Darcy, The 5hp motor is around 3.7W at no load start-up current would be around 6 times the full load current, which in this case is around 107A (208V). Your 20kw alternator would be rated at around 96A. The alternator's irons shouldn't saturate at the 107A but the rather abrupt current drawn will produce a voltage dip. The only way around this with the gear you have, if you're lucky, is to see what adjustments are available on the AVR. Most decent AVR's have at least 2 adjustments, response time, and stability. If you can get the AVR to respond quick enough you might get the voltage dip to lessen in it's severity but you could end up with an alternator who's output voltage hunts. Another problem you'll run into is the engines governor and the power rating of the engine. If the engine is weak compared to the load you are placing on it then no matter how fast the governor responds the engine will not be able to keep up the revs and thus the frequency dip will also upset any electronic controllers on the router. An alternative to buying a larger alternator might by to by another alternator and run it in parallel. With this set up though you will need some kind of syncroscope to bring the 2 alternators on line and the avr's should also have droop control so that you can keep a lid on circulating currents (Power Factor or cos phi). I believe the cheapest alternative would be to replace the motor with a single phase one until you get 3 phase installed and the get the existing motor/s rewound to what ever is the standard 3 phase voltage there (415V in Oz) going to a higher voltage will reduce the current drawn by the motor but you might have to upgrade contactors etc to handle higher voltages
Regards, Alfonso -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Darcy Davis Sent: Saturday, 17 December 2005 11:10 AM To: [email protected] Subject: [OT] PCB router Hey Guys, We've found ourselves in somewhat of a bind. We've got a PCB router in house which is powered from 3-phase 208V. Its a very, very long story, but its going to be 10wks till our utility supplies 3-phase power. Currently we have 240V single phase power, so I've looked into a phase converter but we still need to bring the voltage down to 208V. The other option we've been trying is to use a generator. Turns out that when the 5hp vacuum motor fires up, the generator doesn't respond quickly enough to counteract the effect, so we suck the voltage (and frequency) through the floor. This of course causes the motor controllers to complain. We've got a 20kW generator already (for a ~4kW load), so I don't think a bigger generator will fix the problem. Is there another way around this with a generator? (Ie, could we try to run the controllers from a UPS or will we kill the UPS?) If we were to run a 3-phase motor load continuously while we run the router, would it tend to buffer the effect? Power systems is well out of my league, so any comments you have would be welcome. Thanks, Darcy Davis Design Engineer ========================================================= Dynastream Innovations, Inc. Ph: (403) 932-9292 ext. 132 228 River Ave. Fax: (403) 932-6521 Cochrane, AB T4C 2C1 Web: www.dynastream.com Canada ========================================================= ____________________________________________________________ You are subscribed to the OT discussion forum To Post messages: mailto:[email protected] Unsubscribe and Other Options: http://techservinc.com/mailman/listinfo/ot_techservinc.com Browse or Search Old Archives (2001-2004): http://www.mail-archive.com/[email protected] Browse or Search Current Archives (2004-Current): http://www.mail-archive.com/[email protected] ____________________________________________________________ You are subscribed to the OT discussion forum To Post messages: mailto:[email protected] Unsubscribe and Other Options: http://techservinc.com/mailman/listinfo/ot_techservinc.com Browse or Search Old Archives (2001-2004): http://www.mail-archive.com/[email protected] Browse or Search Current Archives (2004-Current): http://www.mail-archive.com/[email protected]
