Electric Vehicle Discussion List mailing list wrote > OK, this topic has induced me to resubscribe to the EVDL, it's > probably been 20 years since I was officially signed up. I've > occasionally passed replies through several members (thanks Lee, > thanks David), but maybe it's time to get out in the open. > > What you have there is similar to the shunt-wound motor in my > factory-conversion SCT Rabbit from 1981. I can't tell you anything > about the controller, but the motor is very familiar. > > Shunt wound motors differ considerably from series wound motors. For > one thing, they have regenerative capabilities as a native behavior. > The field windings are energized separately from the armature (they > are also known as "separately excited" motors). I'll leave it to you, > or others to do the research on the technical principles involved, > but suffice it to say, the armature runs at 100% voltage (direct > connection to the batteries through a contactor), while the motor > speed is controlled by ~weakening~ the field voltage. That's right, > ~weakening~! > > You can not run this motor by simply applying a voltage and watching > it spin. There is a startup sequence, which consists of applying full > voltage to the field windings, and a current-limited (via resistors > or other current limiters) voltage to the armature. This causes the > armature to come up to an idle speed slowly (4-5 seconds), at which > time the controller applies full battery voltage to the armature. > > These motors have poor stall torque, so it "idles" when not actually > driving the vehicle forward. Mine idles at about 1,800 RPM (120 volt > nominal battery supply). This is with full field. As the field is > weakened (by a PWM or "chopper" circuit), the motor speeds up. > > This type of motor allows a fully functional "one pedal" driving > style. Step on the accelerator to speed up and let off to activate > *very* powerful regenerative braking. I see 200+ amperes while > downshifting through all gears (I realize that your vehicle is locked > in 2nd). Using the service brakes is not necessary except in an > emergency or to come to a complete stop. > > Before you do anything else on this van, you MUST check a few things > beforehand. > > On the end of the motor that you have pictured is a conical shroud > held on by clips/clasps. This is the brush end of the motor. There > are eight armature brushes under this shroud. If the van has been > siting for any length of time, you would be well advised to pull this > shroud and check to see that ~all~ of the brushes are free to slide > in their holders *and* that none of them are stuck to the armature. > also clean out any dirt/dust/cobwebs/insect or rodent nests you see! > > Now, as for your test to see if it ran. Did you twist the key over to > the "start" position? Because the motor has a start sequence, there > must be some method of engaging the field voltage and armature > current limiting circuits. Installing a fresh 12 volt accessory > battery will likely be necessary, as the controller obviously > requires a low voltage supply in addition to the traction battery. > > Until last week, I had a web site with extensive documentation on my > SCT Rabbit, including information on the motor, etc. Some of this may > be useful to you, so drop in to the archive.org Wayback Machine and > check some of the PDF files that got saved in a snapshot of my site > from seven or eight years ago: > > http://web.archive.org/web/20111109054159/http://www.mrsharkey.com/SCT/index.html > > Glad to answer and questions you have, sorry to be completely > ignorant about your controller.
Awesome, thanks so much for the information. This is a great start towards making this thing work. When I was in college, one of my computer science professors explained that the people in the factory put the magic smoke into the electronic components, and it is our job not to let the magic smoke out. I have taken this to heart when working on electric stuff like this which I know very very little about. Thus I am unwilling to just put voltage to a component like the motor and see what happens. Normally, when I go to work on something I have a massive technical library to draw upon, but in this case, I am starting out in the dark and this has shined some light. On the operational characteristics of this motor, by the field having full voltage at stop (or just more voltage than the armature), it overpowers the armature and creates drag buy forcing the system to generate electricity, and when the armature has more voltage it uses the battery power to turn. Is this correct? Not that it necessarily helps in getting it running, but I like to know how/why things function. I turned the key on, and to the start position a couple times, but I got nothing to indicate than any electrons were flowing anywhere in the system. I figured that the start position was just a relic of a standard ignition switch. I did not have a 12v battery hooked up, which is likely one reason things didn't work. I had scavenged every easy to grab battery around the shop, and I had 10 12v and 2 6v strung together in the battery tray, and none left over for the vehicle. I will scrounge up a couple more batteries to make this work. I tried to take the cover off the motor, but to didn't want to pop right off. I will play around with that some more. The brushes are not stuck to the armature, as I have made it turn manually, but I don't know that they slide freely in their housings. One thing that I read about this specific system is that it has regenerative braking from 43mph down to 30mph, and another source said that it has regenerative braking down to 0mph. The top speed is 43mph. Either way, it is not all that important, as it works one way or the other. The brake pads show very little wear, but the vehicle only has 11,000 miles on it. An interesting thing with it is that there is no vacuum brake booster like is seen on every other VW with disc brakes. That makes more sense with the regenerative braking. I will play around with this more next week and report back on my progress. -- Sent from: http://electric-vehicle-discussion-list.413529.n4.nabble.com/ _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
