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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
 
 
----- Original Message -----
From: RJ Kanary
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 -----
From: RJ Kanary
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
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&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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