13th February 2008 08:54 PM
solar power supply + backup power
Yep, it's me again >_> , taking advantage of this great forum
I'm looking for a simple circuit about solar power supply with a backup power for nightly operation.
The circuit I have consumes 20mA @ 5V (it is a clock + thermometer )
Links and ideas are welcomed
13th February 2008 09:58 PM
The CLock/Thermometer looks really cool!
For a House supply oops (EDIT)
As for Solar power back up, I would get high wattage solar panels and charge up a battery bank (think car batteries) and run a 120VAC inverter on it. Not very descripitve, but should point you in the direct direction.
FOR YOUR CIRCUIT
Seeing that it only draws 20ma at 5V, lets make it safe that it could for what ever reason start to want 50ma. I would get a 6W solar panel (12V 500ma) and run that into a 5V regulator. That should work great, and for night time put a 9.6V battery or whatever voltage would suit it and attach that across the input voltage (12V solar panel) and ground it electrically to the solar panel. Make it a NiCd or NiMH. This is just a vague suggestion, I would wait for some of the other pros to state their opinion too.
14th February 2008 06:26 PM
i would def go for batteries meant for use with solar panels, cos car batteries are ment to have large amount of power drawn from them and are not so good for long "light" discharge
15th February 2008 04:50 PM
Six NiMH cells powering a LM2936-5.0 will do.
You can eailly trickle charge the batteries at C/10 using a simple series resistor and schottky diode, to prevent them from discharging back into the solar cells.
16th February 2008 08:15 PM
16th February 2008 10:17 PM
The circuit for the LM2936-5.0 can be found on the datasheet.
Here's a circuit for a simple battery backup.
DC UPS Circuits
Replace the 1Ω resistor with a higher value that will trickle charge the NiMH cell at a safe current.
Replace Rl with the LM2936-5.0 circuit.
17th February 2008 10:13 PM
Thank you for the info Hero999
26th February 2008 04:53 PM
ooooppsss I guess i missed about the battery sizing all together
19th March 2008 11:21 AM
Thank you for the information
21st March 2008 05:22 PM
It looks like the LEDs consume most of the power. Is it feasible to turn them off, or reduce the power to them?
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