We were testing robot, and all of a sudden, the VRM disconnected and shut off. When we touched the top of the VRM, it was hot. Now, the lights on the VRM do not turn on or work. We measured the power going to the VRM and it’s measuring approx. 12 V.
We aren’t sure what we can do except purchase a new VRM. Any tips on troubleshooting?
What is connected to your VRM?
What was connected to it? Specifically what things were drawing current, and how much?
We only have the radio and some LED lights connected to it.
What’s the current rating on the LEDs
From what I understand, the VRM has a peak current rating of 2 amps and a continuous load of 1.5 amps, and the radio has a 1.5 amp draw. Bit of a design oversight in my opinion, because if your robot has any other electronics that need a regulated voltage, you need another module.
For LED ring lights, I suggest you run them straight off the PDP, unless they aren’t rated for 12 volts.
http://content.vexrobotics.com/vexpro/pdf/217-4245-VRM-Users-Guide-20141230.pdf
look at the bottom of page 7
Fixed that for you. The radio draws closer to half that continuous.
Maybe this could be a teaching moment…
Our team did the same thing and now it is a paper weight. Why would they release this product with this big of a flaw?
Our team is debating getting a new one, or wait for a fixed version to be released. Since we have till week 4 for our first comp.
It is sad to know that this is going to be a common occurrence this year.
I mean in general you should never really have LED lights hooked straight to a power source without a resistor between them.
If you guys want to drive LED’s, use the GPIO ports or a spike to drive them, don’t hook them up straight to power…
The LED’s we have are rated for 12 volts, so go on that port of the VRM. Use resistors, and/or hook them up in series to drop the voltage if you have 5v LED’s. Or, make sure you don’t overwhelm the 5V 500ma socket.
IMHO, other than the radio, don’t put anything else on the 5V 2A socket of the VRM.
I wouldn’t wait. The VRM is a mandatory item to power the Radio, and I doubt they can get “fix” out for this season. If you wait, and Andymark runs out, you are toast.
They still need current limiting resistors regardless of their voltage rating.
If your LED’s are “rated for 12V” or “rated for 5V” they probably already have the proper current limiting resistors (or some other current limiting device) integrated into them. If you are connecting a 5V rated LED string to 12V, you will have to first find out how much current the the LED’s draw, then calculate the series resistance value needed to drop the voltage across the LED from 12V to 5V.
There should be no need to connect the LED’s to the VRM. The Voltage Regulator Module is for powering devices that are critical to the proper functioning of your robot and are sensitive to voltage fluctuations, like your radio. Your LED’s are not a critical function of your robot (though some of the students on our team would debate me on this issue) and short voltage fluctuations will probably not make a noticeable difference in how they operate.