I new to electronics and I have a question. I ordered these parts from spark fun
https://www.sparkfun.com/products/10256 (pwm switch)
https://www.sparkfun.com/products/10160 (rt clock)
Iv’e got it all wired up and ready to go. I’d like to use it to control this drill:
Basically I want it to control the drill to power it on for 10 seconds twice a day. My problem is that a 9V to power the board isnt lasting all day. Is there a way I can use the drill motor battery to also power the board without frying it?
Thanks in advance!
It might work. The regulator on the Arduino is recommended for 7-12V, but the actual limits are 6-20V (See [u]this page[/u].)
I think you'll be OK. However if you are powering the LCD and clock from the Arduino's regulator, you might be stressing it. (The more voltage you "drop" across the regulator and the more current through it, the hotter it gets.)
Another option is to use a [u]7809 Voltage Regulator[/u] (and a couple of capacitors) to knock the 18V down to 9V. That way, your external (bigger) regulator is doing most of the work.
There are also 8 and 10V regulators commonly stocked if the 9V isn’t findable.
You will need some heatsinking on an external regulator, a clip-on one ought to be enough but
you can calculate the heat dissipation and work it all out if you measure the current consumption
of your Arduino and its LCD etc.
The power dissipated in a regulator is the difference in input and output voltages (in volts) multiplied
by the current (in amps) - gives power in watts directly.
Heatsinks have a C/W specification which is the temperature rise per watt dissipated (in free air), and
so you can choose a heatsink that will keep the regulator cool enough.
You can also use a switched power converter like SKU: 142488 from dx.com. This is adjustable for the output voltage that you want. Best would be to adjust for 5 volt and supply that to the Arduino. Its cheap, and you wont heat up anything. There is hardly any power loss. They have several types so have a look and make your choice.
A DC-DC converter is needed really, the 1.3Ah capacity of the lithium battery would mostly be wasted
powering the Arduino inefficiently otherwise. 18V → 5V conversion will reduce the current drain from
the battery by a factor of about 3 compared to using the on-board linear regulator.
Note this in the description of that MOSFET breakout board:
Note: While the MOSFET is rated to 60V 30A, the circuit board traces are only rated to 3.5A.
Find a better logic-level MOSFET (lower on-resistance, perhaps < 10 milliohm), and don’t use a PCB
breakout, either solder or use miniature terminal blocks - drill motors pull a LOT of current, perhaps 20A.
The MOSFET may need a heatsink too, although a 10s duty cycle may make that unnecessary.
I wonder if the OP had any luck with this project in the 5 years since the thread was started?