Only one side of our VRM works

Technical Electrical
1

Hello,

We are wiring our robot’s cancoders, and while debugging connection issues we found out that only one side of our vrm works. Any ideas or thoughts on what we are doing wrong?

Thanks!

2

I would suggest you route all of your wires into the 12 volts side as the minimum amount of volts required is 6 volts (I believe) which is more than the 5 volts that the other side of the VRM.

3

When you say that only one side of the VRM works, do you mean the side that is labeled 5V/2A and 5V/500mA? Or what consists of a side?

If the problem is that the cancoders aren’t working when plugged into the 5V side, then as @scimn27 mentioned the issue isn’t that the VRM isn’t working, it’s that Cancoder’s require at least 6V (and up to 16V) of power based on their specifications (available here).

Having said that, you have some other options on how to power these depending on what you have available/what you want to do.

  • From the same spec sheet above, at full draw Cancoders will use 60 mA of power. So you can run up to 8 in series off of a single 12V/500mA port on the VRM without issues. Credit to this thread from 2021 that raised this as a solution.
  • I’ve also seen teams use a Rev Mini Power Module to give individual power runs to peripheral devices like Cancoders. All 6 ports send out 12V of power.
4

Hold on, I thought all four CanCoders should be wired to one port on the PDP.

5

Trouble-shooting question:

Have you checked the VRM with a multimeter to verify that it isn’t producing the specified voltage?

6

There isn’t really a rule defining how CANcoders should be wired (other than maybe one requiring appropriately-sized wire). They’ll work when powered by a PDP, PDH, VRM, or anything else capable of producing 6-16V. Using regulated voltage is one way to eliminate some uncertainty (if your main voltage drops below 6V, your CANcoders would stop working temporarily if they’re plugged directly into the PDP… but so would a lot of other things). The tradeoff of using VRM-regulated voltage is that you won’t be able to draw as much current as you would from the PDP/PDH, but CANcoders don’t require very much current anyway.

Per CANcoder - CTR Electronics, CANcoders draw 60mA max, so you should be able to power at least 33 CANcoders from the 12V/2A rail of a VRM. Plenty for a swerve.

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7

Hey all,

We sincerely appreciate the help given here.
We are somewhat inexperienced with electrical, and realized we just could route the cancoders together with wagos (we also for some reason didnt read the voltage labels on the vrm).

Thanks.

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