Car electric capstan USES original car battery power, capstan's negative electrode (black line) connect iron connection to connect directly to the battery negative pole is different, what effect?
It is easy to make contact with poor contact with the battery
The connection is convenient but there is a certain contact resistance, which produces voltage loss. Direct connection to the battery is slightly troublesome, but there is no voltage loss.
When you take the iron, it loses much power. (you also know that there is no iron in the wire.)
