Victor connect to 30 A instead of 40 A

Technical Electrical
#6

I think “less is better” isn’t accurate.

Using a 30 amp fuse does not mean “less current” flowing. It just means that once the current draw reaches 30 amps, it’ll pop, instead of at 40. That is to say, fuse doesn’t determine current… a victor in identical conditions will draw X current in both the 30 amp and 40 amp fuse, but will not draw > 30 amps in the 30 amp fuse.

Motor controllers cooler - not really. Again, this is dependent on the stress involved. They’ll only be cooler by the consequence of stopping due to a fuse pop.

Fuse trips easier - no bueno.

Thinner wires - more resistance, meaning hotter wires. For most motor applications you can end up pulling quite a bit of current which in extreme cases could even melt your wires.

#7

When choosing breaker (and subsequent wire size), I typically consider 2 factors:

  • Motor selection
  • Duration of usage in match

I use 40amp on CIMs almost exclusively due to their power draw. For smaller motors like PG71/188, usually or 30 amp unless its a continuous-usage motor (for example some conveyors) because of the heat produced in the wiring. Window motors usually 20 amp, Mini CIM either 30 or 40, Van Door/Snow Blower 30 amp.

Moral of the story, determine the power draw based on your motors, not speed controllers. I recommend checking the stall current draw for each motor (those specs are widely available) and judge accordingly.

#8

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.

#9

Wire size is not a problem. The wire size is a minimum not maximum. You can use the same size wire on a 30a as you can on a 40a.

#10

Only as long as the wire gauge is good for 40A

#11

The idea that the breaker is sized just to protect the wire is facilities logic. When you size breakers or other over current devices on a piece of equipment, like a robot, you size them for the protection of the load. You size the wire to suit.

A smaller breaker won’t hurt your victor, it might save your motor.

#12

Sorry, FrankJ, but I respectfully disagree.

A breaker or fuse is no where near fast enough to protect a load from overcurrent (look at the trip specs).It is, instead, there to protect the rest of the wiring from an overcurrent event once a electrical failure has occurred. Thus, you size the wire to suit the load and you size the fuse/breaker to protect the wiring.

#13

Daniel, a breaker is there to protect load and the wiring. If you use 12ga wire instead of 14ga with a 30a breaker you are actually adding a level of security. The wire will be much less likely to be damaged if you have a load that trips the breaker.

#14

Admittedly the snap action breakers we use don’t have the best protection. The right fuse will clear in half a wave length. The right circuit breaker is right behind that.

Most of the legal motors have out grown the Spike since a momentary stall or loaded start will blow the fuse the spike. So that leaves the talons, victors, & jags that will happily burn out the smaller motors. Sizing the breaker closer to the running load of the motor will give some protection since that is the legal option.

In other applications… You use molded case breakers or fuses for dead short protection for motor/controllers in conjunction with overload devices that are not fast enough for a short. The rectifiers in my plant use fast acting fuses to protect solid state components. I use fuses on my plant IO so one short doesn’t take down the entire control system. A typical industrial power supply will current limit & chug happily along at a dead short so wire protection is not an issue.

#15

A robot battery, on the other hand, will happily dump hundreds of amps into a short. Protecting against wires catching on fire is definitely an issue.

There are only two things that can reasonably cause a robot circuit breaker to trip. One is a short in the wiring – perhaps a connector has come loose and randomly touches something it shouldn’t, or a mechanism has damaged the insulation. The breaker must be sized to keep the current from exceeding what the wires are safely capable of carrying. The other is a fault in whatever the wires are connected to – either an electrical component has failed and is pulling much more current than it’s designed to, or a motor is stalled because of a mechanical (or design) failure. In almost every case, the damage is what causes the overcurrent condition in the first place, so even a fast-acting fuse won’t prevent it.

#16

I did sort of diverge a bit. My point was and still is the breakers are there for more than protecting the wires. Stalling motors or a bad motor controller is probably the most common way to trip the snap action breakers on the robot.

I heard tell last year that some of the 6 cim drives were tripping the main breaker last year.

#17

Guys,
The breaker vs. wire size tables are lifted from the NEC (National Electrical Code) recommendations for open frame DC wiring based on temperature rise in the wire. A little adjustment has been made based on short time periods instead of continuous loaded currents. Snap action breakers do not limit current. That is to say, a 30 amp breaker will pass 100 amps as well as it will pass 30 amps. The only difference will be the length of time it will continue to pass that current.

#18

I thought the whole point of a breaker was to limit current? Better to say how fast they trip depends on % overload?

#19

Frank,
All of these breakers, the main included, can withstand several seconds of 600% overload without trip. It is the sustained current over rated current that trips the mechanism. The auto reset limits current in a fashion as the reset features restores current flow rather quickly. In a sustained over current situation these may actually “buzz” as they open and close rapidly. This in effect limits current by changing the average current passing to the load. Not what I would call predictable or effective current limit.

#20

Point taken. You can see substantially more current than the number on top of the breaker. The trip time for the Snap Action is in the <.1S range for 600% overload. 1.5 to 3.9 S for 200% overload.

#21

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”

#22

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.

#23

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.

#24

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.

#25

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.