"William Noble" wrote in message
.. .
it might work, but little 110 to 220 transformers are really cheap ( a few
dollars each), why not just add a transformer - if this is in the USA,
just pull a neutral to the lathe and you have 110 as well as 220. But I
think I can assure you the VFD won't need extra cooling - if you meant
extra cooling for the motor, I think you will find that 220VAC muffin fans
are much cheaper at surplus stores than 110 ones.


"Paul" wrote in message
. ..
There's metal content as this will be part of a lathe repower project.

If one were to take two fans, something like square framed heat sink
fans,and stack them one after the other would they act as a 'two stage'
fan, so to speak?

I'm changing my lathe over to a VFD and as the motor will be running at
slower speeds I think extra cooling will be required. There's no 120 VAC
on the machine but I can easily get 220 VAC. Yes, I could buy or
scrounge a 220 volt heat sink fan but I'm thinking about wiring two 120
volt fans in series as those are much more common and as long as I was
going to have two I started thinking if stacking them would offer any
advantages.

regards
Paul


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As a general rule, fan in series increase the head pressure allowing air to
move through a more restrictive path without loosing a lot of volume CFM.
Usually are better if placed one at inlet and one at outlet, staked the
second fan works in the wake of the first and is not that efficient.

Side by side, in parallel, they produce more volume, more cooling assuming
the air path is not so restricted to reduce the volume.
The fan curve is similar to an electrical generator.
Plugged it provide maximum pressure but no volume and absorbs minimal power.
In free air it uses up all the available energy to increase the air velocity
giving maximum volume but minimal ability to compress the air and push it
trough a restrictive path.
In a real application it works somewhat in the middle of the curve. It
spends some energy to impart kinetic energy to the air and some to compress
the air creating the pressure necessary to overcome the resistance of the
path through the enclosure.

Assuming that two fan in series (electrically) is really the final design, I
would place them side by side blowing on the side of the motor, rather than
stacked coaxially with the motor. The reason being that the air path is very
free and open and you get the fasted air and highest volume.

Mauro