Issue with power distribution board

[Jon Stratis]

Hey all - we did our first power-on test of the competition robot today. After fixing some wrong wiring for a spike (I think someone on mechanical did it when they moved it) that was popping a breaker, everything seemed to work except the radio.

We pretty quickly figured out it wasn't getting any power. The 12V light on the PDB is NOT lit, and the Wago connector next to it where the leads from the radio plug into does not get power. Powering everything off, pulling the Wago connector out, and powering on gives the same results - no 12V LED and no power to the two pins. So, a few questions:

1. Does anyone know what the internals of the PDB look like? Is it possible we shorted the wire and have a blown fuse in there somewhere?
2. Is this something likely to be user-fixable (we have a fair amount of skill, talent, and experience available, we just haven't been able to take it apart yet)?

If anyone has any ideas, please post them. Right now, the plan is to show up a little early for the meeting and swap it out with our PDB from last year (which was on our practice robot and working great), but i'd like to salvage this one if possible - otherwise we'll have to buy another one to have a replacement if needed later.

[Geek 2.0]

http://usfirst.org/uploadedFiles/PD%...39%20PM%29.zip

[Jon Stratis]

Now, if only i had Altium designer here to open those with... Thanks for the post, but i had already seen that and was hoping someone could post from their own knowledge as i can't get those open tonight.

[Radical Pi]

Make sure your battery is charged

[Jon Stratis]

It was a fresh battery. We measured at the PD terminals 12.6V, and with no motors running at all, that should be more than enough.

[kstl99]

I found a viewer fir Altium:

http://altium.com/community/download...loads_home.cfm

I did not see anything obvious but this will open the drawings.

I hope this helps

[eovnu87435ds]

it might sound dumb, but use a digital multimeter to test voltage in various places on the PDB. something similar happened to us last year, after we fried our gaming adaptor, that is...

[Jon Stratis]

Everything else checked out at the time - we had 12V going to the spikes, victors, jaguars, and everywhere else we had a breaker. The cRio was getting its 24V, and the camera output showed 5V. The other LED's were on. The problem was completely confined to the 12V output for the radio and the associated LED.

From what i know about the PDB, the breaker terminals are (more or less) straight connections to the battery, while the 12V output for the radio is regulated to remain at 12 V (it tracks to the battery above 12V, however it won't drop below until your battery gets really, really low).

[Al Skierkiewicz]

Jon,
The 12 volt radio output is a boost regulator designed to keep the radio up under brownouts on the battery. According to the schematic there is a fuse on the input of the supply and a solid state fuse on the output of the supply. I would try keeping the radio disconnected for several minutes, turn the robot on and checking the voltage again. You might have a shorted radio cable and the several minutes allow the solid state device to reset. These are surface mount devices. If that doesn't clear the problem, I would contact Frist and see if you can get another one or get yours repaired.

[EricVanWyk]

Al said everything I wanted to say that is relevant to the actual thread.

However, I'd like to remind everyone that they can get a free copy of altium at http://www.altium.com/frc2010/

Also, the 2010 files are at http://usfirst.org/roboticsprograms/....aspx?id=16337 , and the schematic is in that .zip as a .pdf.

[Jon Stratis]

Yeah, my problem last night with altium was mostly that I only had Mac's available, and didn't want to waste 2 hours standing up a virtual Windows environment.

That being said, we just finished swapping out the old PDB. Unfortunately, after sitting all night unplugged, the 12V connector did not come back to life, so i'm guessing we burned out something other than the solid state fuse.

In reconnecting everything, we checked the radio power wire, and it was sound - no shorts. We also checked the frame, and discovered a short there. After some digging around, we finally found a pinched wire near one of the Spikes. I'm guessing the plug for the radio shorted to the frame while the robot was on, and because of the pinched wire exceeded the 2A fuse.

Thanks everyone for your help!

[Russ Beavis]

What precisely did you mean by "We also checked the frame, and discovered a short there."?

The cases for the cRIO and Axis camera are internally connected to their power supply's ground connections. As a result, if you DON'T intentionally isolate those modules from your robot's frame, your frame will be directly tied to battery ground. When this happens, it becomes VERY easy for a short to the chassis to occur and ruin your day (and your PD and ...).

As the rules and inspection checklist require, it's not just a good idea to "float" your robot chassis, it's a requirement. Everyone should be using the newly-released inspection checklist over the next 2 days before shipping your robot.

Russ

[Jon Stratis]

We ran the multimeter between the + terminal on the PDB and the frame - the pinched wire made the frame positively charged, and we think the plug for the radio then hit the frame, completing the circuit and blowing the 12V output.

As you can see here, we've gone to great lengths to ensure the cRio is completely isolated - an ESD safe, non conductive plastic mount, and surrounded on all sides with an ESD safe, non conductive foam. The cRio is definitely NOT connected to the frame. Likewise, the camera is mounted on the same ESD safe, non conductive plastic as the cRio, ensuring it is NOT connected to the frame.

Once we fixed the pinched wire, we didn't have any more trouble with our frame, within the limits of the rules/checklist.

However... being as overly paranoid as we are, we did discover a small short with one of the CIM motors. There's no visible shorts in the motor leads (we checked), but we did measure 5-6 M Ohms between the motor lead and the chassis. The other 4 CIM's did not exhibit this behavior. Any ideas on that one?

[Al Skierkiewicz]

Jon,
What you describe is the "smoking gun" we all look for. The pinched wire and the radio connector contacting frame would have produced a significant short on the +12 volt power supply. The megohm reading on a motor is not significant, and in all probability was the person who performing the measurement leaning on the frame or touching the motor. You were likely reading the resistance of the body. This reading is also influenced by humidity. If that motor was in a draft and had a little condensation inside, the reading would also be in that range.