EVDL Administrator via EV wrote:
Is there any reason you couldn't build a simple series-parallel stepped contactor controller?
A contactor controller works, is cheap, and about as simple as dirt. The controller itself is essentially 100% efficient; it's nothing but switches, after all.
However, it's about as old-school as you can get. It only works with DC motors. It only provides a small number of discrete speeds -- if you need to drive at some other speed, you'll need to constantly cycle between steps, or add resistors, or shift gears, or change motor windings -- all of which will lower efficiency.
It's also not the sort of thing to impress people with your high-tech smarts.
For a very simple, low-cost, do-it-yourself EV, contactor controllers still have their place. But in an efficiency racing contest, I think you'd be hard pressed to "tune" everything so precisely that you could hit the "sweet spot" with a contactor controller. It would require that you compete on a flat track on a windless day with a fixed-weight vehicle, so you know precisely that full pack voltage is the optimum value to apply to your motor.
If you use a brushed DC motor with a separate field, you can get finer speed control by varying field current too. Since in a sep-ex motor the field uses much less current than the armature, a field controller is easier to build. It could even be a rheostat.
That's true. But field controlled motors lose a few points of efficiency due to the power needed for the field. That may not matter for general driving, but it could make all the difference in an efficiency contest.
For more information on the history of EV controllers and examples of the various types, see
http://www.sunrise-ev.com/controllers.htm -- Knowledge is better than belief. Belief is when someone else does your thinking. -- anonymous -- 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 Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
