Voltage Drop and Amperage at a Windlass

Question:

In one of Jeff's videos, he mentions several times that if an electrical DC motor (1500W) has a bad connection then the Voltage will be lower on the motor connectors.  He then says, to hold the same P (1500W) the Current will raise.
I don’t understand that, the Connection R will lower the current as its like a series?  I would think the Torque and revs on the motor would drop but not cause the I current to raise and open the breaker?  Can You explain this?  Thanks, Thomas

Answer:

Hi Thomas.  Thanks for the feedback.

Let’s use a 1500 watt windlass for example, two scenarios:

1) Large 200 amp alternator running and battery voltage at 14.4 VDC

2) No alternator running and battery voltage at 11.5 VDC

Let’s assume, battery voltage and voltage at windlass are the same (their not, but makes the example easier)

When you run the windlass on:

Scenario 1, you’ll get 1500 watts / 14.4 VDC = 104 amps of current

Scenario 2, you’ll get 1500 watts / 11.5 VDC = 130 amps of current

The lower the voltage the higher the amperage to run the same load. Voltage drop caused by line lost and bad connectors will make this amperage number go even higher.

Jeff