We had to replay a match a few minutes after a quals match and ended up blowing a 20 amp fuse for our pneumatic hub in the middle of the round. Upon closer inspection of logs, we found that when compressing, the compressor draws ~8-10 amps but the robot browning out for a fraction of the second led to a current spike that blew the fuse.
This actually isn’t the first time this issue has happened but we aren’t sure whether this could be a problem with certain pneumatic hubs and their soldering connections, a poor wire connection somewhere, or another problem entirely.
I’ve attached the log for the match here and code is here
I would suggest putting it on a 20 amp breaker (if you have the slot). A shorter spike of current that would burn out a fuse wouldn’t flip a breaker due to a breakers longer trip time. Also, a breaker would reset during the match if it did blow, allowing your compressor to come back before the match ends. We had blown multiple fuses on our PH too, and we haven’t had any issues after we switched it to a breaker.
We had this happen at week zero and subsequently change it to a breaker rather than a fuse. Glad to know we’re not the only ones with this issue but as Usernam3 said I would recommend switching to a breaker if you have an open PDH slot
It looks like both ends of your PH power wires have exposed metal. This may not be causing your problem, but I would check/rewire those connections.
Also, it’s hard to see clearly in these photos, but it looks like some of your ground wires are black with a red stripe. This would not cause electrical problems, but may put you in breach of R624.
There are multiple points in time where the battery voltage dips low, but the compressor current does not spike. So why does it only spike at the last point in time? If this was directly due to the lower voltage increasing the current, you would see the current increase way more frequently. The only different I see between the failure point and the other points in the match is the compressor starts when the battery is low, and the voltage dips slightly lower for a moment.
Here the voltage goes low for some time, but the current stays low:
At the failure point, the voltage is not much lower than the above case. The only difference is the voltage dips slightly lower for a moment, and the compressor also turns off and back on at that moment.
I would try to find some other cause for this failure, maybe the exposed wiring as pointed out above. If it was purely due to the voltage dip this would be a considerably more common failure mode.
I agree with @bovlb that there are exposed connector pairs that my experience shows makes one vulnerable to intermittent shorts. A stray strand on one of the wires could cause a short when the robot is subjected to vibration or shock.
Use a bright flashlight to look at the area where the wires enter the connector. If the strip lengths are in the correct range and the wires are properly inserted, one should not see anything shiny in that one area. The insulation of the wire should go into the connector just a little.
Ok, so at 137.8 the battery voltage crashes enough such that the compressor switches off (more accurately ‘is switched off’) but a moment later it is switched back on again.
Start-up current is higher than running current, battery voltage is particularly low, and you have a perfect storm. Poof.
My intent here is to explain why the fuse blew. The solution is as stated above, use a breaker.
I was RI at FMA District Champs this weekend and we had a similar problem. Did you remove the check valve from the compressor? I’m assuming you are using AM-2005 compressor. If not, please post which compressor you are using.
We blew a 20A fuse with the PDH at SVR this weekend, right before our first Quarterfinal match.
Viar 90C. I’ll see if I can get logs by next weekend.
We locked up our drivetrain at the end of our prior Qualifying match, maybe there was stall current flowing resulting in major voltage sag, at the same time as the compressor tried to start up?
This is legal? I have it in my braincase I need to put the PDH on a fuse, but just got back from comp and no braincells left to go look in the rules myself.
To be honest, I have never seen the wisdom of putting the compressor on a fused circuit. Especially like the one on the CTRE PDB that also has the radio on it. Another issue that can aggravate the problem is 18G wire is a bit small to run 20A on. You will see a lot of voltage drop which aggravates the problem. If you have a substantial distance I would run a heavier gauge wire and downsize it at the PH to fit the terminal.
I know we (422) and 4099 had it occur at chcmp as well. We were instructed by a CSA to use a 30a fuse and have not had any issues since, I believe 4099 switched it to a breaker and to my knowledge also had no issues.
Agreed. The starting surge for a motor can be 6-8 X the normal running current. It is especially bad with “high-inertia loads” such as pumps and compressors. It is possible that the breakers have a longer thermal-time constant than the fuses.
Not only possible, but reality. While you can get slow-blow or time delay fuses in other form sizes I don’t think you can in the ATC-mini. Which is why in the spike relay and thomas pump days you where allowed to replace the spike relay fuse with a breaker.
In typical integer HP motor applications it is not uncommon to have the fuses sized to twice the full load amps and a second over current sized closure to the running amps with a high time delay.
The problem may also be due to the fact that those slots in the PDP are only rated for 15 amps. I recommend the same thing everyone else has, just put it on one of the 20 amp auto resetting breaker.
