Fans in Series

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.

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

Good idea about the surplus store. The two stacked fans was one of those ideas one briefly considers while deciding how to do something, I was just wondering how it would work.

I'm pretty sure the 220 volt fan is how it will go, and it is for motor cooling, the VFD should be fine on it's own. 120 volts would require a neutral, as you point out, and that would require allot of work, machine and circuit is 220 three phase.

You would save a large amount of time and effort if you buy a 220v fan. Or you can go with a 12v transformer and a 12v fan, I can give you a 12v tfansformer, I give 80% probability that I have one.

i

would it be easier to just run a neutral wire back to the panel and use one of the existing hot leads, and run your fan on 110?

Fans are designed with curved blades (pitch changes from leading to trailing edge) so that air flow across the blade is tangential. Putting a second fan directly behind the first will put faster moving air in contact with the leading edge, which will not be pitched correctly. It would be like trying to push a car that is moving as fast as you can walk.

Iggy

Thanks for the offer but I know I can find some 120 volt fans laying around, we're always junking obsolete controls at work. There might even be some 220 volt available.

Paul

Leo

I like your analogy, and that's sorta the way I though it might work!

Paul

Your idea to install a fan is a very good one. With a fan, you could run your motors slowly all day long.

i

I would recommend getting a small 220 to 110 transformer that could be run off the three phase and supply 110 to the fans,lighting and your dro. This would eliminate having two separate power sources coming to the machine. Most machines use a step down transformer to get 110. The only thing is make sure the outlets are fused and that you don't plug in a toaster or some high current device that would overload the transformer or get a bigger transformer.

John

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Aside from that -- since I gather that you were considering them to be both in series electrically and in the airflow sense, I see a possible problem -- even assuming that they are identical fans. The bearings tend to fail in these over time, and once that happens, one fan stalls, putting more voltage across the other, and frying its windings. (And that bit above about the blade curvature might mean that two close coupled in airflow series would be unbalanced anyway.

Enjoy, DoN.

220/240 VAC fans are in the $10 to $30 range at just like 120 VAC ones. No need to buy used/surplus, really. If you need more air flow, don't use square 'muffin' fans, but go to a squirrel-cage blower (they have lower cubic-feet-per minute CFM ratings, but better performance with backpressure).