Auto Reset Circuit Breakers

[brulaz]

Have been told that the electrical motors on Lippert Stab jacks should stop when the motor current rises causing the 12VDC auto resetting circuit breaker to pop (or you take your finger off the button). The breaker *should* protect the arms from kinking under heavy load. Unfortunately mine weren't working that way. The motors would stop when fully retracted up against the frame, but when extending the arms, it was possible to kink the arms first.

Think these circuit breakers are the lozenge shaped items I once saw deep under the trailer floor near the battery. etrailer sells them: http://www.etrailer.com/dept-pg-Accessories_and_Parts-pc-Circuit_Breaker.aspx
My trailer has about 4 or 5 of them down there IIRC.

Is this a general approach to motor control in RV's?

Just looked at my trailer's slide mechanism and can find no limit switches, so perhaps it works the same way? Unlike the stab jacks, the motor does stop at full extension and retraction. But I'm having problems with shear pin popping when retracting against the shell (and now a mangled drive shaft). The motor doesn't seem to stop soon enough.

What about the electric awning?

But I've also read on this board: "It is a thermal auto reset breaker. Keystone customer service told me that if it has tripped and reset 5 or 6 times it is time to replace it." Which doesn't fit with these circuit breakers being used as a routine motor switch. We've probably used our slide and electric stab jacks close to a hundred times so far. But maybe there are different types of circuit breaker. Is it a difference between "thermal" and "auto resetting" circuit breakers?

If these are being used to cut the juice to a motor, their current limit needs to be better matched to the mechanical system. The auto-recyling ones on the etrailer site range from 20A to 50A in 10A increments. Would it be reasonable to buy a few and try reducing the current cut-out value to my slide? (the stab jacks have already been fixed by strengthening the arms)

Has anybody done anything like this?

I would appreciate an education on these devices and their usage as they are totally new to me.

[ktmrfs]

IMHO toss any autoreset breakers in the trailer and replace them with the same footprint "push to reset" or remove and reinsert to reset type. they cost very little more and AFAIK for every autoreset, a manual reset version is available. yes, a little more inconvienent but WAY safer.

the biggest issue with the autoreset is they do just that. trip, cool, reset, trip, cool, reset.... forever if the overload is NOT removed. so if you develop a short downstream of the breaker that you can't interupt, well.... sooner or later the wire gets to hot or the breaker finally gives up in the open position and not the shorted position.

[MEXICOWANDERER]

Curious?

Check out what a cheap thirty ampere breaker "breaks at" at 40C

Then check out the same breaker's performance at 10C

Both are reasonable temperatures.

Better quality breaker specifications at least remain reasonable, but the cheapies are in a different universe.

[wolfe10]

MEXICOWANDERER wrote:
Cheap auto reset circuit breakers are about as efficient as a Mexican Stop Sign

OK, the really good ones are "about as efficient as a Mexican" TOPE.

[ScottG]

I think your expecting the breaker to trip under normal conditions - like extending or retracting the slides. THey aren't meant to be electrical stops under those conditions. They are meant to trip during an abnormal overload.

[MEXICOWANDERER]

Cheap auto reset circuit breakers are about as efficient as a Mexican Stop Sign

[BB_TX]

...

[BB_TX]

The auto reset circuit breakers are to prevent too much current flowing thru the wires, just like any other circuit breaker. If the stalled motor current exceeded the breaker rating it should trip. Otherwise it is not there to specifically protect it.

The auto reset circuit breakers sound sophisticated, but are nothing more than a single piece of bimetal with an electrical contact on one end. When the bimetal heats enough to cause it to bend and open the contact it cuts the current to the device. But as soon as it cools, it recloses that contact allowing current to start flowing again if the switch is still being held. Each time it opens it burns the contact a little. And each burn causes it to heat faster next time.

Here is one with a burned contact. DC current is hard on contacts when they open while current is flowing as the current continues to arc across the contacts (and create excessive heat) until the space is too far for the arc to continue.

[time2roll]

Circuit breaker needs to be matched to the wire size. 40 amp for #10, 50 amp for #8 or better. If you have less than #10, pull new wire. For more than 50 amp I recommend moving to Bussmann High Amp series circuit breaker and wire to match.