Anchor windlass circuit breaker sizing

Discussion in 'OnBoard Electronics & Controls' started by sabahcat, Oct 26, 2011.

  1. sabahcat
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    sabahcat Senior Member

    I currently have a Maxwell vwclp1500 12v with 1200 watt motor

    Maxwell are saying I need a 135 amp circuit breaker, which I don't have on hand, but I do have a 100amp and a 150 amp.

    Would either of these be close enough or do I really need to get the exact amperage?

  2. Frosty

    Frosty Previous Member

    You can start a fire with 10 amps or less. If your breaker is 100amps (which is not enough) of what value is it?

    If there is a short your breaker will quite happily continue to supply 99 amps,--enough to weld with.

    I dont agree with breakers on this application and include the warning that this special piece of equipment needs carefull operation by some one that unerstands its load and does need to over load it or knows how to overload it safely.

    Thers is nothing worse that hauling anchor in a dangerous situation and the beaker keeps trpping.
  3. gonzo
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    gonzo Senior Member

    Too low will trip when you need it and too high may start a fire. The correct size is ideal.
  4. Frosty

    Frosty Previous Member

    The correct size is un definable. The ampage used varies wildy during its operation.

    Its not the breaker that starts the fire its the operator.

    Simple fall windlasses use a starter motor , you dont have a breaker on a starter motor.
  5. rxcomposite
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    rxcomposite Senior Member

    Rule of thumb says cranking ampere in stalled condition + 50% more then round it off to the next higher rating. So if you are using breakers rated at stalled condition, it will always trip everytime it stalls even for a microsecond.

    Breaker ratings are rounded off so it is best to use the 150 amps. If you want to be doubly sure, check Maxwell ratings for stalled condition and calculate the ratings.
  6. Frosty

    Frosty Previous Member

    So If you get a short on your foot switch and the solenoid welds together with the anchor in a locked position the breaker will continue to feed 150 amps without breaking.

    Thats enough to weld 1/4 plate. note the breaker will not break untill it exeeds 150 amps.

    I nearly had a fire for this reason. The bridge windlas sw was on under the awning and this happend when I turneds on the batteries. A breaker would not have changed anything. I now have an alarm --a very loud alarm when the solenoid is energised.
  7. CDK
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    CDK retired engineer

    My advice is to use a fuseable link for that purpose.
    A short piece of AWG 15 copper wire, firmly clamped between two posts, away from any combustible material. It will fuse at approx. 140 amps but accepts a higher inrush current for a few mSec. Slide a piece of silicone tube over the wire so the copper droplets will be contained in case you fuse blows.
  8. rxcomposite
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    rxcomposite Senior Member

    Let us dig deeper.

    A 1200 watts at 12 volts consumes 1200/12= 100 amperes. From other sources, Maxwell list their similar windlass as consuming 110 to 135 amperes @12 volts hence their recommendation for a 135 ampere circuit breaker.

    Circuit breakers are standard at 100amp or 150 amp but a special 135 amp is available as surface mount or panel mount. Circuit breakers are adviced to be mounted near the source (battery). When does the circuit breaker trips? the following table gives the time to trip:

    % of rating/time to trip (seconds)

    The 135 amp given by the manufacturer is a safe rating assuming all conditions are ideal. It is also assumed that the circuit will fail if the motor stalls or overheat.

    In less than ideal situation, this could be a bugger. Depending on the wiring and ambient temperature, all thing will not work.

    Wire size will add resistance, adding a solenoid would increase contact resistance, high temperature will decrease the current carrying capacity of the breaker as its has a thermally activated element, a less than ideal battery charge would increase current consumption. So all things considered, the 135 amp breaker will trip in less than ideal situation.

    The circuit breaker will not protect your motor but will prevent fire as the time to trip is only seconds depending on the overload. If there is a short, either on the motor or wiring, current increases, wire becomes hotter decreasing resistance and the breaker trips quicker. Use a wire that has high insulation rating. Refer to the chart attached for guidance.

    Since you want to protect your $1200 windlass motor, a 135 amp c.b. will work but will trip more often and a 150 amp. will give you at most 20 second overload. Your choice.

    Attached Files:

  9. Frosty

    Frosty Previous Member

  10. michael pierzga
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    michael pierzga Senior Member

    At 12 volts the motor needs 100 amps.... remember loss thru the solenoid,, cabling, , voltage drop from a low battery . You may see 11 volts in your power supply which could add an addition 10 amps . 130 sounds like a good choice
    The control circuit will naturally be fused separately.
  11. michael pierzga
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    michael pierzga Senior Member

    Another detail worth examining on a new high amperage installation is the solenoid relay. I dont know the supplied Maxwell relay. I prefer open style relays were I can inspect the contactors.
    The way you destroy an expensive motor, ruin an anchor winch or burn up your whole boat, is when a relay ages and the contactors weld themselves into the closed position. The motor now runs out of control till destruction. With an open relay you can observe any arcing then service or replace.
  12. Frosty

    Frosty Previous Member

    That kind of solenoid would be automotive. It also has a button at the bottom so you can over ride the primary circuit.

    I happen to have one of those too.
  13. gwboats
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    gwboats Naval Architect

    Breaker Size


    Maxwell show their own UL approved breaker/isolator in their manual for this windlass. Fitting any other protection (or none!) may invalidate any warranty or other claim. Follow the manufacturer's manual if in doubt; they should know.

  14. rxcomposite
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    rxcomposite Senior Member

    The motor is said to be stalled when starting (0 rpm) with high load OR when stopped because the anchor is stuck. Thus, motors have high initial starting current or high current consumption when stalled.

    Prolonged operation in this condition will cause the internal winding to rise in temperature. Copper wire loses resistances when the temperature rises. The lowering of resistance causes a rise in current measured in amperes. This can be shown by the formula I=E/R. Thus if the resistance of the winding is 0.12 ohms at operating temperature we get Iamp=12/0.12=100. If the resistance drops to 0.10 we get a rise in current (120 amps).

    The rise in current is sensed by the c.b. and trips at the rated current. The c.b. is derated when the ambient temperature rises. Thus;

    Temp F / % of rating
    75 / 100%
    100/ 90%
    125/ 80%
    150/ 75%
    175/ 65%
    200/ 45%

    Thus, if you are operating in the Gulf Coast or Florida area, you must derate accordingly, otherwise the c.b. keeps tripping.

  15. Frosty

    Frosty Previous Member

    Are we having difficulty in finding the correct ampage rating for the breaker? Oh really?

    And we havnt got round to what size batteries its running off yet single 90 , 120 twin 90 's perhaps or even one sited in the front for its specific use? problems problems.

    I wonder how long the cables will be or if the engine will be running, --Oh !!!
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