I know It is legally required to power the radio from the 12v 2a port on the VRM, but for a practice bot that will never see inspection, is it possible to power the radio from a PDP Wago with a 20a breaker?
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Yes.
If so, what is the purpose of the Voltage Regulator? I assume it ensures that the outputs receive a more steady 12 volts that doesn’t vary with battery voltage… does this mean that if we go directly from the PDP then the router will go down on brownouts?
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Yes, the VRM is regulated, so it will work even if the battery voltage drops out. You also get better current protection since the radio consumes like 1 A max, and you’ll get a faster response if there are electrical issues like short in the wires.
The radio has a very limited operating range, and can’t handle the fluctuation from the battery voltage which can vary from 13.4 to 8-9 volts.
While you technically can power the radio from a normal 12V port, this is HIGHLY discouraged. IE, don’t do it.
If you ever look at the driver’s station logs, check the battery voltage. Even on a practice bot it’s all over the place. The radio won’t work when it dips low, and spikes from the motors can even damage it. Get a second VRM; it will output a steady 12V for the radio regardless of the input.
The VRM according to CTRE specifications can accept input voltage from 5-16 volts and still produce rated output voltage at rated current. The output of the PDP will vary with total system load and regularly will drop to 5-7 volts depending on drive train and driving conditions. The majority of this drop is due to IR losses in the internal battery impedance and the resistive nature of wire, primarily in the #6 primary wiring.
Agreed. Last year we put one of our LED ring lights directly into the PDP and you could see the brightness of the LEDs vary considerably with battery conditions. I would hate to drive something as voltage-sensitive as the radio directly from raw battery voltage, especially since it’s literally the one component on the robot that you do NOT want to have power down in the middle of your driving – practice or otherwise.
Yes.
In effect, yes. Technically, no.
The roboRIO goes into brownout protection when the input voltage dips below insert correct number that’s somewhere around 7 volts. Brownout protection means it shuts off power to all of the motors, which should hopefully raise the voltage back to working levels. Without a VRM to stabilize the voltage, the radio will black out much before the roboRIO engages brownout protection mode. There is no brownout for the radio. If it loses power even for a few milliseconds, it will do a full restart, which takes about 50 seconds.
In short, this is a bad idea.
Yes.
Pretty sure the router will function down to 8 volts at least. Upper limit is 24v, so definitely no problem there. That being said, dips below 8v happen happen quite a bit, so if that’s actually the cutoff it won’t work very well.
It will work, some of the time, but it is not recommended.
The VRM provides 12v when the battery dips.
If this will be a practice, or off season robot that will not be required to strictly adhere to FRC rules,
this Pololu regulatormight fit your needs. It is considerably less expensive than a VRM, but has a single output.