Replies

1. 
   P3Driver | Dec 29, 2004 05:59pm | #1

   While I have never seen a dust collection system with an intermediate fan installed, I don't see why it won't work.  As a Chemical Engineer, I look at this the same way as pumping fluids.  When you have too much line loss, you can put in an intermediate pump to increase the pressure to the inlet of the final pump.  In your case, you'll be using fans instead of pumps.  Same principle, different names.  One change I would make is to have the intermediate fan discharge into a holding tank, a trash can with one of those plastic cyclone tops will do fine, and then have the dust collector attach to the discharge of the tank.  This will minimize any fluctuations in pressure and prevent any large pieces of wood from being fired into your dust collector fan.  I'd also make it a point to start the dust collector first and then the intermediate fan, and shut them down in reverse order.  Finally, make sure you aren't turning the intermediate fan when it is not in use and the dust collector is operating.  If the fan turns, it will turn the motor, which will become in effect an electrical  generator generating electricity and eventually destroy the motor.

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   docotter | Dec 29, 2004 11:24pm | #2

   Not to pick nits, but induction motors and generators are the same beast. There are plenty of people out there using induction motors as generators (e.g., homebrew wind turbines). As I recall from my power engineering course (back in the dark ages) there shouldn't be any inherent danger to the motor itself in operating as a generator. Unless, of course, there's no load, in which case it is conceivable that excesive voltages might be developed, which could lead to dieletric breakdown in the cap(s), insulation failure, etc... In order to do that the motor would probably have to spin pretty fast. Easy enough to check if this is going to be a problem by setting up your system, running the main DC, unplug and turn on the booster blower, and measure the voltage on the power plug (careful!). If the voltage is lower than the supply voltage for that blower, you're probably not in any danger of cooking anything. If it's higher then the heavily engineered solution would be to replace the single pole power switch with a double pole switch and connect a dummy load through the switch for when the motor is "off" (i.e., in generator mode). If you're going to take this seriously, you'd also want to consider the case of the booster motor running and the main DC being off. That'd make the main DC motor into a generator... This sounds like a PITA, eh? Before I did any of that, I'd just install a blast gate downstream from the booster blower. If I'm using the collection ports upstream from the booster, then the gate would be open and the booster and main DC would be on. Otherwise I'd have the blast gate closed since I wouldn't want to load the rest of the system with the unused branch.

1. 
   P3Driver | Dec 30, 2004 06:43am | #3

   Thank you for confirming what I had previously stated.