FP burning out

[Max Lobovsky]

Today we had an FP burn out on us when using it as the winch in our forklift. I'm trying to figure out why it happened and i was wondering if anyone had experience with them burning. Potential causes in this case were

a side-loaded output axle
sawdust, aluminum shavings, or other particles in the motor
stalling

Because the motor has a 70 amp stall current and we had the 40 amp breaker on and because it stalled at most for 2 or 3 seconds before releasing serious smoke, I'm tending to think something got inside. If anyone has any idea, that would be a great help, thanks.

[Dan Richardson]

We had 2 motors burn out today, and we have a 30 amp breaker on it ( your only supposed to use the 30's I believe... not the 40's ) I think you were also a bit off on the stall I think its only at 58 amps.

However, just because you have a 30 amp fuse on it.. it can still spike above for a short period of time before the breaker trips or you blow the fuse. You could be spiking for a few seconds getting it really hot and then off. Thats what seems to happened to ours.

Also, be careful not to run them for too long at under too high of torque. It seems in our motors the insulation actually burned off and the coils began to touch. Shorting the motors and binding them up quite a bit. They would still work but when ne sort of torque was applied to it.. Smoke everywhere.

All in all, our team seems to finding that what these motors are " rated " at don't seem to be holding true. We doubled up on the motors and had extreme overkill ( as in 1 motor could do all the work ) and made sure with amp current sensors that we had an equal share and they still burned out very quickly when it locked for a very short second.

They heat up quickly, so let them cool off a bunch don't run them constantly, and try to keep the amps down around 20.. their constant running is rated at 28 amps their techinical " safe zone. " So try to shoot below.. when in doubt overkill but if you can't.. make sure you make sure! that they are running correctly..

These are but generals, I can't come to particulares without knowing your system better or offer ne other advise .. all I can say those fp's can be a pain so be careful with them. Bring plenty of spares to comps.

Dan

[Max Lobovsky]

Originally Posted by Stud Man Dan

we have a 30 amp breaker on it ( your only supposed to use the 30's I believe... not the 40's ) I think you were also a bit off on the stall I think its only at 58 amps.

I'll have to tell the electrical people about the fuses but I'm almost defenitley sure that this year the stall current is 70 amps (compared to 57 from previous years, i think thats what your thinking of). You can check some posts in this forum about the stats.

Regardless, I really dont understand how it could fry itself so completely in 2 or 3 seconds. What insulation burning off were you referring to?

[shawny963]

Attention!!!!

all the fp motors seem to have been manufactured such that the brushes are turned 90 degrees from where they should be. So essentially they are contoured incorrectly with relation to the commutator. This requires in a dramatic decrease in contact in the motor. Im no electronics expert but this obviously causes to motors to run less than optimally and have a shortened life. This can be fixed, but id rather you talk to someone on my team who knows more about this issue than I so I dont give bad advice on the process. If you need help to fix this email me at shawny963@wi.rr.com immediately. This can be fixed in minutes.

[Adam Y.]

Originally Posted by shawny963

Attention!!!!

all the fp motors seem to have been manufactured such that the brushes are turned 90 degrees from where they should be. So essentially they are contoured incorrectly with relation to the commutator. This requires in a dramatic decrease in contact in the motor. Im no electronics expert but this obviously causes to motors to run less than optimally and have a shortened life. This can be fixed, but id rather you talk to someone on my team who knows more about this issue than I so I dont give bad advice on the process. If you need help to fix this email me at shawny963@wi.rr.com immediately. This can be fixed in minutes.

Its not surprising. The same situation is present with the drill motors. They do that on delibrately because it provides more speed?? in one direction. Its called changing the timing. The power output should be the same no mattter what. Personaly our team never smoked a fisher price motor when it was on our drivetrain one year. Unfortuantely the gearboxes failed. Also you can't change the motors in any way.

[Joe Ross]

Circuit breakers don't trip immediately when the current exceeds the limit. It takes time for the materials inside to heat up and open the circuit. The more current you put through it, the faster it heats up and the shorter time it takes to open the circuit.

If you look at the spec sheet for the 20 & 30 amp breakers, you'll see that it takes them between 3 and 6 seconds to trip at 200% of thier rated current. The 40 amp breaker would take even longer to trip. Thus, you were able to burn out the motor before the breaker tripped. That is one reason that FIRST requires a 30 amp breaker on the FP motors, rather then a 40.

[Joe Johnson]

Originally Posted by maxlobovsky

Today we had an FP burn out on us when using it as the winch in our forklift. I'm trying to figure out why it happened and i was wondering if anyone had experience with them burning. Potential causes in this case were

a side-loaded output axle
sawdust, aluminum shavings, or other particles in the motor
stalling

Because the motor has a 70 amp stall current and we had the 40 amp breaker on and because it stalled at most for 2 or 3 seconds before releasing serious smoke, I'm tending to think something got inside. If anyone has any idea, that would be a great help, thanks.

The Fisher Price motors are EASILY the highest power per volume motor in the kit. More importantly, it has the highest power per surface area of the motor.

Since power in = power out + heat generated, the heat generated per volume is much larger than the other motors. Again, more importantly, the heat generated per unit surface area is larger than the other motors in the kit.

Since heat disipated is proportional to the (surface area * Delta T), basically, the delta T of this motor (its rise in temperature above ambient) is higher than other motors in the kit.

Bottom line: We FIRST teams toast more Fisher Price motors than your typical dinner toasts bread ;-)

Try not to stall them for very long (if ever) and you will be fine, run them near stall for more than a hand full of seconds is just asking for the sickening smell of fried insulation.

Joe J.