Originally Posted by Scatterling
My 700 watt Simpson Lawrence
windlass has finally succumbed to corrosion
and is sadly deceased. The replacement offered by Lewmar (who bought SL) is the V1. My SL unit had a 70 amp breaker which makes sense when I do the calculation: amps = watts/volts or 58 amps. My question is, why does the Lewmar, which also has a 700 watt motor, come with a 100 amp breaker?
Under no particular load (e.g. if you have motored up to your anchor so the chain is not under tension) you can expect your windlass to draw perhaps the 58 amps of your math calculation.
Should you use your windlass to draw your boat
forward to the anchor, then the greater load will see your motor draw more current.
And should you get into the situation such that the load on your windlass via the chain stalls the motor, and you continue to keep the motor in the stalled load mode, then the motor might draw 200 or more amps (should you not have a 100 A breaker).
anchor windlass motors are not that different from the starter motor of a car. They do not have heat sinks etc. In that sense, they are not designed for long and high loads (starter motors are great at 30 second bursts).
So the 100 A breaker is there to give you some leeway in operation (of course the motor and the mechanicals will always last long if you motor to the anchor such that your windlass is only lifting the mass of the chain and the anchor, but most everyone has to cheat at one time or another). It's also there to protect the motor and the mechanicals from getting into the stalled load situation (overheating the motor, stressing the mechanicals).
That potential for high current draw is also why the usual recommendation is to have your auxiliary engine
running when weighing anchor. The engine alternator
the voltage to 13.8 V, reduce the potential for fast current demand on your battery
bank, and encourage you to motor to the anchor.