The Paseo gets an alternator disabling switch

Discussion in 'Toyota' started by Daox, Jun 14, 2009.

  1. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    That sounds like a really interesting mod... Let us know how it turns out, okay?
  2. cpeter38

    cpeter38 Right Lane Dweller

    I'll do a proper write up once I have some data. My only "concern" about this change is cooling the DC/DC converters. I'm actually planning on having some sort of fail safe mode that will still provide for ignition if there is a failure of the DC/DC (right now I have two potential failure modes that concern me - heat and quality of circuit board/components).
  3. JusBringIt

    JusBringIt Be Inspired

    well one's certainly out of your control at this point.
  4. standard7452

    standard7452 Active Member

    Ok i think the idea is interesting but....

    The only problem is that since the Paseo only has a 70 amp Alternator the max wattage that it could pull instantaneously is 966W or .966KW if the thing was maxed out.

    Wattage=Current x Voltage, thus 13.8 x 70=966

    About 1.3 HP IF AND ONLY IF the alternator was operating at max load continuously.

    In any case, your alternator is not generating its max power all the time so the hp drained from the engine is negligable.

    In comparison, an airconditioner can use up to 10HP on a hot day.

    Plus if I am not mistaken, spark plugs are fired using the counter-electromotive force generated by an inductive system (ignition coil, coil pack etc) so the load on the battery is probably not that high---the fuse on most fuel injection systems is only like 10A so the biggest draw would be like 150W or so.

    Anyway, all of those systems are probably voltage regulated and will simply fail to operate if you take them too low---at that point the engine could no longer operate to run the alternator to charge the battery.

    Good idea, but I think it would be more practical just to put a second battery in the car and run all the accessories off that so that you could minimize the pull on the engine and charge that one.
  5. cpeter38

    cpeter38 Right Lane Dweller

    1.) Daox P&Gs and FASes. That means that the alternator IS running at a much heavier average load when the engine is running.

    2.) The alternator in most vehicles is not a very high end electrical component. I would be fairly surprised if it is more efficient than 65%.

    3.) It is pretty unlikely that either the coils or injectors are run as voltage regulated components. Typically, they run at system bus voltage. It would be very expensive to run either of these as a voltage regulated component. the cost of the mosfets would not be justified in the marginal increase in performance.
  6. standard7452

    standard7452 Active Member

    What you write agrees with what I am saying.

    If at best the electrical load was even 165% of said 70 AMP rating, so in total, to get the 70A draw it would take:

    13.8V x 70A=966W

    966W*1.65=1594W which is a little more than 2 HP

    But it is only two horsepower if the thing has the full 70A load on it. which probably almost never happens or the car would have a 80A or some higher alternator.

    If you are driving the car during the day with no headlights, heat or air conditioning, or a radio on where is that 70A load?

    If there was always a 70A load on the alternator to run the basic engine components you could not even turn on the headlights without killing the battery within a period of time.

    Then look at the fuse ratings for the engine control system.

    At max without blowing the fuse you are talking about 30-50A

    That would be assuming the devices operate at those currents and they just don't otherwise people would blow fuses all the time.

    As far as voltage regulation the components have to be protected, if they weren't every time your alternator had a quick load increase stuff wouldnt work right. Even if it was zener diode it is still voltage regulation.

    Bottom line is that maybe you can save 1 or 2 hp by breaking the alternator circuit, but the minute that you have to turn it back on the load on the alternator is going to skyrocket to correct the battery's deficiencies.

    That said I think it is a cool idea, but your main current draws are for accessory loads like headlights, fans, radio, interior lights, etc.

    So what I am saying is that an accessory only battery that you charge makes more sense to me than taking a chance killing the battery that runs the car.

    In addition, to mitigate power and FE losses on the main battery put a stiffening cap on the system to minimize voltage drops.
  7. cpeter38

    cpeter38 Right Lane Dweller

    Let me share my personal experience. I have found that I pulse and glide enough that I cannot keep the interior fan and the radio on at the lowest usable level. The two loads together create more average current draw than my 90A alternator is capable of dealing with (therefore my battery's SOC continually depletes unless I charge it). If I drive at night, I have no option but to recharge before the morning.

    The point of this modification IS to charge every night. The point is to not "turn back on the load to correct the battery's deficiencies".

    BTW, my ignition fuse alone is a 20 amp fuse. I think my ECU fuse may be even larger. There is also the fuel pump, the braking modules, the timer module, etc. every one of those has some level of continuous current draw. If your pulse time averages 15 percent of your drive time, the alternator load during pulse is a significant issue. The question of how much FE savings is available is a totally different question. I would be very interested to see Daox run and ABA comparison, (I plan to when I get me DC/DCs in) ...
  8. standard7452

    standard7452 Active Member

    That was where I was going with this I am not trying to flame...sorry if it came off that way.

    This is where I am coming from...nothing to do with

    OK, you know how these people that are into stereo systems (Bass)?

    So, people tell me about how they have a 3000W system in their car/truck whatever...

    It is impossible because the alternator in their vehicles are not large enough...

    Power(W)=13.something (V) x Current (A) (70A in this case)

    So let's just say that this guy puts this in a 1997 Paseo with a 70A Alternator...The max wattage that he can actually put out is 966W, unless he has a stiffening capacitor and at best that would only be instantaneous.

    It all comes down to RMS of the power output.

    So lets just say the fuse is rated at 20A, the manufacturers treat the circuit as is if it was 60% or so of its actual power rating.

    Now I understand with the pulse and glide, 15%, whatever, that alt load is a big percentage of total engine output, but no matter what your alternator is making up for the diff in the battery's voltage/amperage/combination of both.

    ....but blah blah blah....

    i just have to laugh at myself for this idea....

    ....if one could make sure that voltage/amperage was kept constant in the engine components it would be possible to push an ICE over its efficiency over and above the techniques we all use... the alternator/battery could PUSH power into the engine over the same distances the author of this post are about...


    thanks for making me think cpeter38
  9. NiHaoMike

    NiHaoMike Well-Known Member

    What about make a circuit that enables the alternator only when the brake lights are on and the car is moving faster than a given speed? Regen on the cheap.
    10HP translates into 10-15 tons of A/C, which is a very big A/C. (In comparison, most home central A/Cs are 5 ton or less.) A typical Danfoss low voltage A/C compressor only uses about 250w. (About half as much as a small window A/C, which is about right considering the small space but high solar load.)
  10. Daox

    Daox Well-Known Member

    I haven't done any real testing. Others have, namely MetroMPG. He went all out at the time though and removed the belt from the alternator (which did lead to other problems, but I digress). He also did steady state cruise testing, not P&G. I'd imagine that using P&G would reduce the gains seen with disabling the alternator.

    The regen on the cheap idea is great, but falls short when you remember that the alternator is still in line with the engine. So, you need to be in gear and turning the engine to get regen. It would be great if you moved the alternator off the engine to be driven off the transmission or drive shaft though. However, I don't believe the gains there would be worth it.

Share This Page