Solar Battery Charger (you knew it would happen :D)

[Krumlink]

Ok. Lets try this one again

I want a simple Solar battery charger, that once it is done charging, it will make the battery power the device. NOT A SOLAR GARDEN LIGHT!!!

This is for some solar robots, and it will use some AAA or 1/3AAA Batteries to power it (solar walker, pretty sweet wait and see). It will charge and charge, and once it is full, it turns off the solar panel and runs the batteries. I will need:
The circuit
Some help
anything else that I cant figure out

I still want some 1/3 AAA batteries, so if you have some tell me!

 

[audioguru]

Isn't it nearly winter in Michigan? Sunlight is weak and for only a few hours each day? Solar power might work in the summer.
At this moment I am charging the batteries of my solar garden lights in a battery charger!

A Ni-Cad or Ni-MH cell is about 1.4V when fully charged. Just make a comparator to compare the battery voltage to a voltage reference to turn on the robot.

Simply connect the solar panel to the battery through a series diode to stop the battery from draining into the solar panel at night. A 80mAh solar panel will produce 80mA at noon in the sahara desert when it points straight up so in Michigan in winter its output will be nearly nothing.

 

[HarveyH42]

120 mAH batteries won't last very long. Why not just use AAAs, Walmart sells them.

 

[iONic]

I don't think I'd set the trigger voltage as high as 1.4V. A brand new NiMH battery might get to 1.4v for a while, but used ones may only avg. between 1.3v and 1.36v.

 

[audioguru]

Hi Ionic,
I have an electric RC airplane. Its AAA Ni-MH cells become warm when they are charged to 1.48V each.

Battery manufacturers have graphs for the charging voltage of their Ni-MH cells:

 

[iONic]

Hi Ionic,
I have an electric RC airplane. Its AAA Ni-MH cells become warm when they are charged to 1.48V each.

Hi AudioGuru,
You are probably right AGAIN! When charging with a solar cell there is no mechanism for "charge complete" notification as is with the "Smart Chargers" on the market.

 

[Armagdn03]

I don’t think a comparator circuit will work (though I admittedly know little about it)
Say you have the system set up to stop charging at 1.3 volts, then switch the robot on, once the power dips below 1.3 solar kicks back in, you would have a weird solar oscillator going

 

[audioguru]

When charging with a solar cell there is no mechanism for "charge complete" notification

I think my solar garden lights over-charge their Ni-Cad battery on sunny days in the middle of summer but they still work fine.

 

[iONic]

I don’t think a comparator circuit will work (though I admittedly know little about it)
Say you have the system set up to stop charging at 1.3 volts, then switch the robot on, once the power dips below 1.3 solar kicks back in, you would have a weird solar oscillator going

An epileptic solar bot, neat.
What you would use is something like a window comparator so that the robot would run when the battery voltage reaches 1.35v and shut off and eat when it reached 1.1v - 1.2V.

 

[iONic]

I think my solar garden lights over-charge their Ni-Cad battery on sunny days in the middle of summer but they still work fine.

Yes, I've heard that this is an issue with NiMH batteries and solar chargers.

That's sorta why I like the 9V battery and the op amp. Not only does it allow for a greater light sensitivity, but you could also use it as a window comparator to stop and start charging of the 1 or 2 rechargeable batteries. The 9V battery should last a good long time in that capacity I would think.

 

[audioguru]

A 9V Ni-MH battery has 6 tiny AAAA cells inside and they are so skinny that their capacity is only 175mAh. Their nominal voltage is only 7.2V.

 

[audioguru]

I used a Ni-MH charger for the low-capacity 600mAh AA Ni-Cad cells in my solar garden lights this morning. Now they are HOT because my charger is only a timer with a much higher current for 2500mAh Ni-MH cells.

 

[Krumlink]

I was thinking along the lines of a solar engine, where the cap would be replaced with 4 batteries (4.8V). That way it would charge then discharge. I found a 1381 solar engine that I think I would like to incorporate into the design. Once it got to a preset level, it would turn on and run. A zener diode rated at 5.1 volts or somthing would turn on when it reached a good level. The solar panels could charge each individual Panel with diodes on them to keep them from connecting in series, so each of them charge their own battery, while the batteries are connected in series and would then trip via a zener or 1381. any tips, because this method sounds good to me if we can get it.

**broken link removed**

go under circuits, solar engines, type 1, and 1381 or zener based.

 

[HarveyH42]

How do those solar lights look buried in snow? I have seen snow in more than 20 years, wonder if it's still as cold as I remember...

Anyway, back to the thread...

Krumilink, you've read a few things a about BEAM robots, must have been to Solarbotics.net, how come you can't use one of the circuits posted there? For what you want to do, you won't find anything better. There are a dozen or so solar engine circuits, most give very detailed theory. Just start reading until you find one that fits your needs. Most of the ones using super or large value capacitors, should work with batteries as well.

 

[audioguru]

If you use 4 little Ni-Cad cells then the solar panel to charge them must be at least 6.7V. Each cell will charge to about 1.5V and the diode is 0.7V.
Never mind switching them to charge separately then switching again in series.

My solar garden lights run until there is lots of light detected or until the battery goes dead. When one transistor is turned on by enough voltage from the solar cell then it shuts off the light. Yours could detect the battery voltage.

 

[Krumlink]

I thought of using solar panels to get a good 6V going, then using this solar engine to power the circuitry. The only problem is finding where I would put the circuitry. Would I place the anode and cathode in their respective places on the circuitry? I will place a zener diode in series with the solar panels, so they will only conduct at a good level enough for the batteries. I could use AAA nimh batteries too, I dont care what they are.

Thanks

 

[audioguru]

Placing a zener diode in series with a solar panel doesn't do anything.
The 1381 is what detects the voltage and turns on the transistors that turn on the motor.

 

[Krumlink]

So what 1381 should I pick to flip the switch on this robot (3.6V)?

They have:

3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6

I am probably going to pick a 3.8 Volt 1381 and use the above 1381 solar engine, then attach the circuitry (anode bus to anode and cathode bus to cathode) where the motor is. Will this work? I dont see why not.

I want to use 3.6V batteries.

 

[audioguru]

Look again at the charge curves I attached before. A 3.6V Ni-Cad battery is fully charged when its voltage reaches 4.2V to 4.5V.
At only 3.8V the battery has hardly any charge and is almost dead.

 

[Krumlink]

a 1381 has a general voltage gain of about .5 to 1 volt, so it would be a 4.3 to 4.8 1381

I got ya!