Victor connect to 30 A instead of 40 A

[seg9585]

This is not quite right.

When choosing a breaker, choose it by the wire gauge attached to that breaker as breakers and fuses only protect the wiring.

Now to go further, you choose your wire gauge and drive circuit(victor, talon, spike, etc.) by the load (motor, solenoid, etc.) on the wire.

What’s “not quite right”? I don’t know about you, but I choose my wire based on the motor and its associated load, and select a breaker current limit accordingly. You really do it the other way around?

With that logic I feel like this would be a real conversation:

Student: “This CIM will give us all the torque we need to run our shooter!”
Mentor: “Yeah but we already cut and crimped this awesome 18 gauge wire, so pick a different motor compatible with it”
Student: “But we won’t get enough torque from anything pulling under 20 amps”
Mentor: “I guess your CIM solution was destined to fail then”

[Daniel_LaFleur]

What’s “not quite right”? I don’t know about you, but I choose my wire based on the motor and its associated load, and select a breaker current limit accordingly. You really do it the other way around?

<SNIP>

My previous statement was, in effect, you choose the wire size by the current draw of the load (motor, etc.) and then you choose the breaker by the wire size.

Breakers (and fuses) do not limit current. they open the circuit when the bimetallic surfaces get too hot. In the case of auto-resetting breakers they then close the circuit when the bimetallic surfaces cool.

Again, size the breaker (or fuse) for the wires connected to it.

[FrankJ]

Breakers (and fuses) do not limit current. they open the circuit when the bimetallic surfaces get too hot. In the case of auto-resetting breakers they then close the circuit when the bimetallic surfaces cool.

Granted they don’t limit current in the same way as certain power supplies do (like the jag), but they do limit current. That is pretty much their function.

[Alan_Anderson]

Granted they don’t limit current in the same way as certain power supplies do (like the jag), but they do limit current. That is pretty much their function.

I can see how it’s possible to choose definitions so that your viewpoint is valid. But I think the common definition of “limit current” in this context disagrees with you.

The function of a circuit breaker is to interrupt the current, not to limit it. A 20 amp fuse or circuit breaker does not limit the current to 20 amps. If you try to draw more than 20 amps for long enough to trip the breaker, the current is stopped. That’s not what current limiting means in my book.

[Al_Skierkiewicz]

I make recommendations based on motor design. If your design goal is based on getting a full 12 volts to the motor, then you need to increase the size of the wire feeding the controller and the motor and then make them as short as possible. The rule of thumb I came up with is the “wire foot”. 1 foot of #10 wire passing 100 amps will drop 0.1 volt. So if you have a CIM motor that you expect to run in the high current part of the motor curve, and feed the motor controller with 1 foot wires and then the CIM motor has 1 foot wires, that is a total of 4 feet of wire. (Remember the red and black wires carry the same current.) So that is 4 wire feet, 0.4 volt drop. Add 4 wire feet for a Jag or Talon, 6 for a Victor and your design curve CIM is now running at 11.2 volts on a good day neglecting any loss in the #6 and PDB. So as these losses start to add up, you can guess why some electrical designs cause robots to drive anything but straight. 4 feet of wire on one drive train compared to a few inches on the other side, unbalances the current sent to both sides. You cannot drive straight unless you compensate for the imbalance.