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HI guys:
Although I have been lurking here for some time,this is my first post at this forum, so first let me tell you a little bit about me and my Geo Metro.
Im a retired 70 year old that shares your passion for improving mileage, and I am working on controlling the alternator on my 1994 stick shift 3 cylinder Metro to save gas as well.
I recently installed a Xantrex Link 10 Battery Monitor in the Metro and optima red top 44 AGM 44 amp hour battery.
Next I tore into the stock 55 amp alternator and brought out two wires which allows turning the field on by connecting the ends of the wires togather, or turns it off when the wires are disconnected.
The internal voltage regulator, and the alternator, function normally when field is on and alternator does not charge when the field is off.
I rigged up a 3 way switch on the dash, and a bit of circuitry, such that in one position the alternator never charges, in another position it charges normally all of the time, and in the final position it charges only when the fuel injectors are cut off during deceleration for regenerative braking.
With a fully charged battery and with the alternator off, when the engine is cold it uses about 7 amps, but when it warms up it drops to about 3 amps. All in daylight with no accessories on. I still haven't figured out what is on when cold that draws the extra 4 amps, not that it it matters much.
I am really surprised that the the injector, fuel pump, and ignition together use only about 3 amps, but that is what I am observing.
With the switch set to charge only while decelerating, giving regenerative braking, the amount of charging, and braking, depends on the state of charge of the battery during deceleration. When the battery is full maybe 10 amp or so, rising to a full 55 amp as the battery nears full discharge.
If you are going to do regenerative braking, you must leave room in the battery for the generated charge to occupy by running with a partial charge in the battery normally!
I read somewhere that BMW uses 80% charge on their new system.
Also there is the old rule of thumb for charging lead acid batterys that says that a safe rate of charge, in amps, is equal to the number of amp hours out of the battery.
Thus if my 44 amp hour battery is half discharged, a safe rate of charge is 22 amps, and I am exceding that rule. Probably ok for short periods, but it is clear that for big alternators and heavy regenerative braking, big heavy batterys are needed.
Another interisting rule of thumb used by those who sell 12 volt alternators is expect 1 horse power to be required for each 25 amps of alternator output.
With my present set-up and my normal driving around Tucson, regenerative braking only does not keep the battery from becoming more and more discharged.
At present I am considering a solar panel to supplement it.
Anyway, thats my two bits worth for tonight. Take care All.
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