Wiring something off the VRM in parallel

Hello, my team is brainstorming ideas for adding a simplistic system of ball detection to our robot. We have created a fast modal using TF Lite that is able to read and update info to network tables. Now we need to mount the thing and was wondering if anyone knows how we could get 5v 3 amps to it. I’m thinking that we can wire it off the VRM in parallel from two 5v 2a ports to get a total of 5v 4a. I was wondering if anyone knew if this was FRC legal.

The 5v2a ports are on the same circuit- the rating is 2a total.

I’d recommend getting a dc regulator on Amazon or elsewhere.


I didn’t see this image thank you though

If you are asking about putting the outputs of two VRM’s in parallel, not a good idea. You will probably need to find a custom buck/boost or SEPIC converter. Some converters are designed to step-down to 12V, but won’t handle brownouts well. A converter of the correct type should be able to handle this, but check the specs. You might also be able to slow the clock or take other steps to get current draw on your board down under 2A – or use a phone :-).

Here’s one from SparkFun, but only spec’ed down to 8vdc input.

Aside from any FRC legality issues, this will not work electrically. The two VRM’s will not have exactly the same output voltage so the one with the higher output voltage will try to provide all the load current until it cannot and goes into current limit, if it has this feature.

Some coworkers tried something like this, even after being told it would not work, and it failed miserably.

Get a separate buck converter instead of using the VRM. This would all go under the rules for “Custom Circuits” if you want to confirm that adding such a device would be legal, which it generally has been for years and is how many teams have powered Raspberry Pis and similar SBCs on their bots.

The big consideration when picking a Buck Converter, after some level of quality control ofc, is the minimum input voltage, you want one that will work with the lowest possible voltage to avoid potential voltage drop conditions in the match that could cause your device running Tensor Flow to reboot or otherwise malfunction. I have seen some that go as low as ~6v recently on Amazon which would probably be best for FRC Bot conditions, anything with a minimum above 8v is going to have issues on an FRC bot when motor current spikes cause voltage drop from the battery.

I bought an “off-brand” from Amazon that was adjustable current and voltage (little screws in potentiometers) and was disappointed with how much variation there was over a short time and between power off/on cycles. We’ve always done well with Pololu devices and they aren’t out of stock so much recently but may be constrained. (But we haven’t tried this particular device.)

This converter is maybe a good choice, but you’d want to test under brownout. If I were putting this on a 'bot, I’d probably look carefully at the current draw on the board you are using. Also you do not want a buck (vs. buck/boost) converter, since bot’s can have voltage drops to (or even below) 5V.

Thank you guys for all of this incredible info, I will eat my team know, most likely we will go with some system of a buck/boost system!

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