The DP module is label 7 - 30 volts, but it gets pretty hot when I use a transformer that puts out 9 volts. What is the best range for using this module? Can it damage a mainboard at higher voltage?
Is it hot that you can not touch it?
9V sounds a good choice to me.
It gets a lot warmer than running from the computer USB port. Not too hot to touch, but it makes me wonder what would happen if I used 30 volts. Some combinations of modules do run better with 9 volts than from the USB port of my laptop.
A linear regulator will dissipate excess energy as heat. So, if you put in 100mA @ 5v from usb and take out 3.3v, it will dissipate almost half. At 9V 3 times and at 30v 10 times… So you’re right… It will get very hot at 30v.
It’s all about the current though… So maybe 100mA current draw might be ok but hook on some extra modules and it will get hotter.
Bottom line… Stay as low as possible and close to what you need.
I’m quite sure that the DP module uses a switching regulator.
It might get a little warm. Dont worry about it. When it burns a blister, then something is wrong… 
I stand corrected.
Looking at the photo of the module it does indeed look if it is a switched mode power supply (you can see from the large inductor). [url]http://www.ghielectronics.com/images/catalog/280-0_large.jpg[/url]
![http://www.ghielectronics.com/images/catalog/280-0_large.jpg[/url]](http://www.ghielectronics.com/images/catalog/280-0_large.jpg%5B/url%5D){kind=link}
I can’t say what the SOT-23 package on there is… maybe a linear 3.3V regulator?
Anyway, 30V should be fine.
PS. Are the schematics for these modules available anywhere?