A lot of these are about 12" x 10".
So what would be the specs on a panel that would work to top off a 7 Ah.?
? Volt, ? watt and ? mA.

GPo

 

[Jon5ja]

The solar panel Tim referenced actually puts out 22 volts open-circuit. So, it probably stands about the same chance of overcharging a 12-volt battery as it does a 6-volt battery. It will charge the battery however high the battery will go with 120 mA of charging current (assuming there was no drain, and the panel was in full sunlight). However, to put this into perspective, using one battery manufacturer's recommended factor of 1.75 times the rated capacity it'd take 102 hours of full sunlight to recharge the 7 AH battery in question... so, I don't think it's likely to hurt it.

The main downside is that you're wasting half of the capability of the solar panel... if you re-wired the solar cells in the panel to get half the voltage but twice the current, you be able to supply 240 mA of charging current to the 6V battery instead of 120 mA. I suppose it's possible that some of the panels you referenced may be reconfigurable to trade volts for amps.

You should size the solar panel to provide (on the average) something more than the amount of current you drain from the battery. Picking one that will average out to that over day, night, sunny times and shady times, will probably be a trial-and-error exercise. Depending on how the panel is situated, I'd guess that Tim's panel is about the right size to keep a battery charged to run a D-380, maybe in fast-shutter mode.

Watts = Volts X Amps

So, if you know any two of those numbers, you can calculate the other. Amps (or milliamps) is what's going to charge your battery. If you put a 12-volt-capable panel on a 6-volt battery, the amps stays about the same, but you've halved the volts, so you're only getting half the rated wattage of the panel.

Sorry, this guesswork is the best I can do without doing some actual measuring.

 

[Elk Bowhunter]

I had a 12 volt solar feeder that went out. The company replaced it, but they sent a 6 volt feeder because they no longer made the 12 volt version. They told me to cover up 1/2 of my original 12 volt solar panel. I am not sure if that is the right way to do it, or not, but that is what they told me to do.

 

[Tinhorn]

I don't know much about Solar Panel Chargers

but I know there are Voltage Regulator Modules available that are used to control the Panel's output connected to 12 volt batteries and I assumed they were to prevent overvoltages to the battery from occuring and charge shutdown when the batt is topped off. It seems to me there would be a danger of battery damage from charger overvoltage but, like I said, I don't know much. Maybe it would be self regulating

I don't know how energy efficient they are but maybe a cell phone cigar-charger could be used to provide 6v regulated to the battry from the Solar Panel, or if it turns out the panel can be connected to the batt directly then the adapter could go between teh batt and cam/PIR circuitry to knock down the 7+ batt volts to a safe level of 6v

About everybody that uses cell phones has some left over cigarette adapters laying around and at least some are for 6volts.....

but I don't know how much current the adapter itself draws, since a solar panel is being used, the continuous charge mite make up the diff anyway

On another note, don't know if access to the panel is possible but maybe it could be re-wired to provide ~7.5 volts output by paralleling more of the cells, I think each cell has a rating of 1/2 volt ? ? ? if it has no built in voltage regulator that is.....

Tinhorn

 

[Archilochus]

Try this keyword search at http://www.google.com

solar "battery charger" circuit OR schematic OR schematics

More solar battery charger information than you'll ever need! From the absurdly simple, to circuits of Machiavellian complexity - buy 'em or even go so far as to make the solar cells at home!!