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Re: (ET) GE Sep-Ex controllers?
Yes,
That's what I thought. Therefore, when the switching transistors are
"off" (say on the off side of a 50% duty cycle), there is no source
(battery) current flowing to the motor...true? And, during that off-cycle
of the switching transistors, the freewheeling diode is conducting the
kick-back from the motor windings shunting around the transistor. Also,
the kick-back current is only a minuscule transient, and the freewheeling
diode is not conducting kick-back current during the entire time the
transistor is switched off...true, also? What do you think?
I guess I misunderstood the original e-mail in this thread. I thought the
writer was saying the freewheeling diode was conducting battery current
during the entirety of all the off-periods. That's where I was starting
to
think I may have the wrong idea about how these things work.
Thanks for your help!
tjwilhelm
----- 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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> >
> >
> >
> >
> > _____
> >
> >
> >
> >
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> >https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak
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> >
> >
> >
>
>
>
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>
>
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