Quote:
Originally Posted by pete c
I would love to see more info on this generator, assuming it's not of the" I could tell you, but I'd have to kill you" trade secret kinda stuff.
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The POC info is does not apply to the production version, but is illustrative... so no, I won't have to kill you. I hope I made it clear over at the Aptera site that the 49 lb applies to the unit in the POC. The production one is unfortunately twice as heavy despite being only 30% more powerful.
In the POC, the electric machine is an Etek permanent magnet motor, which weighs 22 lbs. To get the desired output voltage matched with the engine's peak efficiency point (which occurs at 2800 rpm) requires a step up drive. I don't have the spreadsheet in front of me, and am not sure if I put the belt and pulleys in with the 49 lbs. As I type that number, I'm thinking that it can't be right. I think, (although now I am having doubts) the engine ended up at 32 lb after removing it's fuel tank, muffler, recoil starter, and some miscellaneous pieces. So 22 + 32 is 54, and I probably added 5 lb for the belt drive to get 59. The engine (250 cc B&S) ships at 40 lb, and I doubt the the packaging, starter, tank, muffler and a couple bits come to 13 lbs (to make an engine weight of 27 lb.)
So I think your BS detectors are working correctly: It is probably 59, not 49. (On the other hand, it doesn't feel as heavy as a 50 lb bag of sand -- getting it in and out of the subframe requires lifting at odd angles, and I'm a weakling, etc.) Next time I have it out of the car, I have to weigh it.
The efficiency curve of the Eteks (which are no longer available) looks like that of
the PMG 132, but the ones I have are about 1% lower at peak: 89%. This is an actual curve from the dyno test of the motor itself (each Etek shipped with it's own dyno curve from QC test runs) whereas the published curves for the Perm are likely to be averages from dyno tests. The Eteks were often advertised as being over 90% efficient -- perhaps some were. Mine may be lower than average.
In the POC, the generator operation is manual. I do all sorts of thing "wrong" in testing the POC, but in anything like the operation of the real deal (in which the driver determines when to start the generator, but the microprocessor determines when to shut it off) the load on the generator is constant, and the engine runs at full throttle. The ammeter is always at 50-60 amps. There comes a point in the charge cycle when the amperage drops. At that point, it no longer makes sense to run the engine, because load is falling off. In the POC, the batteries are 60 AH and can accept a 3C charge -- an amount the engine cannot produce. So regen continues to function with the generator running, albeit not quite as well as with the engine off. In ordinary driving the friction brakes are never used, but only if you are a bit more conscious with the engine running.
In the production version, the generator will be PMAC (brushless) rather than brushed. The better versions of these are typically 93-94% efficient over a reasonably broad range. Specs for the Perm PGS 150, for example are here:
Permanently Excited Synchronous Generators - Perm Motor GmbH