Once again Lee I thank you greatly!! This reply and the previous are tremendously helpful and greatly accelerates my learning curve! Since these are the motors I have I will move forward with the advice provided here and report back my successes and failures in regards to this matter!
Thank you so much Sent from my iPhone On Feb 10, 2013, at 8:29 AM, Lee Hart <[email protected]> wrote: On 2/10/2013 7:27 AM, Jeffrey Jenkins wrote: > Drewcifer wrote >> I thank you for the link am I have read it twice and as a non scientist I >> don't understand how it applies to the below information suggesting that >> pmdc motors should not be run in parallel. I apologize for my ignorance. >> ... > > I really don't know how else to explain this without repeating what I, Lee > Hart or Bill Dube have already wrote. Put as simply and succinctly as > possible, PMDC motors have a fixed and fairly "stiff" relationship between > voltage and RPM, and because no two motors are exactly alike, no two motors > will have exactly the same Volts/RPM ratio (usually referred to as "Kv"). > Thus, unless both motors are allowed to spin at different RPMs, the motor > that spins faster at a given voltage will hog all the current, with some of > that current coming from the external supply, and some coming from the other > motor (acting as a generator). > > This is pretty much bad news no matter how you slice it, hence, the advice > to not drive two or more PMDC motors from one controller. ...or when the motors are wired in series. The situation the original poster has proposed (two PMDC motors, each driving one wheel) isn't optimum, but it isn't hopeless either. If you have the motors, try them. Wire them in parallel, and measure each one's RPM to see how closely matched they are. If they are pretty close (say, within 5%), I'd give it a try. Your controller can switch the motors in series/parallel. At low speeds or whenever you're turning sharply, run them in series so they won't fight each other. Include an ammeter in series with each motor. Then you can *see* when the current are unequal, and whether they are fighting each other. If there's too much fighting, then you'll need to add a second controller. -- Don't worry about people stealing your ideas. If your ideas are any good, you'll have to ram them down people's throats. -- Howard Aiken -- Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
