Alternator Cut-out

Discussion in 'General' started by tommyt31, Jun 30, 2008.

  1. tommyt31

    tommyt31 Active Member

    I was thinking of dissabling the alternator via a manual switch to help reduce load on the engine on short trips (everyday, i drive 3 miles to work). I proved that the car would run for at least 20 minutes last week. My alternator died and I continued to drive the car around town. The battery went down to about 11 volts by the time I got home. I charged it up and all was fine. Of course, I would replace my starting battery with a deep cycle battery to ensure I don't reduce the life of my starter battery. Then I could charge the car each night at home. I thought someone had tried this already. My problem is I don't know what wires to intercept on the alternator. My alternator has a large red wire (positive from the starter) and 2 small wires going into it. The two small wires are on the same plug. I am assuming one of them controls when the alternator is charging and when it isn't. I drive a 96 Saturn SC2. Anyone know the answer to this?
  2. Xringer

    Xringer Older Member

  3. tommyt31

    tommyt31 Active Member

    Thanks! That helps.
  4. Xringer

    Xringer Older Member

    "The alternator's load on the engine is the alternator belt."
    Actually, since the belt doesn't get real hot, it's not dissipating much power at all.
    The electrical load (lights, rear window defroster etc) is what loads up the alternator and
    that (now mechanical) load is placed on the engine via the belt.

    " Removing the alternator belt and running the engine just off the battery will shorten the battery life."
    tommyt31 did say he was going to replace the battery with a deep cycle battery,
    so, maybe his idea will work ok..

    "Draining down the battery and then periodically turning on the alternator with a switch to recharge it might shorten the life of the alternator."

    If he watches the battery voltage and doesn't allow it to get too low, recharging it with the alternator shouldn't cause an abnormally high load.
    Since tommyt31 is going to charge up his battery at night off the AC mains, it seems to me
    that the alternator is going to get less use and should last a lot longer.

    "Turning the alternator on and off with a switch would not affect mileage because the engine is still turning the alternator via the alternator belt."

    If he is removing all the electrical load off the alternator, it's going to be real easy to turn.
    (When you have the lights, etc turned on, it takes more work to turn the alternator,
    to generate power: Watts)
    And if the engine is not doing as much work, then he should get better MPG..

    "whenever sensors detect the electrical load has increased when the engine is at idle. Turn on the headlights at idle and the engine will automatically speed up to increase the alternator output to the battery so the headlights don't start draining the battery."

    My take on that is, when you turn on the lights, you electrically load down the alternator,
    it loads down the engine, which has an idle control unit which wants to keep the engine
    from stalling (when RPMs drop too low), so the idle control gives the engine more gas..

    Any time tommyt31 charges his battery at home, he is not using gasoline..
    His car will be working like a Plug-in Hybrid. But not saving a ton of gas
    like the real deal (Honda Insight)!! :D
    But, it sure seems like he will be saving a small amount of fuel..
    Most likely not an easily measurable amount!
  5. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    MetroMPG did some testing of this and the gain was on the order of multiple mpg IIRC.

    The Insight doesn't even have an alternator -- partly for this reason. ;)
  6. basjoos

    basjoos Well-Known Member

    If you have a SuperMID installed in your car, you can see the electrical loads that various accessories place on the engine. You can sit there with your warm engine idling while you turn on the lights, fan, radio, A/C and note how much the injector pulsewidth increases from the idle pulsewidth with only the electrical load required to run the car. The pulsewidth takes only a few seconds to show the new load.
    Last edited by a moderator: Jul 5, 2008
  7. tommyt31

    tommyt31 Active Member

    Great info, guys. I'm not sure what a SuperMID is, though.
    I asked Mike Rowand about my question (he is the guy that owns the website with the alternator wiring schematic above that Xringer posted). He said that drag racers do exactly what I want to do to gain a few hp on the quarter mile. The problem is if you run your electrical system at 12 volt (more like 12.5 volt) instead of 13.5-14.4 volt (alternator output), you could see a reduction in the intensity of the spark. I don't know if that would have a measureable effect in FE, though. I guess I could try it, but I still don't know what wire to intercept. I wanted to avoid messing with the main positive wire because of the amount of amps going through it. I could pull the fuse for the alternator and see if that works but I would be guessing.
  8. basjoos

    basjoos Well-Known Member

    A SuperMID is a fuel consumption measuring device that was originally designed for the Prius, but also works on OBD1 (pre-1996) fuel injected 4- cylinder cars that won't work with a Scangauge. It has a number of displays not found on the Scangauge that are useful for FE driving.
  9. tommyt31

    tommyt31 Active Member

    Cool, thanks! That would be handy on my 85 Daytona.
  10. Xringer

    Xringer Older Member

    I'm not sure you would see "a reduction in the intensity of the spark". Logically, on a well designed system, the spark should stay the same, since the alternator & the loads can vary all the time.
    When I'm driving along, I can see my SG2 displaying between 12.6 & 14.x randomly. I'm pretty sure that the spark isn't effected much..
    I think it would be effected more by old spark plugs and spark plug wiring.

    Anyways, 1 watt = 0.00134102209 HP. So, 200W headlights are eating up around 1/4 hp..
  11. tommyt31

    tommyt31 Active Member

    Good thought, Xringer. I am still thinking I am going to try this. I was thinking of using a battery disconnect switch ($7-$8 at wallmart) on the main positive wire to the alternator. That would surely take care of it. I might try just pulling the fuse first, though to see if that would do it.
  12. pdw

    pdw Well-Known Member

    Bad idea (good thinking though).

    I tried this for solar-electric only ... to disconnect the alternator.

    The solar people ended up convincing me to use a switching system between batteries instead.

    When the engine is off while coasting engine-off .... or for decelerating with engine power (charging drag) on occasion, switch in the regular size battery (the one that you charged at home) into the electric system .... which will drain it for supplying the engine-off electricity drawings and not draw from your acceleration power on the next upspeed.

    To keep the alternator happy during bursts of power, I may be trying to keep a tiny (good-shape) motorcyle-battery engaged to the alternator the rest of the time. The small lead-acid needs little power to keep up, thus pulling very little torque onto the alternator shaft.

    Plus, it will keep the 14volt spark-base .... which equates to better combustion. I noticed this when using the extra 15volt charged European battery for the solar panel at that time. The engine fired up noticeably perky because of the extra voltage ....and that seemed to promote cleaner combustion and optimum power.
  13. Xringer

    Xringer Older Member

    Basic info:

    Here's a ton of posts on the topic..

    One of the things I found reading that thread was, some folks think that a cut-off switch
    in the alt + output line can harm the regulator..

    I do like the idea of regen. Switch the magnet coil on when you are coasting down hill
    with your foot off the gas, or when the brake light comes on.. :)
  14. tommyt31

    tommyt31 Active Member

    Thanks for the info!

    I can see why this would be a problem, since the alternator (if self-exciting) would keep charging the battery anyways even if you did disconnect the field current supply and the control voltage input wires.

    As far as damage to the regulator, it looked like that would happen if you ran the car without the battery and just used the alternator. That is not my goal, of course.

    I think the best way to do this is what I believe pdw is saying. If you could take your control voltage input wire (sensing voltage wire) and hook that to a well charged smaller battery that wasn't hooked to any load, the alternator would not try to charge the starting battery at all (or hardly at all). You could use a double pole switch to switch the sensing voltage between the starting battery or the smaller battery (maybe my Ni-cad 12volt drill battery would work?). Remember, the alternator would still be directly connected to the starting battery, it's just the sensing voltage wire that would be connected to a switch to go between the 2 batteries. Seems like it would work to me. Anyone have any thoughts on this??
  15. pdw

    pdw Well-Known Member

    When the 60AMP alternator in the 94 Saturn gets a new battery switched into it that way .... one that is 10-30% discharged ... I can definitely feel there is some horsepower demanded by that alternatorshaft at that point.

    At that point the alternator goes to full production and full cooling (lots of airflow by its own fan). I see it as good practise to allow an alternator to perform this way (main-battery switched in) at approx 1800rpm .... which is (safe to say) an efficient power-making rpm to use for that purpose.

    Where I see some potential gain using this method .... would be where I've already seen the airconditioner trick work (same concept). I click in the aircondtioning on hot days
    .... but only when I'm into estimating when to FAS towards the end of an upspeed. Once I've flicked the tranny into 5th gear, I'm already searching for the best place to reduce the engine for the glide, and that opens a short time for both cheaper airconditioning power supply and also full-alternator (not to forget also on a downshifting decel instead of using the rotors). Those extra seconds at 1800 cool the condensor quickly, and also sends enough charge into that alternately switched-in battery ... so the cheaper-to-run fan can warm the condensor at full-setting (still keep cooling the interior) while coasting engine-off with necessary electrics on, .... power that then is drawn proprtionately more from the switched-out battery because it is so much bigger.
    Last edited: Jul 13, 2008
  16. diamondlarry

    diamondlarry Super MPG Man/god :D

    If you were to put a switch in the field wire going to the alternator this would allow/disallow the alternator to charge or not. The voltage regulator varies the amount of juice going to the field coils which is how the alternator knows how much to charge. So basically, no field current, no charge. I'm not sure where they are at the moment but, my son has a complete set of Saturn factory service manuals that would apply to the '96-'02 models.
  17. psyshack

    psyshack He who posts articles

    On some of the old rwd muscle cars folks use to run the alt's off the drive shaft. Others just put under pulleys on them.

    I use to custom build mine. I would build up a say a 105 amp alt. then put a 65 amp regulator in them with over current protection. So when The big alt. put out its massive amps when I was on the throttle. The reg would just open up and the alt would go to no load operation. Then when the rpms dropped it would charge. It would charge hard then drop out. GM junk liked to burn up from time to time like the rest of there junk. But I never had issues with Mopar or Ford Alt's.
  18. tommyt31

    tommyt31 Active Member

    DiamondLarry wrote: "So basically, no field current, no charge"

    DiamondLarry, I thought the opposite was true. I thought at 12.5 - 13.0 volts = no charge, but at 0 volts of field current the alternator should be trying to achieve the max charge. I know more than one person has disconnected the field current wire and found that the alternator was still charging the battery.
    I heard the term self-exciting thrown around. That could explain why the alternator was still charging.
  19. Xringer

    Xringer Older Member

    I think it might depend on the type of alternator you have. Some of them (maybe older models) have an external regulator and you can access their wires.

    I think those models that have an internal regulator may also have internal wiring from the reg to the field current coil.
    Therefore, you might be able to install a switch in-line with the ignition line (in-line with the 8-Amp fuse going to the alt) and cut the alt off..
    Since that line provides power to the reg, which provides power to the field coil..

    When I was a kid in a Ham radio club, we had a gas powered generator that had no AC output.
    I put a screwdriver near the generator and found it had no magnetism.
    So, I asked an older ham "how power could be generated without a magnetic field"..?.
    He replied (in phD language) and used the term 'self-excited'.. So, to start up the generator and get it to magnetize a little bit,
    I decided to stick a 12V battery across the output (just for a few milliseconds) while the engine was running.. BAM! It started producing 120VAC instantly! :)
    Don't try this at home!

    Now, 40 years later I was reading a manual for a new 5.5KW AC gas powered generator,
    I found out my '12V battery trick' wasn't invented by me after all.. :(
  20. pdw

    pdw Well-Known Member

    I tried out the battery disconnect circuit design which I'm attempting to win the prize with(based on the same switching system for accomodating solar).... where it leaves only a/the (small) motorcycle battery to hold the fort among the wiring while the car accelerates to best torque rpm each time during FASing.

    Immediately I notice the spoolups are slightly shorter each time ... as well as the accelerations back to speed are noticeably shorter. The switch (with ten second time delay) is to pop the two batterires (small and big) in the battery compartment back together the rest of the time, including for any extra seconds the alternator will then be charging both ... with the car up to speed. This way the batteries are always together for the coasting discharge as well as for any starter action when stopped in traffic.

    The big gain is a healthier spark during those ten seconds. This is because the power to the coil is stronger and burns the fuel better. For the amount of fuel pouring into an upspeed while FASing ... this seems to me to be too valueable a trick to overlook among seasoned hypermilers.

    My temporary switch looks ridiculous. It was hard to make. It feels like a 4mph saving during FASing.... maybe a bit less in the daytime. Maybe that switch doesn't exist ?"

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