Blowing 60 Amp fuse

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Posted by Joe Johnson, Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.

Posted on 3/19/99 5:17 PM MST



Has anyone else had any problems blowing the 60 Amp fuse?

We have had 2 cases in all our practices, matches, etc.

One could have been a fluke. Two scares me to sleeplessness.

We think we have found a pretty good work around to make sure it never happens again, but... I am wondering if anyone else has seen this problem.

Up until this year, we NEVER had one of these fuses blow except when it was protecting against a dead short. Perhaps this year, with all the great motors and the new Victors, we have reached another constaint that teams will have to live within.

I'll have to admit, this is a kind of dangerous game coming so close to the edge of a contraint that essentially means your robot doesn't move any more for the rest of the match, but... ...if it was easy, everyone would have already done it ;-)

Joe J.

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Posted by Allen Smith, Engineer on team #7, Knights, from Parkville High School and Black & Decker/AAI/Raytheon.

Posted on 3/20/99 2:27 PM MST


In Reply to: Blowing 60 Amp fuse posted by Joe Johnson on 3/19/99 5:17 PM MST:



We were your partners when you blew that fuse in the quarter-finals at Philly
so I have been thinking about this problem also. First, I am amazed at the
traction you get from your wheels. Do you have some secret treatment to
keep them from slipping? If your wheels would slip you would of course
have less pulling power but the slipping would act as a "fuse" keeping
the motor operating in an acceptable region. This is what happens with our
robot and we have yet to blow a fuse or burn up a speed controller. A
possible solution, and I'm just speculating here and would love comments,
would be to have 5 to 10 feet of coiled wire between your ground bus and
your battery acting as a current monitoring shunt. Connect the ground bus
that is on the far side of the coil of wire from the battery to an analog
input on the controler, assuming you have a few tens of milliohms in that
coil your controller should be able to sense the total current flowing
and do something about it like light a warning led or cut back on the PWM
signal going to the motors. It would be nice to have a filter on the signal
going into the controller and a zener to clamp it to no more than 5 volts
but with only kit parts I don't think this is possible.

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Posted by Daniel, Student on team #192, Gunn Robotics Team, from Henry M Gunn Senior High School and NASA Ames.

Posted on 3/22/99 12:19 AM MST


In Reply to: Blowing 60 Amp fuse posted by Joe Johnson on 3/19/99 5:17 PM MST:



Hey Joe!
I was wondering what the context was (i.e. what happened just before it blew?). I know the van doors are rated to draw about 30 or so amps when stalled. Could you have stalled both van door motors? Whatever the case, more info would be nice!

Good luck with that!
-Daniel

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Posted by Joe Johnson, Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.

Posted on 3/22/99 6:49 PM MST


In Reply to: Re: Blowing 60 Amp fuse posted by Daniel on 3/22/99 12:19 AM MST:



When it comes to stall current the Delphi Power Sliding Door Motors are babes in the woods!

I think the Fisher Price motors are about 70Amps and the Drill motors are over 100Amps.

Both times we blew that fuse, I think that we basically were picking up the puck with our arm, that put one 30Amp PSD motor in stall. With the extra weight on the wheels we stalled all 4 wheels which means 2 drill motors and 2 Fisher Price motors. Even with each circuit nominally limited to 30Amps by the circuit breakers, that still adds up to 150Amps.

I haven't looked it up in a while, but from memory, I think the 60Amp fuse is rated to blow in something like 20 seconds at 200% nominal rating. So... At 150Amps, it is very possible to blow that fuse in considerably less time

Joe J.

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Posted by Daniel, Student on team #192, Gunn Robotics Team, from Henry M Gunn Senior High School and NASA Ames.

Posted on 3/22/99 8:35 PM MST


In Reply to: PSD motors are babes in the woods... posted by Joe Johnson on 3/22/99 6:49 PM MST:



WOW!

The reason I was wondering if it was the van door motors was because I didn't even know it was POSSIBLE to stall a drivetrain. Our wheels just slip when the robot has that much force working against it! Somehow you guys have managed to get some amazing traction on those wheels of yours!! Please, do tell...what's your secret? =)

-Daniel (in awe)


PS - Looks like traction may be a dangerous tradeoff..