I did not intend to disable the electrical system, just turn off the alternator. I have driven 60 miles at night with headlights on after my alternator failed, so I know for a fact I can do this. I will of course have to substitute a larger battery for full function if it proves to work. The plan is to install a remote switch to turn the field winding on and off, which of course will stop the alternator from producing any current. The only question I still have is whether or not the alternator will act as a load with the field de-energized. I doubt it, since they almost all use full-wave bridge rectification, but I need to look.
In fact, it is better for a lead acid based battery to be charged and discharged than to let it sit. At least, when I went to school we spent a lot of time talking about charge-discharge cycles. The real enemy of a lead-acid battery is drawing the cell voltages too low, e.g., less than about 11.5 volts total battery voltage. The reason the alternator has such high current capacity is so it can recharge the battery after starting the car. Considering that some automobile starters can draw up to 100 amps or so for a few seconds, and some folks maintenance habits are poor, resulting in a lot of cranking to get their vehicle started, it is necessary to really overdesign the alternator. It is true that the battery is there to start the car, but it also serves as a sort of filtering device for the output of the alternator. If you knew that you would only start your car twice a day, and that it would start immediately each time, you could reduce the size of the alternator considerably. My guess is that full-load on a small car with high beams, etc., is probably around 10 - 20 amps. Why would you suggest running the alternator off the crankshaft? The rpm is too low most of the time. Great discussion. But I suspect people are growing tired of it, so thanks for your comments. Regards, Jim -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Russell Johnson Sent: Monday, December 17, 2007 2:17 PM To: Eugene Unix and Gnu/Linux User Group Subject: Re: [Eug-lug] hardware query... Darrough, James wrote: > My 1990 Geo Metro XfI averages 50 mpg. If I follow truckers closely, I > can get as much as 60. I am trying to find ways to improve it, like low > rolling resistance tires and LED lamps in all the sockets, but during > the really cold months, the snow tires are reducing my average mpg to > around 48. Also toying with disabling the alternator and just charging > the battery at home. Drive the alternator off the crankshaft. I think you will find that running much of anything requires the alternator unless you never drive more than 10 miles round trip at night, and about 30 during the day. Plan on replacing the battery about once a year, as lead acid batteries aren't designed to cycle that much. The reason cars have a really big alternator and a relatively small battery is because the battery is for starting only. The alternator is for driving all the electronics. Unless you've retrofitted the engine with points, there are lots of electronics in your Geo/Suzuki. But you knew that, didn't you? :) Russ. _______________________________________________ EUGLUG mailing list [email protected] http://www.euglug.org/mailman/listinfo/euglug _______________________________________________ EUGLUG mailing list [email protected] http://www.euglug.org/mailman/listinfo/euglug
