Voltage regulator--how to mount?

[JBotAlan]

Originally Posted by Dave Flowerday

It was legal in 2007:
http://forums.usfirst.org/showthread.php?t=1518

Oh, I know that I had a discussion for awhile during the season here on CD, but I didn't know there had been an official response. Thanks for the link.

JBot

[ntroup]

Originally Posted by JBotAlan

[offtopic] Al, did you guys get your faulty pot wiring figured out yet? It looked like someone had cannibalized those PWM y-cables for pot wiring--every single one of those I've used has turned out defective, so I don't use them anymore. Had you seen that before Atlanta? And was that the problem you were having at Atl?[/offtopic]

Not to de-rail this topic again too much, but I wanted to add an update. After further investigation, the wiring was not at fault at all. We do not use 'cannibalized PWM y-cables', but actually create our own out of bulk PWM wire. The wiring was stressed a bit, but not defective or faulty. The digital pots, however, were where the problem was. Both the elbow and the shoulder pots are the MA2s from usdigital.com, and both died, either due to static shock or strong magnetic field too near them (as they work off change in magnetic fields to determine rotation). We are still investigating the root cause.

Either way, we are fixed, and ready to rumble at IRI now

-Nate

[David Brinza]

Originally Posted by Al Skierkiewicz

Jbot,
The 7805 series regulators have the center pin and the tab at the same potential, i.e. power supply common.

As Al points out, the 7805 case (and mounting tab) is tied to the center pin (power supply common). For some applications, you might need to isolate the regulator from the chassis. (In FIRST, for example, the robot chassis is required to be isolated from the +12VDC AND return/ground). There are thin mica insulators available for the TO-220 package that will provide electrical isolation with minimal thermal resistance. If you use your chassis as a heat sink and wish to keep it isolated from the power supply, you should use one of these mica insulators - with some thermal compound to improve the thermal conductivity between the regulator and heat sink.