2015 Compressor Fuse

It was brought to my attention this week that there might be a fairly major issue with the way the Pneumatics board is powered, and the Compressor. The PD board uses 1 20a mini fuse to power both the Voltage Regulator board and the Pneumatics board. The Voltage board is what is powering the Radio, and there is functionality in the Pneumatics board to power the compressor. Running both of these off of 1 20a fuse could be a major issue, because I remember popping 20a fuses in spikes before we replaced them with the breakers. With the way the system is setup now, if the compressor pops the fuse, it will shut off the radio. Have any of the beta teams talked about this to make sure this doesn’t actually become an issue?

Significant testing has been done with the PCM and the compressor, and I haven’t heard of a single fuse blowing. The PCM is capable of starting the compressor without surging power across the fuse, which was the cause odd burned out spike fuses.

Correction: one Beta Test team did report blowing the 20A fuse. It happened after they intentionally overstressed the VRM’s 12 volt 2 amp output (which apparently resulted in the VRM itself failing as well).

I pointed this out in the beta hardware thread.

Personally, I don’t like this setup, where the radio fuse is non resetting and is shared with a compressor and other items, but I believe the compressor fuse won’t blow very easily because it now has a current limited start.

We have been running a compressor on the PCM since the Alpha test days and have never blown the 20amp fuse.

We have blown the internal (soldered) fuses inside of the PCM and VRM, but that was due to our own destructive testing.

When wired correctly, the PCM and VRM should never blow the 20a fuse.

The VRM has multiple internal fuses, and if there is a short on one of its lines, the fuse internal to the VRM should blow before the 20A fuse is affected.

However, I said wired correctly, if the PCM wires short, or the VRM wires short at the PDP, then yes, you will blow the fuse, the wires won’t short as long as proper wire gage is used, we have been using 18 awg security wire, which has a nice small jacket that slides into the wieldmuler connector. If you used 18 awg speaker wire, the larger jacket may not fit, and some of the wiring will be exposed.

The PCM has a feedback loop running and monitoring the current output of the compressor, the controller can sense and react to current changes way faster than the fuse can, which is why the fuse should not blow.

To help ease everyone’s mind, we have actually replaced our 20A fuse with a 15A fuse on the PDP to see if that will blow, and so far we have not blown the 15 amp when running the radio on the VRM and 3 solenoids and a VAIR 92 on the PCM.

Correct wiring and attention to your setup, should yield a perfectly functioning system.

Now, the only other potential I see if teams trying to power other 5V devices from the same VRM that is powering their radio. I would say “Don’t even think about doing that”. Have one regulator for the D-link, and another for all other 5v items (camera, off-board processor etc.). The VRM can only output 2.5A MAX on the entire 5v Rail, and 2.5A MAX on the entire 12V rail. The D-link wants 2A just for itself based on manufacture spec.

Hope this helps,

The VRM is only rated for 2a max peak momentary.
It’s 1.5a continuous.

Is this information provided by CTRE, or empirically measured by your team? If this is true, which goes against my current understanding of the VRM, how does the 1.5a continuous split across the 500ma Max Channels, and the 2A max channels on the VRM rails?

Based on my discussions with Mike from CTRE, I was under the impression that each rail supplied (12V and 5V) on the VRM has a max of 2.5A, and that the channels for each rail were limited to 2A, and 500mA, but these were all continuous sources, not momentary.


See Copioli’s Beta comments:
#18](https://usfirst.collab.net/sf/go/artf2746#18) (the last statement)

So if you happen to blow one of the 20A fuses on the PDP, where do you find new ones? Neither AndyMark or VexRobotics appears to carry them.

Someone said that these are the same as automotive mini-fuses. Is that true?


  • Brian

I got ours at Pep Boys.

See page 12 of the user guide: http://www.crosstheroadelectronics.com/PDP%20User’s%20Guide.pdf

Both automotive fuses are type ATM automotive blade mini fuses. Spares can be purchased at most hardware stores (Do not purchase ATC as they will not fit).

If for any reason someone cannot find these fuses in your area, our FTC team bought a bunch and have more than enough to last the next 20 years of FTC. I think they can spare a few.:smiley:

Yes they are automotive “mini” fuses available at any auto parts store or Walmart and under the dash and/or hood of many modern cars. Many brands like Fords actually have spares in the cover. I suggest picking up a pack of both the 20a and 10a to have on hand just in case, cheap insurance.

Thanks for the tips everyone!

I have now also found them on Amazon here

and here


  • Brian

A 25 pack seems excessive, the 5 pack at the local store will be more than enough to have on hand to prevent the installed ones from blowing.

Actually R33 says that you MAY wire the PCM into the dedicated (fused) supply terminals. It does not say that you MUST wire the PCM there. If you are worried about blowing the 20A fuse, just wire the PCM into a 20A circuit breaker on the normal WAGO connectors.

I personally would recommend using a circuit breaker since they are self-resetting and fuses are not.

We were doing a demo last night and had our fuse blow and only the radio was connected through the VRM. Thankfully, we had last years robot handy.

Have you done any diagnostic to figure out why? Is it at all possible there was a short in the system somewhere? Simply put, without some sort of catastrophic failure the radio CAN’T pull 20A to burn out that fuse…

I think there may have been a short but upon a quick inspection right after, no excessive wire was sticking out anywhere and there was no sign of any possible way to have a short.

Just an FYI to anyone interested…we had this exact scenario happen today.
Radio went out, tracked it down to a blown fuse in the PDP, grabbed another one and happened again.
Disconnected the PCM from the PDP, and the radio from the VRM and powered up. Checked all relevant voltages and let it sit for a bit. Added the router and re-measured voltages and waited some.
Wired the PCM back in (without compressor), and measured and sit a while.

Added compressor back and checked and waited.
Then, as soon as the compressor was enabled the PDP fuse blew.

We are wiring in a spike, and it looks like we manually have to monitor the pressure switch in software now and enable and disable the compressor.

Not entirely sure why this happened now, but It seems like a bad idea to trust a game to that fusing arrangement.