The Lucas Bedford vans used a sepex motor. Armature control was via an SCR, with the field driven via a bipolar transistor circuit. Battery voltage was 216v nominal of 3KQ11 tubular plate lead acid. It was usually the field controller that
The first version of the Reva G-Wiz is a sepex motor too. On Sun, 26 May 2019 at 18:46, Lee Hart via EV <[email protected]> wrote: > > Mr. Sharkey via EV wrote: > > What we seem to have deduced is that the controller and motor are a > > matched pair. It seems without doubt that the controller manages the > > voltage delivered to both the armature and the fields, otherwise the > > "reverse switch" wouldn't be workable. > > Yes, that sounds likely. > > > I'd image that the sequence would be something like: > > > > 1) accelerator released: controller ready, no field or armature > > 2) accelerator depressed: full field, armature current limited, probably > > ramping up. > > 3) accelerator depressed further, full armature current, full field. > > This would occur at what I'm calling "idle" speed. > > 4) at some point, pressing the accelerator further results in the > > beginning of field weakening while maintaining full armature. > > 5) release accelerator partially: full armature current, restore field > > current to a greater level. Regenerative braking proportional to pedal > > position. > > 6) completely release accelerator: Well, this is a bit of conjecture. > > Dropping the armature at any point during deceleration would result in > > the regenerative braking going away all at once, which might be > > dangerous if the driver wasn't expecting it, so I'd say that the > > controller maintains the armature current until the vehicle has slowed > > to the point where regen is weak or nil, probably the "idle" speed, then > > it ramps down or cuts the armature current. > > That's a good guess. Though, a sepex controller is capable of very > sophisticated motion control. You don't see sepex in fork lifts very > often; but you do find them in more sophisticated EVs, and applications > like cranes and elevators, where the operator wants precise control of > position, torque, and speed. > > My old sepex controller was very crude; but it worked! :-) The armature > had 4 steps; off, 36v with series resistor, 36v direct, 72v direct. The > field had a big rheostat in series to the pack (36v or 72v). > > When the accelerator pedal was released, the pack was switched to 36v. > The field rheostat was 0 ohms, so full 36v field. As you pressed the > pedal, cam switches gave the armature 36v with resistor, then 36v > without resistor. Above that, the rheostat began increasing resistance > to weaken the field and speed up the motor. The field got to minimum > resistance near full throttle. At full throttle, a cam switched the pack > from 36v to 72v to get "full warp speed". > > A characteristic of this setup is that it tried to be a constant-speed > drive. If I held the pedal in one position, the car tended to go at the > same speed, drawing a lot more power uphill, and doing regen down hill. > I didn't want to suddenly push the pedal to a new position, because the > motor would "fight like hell" to get to the new speed as quick as it > could. The only thing preventing me from breaking drive shafts or > getting my teeth planted in the steering wheel was that it was a > relatively small motor (70 lbs; rated 30v 500a) and a heavy vehicle (a > 1974 Datsun pickup with a dozen golf cart batteries). > > > If, like Lee suggests, it might be a low voltage field, then the > > controller might have a buck/boost function for the field, which would > > complicate our armchair diagnosis. > > My guess is that they wound the field for some fraction of pack voltage, > so they didn't need a buck/boost controller. They could get (say) 4x > field by applying 120v to a 30v field winding. > > Your controller just has to be aware of how *long* it can over-voltage > the field before heating becomes a problem. The field has a lot of mass; > it can stand large over-voltages for many minutes, and there is usually > a blower that runs all the time for cooling it. > > > I do remember when I was researching the Siemens 1GV series motors last > > year during my lithium conversion, I ran across some documentation that > > seemed to show some series field windings along with the shunt/sepex > > field. The compound field arrangement might be the key to having > > stall/low RPM torque available so the motor doesn't need to idle. > > Yes. The most sophisticated applications for big DC motors are normally > compound (multiple series and shunt field windings). You can get just > about any imaginable characteristic just by careful choice of which > windings are powered. There are also interpoles, which add even more > possibilities. But that's a whole 'nother topic. > > > Thinking about it, it's entirely possible that the SCT developers went > > with the full-armature/idling motor both because they didn't want to > > have to build controllers that could handle the armature current, but > > also because that thought that a car that "idles" would be more > > intuitive for drivers used to ICE vehicles. > > Well, when people convert ICE's with automatic transmissions, they often > *do* need to keep the motor idling, just to keep they transmission > pumped up and working. And people have come to expect cars to "creep". > > > Earlier this month the local utility contacted me about entering my car > > in the town's annual Spring parade. I had to decline because idling at > > 1,800 RPM in first gear results in a ground speed of 9 MPH. > > The simple fix is to somehow drop the voltage to the armature. You can > make a shunt or sepex motor idle at 10 RPM! Full field voltage, and > something like 2v on the armature. :-) > > -- > If you're not stubborn, you'll give up too soon. If you're not flexible, > you'll pound your head against the wall and miss a different solution. > (Jeff Bezos) > -- > Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.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) > -- Paul Compton www.morini-mania.co.uk www.paulcompton.co.uk (YouTube channel) _______________________________________________ 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)
