Harvey Norris wrote: > --- On Sat, 9/26/09, Stephen A. Lawrence <[email protected]> wrote: > >> From: Stephen A. Lawrence <[email protected]> Subject: Re: [Vo]:Car >> Alternators Vs Old Style Generators To: [email protected] Date: >> Saturday, September 26, 2009, 10:05 AM >> >> >> Chris Zell wrote: >>> The last car to use generators that I'm aware of was >> the VW Bug. I >>> suppose alternators were cheaper to build. > What a coincidence, I remember an incident where my (pre 70's?) Car > Me Ghia? VW had its alternator go out, and was in fact surprised to > learn it was instead a generator. Your post made me remember this. A > freind has a porsche engine in the older VW busses they made. >> That would make sense. Once cheap reliable high current diodes >> became available, the alternator design appears simpler. >> >> On the other hand, I've always heard that alternators are preferred >> because they perform better than generators at low RPM -- in other >> words, their "power band" is wider, which is important for >> something which turns at a fixed rate relative to the engine (no >> transmission on the generator). I've never checked that claim out, >> however. > Because the (car) alternator has its field regulated, it is designed > to constantly produce 12 or 13 volts, probably even at the lowest rpm > available to it by idle of the automobile. The PMG site however > claims that high amperage extraction at low rpms must be avoided as > it will overheat the stator windings. The one I am purchasing will be > used for a small Brown's gas torch; driven by a 10 hp lawnmower > engine. What this means is that the generator that developes higher > voltage at higher rpms will have a load that "kicks in" only after a > certain rpm developes. This is to be negotiated by the number of > cells in series that the unit employs. It would seem then that my > variable speed drive will come in very handy here. As noted with 40 > cells in series, the thermoneutral electrolysis point only being 1.4 > volts/cell, this implies that the load should kick in at 56 volts > from the generator, which is probably just under mid range engine rpm > for an automotive application. HDN
This sounds like you actually want 56 or more volts from the beast, yes? I seem to recall that you can dink the built-in regulator in a typical automobile alternator and get out very high volts from it. Where I read this, exactly what you have to disable, or how high the volts can go before the alternator does an auto de fey, I don't recall just now, unfortunately. >> Most of my experience with generators comes from the old flathead >> Willys Jeep engines we used in my father's boat, back in the day. >> (Two in succession; first replaced when the cylinder walls rusted >> through, due to use of an open cooling system in brackish water. >> It's a tradeoff -- a closed system is more expensive, more complex, >> and takes more maintenance, but an open system requires replacing >> the engine block every ten years or so.) >> >> >>> >> >
