AC/DC circuit breakers?

Is there a difference between AC and DC breakers?
Would this work at 6v DC?
Thanks in advance.

Until you get into really huge currents, AC vs DC doesn’t much matter to most circuit breakers. The main difference is that it’s possible to minimize arcing if you can manage to open the contacts just as the current is zero on an AC circuit.

What you’ve linked to is a three-pole breaker. It’ll work fine as a manual switch, but I have no idea how well it will perform as a 6A breaker on one circuit. What is your intended application?

Yes there can be a huge difference in AC vs DC for circuit breakers. The type you link to is designed for three phase AC power. The trip mechanism is an AC solenoid that pulls on a release tab when the current exceeds 7 amps. The breakers are linked so that if the current on one exceeds the trip, all three poles break at the same time. The 250 VAC refers to the safe operating distance when the breaker is open. 250 volts AC will not arc across the distance between the contacts. This breaker would work as a switch on DC but would not act as circuit protection. Snap action breakers of the type we use are rarely seen in the same applications as the breaker you linked to. Often these breakers are used in environments where the temperature is high during operation particularly if stacked next other breakers in the same panel. Some breakers designs will use both snap action and solenoid release to insure circuit breaks over a wide variety of conditions. Safety is a major concern when using these devices.

What would prevent it from tripping at 7 amps DC?

I’m aware that many DC solenoids don’t function as designed when fed AC, but my understanding of things tells me that the other away around shouldn’t be an issue.

I want to say that thermo-magnetic breakers will respond differently to AC and DC, but I’m not positive.

Not all solenoids are created equal. In AC breakers solenoids are wound such to minimize noise (hum) and optimize reaction time at AC currents. Some are not fast enough reaction time and so are coupled with external stimuli and motors to break the circuit. We use motorized breakers on our transmitter as certain fault conditions must remove power in less than one cycle of the power line. The power supply for the transmitter is capable of sustained loads of close to 50 kW.

Hey Al -

Not to sidetrack the thread too much, but you piqued my interest. What type of faults need to break the connection in less than a cycle?

The output amplifier is a IOT (Inductive Output Tube) The tube runs with 32-35kV on the collector and makes about 2 amps of cathode current in normal operation. The tube couples output power by running the electron beam (magnetically focused) through a cavity tuned to the output frequency. This causes the electron beam to act as a 1/2 turn transformer. If anything happens to drive, output coupling, cooling water, high voltage, filament (I seem to remember we are running at 5 volts, 27 amps on the filaments), or active arc detection in the output cavities, the high voltage must be removed from the very expensive tube to prevent permanent damage. In addition to the motorized breakers, there is a crowbar protection circuit (a gas discharge tube and drive circuits) which shorts across the high voltage should anything in the life support systems signify an issue. To test the crowbar, a test fixture consisting of a one foot piece of #36 wire is placed across the high voltage inside the transmitter cabinet. The bottom of the test fixture is an air operated switch made from 1/2" capped copper pipe and a bladder. A test of the crowbar is determined by stomping the foot operated bladder, shorting out the high voltage with the #36 wire. The crowbar passes if the #36 wire doesn’t vaporize. When the switch engages, circuitry tells the crowbar to fire, and the motorized breakers to pull out. The main three phase power cabinet is 4 feet wide and eight feet high. It contains the motorized breakers and the step start relays for the power supply plus the resistors used for step start. When you stomp the test fixture, the wiring bangs inside the conduit, the transmitter relays and warning alarms go off, and the breakers and all the step relays bang away. Drive power amps also go into protect during this time as well. If you don’t know it’s coming, the noise will knock you down. Everyone on the floor and the floor below know when you run the test. Each transmitter should get tested at least twice a year. The crowbar tube should get replaced if it fails or as part of normal maintenance at some interval.

I think it would be simpler to use DC breakers instead.
Should I use these or these to protect these using a 6 volt (alkaline, probably D cell) motor power supply?
Can alkaline batteries even supply current this high? What is the typical max current draw from alkaline batteries?

Look up the batteries…

has good info.

Usually, breakers and fuses are used to protect wires. If there is a short circuit or overload, the breaker/fuse will pop before the wire gets hot enough to cause trouble (trouble usually = fire).

There are self resetting thermal circuit breakers available at auto parts stores. Or you could use fuses, from an electronics store (even Radio Shack has them) or automotive store.

For a 10 amp circuit, if you use 18 gage wire and 10 or 15 amp fuse/breaker, everything should be fine.

An you could use a normal switch to turn power on and off.

Also, be careful with battery wiring…from the users manual:

"5.4 Reverse-battery

The motor driver boards do not have any protection against reverse-battery. If user connects the battery or power source wrongly it will damage the on board clamping diode and further burn the driver. Thus please be careful during making connection. "

According to my, probably not-so-good calculations, D batteries are capable of outputting 10 amps (1.5/.15=10) in series. So I am probably OK with just a switch and maybe a fuse, unless I have overlooked something.

While D cells may give you 10 amps it will be for a very short time. The discharge curves for D cells here doesn’t go beyond 1 amp and at that discharge the curve dies off at about one hour. I might suggest you look into one of the smaller gel cell battery packs or simply use one of the robot batteries.

Internal resistance is measured by pulling 1/2 amp for 100 milliseconds and measuring voltage. It’s not independent of time and current. You’ll notice that the same internal resistance is listed (150 to 300 milliohm) for all alkaline batteries from D cell all the way down to AAAA cell.

I’m kind of reading between the lines, but I think he was wondering if he even needed to bother with a circuit breaker/fuse, since he’s using D batteries, which probably can’t even produce 10 amps.

Yes, that is the point of my last post. D batteries can theoretically/hypothetically produce 10 amps of current, but if they do, they won’t last long. The motors originally ran on 4 AA batteries so I don’t need any more current.

You probably ought to still use a fuse in the circuit, I’ve seen smoke caused by relatively small batteries!

What size?

on the topic of circuit breakers:
Generally speaking, should you buy a breaker rated for the current the system is rated for, or that trips at or before that current? (trip amps vs. rated amps)

Breakers or fuses are usually sized to the wiring (at least they are in power distribution systems used in houses, cars, and FRC robots).

But you also don’t want it to pop at any normal working loads.

As I said earlier, 18 gage wire and 10 amp fuse/breaker should be fine for your application.