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Re: (ET) GE Sep-Ex controllers?
Many thanks to T Humphrey for stating what I meant !
I re-read my e-mail before I sent it but still did not realize I didn't say
which current the freewheel circuit was dealing with.
Also to set the GE record straight, Rod Hower informs me that when he
worked
at GE they did in fact use freewheel Mosfets (in 1995) in their controller
designs.
Thanks Rod !
TJWilhelm ask about the availability of the Alltrax Separately Excited
motor
controller.
We had hoped to be shipping before the end of this month, but the engineer
decided to change the microprocessor to one with more internal memory.
He had originally thought of having just one motor "profile" loaded in the
software at a time but later changed his mind when he realized that there
are at least three different "profiles" that will be required to support
the
motors we are interested in. Two for the different Golf Car motors now in
use and the third for the ET motors.
The advantage for us ET guys is that we would be able to change to golf car
motors without having to change the software in the controller. The
advantage to Alltrax is we only have to stock one controller for all the
applications. The cost won't change because of this.
To change "profiles" you just click on the one desired using our free
communications software.
I don't know what the ship date is now, after Thanksgiving I'll post the
new
schedule. The new controller is not on the web site yet. We are waiting
for him to stop making changes so the spec don't change after we make it
public.
Thanks for all you patience ! I'm keeping track of everyone who has shown
interest in the new controller..
Steve
scr echoweb net
Alltrax Inc.
www.alltraxinc.com
----- Original Message -----
From: "T Humphrey" <thumphrey mynra com>
To: <elec-trak cosmos phy tufts edu>
Sent: Wednesday, November 26, 2003 8:57 AM
Subject: Re: (ET) GE Sep-Ex controllers?
> No, you're not confused....sort of.
>
> You have the theory correct. When a current flowing in an inductor
> is interrupted, the magnetic field collapses. The collapsing
> magnetic field of course induces a current to flow, but the
> current can't flow without a complete path, so the voltage builds
> ever higher until a spark can jump whatever gap it needs to in
> order to allow current to flow (momentarily).
>
> Thats what the free-wheeling diodes or mosfet free-wheel switches
> are there for....to allow the current to flow and the magnetic
> field to collapse "controllably". BUT, it is the inductor(source)
> current, not the battery(source) current that is flowing.
>
> Stay Charged!
> Hump
>
>
> >
> >-----Original Message-----
> >From: tjwilhelm [mailto:tjwilhelm stelle net]
> >Sent: Wednesday, November 26, 2003 2:12 AM
> >To: Steve Richardson; RJ Kanary; elec-trak cosmos phy tufts edu
> >Subject: Re: (ET) GE Sep-Ex controllers?
> >
> >
> >Hi Steve,
> >
> >I'm a touch confused. Regardless of the freewheeling circuit,
> when the
> >switching transistors are turned off, no supply current is abvle
> to flow in
> >the motor windings, true? I thought the purpose of the
> freewheeling
> >"diode" (in any rapid-switching inductive circuit) was to deal
> with the
> >high-voltage, transient "kick-back" created by the motor windings
> every time
> >the switching stage turns the current off (the same "kick-back"
> voltage that
> >occurs in electric fence chargers and cattle prods every time a
> coil is
> >de-energized, and its field rapidly collapses and self-induces a
> short-lived
> >but very high-voltage spike). I thought the kick-back voltage
> could be so
> >high it would exceed the reverse voltage limits of the switching
> transistors
> >and would actually damage them...but, this is prevented by the
> freewheeling
> >diode shorting the kick-back from the coil, back into the coil.
> Am I wrong
> >on this? Just trying to understand.
> >
> >On a more important note...when will the Alltrax sep-ex
> controller be
> >available? Are there specs available on the net somewhere?
> I've been on
> >the Alltrax website and don't see anything about it. I'm ready
> for one!
> >Where do I get in line?
> >
> >Thanks,
> >tjwilhelm
> >
> >
> >----- Original Message -----
> >
> >From: Steve Richardson <mailto:scr echoweb net>
> >To: RJ Kanary <mailto:rjkanary nauticom net> ; tjwilhelm
> ><mailto:tjwilhelm stelle net> ; elec-trak cosmos phy tufts edu
> ><mailto:elec-trak cosmos phy tufts edu>
> >Sent: Tuesday, November 25, 2003 6:52 PM
> >Subject: Re: (ET) GE Sep-Ex controllers?
> >
> >RJ,
> >
> >Most controller designs use power mosfet transistors for the main
> power
> >switch and diodes in the freewheel circuit. The freewheel
> circuit a
> >designed to keep the current flowing in the motor windings when
> the main
> >switching transistors turn off. Mosfet transistors have very low
> on
> >resistance compared to "normal" transistors like BJT's. But the
> diodes have
> >a higher resistance when they "switch on" than the Mosfets.
> >For that reason our controller does not use diodes in the
> freewheel circuit,
> >instead we use Mosfets there also.
> >
> >I don't know what GE uses in their design, but since they give
> their ratings
> >at 50% I assume they use diodes in the freewheel circuit....
> >
> >Hope this clears it up for you.
> >
> >Steve
> >scr echoweb net <mailto:scr echoweb net>
> >
> >
> >
> >----- Original Message -----
> >From: RJ <mailto:rjkanary nauticom net> Kanary
> >To: Steve Richardson <mailto:scr echoweb net> ; tjwilhelm
> ><mailto:tjwilhelm stelle net> ; elec-trak cosmos phy tufts edu
> ><mailto:elec-trak cosmos phy tufts edu>
> >Sent: Monday, November 24, 2003 6:51 PM
> >Subject: Re: (ET) GE Sep-Ex controllers?
> >
> > Steve, thanks for the reply. Now, for those of us that possess
> just
> >enough knowledge to be dangerous, <G>just how do these two
> controllers
> >differ in their operation. Bear in mind, in my case, the precious
> little I
> >know about DC motor control was passed on to me by my Dad, who
> was an
> >electrician for American Bridge. The cranes he maintained were
> all '50s
> >vintage, brute force control types, operating from an "ignitron"
> (?)
> >rectified power supply.
> >
> >----- Original Message -----
> >From: Steve <mailto:scr echoweb net> Richardson
> >To: RJ Kanary <mailto:rjkanary nauticom net> ; tjwilhelm
> ><mailto:tjwilhelm stelle net> ; elec-trak cosmos phy tufts edu
> ><mailto:elec-trak cosmos phy tufts edu>
> >Sent: Monday, November 24, 2003 9:43 PM
> >Subject: Re: (ET) GE Sep-Ex controllers?
> >
> >Hello Tim Wilhelm and ET list,
> >
> >Just a quick note to set the record straight.
> >
> >The Alltrax controller does not have to be "programmed" by the
> end user.
> >It's "Programmable" such that the end user can change the current
> limits and
> >the throttle response times, battery upper and lower limits, but
> this is
> >accomplished by moving a slider such as the ones you find on your
> volume
> >control in your audio programs. No programming is required.
> >
> >The 50% duty cycle rating RJ Kanary talked about is the lightest
> load you
> >can put on a controller. At 50% the main switching transistors
> are on for
> >half the time and the freewheel components, diodes or
> transistors, are on
> >the other 50%. Anything above or below that point and your
> current
> >capability drops because the main switch or the freewheel circuit
> will be
> >conducting harder which makes the heat generated concentrate in
> those
> >devices.
> >
> >Our controllers are rated over time and at full throttle and
> that's how we
> >test them.
> >
> >Thank you for bringing this to our attention guys !
> >
> >Steve Richardson
> >Alltrax inc.
> >541-476-3565
> >scr echoweb net <mailto:scr echoweb net>
> >
> >
> >
> > ----- Original Message -----
> >
> >From: RJ <mailto:rjkanary nauticom net> Kanary
> >To: tjwilhelm <mailto:tjwilhelm stelle net> ;
> >elec-trak cosmos phy tufts edu <mailto:elec-
> trak cosmos phy tufts edu>
> >Sent: Sunday, November 23, 2003 5:01 PM
> >Subject: Re: (ET) GE Sep-Ex controllers?
> >
> >It appears as though the armature current rating is based on a
> 50% duty
> >cycle. Am I understanding this correctly? If that be the case,
> operating the
> >tractor to it's full capabilities may prove disappointing with
> this control.
> >
> >----- Original Message -----
> >From: tjwilhelm <mailto:tjwilhelm stelle net>
> >To: elec-trak cosmos phy tufts edu <mailto:elec-
> trak cosmos phy tufts edu>
> >Sent: Sunday, November 23, 2003 9:39 PM
> >Subject: (ET) GE Sep-Ex controllers?
> >
> >Hello ElecTrak Folks,
> >
> >Does anyone on this list have any experience with the GE
> controllers for
> >separately excited shunt field DC motor? Any idea of cost? Or
> >reliability? Or ease of installation and use? I found them on
> the net at
> >this link:
> >http://www.geindustrial.com/cwc/products/products/products?pnlid=4
> ><http://www.geindustrial.com/cwc/products/products/products?
> pnlid=4&id=sx2se
> >mtc> &id=sx2semtc .
> >
> >It appears they have an RS-232 interface, so they can be
> programmed like the
> >Alltrax unit. They also come in 4 different sizes. The SX-2 is
> a 400A
> >unit and appears it could handle an E15, E-16, or E-20.
> >
> >I'd appreciate any feedback anyone may have.
> >
> >Thanks,
> >Tim Wilhelm
> >
> >
> >
> > _____
> >
> >
> >
> >
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> >Elec-trak cosmos phy tufts edu
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> >
> >
> >
> >
> > _____
> >
> >
> >
> >
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> >https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak
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> >
> >
> >
>
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