Resistor on Shunt Regulator PC Board

Aural Robert · 3152

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Offline Aural Robert

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on: February 02, 2014, 08:17:15 AM
I'm finally getting back to my assembly and I have a question about one of the resistors I received. On Page 26 of the manual, the top step is installing a 330K5% into the A side of R2 - it's a black cylinder with writing on it.

The resistors I got in my kit are brown dumbell shaped ones, and they clock in around 290K. I think the colors are orange, orange, white, gold. Is this the right resistor? I can't see anywhere else in the manual where the brown resistor I have belongs.

Thanks in advance.

Aural Robert.

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Offline Paul Birkeland

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Reply #1 on: February 02, 2014, 10:44:42 AM
Orange, orange, yellow, gold is a 330K/5% resistor.

4-band color codes

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Paul Joppa

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Reply #2 on: February 02, 2014, 11:58:12 AM
If you hold both ends of the resistor onto the meter leads, then the resistance of your body is in parallel with the resistor. I speculate that's what you did, which is why you got a resistance smaller than what it should be.

Yes I do this all the time, and have wonder "what the heck?!" before I remember this caution.

Paul Joppa

Offline STURMJ

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Reply #3 on: February 02, 2014, 07:34:05 PM
Parallel resistance is one of those things that I understand, But have no clue why.  It seems so counter intuitive that two parallel loads results in a load lower than either load.  It seems that the explanation for this is going to be way above my understanding of electronics,  so I just accept it as it is.


Offline Paul Birkeland

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Reply #4 on: February 03, 2014, 06:43:00 AM
Quote from: STURMJ on February 02, 2014, 07:34:05 PM
Parallel resistance is one of those things that I understand, But have no clue why.

Imagine you have a 5 lane freeway, and next to that 5 lane freeway, you have a gravel road. 

When you allow cars to drive through them both (this is analogous to current), more cars will be able to get through on both the gravel road and the 5 lane freeway than just the 5 lane freeway.  (Though the gravel road doesn't do all that much)

In the resistance model, your body is high resistance (gravel road), and the resistor is the 5 lane freeway.   

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Paul Joppa

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Reply #5 on: February 03, 2014, 05:59:15 PM
Ah! I get that - you just have to remember that a lower resistance is not a lower load.

The inverse of resistance is called conductance, and a parallel resistor increases conductance, demanding more current, and is thus a heavier load.

Paul Joppa

Offline STURMJ

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Reply #6 on: February 05, 2014, 05:14:23 AM
Ahhh now I get it. Thanks


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