My first post

Discussion in 'General Electronics Chat' started by R_W_B, Oct 23, 2011.

  1. R_W_B

    Thread Starter New Member

    Oct 19, 2011
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    Hello, new here so hope I'm not posting in the wrong thread etc. Also even though I know enough to do house wiring and testing, I am still learning in auto troubleshooting and dc discrete or integrated circuits.

    I was studing a schematic for 3 phase alternator (stator) to a voltage regulator that is finally diode rectified into the positive lead of the battery to supply a surplus voltage and current so as to both boost the ouput of the battery and charge it during operation.
    (eliminating a long story of thyristors shorting the alternator coils intermittently as the stator voltage becomes too high to feed into the battery)

    So my question is this. When I saw that the charging system's input was directed INTO the positive (returning electron direction) terminal of the battery, something NEW popped on in my head. I had always (previously) visualized the charging system dumping it's potential into the neg terminal of the battery and in essense creating a oppossing (and stronger) voltage actually supplying the systems needs and forcing the left over current back into the neg battery terminal (speaking in terms of electron flow direction).

    However after seeing this it appears my visual folly was not the case but rather the phase of the AC (thru the direction of rectification) goes into the red positive side of the battery actually JOINING (instead of opposing) the electron flow direction and thereby BECOMING part of the total voltage source going thru the battery and then supplying system needs once thru the battery, but all the while the 'vaccum' of battery plate charges are being replenshed (charged).

    Please comment as to my STILL misunderstanding of this scenario or any input you wish to give. If my question is worded ambiguous please tell me so that I might attempt a different explanation.
     
  2. Adjuster

    Well-Known Member

    Dec 26, 2010
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    To charge a battery, current must be made to flow in the opposite direction from that during discharge. This requires a source of higher voltage than the (open-circuit) battery voltage. This is true whether the battery is charged by an alternator or something else.

    I think you are confusing yourself by thinking too hard about it. Despite the AC and SCR control processes going on within the alternator, what eventually charges the battery is DC, although possibly not very smooth.
     
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  3. R_W_B

    Thread Starter New Member

    Oct 19, 2011
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    I am probably confusing myself as you say but I would like to get under this a bit more since it DID confuse me. I.e. as you said I had always thought that the current DIRECTION had to be reversed to cause a cell plate charge and of course it would take a potential greater than what is available on the neg terminal to accomplish this.

    BUT the direction of flow given by the diodes in the schematic I was reading shows the current flowing > into the pos terminal of the battery. It does not show any hookup to ground at all except to state that during the time periods the thyristor shuts down current to the positive leg (when voltage exceeds battery tolerance). . . . then it shows the current flowing to ground during these time periods shorting (shuting down) the stator output.

    My confusion is given that electron flow direction (by nature of acid battery inherent properties) is from neg TO pos terminals of the battery (thereby going INTO the pos teminal) how can the potential from the charging input show the diode direction facing towards the red (pos) terminal ?
     
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
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    The electron flow in the battery reverses during charging. It obviously has to, in order to reverse the electrochemical processes that take place during discharge.
     
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  5. #12

    Expert

    Nov 30, 2010
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    You've got "conventional" flow and "electron" flow mixed up.

    Conventional flow pretends that positive charge flows, but it really doesn't. It just makes the math easier to pretend that. Electrons flow, and the alternator is actually sucking electrons out of the positive terminal of the battery.
     
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  6. Wendy

    Moderator

    Mar 24, 2008
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    This is where the conventions get really confusing. Electron flow refers entirely to what is happening in the wires, be it steel, copper, or aluminum.

    In a battery the chemistry rules, and it is positive ions that carry the charge. Most people don't worry about the chemistry, and there are a lot of people convinced that conventional flow (the oldest standard, where positive charges move in the wires) is the only correct standard.

    I'm not going to rehash that argument, but you need to know it exists.

    Pick what convention you're comfortable with, announce it to prevent confusion, and carry on.

    If you ever start to read the text book on this site it only uses electron flow.
     
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  7. R_W_B

    Thread Starter New Member

    Oct 19, 2011
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    Now this is an answer I can wrap my head around. At least it adds up.

    My only problem now is . . . . why isn't the diode in the schematic facing back towards the alternator instead of facing the battery ? ?

    Doesn't the diode depiction represent direction of electron (or phase direction) flow by it's very nature ? Or does diode depiction represent conventional flow ?

    Also THANKS for all the answers, I feel like I am getting somewhere with this.
     
  8. studiot

    AAC Fanatic!

    Nov 9, 2007
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    The 'arrow head' in a diode points in the direction of conventional current flow.

    If you allow or make the broad end positive and the pointy end negative current will flow.

    If you do it the other way round the diode will block.
     
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  9. R_W_B

    Thread Starter New Member

    Oct 19, 2011
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    1. Ah so . . . . this whole thing boils down to conventional representation of the diode. Are diodes always depicted using this concept or do they deviate like + and - does on occasion ? I.e. I've seen schematics with a + on the battery neg terminal.

    2. And lastly I have one other question on this stator regulator operation. When the text states the the thyristors 'ground' the stator (when voltage rises too high), I take it they are shorting (or switching if you will) the stator coils to ground, so I surmise this simply allows the BATTERY ONLY potential current to then flow back through the rectifier and onto the same positive battery terminal, essentially by passing the stator. ? . OR does the regulator circuitry just (somehow that I missed) leave the ground (black wire feed) open and nothing at all flows during the time period.

    I can post up the schematic attachment (later) if need be. But I will have to scan it or draw it in Cad and convert the screen to Jpeg. Might not get that done tonight.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    Instead of .jpg use .gif or .png. .jpg is for pictures, and will fuzz out the lines in a schematic.
     
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  11. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Yes an actual circuit is easier to discuss, I usually post a scan in grey scale to keep the size down.

    There is less chance of making a mistake that way, but CAD output is OK too.
     
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  12. R_W_B

    Thread Starter New Member

    Oct 19, 2011
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    1. Ah so . . . . this whole thing boils down to conventional representation of the diode. Are diodes always depicted using this concept or do they deviate like + and - does on occasion ? I.e. I've seen schematics with a + on the battery neg terminal.

    2. And lastly I have one other question on this stator - regulator operation. When the text states the the thyristors 'ground' the stator (when voltage rises too high), I take it they are shorting (or switching if you will) the stator coils to ground, so what exactly happens with the coils of the stator are shorted to ground, i.e. (on motorcyles and autos) isn't this the same conductor that the battery feeds out on ? What in the regulator circuitry keeps the battery potential from shorting itself through the regulator ? Obviously I'm missing something on this one.

    Here is the schematic in GIF format, (click to enlarger in it's own window)
     
  13. Wendy

    Moderator

    Mar 24, 2008
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