Different motors have different characteristics. Permanent magnet motors have a back EMF that looks like a generator with a series resistor. They have a back EMF of V=x*RPM where x is a constant for the motor. As the motor spins faster, the voltage goes up. This motor will regen if you spin it fast enough the back EMF exceeds the battery voltage. Getting it back into the battery is simple because the free wheel diodes in buck controllers will forward bias and automatically put it into the battery.
Series motors have a back EMF that looks like a resistor. The equation is R=x*RPM. As the motor spins faster, the resistance goes up. The cannot generate any voltage unless the field is magnetized by an external controller. Controlling this field controller is the difficulty in getting regen to work with a series wound motor. Joe Smalley Rural Kitsap County WA Fiesta 48 volts NEDRA 48 volt street conversion record holder [EMAIL PROTECTED] ----- Original Message ----- From: "Seth Murray" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Saturday, September 28, 2002 9:52 PM Subject: Re: Motors and such, was How much power am I losing? > hehe, guess I don't know too much about motors now do I?? =) here's a > dumb question - if our motor here is making all this back EMF, if we > are coasting down a hill and keep on winding the motor up and up and up > until the BEMF exceeds the input voltage, would we not have regen? My > understanding was that series motors are tricky to do regen with. Why > would that be, if we have this apparently straightforward EMF thing > going on? Thanks for the info. > > "Us racers swear at them..." someday, Rich, I will give you a run for > your money (or a new PFC) =) > > Seth > > > > On Saturday, September 28, 2002, at 01:12 PM, Rich Rudman wrote: > > > Seth Murray wrote: > >> > >> Peter VanDerWal wrote: > >> > >>> the resistance through the brushes on a moving comutator is different > >>> than on a stationary one > >> > >> I have been wondering about this. Lets say I am driving in second > >> gear. When I first start my EV moving, the motor wants lots of amps. > >> Once it gets up to 4,000 rpms or so, the motor seems to have a limit > >> on > >> its current draw, even if I put my foot on the floor (current well > >> under the current my batteries and controller can deliver). As soon > >> as > >> I shift into 3rd, though, the motor will take all the current my poor > >> batteries and controller dish out. The only thing I could thing of > >> was > >> that the resistance through the motor must change depending on rpms, > >> which because of Ohm's law would allow the motor greater current at > >> lower speeds. I know there are other factors involved, but do I have > >> any clue of what's going on? =) > >> > >> Seth > >> > >> -- > >> QUESTION INTERNAL COMBUSTION > >> > >> My electric truck page, with lots of photos and a 25 page conversion > >> journal. Check it out! > >> http://www.wpi.edu/~sethm (NO MORE POPUPS!!) > >> > >> My EV Album page > >> http://www.austinev.org/evalbum/387.html > > > > HOooooH ha ha HHHHEEEE! Yea rather obvious is the BACK EMF of the > > motor. > > As it spins up it becomes a generator, you need to over come this with > > more volts or your motor will spin up to a certain speed and then wind > > out no futrther!!!! > > Basic V/F ratio. volts to Frequency or RPM same thing. > > All motors have rpm and torque curves. You are just seeing them . > > Us racers swear at them and try to manipulate them to our best uses. > > > > Check the motor curves from Advanced DC and from Rod at EVparts, and > > Ken > > Koch at KTA. > > > > > > -- > > Rich Rudman > > Manzanita Micro > > www.manzanitamicro.com > > 1-360-297-7383,Cell 1-360-620-6266 > > > > > > > > > > > > -- > QUESTION INTERNAL COMBUSTION > > My electric truck page, with lots of photos and a 25 page conversion > journal. Check it out! > http://www.wpi.edu/~sethm (no more popups!) > > My EV Album page > http://www.austinev.org/evalbum/387.html >
