Fisher Price Breaker Size

What size breaker would you recommend using for a fisher price motor?
We were thinking 40 amp but I think it may be to high? Would 20 to 30 amp be better?

Thank you for any help you can provide.


What application are you using it for? This will help determine what size you can use safely. For a generic FP, without knowing what it’s being used for, I’d say 20A is too low, but then again, it might just be an orbit-ball shaker.

The rules are pretty much silent on the matter, which is probably why you’re asking.

Well I believe we are using three. One will be for our lift system. So It will be spinning relatively fast but nowhere near free spin. The other two will be spinning faster but not constantly. The main one I’m concerned about is our lift system one. I’m thinking about moving it a 30 amp breaker since it will probably get hot.

As there are only two FP motors in the kit, and additional FP motors are not allowed in <R51>, only 2 of these motors can be used.

Fast does not constitute power… or amperage… by itself

You need to figure out or have someone help you figure out the power consumption of the motors you are using.

A breaker will not help you with a “hot” motor… A “hot” motor is an indication that you are not at the optimum for that motor… or that you are pushing the motor…

Remember that you must change the gauge of your wiring if you use different breakers… You may always use a smaller gauge of wire…for that breaker but never a higher one. The lower gauge wire will not offer as much resistance because it is bigger. (The higher the gauge of a wire… the smaller it is…)

You can push more current through low gauge wires than you can higher gauges just like pushing water through a big pipe. (sort of…)
but remember that resistance goes up with temperature so hot wires are more resistant than cool wires.

You want cool wires…it will gain you efficiency…

The main thing is to figure out what is the amperage load that you are needing to pull through that wire/breaker system.

Good luck with this!!

A proper mechanical design should never trip it’s breaker unless a very abnormal condition exists. Take a look at the motor curve, see what torque the motor can produce at the current your desired breaker can supply, and design your system for the motor to be loaded less than that.

I traditionally try to use the largest breaker allowed, since it will result in being able to run your system with a higher load on the motor.

If your using three FP you will not be in compliance with the rules.

If an FP gets hot you’re in for trouble. These are fan motors. When they get a bit too hot the plastic fan starts slipping and fails to spin making it even hotter. You may want to consider additional cooling.

The peak power point on the FP is 40 amps at 7500 RPM. I would say that you can safely operate at this point only at 7500 RPM and with additional cooling. If you trip this breaker at lower RPM then you are geared too low.

30 amps is probably a good sizing. It’s best to make sure that you are geared such that the motor runs between 7500 and 15000 RPM and that when loaded it does not fall below 7500.

Only 2 FP motors are allowed and they must be connected to 30A minimimum breaker per the rules. I recommend speed controllers over relays, since the relay is only rated at 20A by default.

I’d appreciate seeing which rules on this. I’ll go with you on the speed controllers, referencing <R54-A>, but I didn’t see any rules on minimum size for a breaker (other than in the wiring rules, which are wires for given sizes of breakers).

I don’t want to get into symantics here, but a 20A relay will burn if it is pushed beyond its limits. One stuck ball and the FP motor will push the current limits before it too burns out.With a relay, there is no stopping the destructive current and possibly both devices will be lost. A speed controller handles the current surge better and may go into protective shutdown rather than release the magic smoke.

You mentioned wire gauge, the fact that FP motors spec a certain guage makes it mandatory to use a device that can handle the current required of that guage. Sure, it may only draw 15A, but catastrophic motor failure in a stall condition may draw upwards of 50A from the FP motor. Avoiding wiring fires is always desirable. Better to plan ahead of the safety inspectors than to hope you won’t be caught in violation.

IMHO the application rules are R46A and R54A.

You have to connect the FP motors to a Jaguar or Victor. A relay is not allowed.

You can supply the speed controller with 20A, 30A, or 40A and it must be dedicated to that speed controller.

20A may be a better choice if you are not sure that your gearing allows the FP to run fast enough not to burn itself up.

Just a personal preference here. 20AMPs

No science or anything behind my reasoning (well… actually there is, but I’m not going to get into the heat dissipation stuff…)

That little motor has to get rid of a lot of heat just at 20AMPs. At 30 or 40AMPs, I can see that motor going up in smoke in a hurry if something goes amiss. At 20AMPs, you at least have a few trips before it really starts damaging the motor.

Jim, I’m not really sure what your post is trying to say.

The FPs must be connected to a speed controller based on rule <R54-A> (as Eric mentioned).

These speed controllers can then be connected to 20, 30, or 40 Amp breakers. The required wire gauge is based on the breaker used.

If someone wants to run an FP off a 20 Amp breaker they would be allowed to do so. They could then use wire as small as 18 gauge to wire this branch. Depending on where on the torque/speed curve the motor is being run, this may or may not produce desired performance, but it is perfectly legal.

In fact, you could wire your CIMs through 20A breakers if you wanted (note: this is almost certainly a bad idea)

In my wiring, I treat the FP as equivalent to a CIM.This motor is powerful and fragile. Allowing only 20A of current is pretty low for this motor, but I do not know what applications you have in mind for it. I prefer to stay on the high side of the curve rather than the low side.

Nippon-Denso 18.6
Nippon-Denso 18.6
Keyang 11.8 19
Fisher-Price 70
Globe 21.58
CIM 133
Mabuchi 6.2
Banebots 37
Compressor start 25
These are the stall currents for the motors in the 2009 KOP.

<R54> All electrical loads (motors, actuators, compressors) must be controlled by relay or PWM output signals sent by the Digital Sidecar to an appropriate power regulating device
A. Each CIM motor and Fisher-Price motor must be connected to one Victor or Jaguar speed controller. They must not be connected to relay modules.
B. Servos must be directly connected to the PWM ports on the Digital Sidecar. They must not be connected to speed controllers or relay modules.
C. If used, the compressor must be connected to one Spike relay module.
D. Each other electrical load (motors or actuators) must be connected to one Victor or Jaguar speed controller or one Spike relay module.

Please note that only motors that are 20 amps or less stall current can be powered by relay(Spike) as that is the relay specification. An exception to this rule is the compressor which has a start current more than double it’s run current. For this relay only you may substitute (read this as “should”) a 20 amp circuit breaker in place of the relay mounted 20 amp fuse.

Any team may choose to run any motor from any breaker as long as the current rating and wire size rules are maintained. However, sound electrical practice and the rules allow you to size your breaker/wire/motor appropriately.
The 2009 game is unlikely to cause high currents in drive motors. That being said my normal recommendation for #10 wire to feed CIM motors and FP motors may not produce significant gains in this year’s design only. Electrical rules allow you to use #12 wire with 40 amp circuit breakers (See R45 for all specifications) and #14 wire with 30 amp breakers. Therefore, should you desire maximum performance over all possible game conditions, my recommendations would be for #12 minimum for FP and CIM motors fed with 40 amp breakers. The Banebot motors can be fed with 20 or 30 amp branch circuits depending on your design, transmission and intended use. Please be advised that the Denso, FP and Keyang motors have internal thermal breakers in addition to any external electrical protection you provide.

This year, any Spike may be operated with a 20 A circuit breaker in place. (Previously, only the one on the compressor could be replaced.)

I believe that is a misprint, so I am awaiting an update. IFI specifications for this part require a 20 amp fuse.

I have never seen any good reason to only allow it on the compressor. I’m aware that the compressor was blowing the 20A fuses and thats why they allowed it, but why stop there, who cares if we put the breakers in the other spikes too, sure, they’ll probably never blow, but why run the risk of one blowing and losing that device for the rest of the match, when it could come back in a second or two.

Actually this year you may do this for any relay per <R59-F>

<R59> The control system is designed to allow wireless control of the ROBOTS. The Driver Station, cRIO Mobile Device Controller, digital sidecar, breakout boards, power distribution module, speed controllers, relay modules, wireless bridge, batteries, and battery charger shall not be
tampered with, modified, or adjusted in any way (tampering includes drilling, cutting, machining, gluing, rewiring, disassembling, etc.), with the following exceptions:

F. The fuse on the Spike relays may be replaced with a 20 Amp Snap-Action circuit breaker.

This is an IFI recommendation that First has applied in the past. Compressor start can go as high as 25 amps but run is only 10-12 amps. This is a guarantee to blow the fuse even though it is an extremely short duration. However, used in other services, a breaker could easily allow more than 20 amps continuous without trip which is enough to destroy the relay.