Warning about using VRM and LED lights

[top.jek]

I'm with team 4593 and I just wanted to say that I experienced an unpleasant surprise this weekend when I plugged in the LED tape to the 12v 2amp channels. They must have drawn enough current to burn out the regulator without blowing the fuse on the pdp. I was foolish enough to do this twice, thinking that the first VRM had just been a dud, so now I know that it was the LEDs that caused the damage. Our team now has two dead VRMs. If any of you guys want to use LED tape on your robots (it looks really good in my opinion and you can pick some up cheap on amazon), plug the leads directly into the pdp; the same channels used to bring power to the VRM work perfectly. Huge shootout to 801 for loaning us a spare VRM so that we could function in the tournament!

[ATannahill]

You should not be putting LEDs on the same channel as the VRM that powers the radio.

[kgzak]

Our LEDs are connected to our VRM. We have two strings running up our lift support arms. Nothing happened to our VRM. Are you sure you didn't do something else to kill the VRM?

[Tom Line]

If your LED's are within the voltage and current limits of the VRM, there is no problem using it to light them up.

If you are using something like this:
http://www.amazon.com/SUPERNIGHT-16-...led+strip+blue

A 5050 LED draws .24 Watts per led. One string has 300 LED's, or 72 watts! That's 6 amps at 12 volts - well beyond what the VRM has available.

[Mark McLeod]

The VRM only supports 1.5a continuous (and 2a only momentary).

During Beta testing the VRM burned out if higher than 1.5a was continuously pulled from the 12v power rail. It worked fine when we kept it under 1.5a.

[MrForbes]

My gut instinct is to use the VRM only for things that require a reliable, regulated power supply. Like the robot radio. That means NOT for stuff like decorative LEDs.

[Mark McLeod]

I agree. Our LEDs are driven by a custom circuit that doesn't use a VRM.
Regulated power isn't necessary.

[Tungrus]

Please double check the current rating on LED strips. Typical 1m strip is rated for about 1A to 1.5A. Longer strips need more current. VRM is rated for 12V 2A, where 2A is peak current and not continuous max current. Its rated for 1.5A continuous. If you have radio on the same VRM, its just too risky for the competition.

[GeeTwo]

Originally Posted by Mark McLeod

I agree. Our LEDs are driven by a custom circuit that doesn't use a VRM.
Regulated power isn't necessary.

Yes. Anything designed for automotive use, such as the LED strips, is designed to handle essentially the same ranges of over/under voltage around 12V as you'll find on an FRC robot. The big thing to watch out for in automotive electrical components is anything with a construction than connects the chassis to the negative lead of the power supply. And illegal motors, of course.