Alternator v. no alternator - 10% gain @ 70 km/h

[mikehallbackhoe]

I have been researching this for a while, and one of the concerns is that without the alternator, the spark will only be 12 volts instead of 14. how about running the ignition system on a seperate circuit, running the alternator with a larger pulley, connected to a motorcycle battery. the rest of the electrical system could be hooked up to a deep cycle battery. now the spark would be 14 volts, and the alternator would not be working very hard. I realize this would only be practical for older cars, but my crx is a 84. as long as I was able to bump start my car, I would be able to get home even if the deep cycle battery was too low to start the car, assuming its not dark. The other option would be to just put the starter on a deepcycle battery, run larger pulley on the alternator, and run a motorcycle battery. my car doesn't have a radio, and without the burden of a starter, it wouldn't take much battery to run the system.

[GasSavers_Erik]

It's not too hard to unplug the round connector from the back of the alternator- this will stop it from charging. Then you could check the drive ability and mpg at 12 volts. A higher voltage aftermarket coil would give you a similar spark at only 12 volts. You could likely even find a coil designed for an external resistor (breaker points system) and leave the resistor out.

IMHO- I don't think that running a motorcycle battery will reduce alternator load- since it still has to maintain the voltage set by the regulator. The motorcycle battery would give you less reserve capacity, but I think the load on the alternator would be the same.

Honda put an alternator control module on the CRX HF's for sure back in 86, I don't know if they went all the way back to the 84 crx 1300. The control module was able to control whether the alternator charged or not. It stopped the alt from charging under certain conditions (probably under deceleration and light loads). The 87 CRX HF had to have a certain model of alternator for this to work properly- the only way you could tell that it was the correct one was from the part number (it looked identical to the rest of the 84-87 alternators).

[mikehallbackhoe]

the reduced load to the alternator would come from the larger pully. isolating the ignition system with the motorcycle battery would hopefully not overtax the slower turning alternator. fuel mileage probably wouldn't be as good as running with the alternator deleted, but the driving range would be greatly improved.

[mikehallbackhoe]

I found a formula to calculate how much hp the alternator uses.
amps x volts = watts
745.7 watts = 1 hp
hp x 40% efficiency loss = hp loss
hp + hp loss = total hp used
example
55 amp x 14.9 = 819.5 watts
819.5 watts / 795.7 = 1.098 hp
1.098 hp + 40 % = 1.5372 hp

[mikehallbackhoe]

after considering those numbers, I took the alternator belt off my crx. cold idle speed went from 2000 rpm, to 2500 rpm.
I just purchased a 31a yellow top optima battery for my dump truck, but I am going to put it in the crx and see how far it will take me.

[shatto]

After an alternator failure and still having to drive hundreds of miles on battery power alone, in a newer all-electronically run vehicle, I wonder how what we are discussing would work with a new vehicle.

[mikehallbackhoe]

I would think with modern computers and so much electrical, it would be a challenge.

[DRW]

That's a good question. I know that newer computer controlled cars have tables that look at battery volts to keep the engine running right so volts can fluctuate without affecting the way it runs. I also know that a healthy 12V battery will drop to approx 9 to 10 volts when cranking and trying to start. It's been a while since I read the manual, but IIRC the ECU shuts down when volts fall below 7 or 8 volts. I believe the Prius and other electric cars and hybrids manage battery charge more strictly than that.

[GasSavers_Erik]

mikehall's CRX is carbed and has a mechanical fuel pump- although reduced voltage from no alternator will result in a slightly weaker spark, assuming he keeps the headlights lights and blower motor off and is driving on the highway (no brake lights) I think it will go at least 2-3 hours before he notices any difference in performance.

I have an old 4 cylinder gas tractor which is missing the alternator and I can run it for at least 5 hours and still have enough juice to start it again (yes the battery is larger than a CRX battery- but it also 9 years old).

[mikehallbackhoe]

the optima 31a yellow top battery is probably the biggest battery I can get and still fit under the hood. I believe it is optima's biggest battery. I also do a lot of EOC, so I doubt I will have any problem running low on battery power