Help with Victor 884s
 

This past Saturday, the team hooked up last year's Victors to this years trannys. (4 motors, each to their own Victor.) Immediately after turning the power on, there was sparking and a cracking sound. We shut power off, pulled the PWMs out of the two Victors that were the problem, and pulled all of the wires from these same Victors. We turned power on to test the other tranny, but the Victor(s) with no wires sparked and made the same cracking sound. On the wooden board, the Victors were mounted so that they were all butted up against one-another.

1. What would have caused the Victor(s) to spark with no wires going to them?

2. When I looked at the two Victors, one of them had the plastic at the base of three FETs on one side that were cracked through. Is it likely that other components on this Victor were blown, or is it just the FETs? (I opened the Victor and cleaned it with IPA.) The second Victor didn't have any cracks near the FETs, and I didn't open it.

Thanks,
indieFan

Re: Help with Victor 884s
 

Wow. What a weird situation. We're in our third year now, and, over the years have hooked up many Victors many times. We've only "toasted" one. (Usually my students are much more efficient at breaking stuff!) I keep it on my desk to show the students how quickly a hundred dollar bill (and change) can go up in smoke.

It happened late one evening in our rookie year... we had pulled the electrical board apart, re-wired it, and put it back in the robot. It was late, we were tired... I didn't check, and the students didn't notice that all three Victors on the board were backwards.... the motor connections were attached to the power supply side and vice-versa.

Amazingly they ran (very little load, the robot was up on blocks) for a little while, but slowly... when one stopped responding we realized we had a problem. Again, to IFI's credit, only one of the three was blown... a good thing, as we only had one spare, and no money to buy more.

The blown Victor had cracked FETs, just as you describe. I haven't tried replacing them... in some ways it has more value as a warning than it would as a functional speed control.

So if your motors were under load when you hooked them up, and the Victors were backwards, that might have caused them to fail instantaneously.

As for the sparking after you disconnected all the wires... totally weird. The only thing I can think of is that when you mount them to a board using #8 machine screws that the machine screws come very close to the power hook ups on one corner. Last year we switched to nylon screws to save weight and reduce the chances of shorting.

Our condolences on the loss of your Victors. Hopefully you have the time and resources to replace them.

Jason

Re: Help with Victor 884s
 

Indie,
The sound you describe is the FETs blowing up. Sometimes there is enough heat build up tha it blows the case off. Only two casues for this, hooking the Victors up backwards, or conductive metal filings in the device. (drilling operations on the robot without covering the controllers.) When they are mounted very close together it is hard to tell where the wires go. An ohm meter check before powering can eliminate this in the future. Check continuity from the breaker panel to the victor before applying power.

Re: Help with Victor 884s
 

Having a compressed air line somewhere helps, clean out the victor's before powering on for the day, will almost always spare you from the metal shavings problem. We've blown two like this... One last year and one this year. If you school has an auto shop they'll most likley have a compressed air line there. At $180 each (I think) it hurts when you lose one.

Re: Help with Victor 884s
 

Or, you could make an air line yourself. We grabbed to of our unopened compressors, a handful of fitting, some teflon tape, pneumatic tubing, a manual valve, a couple 20 amp breakers, Anderson, six (eight?) slot ATC panel, and threw them on some plywood. Mix, stir and viola! A ghetto electronics cleaner. Works pretty well too... unless someone doesn't watch the pressure gauge and it blows up... nobody's done that YET, and hopefully no one will.

Re: Help with Victor 884s
 

Hey Luke, I hope you aren't planning to bring that to competition.

Re: Help with Victor 884s
 

The compressors have a release valve that triggers at about 120psi, so you shouldn't be blowing anything up :p

Re: Help with Victor 884s
 

Uhhhh... I think your information might be a bit bad. When I was distracted for a second it got over 130 psi... then we released the pressure with our output tube pointed straight up. The dust from the ceiling floated around for a good while. Overall though it's quite fun to have, and useful! It might even end up on our cart for this year. (Along with a couple pressure switches.)

Re: Help with Victor 884s
 

There is a pressure release valve in the kit that you are supposed to attach to your compressor. It is set to overflow at 125PSI. If you don't have this piece installed, you really need to do so, or you risk damaging your equipment and yourself.

Re: Help with Victor 884s
 

Joe the pressure relief valve is already attached to the compressor when you recieve it. It is not precise and will pop off between 125 and 135 PSI but a compressor needs to have an electrical cutoff in case the mechanical relief doesn't operate. Hence my query about bringing the device in it's current configuration, to competition. Safety captains be watchful.