This is a multi-part message in MIME format. --Boundary_(ID_eoAvWPQLr+xVLv+0XBoENQ) Content-type: text/plain; charset=us-ascii Content-transfer-encoding: 7BIT The degree and rate of change are not particularly great. The tool is used to drill and retrieve sidewall cores. Mostly things move slow & steady. I have not heard of the servo driven variable transformers. Do you know who makes them ? John Marshall Douglas Butler wrote: > So a variable transformer gives the effect you want. How fast does the > load change? There are servo driven variable transformers that can go > from 0% to 100% in under 100mS. If you are only building a few units > these transformers are probably cheaper than the engineering time to > build something solid-state. > > Sherpa Doug > > > -----Original Message----- > > From: John Marshall [mailto:john@AFBENGINEERING.COM] > > Sent: Friday, March 01, 2002 12:38 PM > > To: PICLIST@MITVMA.MIT.EDU > > Subject: Re: [EE] Controlling Split Phase Motor > > > > > > I guess that what to control is the 1st half of the question, > > with the second half > > being how to control it. The variable transformer technique, > > obviously, controls > > the input voltage to the primaries of the SU-1s. Since we > > need now need to go to > > electronic control, we really don't know which part of the > > equation to control. > > Phase seems to be a problem, since the 8uF cap at the motor > > causes a phase shift > > (90 deg., I think) of it's own. And yes the total power here > > is about 2kW. > > Once again, thanks for the response. > > John Marshall > > > > Douglas Butler wrote: > > > > > Sounds like some of the stuff I do running a multi-kW sonar at the > > > botton of the ocean, etc. > > > > > > What are you controlling about the motor? voltage? current? phase? > > > Sometimes we feed long cables with a current source. We > > often try to > > > make the loads constant power reguardless of how much work they are > > > doing (shunt regulators). Cooling is not a problem for us :-) > > > > > > Sherpa Doug > > > > > > > -----Original Message----- > > > > From: John Marshall [mailto:john@AFBENGINEERING.COM] > > > > Sent: Friday, March 01, 2002 12:05 PM > > > > To: PICLIST@MITVMA.MIT.EDU > > > > Subject: Re: [EE] Controlling Split Phase Motor > > > > > > > > > > > > Spehro, > > > > Thanks for the reply. I was beginning to think that > > > > my question is too > > > > far out there. > > > > Our stuff is so specialized that changing the motor is not an > > > > option. The > > > > physical configuration of the motor, it's ability to run at > > > > 200 C, the power > > > > charateristics, are all quite specific to our application > > > > The wire in question is a 7 conductor cable. Once > > > > again, quite specific > > > > to the purpose of well logging. Using 4 conductors for the > > > > motor power, at about > > > > 11 ohms/1000ft, we have about a 400 volt drop from surface to > > > > tool. We only need > > > > to control from about 85% to 100%, in order to maintain > > > > optimum power factor. The > > > > purpose is to keep the motor running in that part of the > > > > curve where we achieve > > > > optimum performance without generating heat with excessive > > > > voltage. The motor is > > > > optimum at 3450 RPM. By monitoring speed at the surface, we > > > > can auto-adjust the > > > > voltage/current going downhole. > > > > So I guess that's probably more than you wanted to > > > > know, but I'm not good > > > > at short answers. > > > > Thanks Again, > > > > John Marshall > > > > > > > > > > > > > In theory, this could be done by generating two > > > > variable-frequency 600VAC > > > > > RMS sine waves using PWM that are 90 degrees out of phase > > > > (eliminating the > > > > > capacitor). In practice, for a one-off serious application, > > > > this would > > > > > be pretty much insane to try and make. You want to buy a > > > > Variable Frequency > > > > > motor drive and probably replace the motor with a 3-phase > > > > motor. You may > > > > > well need to add some power conditioning stuff at the end > > > > of your 5 miles > > > > > of wire, so talk to an experienced supplier. > > > > > > > > > > Then your main issue will be communicating with the motor drive. > > > > > > > > > > Best regards, > > > > > > > > > > Spehro Pefhany --"it's the network..." "The > > > > Journey is the reward" > > > > > speff@interlog.com Info for manufacturers: > > > http://www.trexon.com > > > > Embedded software/hardware/analog Info for designers: > http://www.speff.com > > > 9/11 United we Stand > > > > > > -- > > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > > > -- > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body --Boundary_(ID_eoAvWPQLr+xVLv+0XBoENQ) Content-type: text/x-vcard; charset=us-ascii; name=john.vcf Content-transfer-encoding: 7BIT Content-disposition: attachment; filename=john.vcf Content-description: Card for John Marshall begin:vcard n:Marshall;John tel;cell:817-917-7190 tel;fax:817-275-8938 tel;work:817-275-1311 x-mozilla-html:FALSE url:niecor.com org:Nova Instrument & Engineering version:2.1 email;internet:John@AFBEngineering.com title:Sr. Design Engineer adr;quoted-printable:;;1817 East Division St.=0D=0A;Arlington;TX;76011;USA fn:John Marshall end:vcard --Boundary_(ID_eoAvWPQLr+xVLv+0XBoENQ)-- -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body