Thanks Lee! I’ve learned a bit about motors messing with ElecTracs, but I don’t think I even know enough to be dangerous.
Googling around I ran across pancake (axial flow) motors and i see some that are close to having the torque in the size needed. But they seem to be very specialized. It would be a big, expensive effort. I was mostly wondering if it was possible. Perhaps another problem is that, as a motor it needs to be designed for low speed and high torque, but as a generator, it would need to run up to many thousand RPM. -Steve > On May 10, 2020, at 4:53 PM, Lee Hart via EV <ev@lists.evdl.org> wrote: > > steve sawtelle via EV wrote: >> So, as a thought exercise, do you think a motor-generator could be >> designed to start these engines yet fit within the physical >> constraints? > > Hi Steve, > > It's possible; the question is whether it would be practical (buildable; > affordable). It would take a pretty special high-tech motor. > > A normal ICE starter is a series DC motor. Such motors can be built with a > very high power-to-weight ratio; but then the efficiency is low. The low > efficiency means the current is very high, and they overheat quickly. The > brushes are solid copper, to minimize resistance; but in turn causing a very > short life expectancy. > > *Every* motor is also a generator: But series motors are hard to control as > generators. The above characteristics of a starting motor (low efficiency, > short life) also make it unsuitable as a generator that runs all the time. > > There are many applications that have combined the ICE starter and generator > into a single unit (aircraft, tractors, golf carts, lawn care equipment). It > this case, they designed it as a generator first; then tacked on the ability > to also use it as a starter. > > A traditional generator is a shunt DC motor. The brushes are carbon for long > life. If it's going to used at high current (like for starting), the brushes > and commutator have to be much larger (making the motor bigger). The field is > separately powered via the voltage regulator. This is an easy way to regulate > the output. But a second series field is required to make it work as a > starter. Having to put *two* field coils and a bigger commutator and brushes > makes the unit bigger. Not as big as a starter + generator; but it's close. > > All this means I don't think you can fit an adequate starter/generator in the > space available for the generator alone with conventional techniques. > > Motors with higher power-to-weight ratios generally use high-strength > magnets. They remove the need for the field coils; but also make it harder to > control. So you're going to need some high-power electronics to control it. > > Another problem with high power-to-weight motors is that (like ICEs) they > need to run at high RPM. This will mean a gearbox. That too is going to take > up space. > > There may be an easy, cheap, clever solution; but right now I don't see it. > Maybe look at other approaches, like a spring starter? > > Lee Hart > -- > When something bad happens, you have three choices: You can let it > define you; let it destroy you; or you can let it strengthen you. > -- Theodor Seuss Geisel > -- > Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > ARCHIVE: http://www.evdl.org/archive/index.html > INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org > Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA) > _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub ARCHIVE: http://www.evdl.org/archive/index.html INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
