Windlass keeps tripping circuit breaker

[rwidman]

Originally Posted by Wotname

................ So in essence, series wound motor is a "special case" where high resistance in the circuit allows the circuit breaker to trip contrary to "normal" circuit theory.....

It is correct that a series wound motor develops the most torque and draws the most current at zero RPM but only if the input voltage remains relatively constant. If there are corroded connections (resistance), this resistance is in series with the motor and the voltage is divided between the resistance of the connections and the motor. Introducing series resistance into the circuit will make the current in the circuit less, not more.

With no significant resistance from the conductors, too much load on the motor (bad bearings, gear train, anchor stuck on a rock, etc.) will slow or stop the motor, increase the current, and trip the breaker. That's what it's there for.

[MinorI]

I am measuring my voltage between each side of the thermal Circuit breaker and the negative post on the battery. At the windlass I am measuring between the hot wire on the contactor and the black cable to the windlass motor.
It still seems to me that there should be no voltage at the contactor or at the open side of the circuit breaker when it is tripped. Is that correct?
I don't want to take the motor out yet if the problem is the circuit breaker.


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[Cheechako]

There should be no voltage on the windlass side of the breaker with the breaker in the OFF position... unless there is something about the circuit I'm not understanding. Is it possible there is another wire feeding voltage on that side somehow?

[sailinglegend]

Originally Posted by rwidman

....To sailinglegend, "repairing" a circuit breaker, except in an emergency and until a proper replacement can be obtained is a very bad idea. A circuit breaker is a safety device and if it doesn't work as designed, it could fail to trip in an overload situation and cause an overload and possibly a fire. You have no idea at this point if it will still work as designed and protect your boat's wiring from overload. Buy and install a new replacement ASAP.

You are absolutely right.

I said the problem was solved - and I did buy a new thermal breaker when I could find the right one.

Another boat on our pontoon had exactly the same problem - and the solution was the same.

The voltage measurements that MinorI has made MUST be done when the windlass motor is running. The simplest way to identify the breaker fault is to follow my suggestion and measure the voltage drop across the breaker WHEN THE WINDLASS IS RUNNING. I'm sorry I didn't make that clear.

[Wotname]

Originally Posted by rwidman

It is correct that a series wound motor develops the most torque and draws the most current at zero RPM but only if the input voltage remains relatively constant. If there are corroded connections (resistance), this resistance is in series with the motor and the voltage is divided between the resistance of the connections and the motor. Introducing series resistance into the circuit will make the current in the circuit less, not more.
.........

This has always been (for me) an interesting conundrum.
Simple circuit analysis suggests that an increase in circuit resistance will decrease current flow and of course this is true - ohms law is always true!

However when considering a series wound motor in a simple circuit, there is a sweet spot or perhaps better put a "sour spot" when the inclusion of some series resistance causes a short term increase in current flow to the point where the breaker operates.

As best as I can understand/explain it, this is what happens.

Normal winch operation has full supply voltage at the motor terminals, the current flow is a function of the load resistance of the motor which is directly proportional to the RPM (higher RPM, higher load resistance, lower current).

When a full working load is applied to the winch, the designed RPM is such that the resultant current flow just a little lower than the circuit breaker. This is lowest RPM the winch should normally be allowed to operate at.

Now add some smallish series resistance by way of say corroded terminals, the voltage available at the motor terminals is reduced and therefore current flow decreases thus reducing torque, this causes the RPM to drop significantly (as load on winch remains the same). This significant drop in RPM causes a significant drop in the load resistance and therefore total circuit resistance has momentarily decreased (even with the addition of the "corrosion resistance"). The current flow increases to a point beyond that of the breaker capacity.

Of course, add too much "corrosion resistance" and Ohms law will dictate a small current flow regardless.

But maybe I'm wrong

[HappyMdRSailor]

Try taking voltage measurements on "either side" of a connection or component (breaker/relayetc..) i.e. NOT positive to negative, but positive line on either side, and negative on either side... You're looking for a voltage difference to identify a bad connection, contact, or component... You're looking for a culprit that steals more than a couple 1/10v... This is all with the windlass running of course...

[MinorI]

I want to thank everyone for your help and suggestions and I know it's been awhile but we left the boat in Puerto Rico and flew home for Christmas. Now that I'm back I believe I have solved the problem. While cleaning all the wiring connections I found that the wire which returns from the switch to the contactor ground terminal was not a ground wire but was a hot wire from another source. apparently whoever wired it took a black wire that was in the windlass compartment paired with a red wire which when pulled tightened up a wire running to a fan in the v-berth and cut it and used it as the ground. The problem was that the black wire has 13 volts running through it. This was sending voltage back to the circuit breaker on the side which should have had no voltage with the breaker open. So I disconnected that wire and connected a black wire to the terminal with the other end connected to the ground wire on the windlass motor as the wiring diagram showed.
I haven't anchored yet but I ran about 60 ft of chain out while on a mooring ball and then brought it all back onboard, nonstop with no problem.
So I am still baffled by the circuitry. It seems that it should not have worked at all without being grounded properly rather than working but overheating and tripping the thermal circuit breaker. So I stand in awe of you people who understand this stuff but apparently there are some people out there wiring boats who know less about it than me.


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