I am modifying a laminator I bought to do toner transfer. its pretty simple, I am basically using a relay to kill +V power to the motor driving the rolls to dwell under heat for 8 seconds, and allowing it to feed the board forward for 0.4 seconds and hold for another 8. Rinse and repeat. I have tested this in a proof on concept mode with a Mega2560 (powered separately) and it works GREAT! I am so pumped. Now the problem is powering an Arduino Nano inside the laminator case to run the the laminator in "PCB mode". The unit takes direct 120V AC and has a transformer board that outputs 24V DC for the heaters. From there a voltage regulator runs all the logic at 5V. Now the Arduino nano says no more than 6V (recommends 7-12) so I dont want to run it on 5V alone and have enough to power the relay.
Question is... I want to Step down from 24V and not over burden the 5V regulator by a 7812 to get 12V to the Nano. Note: I have no good way to heat sync with the remaining room I have left so I do not want to use a 7812 on the 24V line. Which is the better approach. And any suggestions on a transformer/regulator to step down from 24V in a small space and not worry about much heat?
The unit takes direct 120V AC and has a transformer board that outputs 24V DC for the heaters.
You're sure that 24 volts is DC? ...A transformer without a rectifier puts-out AC.
I want to Step down from 24V and not over burden the 5V regulator by a 7812 to get 12V to the Nano.
What??? A 7812 would probably do it. With ANY linear regulator, the heat (and wasted power in Watts) is calculated by the voltage drop across the regulator(s) multiplied by the current (Amps). Somehow, you have to drop 24V to 5V (19V) and with a linear regulator there's a certain amount of wasted power, depending on the current drawn by the Arduino and relay (assuming a 5V relay).
With a 24V supply and a 7812, you have 12V across the 7812, 7V across the Arduino's regulator, and 5V across the Ardunio's active circuitry. So, the 7812 is dissipating about twice the heat as the on-board regulator. Or, you can use a 7805 and bypass the Arduino's on-board regulator altogether. The 7805 shouldn't overheat just driving the Arduino plus a relay that the Arduion can drive directly (less than 40mA).
If you have room for a few more components (including an inductor), a switching regulator would be nearly 100% efficient.
DVDdoug:
You're sure that 24 volts is DC? ...A transformer without a rectifier puts-out AC.
Yes, I measured it and its got a rectifier. Its a whole separate board within the unit to be clear.
Or, you can use a 7805 and bypass the Arduino's on-board regulator altogether. The 7805 shouldn't overheat just driving the Arduino plus a relay that the Arduion can drive directly (less than 40mA).
Thats a great idea and the path I think I will try here first. I would be driving from another 7805 already in the unit, DUH! As I said I dont have room to properly mount a heat sync and dont want to go the 7812 route. Thanks!
If you have room for a few more components (including an inductor), a switching regulator would be nearly 100% efficient.
My engineering degree only included a basic EE lab course, and I am highly interested in modding and always to learn. if you wouldnt mind explaining this a bit I would be very appreciative. Thanks!