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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 -----
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
----- Original Message -----
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 -----
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
----- Original Message -----
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 -----
Sent: Sunday, November 23, 2003
9:39 PM
Subject: (ET) GE Sep-Ex
controllers?
Hello ElecTrak Folks,
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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