[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
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
>
>
>
> _____
>
>
>
>
>_______________________________________________
>Elec-trak mailing list
>Elec-trak cosmos phy tufts edu
>https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak
>
>
>
>
> _____
>
>
>
>
>_______________________________________________
>Elec-trak mailing list
>Elec-trak cosmos phy tufts edu
>https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak
>
>
>
>
>