voltage question

Discussion in 'Sparky's corner' started by GSX-PKV, Aug 5, 2011.

  1. RAbarrett

    RAbarrett Well-Known Member

    First, before discussing this issue, let's refresh ourselves on how the alternator works. This device is an electromagnetic device, using coils of wire to "induce" current into other coils.
    The rotor, which is connected directly to the regulator, produces a magnetic field, using current drawn from the battery. The strength of the field determines how much current is available from the alternator. If, for example, the rotor current is at maximum, the alternator will put out its rated current, +- 10%. If the current at the rotor is at a minimum, the alternator will produce little or no current. This rotor current is determined by the voltage regulator's assessment of the demand from the alternator. The regulator will control the rotor's current, and will then, indirectly control alternator output.
    The magnetic field produced by the rotor "induces" or magnetically creates a current in the stator. It is the stator output that charges the battery, through the diodes, or one-way devices.
    If, for example, we want to build an alternator with a higher capacity, or amperage output, we will need to create a stronger magnetic field, in both the stator, and the rotor. In order to produce this extra magnetic field, we will need to use a larger wire, to create extra current, strengthening the magnetic field. It is the larger wire that draws the extra current, temporarily increasing the current draw from the battery. This, in turn, will require a slightly higher alternator rpm before the extra current output exceeds the draw from the battery, which then charges the battery.
    In incremental changes, say for example going from a 63 amp unit to a 75 amp unit, the draw may not be noticable. In my case, I built a 300 amp alternator, which works VERY well with the extra demands of the stereo and lighting, but at engine speeds below 800 rpm, the voltage stays at battery voltage. It is not until the engine speed exceeds 800 rpm that the alternator output increases to 15 volts, and everything comes alive. When the battery is fully charged, the regulated voltage is 14.6 volts, and it will stay there until the engine speed drops below 700 rpm. Since my engine idle in drive is 550 rpm, with either the AC on or off, the volt meter drops to about 13 volts.
    This situation can be likened to a supercharger's using horsepower to make additional horsepower, or the impediment a turbo creates to the exhaust until boost is there. It takes power to make power, and as always, the additional power arrives at a higher rpm.
     
  2. BRUCE ROE

    BRUCE ROE Well-Known Member

    So, you rebuilt an alternator in the 63 amp class for 300 amps? The rotor
    of usually a dozen ohms was rewound with larger wire to more like 2 ohms,
    to allow more like 5A instead of 1A? What did you do with the regulator
    (internal?) so the transistor could drive this larger current?

    Then the stator was rewound with much larger wire than the usual 14
    gauge, for the extra output current? Or done another way? That would
    reduce the number of turns drastically, no wonder it would have to be
    revved up to get enough voltage for charging. Then how would 6
    100A diodes be set up, since the originals couldn't handle that power
    level either efficiently, or for survival? What kind of output stud,
    maybe 1/2" copper? What about an enhanced cooling fan? Any pictures
    of this stuff?

    At what rpm was an output ammeter able to register 300A? What was
    done to keep the belt from slipping at this power level, I have trouble
    at stock levels? Bruce Roe
     
  3. RAbarrett

    RAbarrett Well-Known Member

    The entire unit was upgraded, starting with a 12si unit. The diodes, and regulator were replaced to handle the additional current. The output post was kept original, but the charging wire was upgraded to a 6ga cable. The output of actually 297 amps is obtained at 3000 rpm and above. The stator and rotor were replaced with aftermarket units. As long as the belt is kept in good shape and tight, I have no issues at that level. One thing I did was to obtain a belt that is slightly wider, allowing it to ride higher in the pulley. The gripping surfaces are slightly wider as well. I have also upgraded to relays for the headlights, operated by the switch, making them noticably brighter. This setup appears to allow the batteries to last well beyond their warranty periods as well. I now have a 72 month battery lasting at least 84 months and counting. I have always contended that the electrical systems in most cars are marginal at best, and have taught my students that in class. Several students, having kept in touch, have noted that their upgrades have improved their vehicles' performance as well, including stereo and ignition performance. No pix, as the upgrades were done five years ago, and to the untrained eye, it looks completely stock, other than the heavier wire between the battery and the alternator. Ray
     
  4. 65specialconver

    65specialconver kennedy-bell MIA

    Ray,i get the feeling your an electrical engineer......design is a lot different in the field than what you read in a book or think what theory is,trust me!:Dou:
     
  5. 65specialconver

    65specialconver kennedy-bell MIA

    No frikin way:Dou: :Dou: :Dou: Man i'm calling Ray out on this one!:Brow:
    17 SI units are a 6amp field,10 SI 4amp,10 Dn's are 2amp.:TU:
    I'm so tired of the BS people throw around on websites!:puzzled: :rant:
     
  6. 65specialconver

    65specialconver kennedy-bell MIA

    Bull-frikin-hucky! Show me a video of it...please!:bla:
     
  7. tom_gonzalez@ve

    tom_gonzalez@ve Well-Known Member

    Pardon my scepticism, but-
    1- #6 wire is good for 65 Amps, not 300.
    2- Heavier gauge wiring in the alternator would theoretically allow greater current flow which could result in a stronger magnetic field in the rotor and stator. However it will also require more power from the engine to compensate for the additional drag produced by tye stronger magnetic fields interactions. It would become self defeating unless driven fast enough to provide current for itself and the required charging current.
    3- The greater wire size needed to get 5 times the current flow would also be much greater than the rotor and stator clearances would allow. Sort of like building a blivet.
     
  8. 65specialconver

    65specialconver kennedy-bell MIA

    One misconseption people have is that the positive battery cable is the only current path.Wrong,the path is completed to ground.When the alternator is charging,it's power in to exite the alternator,charging the battery for the required load,via the negative ground.
     
  9. tom_gonzalez@ve

    tom_gonzalez@ve Well-Known Member

    Let's look at this using the conventional theory and assume current flows from positive to negative, rather than the electron theory which states current flows from negative to positive. The alternator is grounded to the negative polarity as you stated, and a portion of the current the alternator uses for the field (rotor excitation) flows from the battery positive through voltage regulator to the alternator slip rings and then to the stator casing to ground. That current is basically internal to the alternator and is not factored into alternator output Amperage ratings. The rated alternator output current exits the alternator through the #6 cable. Whatever current is used to charge the battery and other circuits is fed by the #6 cable. #6 cable/wire is rated for 65 Amps not 300.
    I still maintain that the physical size of the alternator precludes the upgrading operation by increasing wire size as described by the OP.
     
  10. pmuller9

    pmuller9 Well-Known Member

    Bruce

    No one ever answered your question:

    It could be a regulator that had a variable current source for an output and was independent of the battery voltage.

    Paul
     
    Last edited: Sep 15, 2011
  11. BRUCE ROE

    BRUCE ROE Well-Known Member

    Yes, I was hoping Ray would describe the unit he uses in a car. I have a
    patent on such a device, 6,979,964. But it's not suitable for this appliction.

    There are diodes capable of 300A in a 3 phase bridge. But even big diodes
    still have about 2 volts forward drop in a bridge; the alt coils have to put
    out 16 volts to deliver 14 volts to the battery. 2 volts drop at 65 amps is
    130 watts; a big contributor to why the alt case gets hot. At 300 A the
    diode heat into the case would be 600 watts. Of course its possible to
    bring the 3 phase wires out, and mount the diodes on an external heat
    sink. But we know that didn't happen, from the output stud discussion.

    Anyway, we learned it is/was possible to buy a regulator, rotor, stator,
    and diode set to convert a 12si altto 300A at 12V. I would like to hear
    more about how/where to buy these parts. Pictures, great!

    People across the street from me (FERMILAB) managed to feed huge
    currents through wires, using super conductivity. But they had to built
    the worlds largest liquid helium plant to keep them cold. Guess thats
    not the way to do it.

    I read those alternators can be made to put out 120VDC. Probably
    takes huge torque to turn it at big current. Follow the output with a
    DC to DC switcher (buck regulator) to get regulated 12V, and you
    have a powerful system.

    amused, Bruce Roe
     
  12. pmuller9

    pmuller9 Well-Known Member

    Bruce

    Not only is the diode drop dissipating a large amount of power, if the current in the stator is quadrupled, the "I" squared "R" losses increase by 16.
    Even if the resistance of the wire is decreased in half by going down 3 gauge sizes on the stator, that is still 8 times more power going up in heat.

    The reality is, the max rating is never expected to be used for any length of time and the increased field intensity it mainly for the low rpm advantage.
    If you google high output alternators you will see conversions up to 350 amps.

    The bottom line is, the continuous power rating is directly proportional to the amount of copper and the amount of cooling so if you really need big power all the time
    you need a physically big alternator or supercooling.

    You will notice that some of the competition sound system vehicles run multiple alternators.

    Paul
     
  13. RAbarrett

    RAbarrett Well-Known Member

    As stated previously, the diodes, rotor, stator and regulator were aftermarket purchases. With my experience with rebuilding alternators for GM, I wanted to see what I could get under ideal circumstances. The test was under controlled circumstances, maintaining 14 volts for the control devices, and the battery was fully charged, minimizing the current drawn by the battery. Measuring the current drawn by the battery, and that drawn by the load, the total current available was 297 amps, at peak, for a short time. These alternators can get hot very quickly, as the ventilation for them is minimal at best, so the test was run long enough to assure the readings.
    In actual operation, the current drawn by the battery is less than 60 amps, right at start, and the battery, in excellent condition, charges quickly, allowing the current to drop to about 10 amps within 10 minutes of driving.
    The system works very well, and the resulting electrical performance of peripheral devices, such as lighting, ignition and the stereo have shown a marked improvement. The battery life speaks for itself.
    It is too bad that there are those having difficulty seeing the forest for the trees. For the record, there are some individuals advertising alternators exceeding 300 amps, for nearly $600. I wanted to see if my experience with these devices could beat that price, and my alternator needed rebuilding at the time anyway. Apparently, I succeeded. Ray
     
  14. pmuller9

    pmuller9 Well-Known Member

    Thanks Ray for clarification.

    I think it was a simple misunderstanding between peak power versus continuous power concerning the 300 amp output.

    The arguments still provided a lot of good material for others to view.

    Paul
     
  15. BRUCE ROE

    BRUCE ROE Well-Known Member

    What is the device for stabilizing the voltage as alternator rpm drops?

    Bruce Roe
     
  16. pmuller9

    pmuller9 Well-Known Member

    No additional device needed. By virtue of the upgrade, the alternator produces 14 volts at a much lower rpm.
    As you already know an alternator's output voltage is directly proportional to the rotating field strength and the rpm.
    Since the field strength was increased the rpm can be decreased to provide a given output voltage for the same load.

    In Ray's case he did the upgrade so the alternator would always be charging the battery even at very low rpm
    and not because he needed the increased peak output of 297 amps.

    Thanks for asking because this is an important point and something I hadn't thought about.

    Paul
     
  17. RAbarrett

    RAbarrett Well-Known Member

    Paul,

    Thank you for clarifying my point. The concept of the 300 amps is not the point. The concept of the increased output, which nearly doubled, at my normal 2000 rpm cruise, allowed for the use of the high output stereo, and the additional lighting, and still quickly charge the battery. The battery now stays charged, even after short trips, and the stereo sounds noticably better, due to the increased supply voltage. The lighting is also noticably brighter, allowing for the increased use of low beams, even on dark, curvy roads, allowing for slightly higher speeds on these roads. On those roads, when the high beams do not offend other drivers, they practically act as a sunrise, without discharging the battery. Something to consider here as well is that, if correctly built, the higher capacity alternator will operate at higher loads, longer, without damaging things due to heat.
    One thing I noticed right off the bat was that the higher output allowed me to charge the battery at idle, with the A/C on high blower, which would before that cause the volt meter to drop below 13 volts. It now stays @ 14 volts at idle. The only time the voltage drops below 13 volts is when, at normal idle, with the A/C on, I shift into drive, when the engine speed drops to 500 rpm.
    It was the additional current available below 1500 rpm that charged the battery quickly, and allowed full operation of other voltage dependent devices. One more thing I noticed was that my ignition system, now operating at full voltage, at all times has completely eliminated misfire, allowing me to lean out the choke during warm-up, saving me fuel during cold driving. Mileage has risen about 1.5 mpg as a result, even with the additional load from the alternator.
    The higher available current right after a start-up allows the battery to charge faster, reducing the output noticeably sooner, as noted by the volt meter's performance. This allows full current to other devices while still reducing output from the alternator.
    Maybe 300 amps was overkill, but the parts were available, and curiousity overcame my caution. It paid off. This unit cost me less than half what was being asked for high-output alternators, and, after 5 years, is still performing perfectly. I did not expect to cause such a stir, but I hope some of the points made here were valuable. Ray
     
  18. BRUCE ROE

    BRUCE ROE Well-Known Member

    Needed or not, I want to know what is " a device for stabilizing the voltage as alternator rpm drops. " mentioned on 5 Sept. Bruce Roe
     
  19. RAbarrett

    RAbarrett Well-Known Member

    When I worked at Mr. Gasket, we had a device, called an Accuvolt, which used several devices, including an oscillator, driven by 12 volts, and a bank of electrolytic capacitors, which, depending on the current capacity needed, would stabilize and smooth the supply voltage. The concept is a simple one of storing and releasing voltage as the sysyem voltage rose and fell. It was very useful for the stereo and ignition systems, and the lighting, as it provided the necessary voltage to drive these devices with less variation. For the most part, however, these devices were a needless expense, as the combination of the battery, and voltage regulator, as well as the capacitors supplied in various circuits by the manufacturer, typically did the job. It did very well, however, at stabilizing voltage where the alternator lacked capacity. I am not sure whether these devices are still available, but they were somewhat pricey. Ray
     
  20. stellar

    stellar Well-Known Member

    Jamie, if you find a line on those stators and rotors could you put it on the reman forum. I have been looking for them for about 25 years.
     

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