Hi all,
I have an arduino connected to a garage door opener. It uses xbee and a relay to open the door. All works fine, but I have to make it work without batteries, and I can tap 30VAC from the transformator. Does anyone know of a simple rectifier I could use to make a stable supply for my arduino?
Thanks in advance,
Joachim
4 x diode = bridge (1N4007 for example). Capacitor 470 - 1000uF for min. 30 * sqrt(2) = 42V, use 50 or 63V.
7805 blocked with two 100nF caps, in series with a power zener diode (12 - 15V / 5W) because max input is 35V and you have 42.
Thank you for the prompt response. However I have difficulties in picturing your proposal. I thought the 7805 made 5v, and that the caps for the 7805 should be in the uF range?
Joachim
If you have an AC outlet nearby, you can power the Arduino from one of those USB cell phone/device chargers.
If you have an AC outlet nearby...
Perhaps the one that powers the garage door?
Don
I thought the 7805 made 5v,
It does but you can only feed it with 35V maximum so you need to cut this down with a zenner diode first. Either that or a regulator with a higher input voltage.
the caps for the 7805 should be in the uF range?
They are on the output of the diodes he says:-
Capacitor 470 - 1000uF
Note you need a 50 or above working voltage on these capacitors.
7805 blocked with two 100nF caps,
That means a 0.1uF cap on the input and output of the 7805, although I would go for something bigger, say 4.7uF on the output side.
Some switching supplies while requiring a mains input could work at 30V AC.
Thank you all.
Of course I could take 220vac out from the main winding of the trafo, but where's the fun and learning in that? Besides, I don't want it to look too invasive, as we are sharing the garage with others...
Will this work?
Joachim
Will this work?
Yes in a big ball of flame ;D
You need a resistor in line with the +ve of the diodes and the zener diode. This will limit the current through the zener and drop the excess voltage across it.
The value must be calculated by taking the maximum current and the difference between the zener voltage and the input voltage, then work out the resistor value from that. It will also burn some power so calculate the power dissipation as well.
Your schematic is a smoke generator based on diodes 
Zener D5 must be after C1 : connect it between a plus of capacitor and the 7805 input (triangle in diode symbol points to C1).
D5 must be after C1
Makes no difference being before or after C1, that's just topology, you need a current limiting resistor.
Shouldn't D5 be in series with the input to drop the voltage going into the regulator? You would need a zener that can handle a few/several watts.
That would work as well but you need a different zener voltage than the shunt solution being proposed here.
Thinking about it it is probably more efficient to do it like that, series that is, then you don't need a resistor.
I must acknowledge: pepe34 has been trying to tell us this since the first reply to the OP. I didn't realize that is what he was trying to explain until just now.