2015 Compressor Fuse

[plaidwarrior]

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.

[2508electronics]

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.

[Jon Stratis]

Originally Posted by 2508electronics

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...

[2508electronics]

Originally Posted by Jon Stratis

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.

[dougwilliams]

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.

[Mark McLeod]

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

[dougwilliams]

Originally Posted by Mark McLeod

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

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.

[Mark McLeod]

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.

[GeeTwo]

Originally Posted by Mr V

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.

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.

[dougwilliams]

Originally Posted by Mark McLeod

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.

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?

[tStano]

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.

[Mark McLeod]

Originally Posted by dougwilliams

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 comprtessor) have to be powered from that PDP 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

[philso]

Originally Posted by dougwilliams

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.

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.

[Mr. Rip]

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

[RyanN]

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?