Does any one know if you could us 40 amp maxi fuses for the new fisher price?
Use 20 or 30 amp breakers with the Fischer Prices.
You could, but I wouldn’t. Since a FP stalls at 60-70A (don’t remember the specs for the new 9015 too well), a 40A breaker will only pop after it has been running at around 1/3 of free speed for a while; unfortunately, FPs don’t like being run that slow for extended periods. We ran one on a 30A last year without issue, and will probably do the same this year (assuming we use the FPs this year). A 20A would probably work well too.
The Fisher Price motor is speced at 70 amps in stall. You can run whatever size breaker you want as long as it is sized for the wire you are using. If designed for running at well less than 30 amps then you can install a 30 amp circuit breaker if that meets with your design criteria.
A word of caution, however, the FP motor is very unhappy when running on the low RPM side of the curve. The internal fan is not very efficient at low RPM so the motor tends to over heat. This is normally not a problem if it weren’t for the thermal breaker inside the motor. Once the motor temp is hot, the breaker trips and the motor stops for a period of time. Once the temp is elevated, each trip occurs at a lower current and there is a greater amount of time before reset.
Just as a small word of caution… I had a VEX project that used the FP motor as the drive motor, and had a 20AMP circuit breaker on it, yet, the FP motor still burned up and gave a nasty rotten odor off. (It still ran, but it didn’t sound good, and it smelled aweful). Now imagine it with a 40AMP… not a very good idea. If we had a choice, I would run it with a 5 or 10AMP breaker.
What would happen if we run the FPs with a high load but for very short periods of time (one revolution or less)?
Kat,
It is hard to predict. If you are asking that the motor only runs for a turn or two at heavy load then the answer is likely no problem. It you are running at normal speed with intermittant heavy load, the answer is dependent on how often the heavy load is applied. The FP motor is a powerful motor for it’s size but as with any motor, getting rid of heat is an issue. The FP designers made some tradeoffs such that the integral fan needs to spin at high RPM (the fan is attached to the motor shaft. You can see it if you look in the slots of the motor.). One little quirck about this motor is when it gets hot, the fan blades release from the shaft and stop moving altogether. If you look at the motor curves you can get an idea where the more efficient operating RPMs occur. Base you design on that type of decision. Don’t hide the motor inside an enclosure and make sure the cooling slots remain open in your mounting design.
Ok thank you, Al.
Circuit breakers are not intended to protect motors. They are there to protect the wiring. You can burn up a Fisher Price motor at relatively low current if you run it at low speed under a moderate load for enough time. You can also run a Fisher Price motor at high current for a long time if it’s spinning fast enough for its internal fan to be effective.