PCM Solenoid Fuse

[Anthony Galea]

Not sure whether this is more appropriate for pneumatics or electrical, but here goes.

So, today we were driving our robot around getting drivers practice, but every once in a while one of the solenoids would stop responding, and we hooked up the roboRIO to the computer to look at the webdashboard, and it said there was a solenoid fuse fault. What could be causing this? We did realize after practice ended that the PCM is set to 24V when the solenoids (AndyMark Mead Double Solenoids) are 12V solenoids. Is it as simple as that? Thank you in advance for your help.

[ILAMtitan]

That might be all it is. The next time your pneumatic drop out, check the status light on the PCM for a local fault indication. Section 3.3 of the PCM users guide lists all the possible conditions (http://content.vexrobotics.com/vexpr...-20150219.pdf).

[Mr V]

Far and away the most common reason that I've seen cause the PCM or VRM loose power is that the fuse is not properly installed.

The terminals that the fuse connects to are not perfectly centered in the hole. So many teams insert the fuse and when the fuse body hits the RoboRio's case people call it good. You must wiggle the fuse/deflect it to the side so that the fuse body can go into the slot. A fully inserted fuse has about half of it's body below the top of the RoboRio case.

As an inspector I've seen properly inserting the fuse to fix the loss of power to the PCM and VRM a number of times.

[JPBlacksmiths]

If your using 12V solenoids then definitely switch the jumper on the PCM to 12 volts. If that doesn't solve the problem then I would change the fuse on the solenoid.

[Al Skierkiewicz]

Anthony,
I would check the fuse on the PDP to be sure it is still good. Visual inspection may not show an open so use a meter. Replace as needed and be sure to get it installed so that it is only about 1/8" above the PDP surface. This is tricky so just be patient. Then move the jumper on the PCM for 12 volts. At 24 volts, the solenoids might fire but the current is usually double what it is expected at 12 volts. In some cases solenoid damage may result.

While we are talking about fuses on the PDP. I have seen some teams modify the PDP to allow different fuses. This is not a legal modification. See R66 for further info.

[FrankJ]

A quick look for "solenoid fuse fault" in the PCM manual didn't find a description of exactly what that means. I suspect that it is something internal to the PCM rather than the supply fuse. Perhaps the 12 volt solenoids are overdrawing the 24 V supply and disabling the solenoid outputs. If the fault was referring the PCM supply fuse, i think it would be worded differently.

I like connecting the PCM to a 20 amp breaker slot rather than the fused output. I read table 4.2 of rule R48 as allowing that.

[Al Skierkiewicz]

Frank,
I don't think that is what R48 is saying. It is referring to only one load is allowed on the outputs designated for the PCM and VRM. It further speaks to the branch circuits in general. R44 actually points to using the PCM output marked on the PDP.

[Joe Ross]

Originally Posted by Al Skierkiewicz

Frank,
I don't think that is what R48 is saying. It is referring to only one load is allowed on the outputs designated for the PCM and VRM. It further speaks to the branch circuits in general. R44 actually points to using the PCM output marked on the PDP.

R44 allows a PCM to be connected to the same fuse as the VRM, but does not require it. R48 allows a PCM to be connected to a circuit breaker.