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?

Re: 2015 Compressor Fuse
 

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.

Re: 2015 Compressor Fuse
 

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).

Re: 2015 Compressor Fuse
 

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.

Re: 2015 Compressor Fuse
 

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,
Kevin

Re: 2015 Compressor Fuse
 

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

Re: 2015 Compressor Fuse
 

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.

Regards,
Kevin

Re: 2015 Compressor Fuse
 

Both.
See Copioli's Beta comments:
#21
#18 (the last statement)

Re: 2015 Compressor Fuse
 

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?

Thanks,
- Brian

Re: 2015 Compressor Fuse
 

I got ours at Pep Boys.

Re: 2015 Compressor Fuse
 

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

Re: 2015 Compressor Fuse
 

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.:D

Re: 2015 Compressor Fuse
 

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.

Re: 2015 Compressor Fuse
 

Thanks for the tips everyone!

I have now also found them on Amazon here

http://www.amazon.com/Bussmann-VP-AT...gy_auto_text_z

and here

http://www.amazon.com/Bussmann-VP-AT...gy_auto_text_z

Thanks,
- Brian

Re: 2015 Compressor Fuse
 

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.

Re: 2015 Compressor Fuse
 

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.

Re: 2015 Compressor Fuse
 

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.

Re: 2015 Compressor Fuse
 

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...

Re: 2015 Compressor 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.

Re: 2015 Compressor Fuse
 

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.

Re: 2015 Compressor Fuse
 

Try the PCM alone on a regular Wego with a 20a snap action breaker.

Re: 2015 Compressor Fuse
 

Will try tomorrow- I think I want to do some more investigating then as well. With the router and compressor it shouldn't really be more than 12A ever. But, I suppose it could be drawing a kick at startup.

Are the breakers slower than the fuse?

I'm going to run the compressor direct with a ammeter and double check the PCM for any errant wire-threads as well.

Re: 2015 Compressor Fuse
 

That removes the VRM load sharing the circuit.
The snap action does take longer to cut over current and also resets, but by separating the two loads it shouldn't happen. You'll let us know :)

I imagine you have a compressor pulling more current than you expect.
That plus the VRM load can push the total current up high enough to melt the fuse. Separated the two loads and they will probably be okay.

Re: 2015 Compressor Fuse
 

I agree, especially as I'm rather certain that there's an auto parts store or a Wal-Mart within 15 minutes of most FRC events. By the time you've blown 3 at a single competition, you should sent someone on a shopping run, and also started looking for the real cause.

Re: 2015 Compressor Fuse
 

So the actual problem was that the wiring from the PDP to the PCM was too small (I believe it was 18). When the compressor kicked it blew the fuse. We went to 16 and everything is fine. That seems like a fine line - but no blown fuses since.

I did compare a few compressors and all operated similarly (VIAIR 90).

Is my wiring arrangement legal though? I have PCM power from a 20A snap action breaker in the PDP, then going to the compressor. The VRM remains on the separate fuse, and is only powering our router. The breaker will reset if it does trip and won't kill the router.

Does the PCM (and subsequently the compressor) have to be powered from that PDP fuse?

Re: 2015 Compressor Fuse
 

No, it does not have to be powered from that fuse. I'm too tired to look up the specific rule right now, but your setup is legal.

Our 20A fuse also blew powering nothing(we didn't even have a radio on at the time). I see no damage or shorting opportunity. I am inclined to believe the fuse was bad out of the box. Luckily, we had bought extras.

Re: 2015 Compressor Fuse
 

R37 allows a PCM w/compressor on a regular 20a PDP circuit

The VRM with the radio must be on the special output per R33

Re: 2015 Compressor Fuse
 

Changing to a larger wire size should not prevent the fuse from blowing. For the short wire lengths used in FRC robots, the difference in wire resistance will not make a measurable difference in the current through your load. It is more likely that you had a "stray strand" in your old 18 AWG wire that was causing a short between the positive and negative terminals of the PCM. Those terminals are only 3.5mm apart, center-to-center (just a bit over 1/8 inch) so a stray strand can be difficult to see. You may want to use a bright light to visually inspect all of the connections on these small Weidmuller connectors on the PDP, VRM and PCM. Please note that these terminals alternate between positive and negative so it is possible to short between the positive terminal of one circuit to the negative terminal of an adjacent circuit.

Re: 2015 Compressor Fuse
 

Hi Phil,

So we had a similar problem where the PDP fuse "mysteriously" kept blowing. After four or so more such incidents I decided to check on Chief; the electrical team wanted to replace the PDP to see if that would fix the issue. Our problem happened to be where power comes into the PCM.

To eliminate the chance of that happening again, I had them very lightly tin the end of those wires. Is there any reason not to do that for all those connections?

Mr. Rip

Re: 2015 Compressor Fuse
 

I can't be 100% sure from the rules this year (2016), but I can't find anywhere in the rules where it says the PCM must plug into the VRM/PCM power header on the PDB this year.

R48 sort of hints to the fact that it is legal in stating that the PCM can have a 20A breaker.

Anyone else want to chime in on this? It was legal last year, is it still legal this year?

Re: 2015 Compressor Fuse
 

R53 says the compressor can be controlled by a relay module
R66D allows you to put a Snap Action breaker in the relay module if powering the compressor

Not sure if that is what your are asking, but as in previous years, the compressor can be controlled by a SPIKE and gets rid of the problem described by the OP.

This is the way we will power our compressor.

Re: 2015 Compressor Fuse
 

Not really, but thanks for answering. I want to avoid additional electronics if not necessary.

Re: 2015 Compressor Fuse
 

Yes, it is legal to connect the PCM to a 20 amp Breaker, and not the PCM connection on the PDP.

The Robot can have One and Only One compressor. R48 says "PCM - with compressor". If the compressor had to be connected to the PCM at the PCM connection, then it would be impossible to also have another PCM with a compressor connected to a different 20 amp circuit.

In addition, you are not required to use the PCM to control your compressor. You could use a Spike Relay as rsisk mentioned. Again, if you had to use the PCM, then there would be no reason for R66-D.

Re: 2015 Compressor Fuse
 

I don't see anything in the manual that requires the PCM to be powered by the connection at the end of the PDB.

I don't see anything preventing power from coming from a PDB circuit with a 20AMP breaker.

And finally, don't see anything about it on the inspection worksheet.

Unless directed otherwise by FIRST, I would pass it at a competition.