Suicidal Victor 884's...

[Caleb Fulton]

We had a Victor start to smoke on our prototype bot after only around 5 minutes of running around on the ramp...

We took off the fan and saw that one of the SCR's or (whatever they are) had cracked IN HALF and shorted out the two next to it, causing the plastic to melt and smoke, etc...

We were using the Bosch motors with a 30 amp fuse (the 40's were not here yet) and it was a very random event... Does anyone have any ideas as to what went wrong? Are these things still under warranty?

[HolyMasamune]

The power it draws was probably too much for ur 30 amp fuse box to handle...there IS a reason why you need 40 amps for motors...

[Curtis Williams]

But that shouldn't cause any problems. It would actually make them less likely to fail due to current.

[Caleb Fulton]

The 30a would just trip if it was drawing too much power...

If I were using a 60a, for example, then I could see why this could have happened.

[Harrison]

Had the victor been dropped or something? Like, was it already damaged, and it just took those 5 mins for it to heat up enough for it to smoke?

I would contact FIRST (and/or Innovation First) about this - you shouldn't have to pay for it if it came like that.

(also, running the 30A fuse w/ the 884 should ensure it NEVER gets too much current [we have 884's this year because we now have 40A fuses])

[Al Skierkiewicz]

The events you describe are unusual for speed controllers unless they are hooked up backwards or shorted. The devices you saw when you removed the fan are the FET (field effect transistors) that do the switching to the motor. There are four sets of three FET in parallel. When the motor is running two banks of FETs are turned on at a time.
It is possible you had a early failure (we call it "infant death" since it occurs very early in it's life) due to defective parts but I suspect shorted wiring, metal flakes in the controller or damaged motor. Since you were using the new drill motors and there are known problems with these when handled wrong, I would check the motor and make sure the brush assy is still in good shape.
"We took off the fan and saw that one of the SCR's or (whatever they are) had cracked IN HALF and shorted out the two next to it, causing the plastic to melt and smoke, etc..." This is a normal failure mode for these devices in that at high currents, there is a lot of internal heat generated. However, one dead device probably did not kill the other two, they all went together as a team. Inserting another engineering slogan here..."They gave their life to save a fuse!"

[Caleb Fulton]

The wiring couldn't have been backwards because it was exactly the same as the other side.

Could I assume that a short would trip the fuse before it started SMOKING?

Is it possible that it was a random defect?

[Matt Reiland]

Check this out

http://forums.delphiforums.com/n/mb/...jpg&frames=yes

Specifically related to Victors tearing up the FET's, one guy uses a zip tie through the hole in the FET's on the corners to insulate them from their neigbors and there is a nice pic.

[Al Skierkiewicz]

Caleb,
Like I said in an earlier post, infant mortality is always a possibility. There may even be a defect in the controller. (solder splash, incorrect device, etc.)
Yes, the breaker should have been tripping, RC should have been resetting, etc. if there was a wiring error. Be sure that the controller was the cause and not the effect before powering up a new controller. A picture would be a nice thing if you could post a closeup of the damaged transistors. Most people never get a chance to see solid state destruction at it's finest.

[Lloyd Burns]

Another possibility is this:

When the Victor tells a motor to stop, the motor, in its obstinate way complains, "I can't, I got this stupid robot on my back, but I'll try." The motor continues to generate current (Lenz' law), sending it through the Victor's FETs in a loop. This loop is independent of the upstream fusing, occuring between motor and Victor only.

IFI used to have a paper that 'bragged' about a spike of 300 A being handled by a Victor (883), when subjected to full forward, , accelerate to speed, arrrgh...no!!!!, full reverse.

Perhaps you were in brake mode, which would make it more likely.

As Al says, this could be normal mortality. I suggest you talk to IFI about it. They may replace it.

-=-=-=-=

After reading AL's last again, I must caution against drilling Aluminum over Victors. Once the controls are mounted, all machining must be done in another room, even another country, as Aluminum has an affinity for the circuit board material in Victors, and will easily swerve 20 feet to the side in falling 3 feet to the floor.

To quote a Rudyard Kipling phrase, it is due to "The Heartbreaking Perversity of Inanimate Things".

[Joe Ross]

I heard a story that when IFI did the first victor speed controllers, they had everyone send the failed ones back. They received 6. 5 were dead because of metal shavings inside (team's fault). The 6th was so badly damaged that what cause the damage could not be determined.

Whether that story is true or not, I don't know.

[Caleb Fulton]

Thanks for the help, everyone...I'll try to post a pic soon

[Lloyd Burns]

Originally posted by Joe Ross
I heard a story that when IFI did the first victor speed controllers, they had everyone send the failed ones back. They received 6. 5 were dead because of metal shavings inside (team's fault). The 6th was so badly damaged that what cause the damage could not be determined.

Whether that story is true or not, I don't know.

The first Victors, a big improvemant on the tiny Tekins, did not have the cover of plastic in the area inside the FET quadrangle. They probably cover the circuit board better now than they used to. We turned in one in Florida, that year.

[Lord Nerdlinger]

Same thing happened to our first victor, ran for a few minutes and then sparked and started smoking (also running off the 30 amp) it burst into flames before we hit the off swtich.

We ended up not neating that 4th victor, but should we try to get a replacement anyway?

[Rob Colatutto]

the motors shouldn't be drawing more than 20amp...the bosch under normal driving only draws about 16amp. the reason they have 40amp breakers this year was so people would start designing thier bot to be strong, they want to see crazy transmitions