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  • Alternator AC noise explain in detail

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    Mike is correct...the large current load on these 3 phase hairpin stators in conditions where all the available current is delivered does tax the design of the factory alternators. The diode's are all created on a single silicon substrate to assure uniform junction characteristics. This method allows for the PIV (peak inverse voltage) to closely match across all six diodes in a "three phase" rectified bridge. The old school would be to use individual large stud mounted diodes however; they would have to be curve traced to create a matched set of six diodes with close PIV and forward current avalanche voltage drops. All silicon diode junctions have a .6 volt drop turn-on when forward biased or conduction. Variations of these characteristics cause a dirty wave-form of the desired sinusoidal wave appearance. Hence; we have "ripple" witch is what Mike has explained so many times and why we must avoid this situation. 


    Our trucks arrived with a "bare minimum" alternator design to get the vehicles off the sales lot. The grid heater configuration along with head lights and a fan blower for heat or defrost on early cold mornings takes the demand for these wimpy alternators to their design limits. Once we begin to "pound or beat" these diodes into forward and reverse current conduction we begin to see changes in the silicon junctions. It is cumulative and in time between hot summer and cold winter conditions our diode bridges become "leaky" and the "ripple" (AC component) becomes excessive and certain electric system devices begin to balk or react strangely with the imposed "ripple" floating on the DC(direct current) rail.


    Excellent mil-spec electronic devices or space-bound instruments MUST HAVE bullet proof power supplies. PURE DC hard-core power supplies are normal components and can be built without much effort today. Our alternators and dual batteries ARE the DC supplies for our trucks. The error is budget on Daimler/Chrysler's decision to put these 135 amp alternators into the Cummins platform. 


    The standard rule of thumb for all electronic design regarding power supplies is, "If you have a demand of 100 amps maximum in a given system, you build a supply with 50% more headroom minimum. Now, take conditions into consideration...heat, cold and perhaps a poor matched battery in a dual battery (paralleled batteries) storage supply and the occasional "starter" operation (the Cummins starter is INSANE on current demand!) and WE have a real MONSTER to feed!


    Boys and Girls...if you want bullet-proof DC, double the available current at idle. Yes...this is correct...go with a 6 phase (twelve diode pack) and a hand-wound "square wire" hairpin-stator. The six-phase stator and companion rotor  will cut the ripple to near zero in conjunction  with proper storage capacity (really good paralleled batteries) you will have the power supply for your Cummins. The "square" wire wind is best for current demand when an "AC field wave-form" is cutting the coil to impose current into the inductive system. It is the cutting edge in design for transformers with high efficiency and LESS HEAT. Heat is "loss" and also destroys the surrounding aspects of the generating device.


    BTW...not even Nations builds to these specifications....they buy their upper-end higher current devices from a source in Riverside California.


    Just for grins... 1 Amp...what is this? Electronics 101:


    Current flow is "electrons" ( remember 5th grade science?) the Atom is composed of three elements the Proton, Neutron and the little Electron flying around the other two elements like an orbiting satellite. It is the "electron" we are interested in when it comes to DC (direct current) when we refer to "current flow" in a circuit.


    SO...the question is? When we measure "current flow"  the term Amps is used....how many "electrons" flow through a piece of wire at a given point in "one second" ???


    One Amp is (physics term "Coulomb" ) equals 1x10 to the eighteenth power....hence; when you start your mighty Cummins you are transferring 1x10x18 x 600 electrons in order to spin the Beast into run condition ! Take a look at the size of this number ! This is why you need "FAT" wire to allow all those little (minions) electrons to race at the speed of light through the wire to the given load. 


    As you can see...current flow is from "negative" to "positive" in our world. The battery has a "positive" terminal and it is "sucking" to become satisfied. It attracts ("sucks") electrons off the frame-rail of your truck "as current flow" in order to spin the armature of the starter motor.


    SO..."negative" (electrons) flow towards the "positive" (hole or sucking-action)....seems we have an "upside down" world !!!!


    Now this leads us to another interesting Physics observation...you see...lights Do Not Give Off Light ! They suck "dark" and you will notice when a light bulb "burns out" and no longer provides luminescence....we say "it is burned out" however; we now know that is not true!.... IT IS FULL of Dark and we need a new bulb :)...Look at the bulb...it's "dark".


    Sorry...had to share this funny tid-bit...none the less...our Cummins platforms were not produced with Mil-Spec in mind. Sorry, our ECM and PCM's must be provided "clean" stable DC in order to function correctly. The design guys never considered 6 millivolts  of "ripple" to be critical for converter "lock and unlock" syndrome and yet we see the result and unwanted operational characteristics. 


    I build killer DC power supplies for various electronic devices...you need a shop oscilloscope to even see the minor "AC ripple" and as for regulation, from zero to 100 Amps at 14.8 volts there is NO DC drop in voltage. It is like taking and engine from "zero" to "red line" in a heart-beat and you don't even see a fraction of a voltage drop...this is called a "Stiff DC Regulated Supply".


    Build your DC Supply...the Cummins platform is a Nobel Beast....feed it a good stiff DC diet with NO sag and Zero ripple and all will be well.


    ALSO...guys I lurk around out here...I've seen photos you have all taken "under the hood" of your beloved vehicles...gosh golly!!! The appearance of the battery terminals and cable connectors...it is pretty sad. You can't transfer billions and billions of electrons (with NO heat) through the scum I have viewed. 


    Again...No worries...we are all in this together... I share this respectfully as intellectual content with just a touch of humor :) 



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       3 of 3 members found this review helpful 3 / 3 members

    Great write up. Helpful to even the electrically challenged as my self.

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       2 of 2 members found this review helpful 2 / 2 members

    This is getting an education and a privilege to read. Thank you

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       1 of 1 member found this review helpful 1 / 1 member

    I used new wire and crimped new ends, also used military style terminals. Noticed truck acted better after, always nice to upgrade old parts to new that actually make a difference. 

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       1 of 1 member found this review helpful 1 / 1 member

    Long read but well worth it. Very helpful content

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    This is a great write up.  


    I found this article when I first got my truck.  The one thing that jumped off the page for me was that my battery terminals were in terrible shape.  The stock connectors were not saveable. I replaced them all as well as the connecting wire between the batteries with military connector (which was full of corrosion) and soldered eyes.  I was having some odd ball problems that all magically went away when I got my battery connections all sorted.

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