On Monday, 15 August 2016 14:01:41 UTC+1, Dave Plowman (News) wrote:
In article ,
tony sayer wrote:
The current is reversed as it passes under a brush turning it into AC.

No Harry .. thats switched reversed polarity DC...

Well, yes. AC is generally a sine wave. Be good to see how you achieve
that with a switch. Many inverters make a pretty poor job of producing a
sine wave. ;-)

AC can be any wave form.
Sine/cosine wave forma re associated with rotating electrical machines.
Simple switching gives a square wave.
In a commutator, the point where the sine wave crosses the base line is where the brushes are ituated.
Theoretically.

Changing the load/reversing needs the brushes to be moved ideally.
If they aren't moved excessive arcing occurs which damages the commutator.