James Sweet wrote:

"msg" wrote in message
...

PeterD wrote:


On Tue, 25 Mar 2008 14:47:09 -0000, "N Cook"
wrote:



Just as I was blowing out, with a 1KW Martindale, the crud of ages from
an
amp and its fans.
Thought - these fans act as DC generators if blown forcefully. Presumably
you could damage, if driving negative volts into ps or fan contol
circuit.
Next time I will jam something in the blades before zapping one with 1KW
of
draught.


All the fans I've seen were 'brushless' AC polyphase with protection
to the driver board (inside the fan) to prevent damage.

snip
Older DC Muffin Fans use DC permanent magnet motors, you can feel magnetic
detents as you rotate the blades.



They all have permanent magnet motors, but they're brushless. You can feel
detents on those too.



Indeed this is true for modern versions, but DC Muffin fans from the 1960s
had brushes (electronic comutation would have been large and of prohibitive
expense).

Michael