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Electrical Misconceptions??
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SyncroHead
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PostPosted: Fri Feb 05, 2021 11:23 am    Post subject: Electrical Misconceptions?? Reply with quote

I'm partway through writing an e-book on the topic of basic vehicle electrical principles. I was inspired by someone once writing...

"The ground wire doesn't need to be a large size like the 12V wire, because it's 'just a grounding wire' ".

I'd like to make sure I cover other misconceptions in the book, so for those here that understand vehicle electrical systems...
What misconceptions have you heard?

Jim Davis
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dhaavers
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PostPosted: Fri Feb 05, 2021 11:32 am    Post subject: Re: Electrical Misconceptions?? Reply with quote

Here's an easy 2 chapters: dielectric <vs> conductive grease... Confused Wink

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shagginwagon83
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PostPosted: Fri Feb 05, 2021 11:43 am    Post subject: Re: Electrical Misconceptions?? Reply with quote

When calculating wires size using this calculator, the 'length of wire' is the wire needed to complete the circuit.

so if you need to run both positive and negative to something 10ft away. You need to calculate it for 20ft.

https://www.wirebarn.com/Wire-Calculator-_ep_41.html
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DanHoug
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PostPosted: Fri Feb 05, 2021 11:58 am    Post subject: Re: Electrical Misconceptions?? Reply with quote

measuring voltage vs voltage drop

battery chemistry charging requirements

EMF from coil kickback

how to use a multi-meter

energy balance between interior heating with electricity vs fossil fuel

firing voltage requirements of spark plugs in free air, lean mixtures, heavy loads

Ohm's Law, period.

and... heh, heh.. crimping vs soldering connections
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dobryan Premium Member
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PostPosted: Fri Feb 05, 2021 12:02 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

Measuring resistance in a circuit vs being able to pass current thru it. Example is the main ground wires. Folks use a multimeter and say that there is no/low resistance therefore the cable/connection must be good when in reality there is only one small strand with good connectivity.
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MarkWard
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PostPosted: Fri Feb 05, 2021 12:30 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

Quote:
Don't let the smoke out!


It's hard to put it back. Wink
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dabaron
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PostPosted: Fri Feb 05, 2021 12:35 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

the myth that direct current (DC) current flows from positive to negative. the lack of electrons in the "positive" pole attracts the surplus of electrons from the "negative" pole.

Ben Franklin had it backwards.
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DanHoug
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PostPosted: Fri Feb 05, 2021 1:19 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

dabaron wrote:
the myth that direct current (DC) current flows from positive to negative. the lack of electrons in the "positive" pole attracts the surplus of electrons from the "negative" pole.

Ben Franklin had it backwards.


this has just bothered me for ages. can't we call the + side the one with a surplus of electrons and the - side the one with a deficit? but then there's conventional current flow vs natural current flow. throw in some semiconductors and now there's holes to be filled.

great article on the controversy of current and electron flow:
https://www.nutsvolts.com/magazine/article/which-way-does-current-really-flow
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Howesight
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PostPosted: Fri Feb 05, 2021 1:28 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

Lead Acid battery basics and voltage.

Misconception:

"Van cranks real slow. Measured voltage and it's 12 volts, so can't be the battery."

*Sigh*
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dabaron
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PostPosted: Fri Feb 05, 2021 1:49 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

DanHoug wrote:
throw in some semiconductors and now there's holes to be filled.


the real fun starts with inductors and coils. my DC circuits class was a hoot.
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dabaron
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PostPosted: Fri Feb 05, 2021 1:50 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

Howesight wrote:
LVan cranks real slow. Measured voltage and it's 12 volts, so can't be the battery."



wait, my 12VDC car system operates at 13.4VDC... how does that make sense Laughing
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hans j
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PostPosted: Fri Feb 05, 2021 2:00 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

Thinking that checking resistance with an Ohmmeter means it can carry correct current.
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valvecovergasket
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PostPosted: Fri Feb 05, 2021 2:03 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

hans j wrote:
Thinking that checking resistance with an Ohmmeter means it can carry correct current.


its the first step past a visual inspection though! Smile

maybe add something about wire insulation thickness not being a universal signifier of its current carrying capacity/not all insulation is the same haha
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hans j
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PostPosted: Fri Feb 05, 2021 2:18 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

It literally only tells you it's connected. The DVOM sends out such a tiny amount of voltage that it only needs one strand of wire to show continuity. It can't show if it's capable of carrying current.

If you are going to have the wire apart to check resistance, just load test it.
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valvecovergasket
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PostPosted: Fri Feb 05, 2021 2:20 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

hans j wrote:

If you are going to have the wire apart to check resistance


except theres no need to take anything apart...

but i agree, load testing works well. ive been stumped by resistance check once recently and we found the drop with voltage. but id say more often than not, the resistance check points to problems pretty quickly beyond the "wiggle test"
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PostPosted: Fri Feb 05, 2021 2:29 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

Howesight wrote:
Lead Acid battery basics and voltage.

Misconception:

"Van cranks real slow. Measured voltage and it's 12 volts, so can't be the battery."

*Sigh*


This! Cover the nominal, 100% SOC, and 100% DOD for all the common battery chemistries. Also a section on the strengths and weakness of the different batteries (flooded, AGM, Gel, LiFePO4, etc). And an explanation of how to maximize discharge cycles for each type.

"How not to kill your house battery! You won't believe number 2!!!"
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SyncroHead
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PostPosted: Fri Feb 05, 2021 2:46 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

Thanks for the excellent feedback. There may be enough for a “Volume 2” book! Smile

dabaron wrote:
the myth that direct current (DC) current flows from positive to negative. the lack of electrons in the "positive" pole attracts the surplus of electrons from the "negative" pole.
Ben Franklin had it backwards.


I may elect to just continue perpetuating this one in the interest of keeping the concepts simple. I don’t intend to describe molecular physics of electricity and won’t be using words like atoms, electrons, ions, etc. My hope is that readers will be able to troubleshoot a circuit, add a new circuit with properly sized wires, fuses, etc.

Please keep the suggestions coming.

Jim Davis
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Ronzo_volvo_guy
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PostPosted: Fri Feb 05, 2021 2:49 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

Dave;

There NO SUCH THING as a "Conductive Grease" (a term invented by marketing departments!)...all grease is non-conductive/aka dielectric and will ENCAPSULATE a connection, but the place there zinc filled grease (which is also non-conductive shows its advantages is at the microscopic level, when the particles are compressed and in contact between two conductors (which happen to also have contaminants which want to corrode). Anti-Corrosive Zinc Paste will neutralize any corrosion, and so protects the connection long-term.

I have studied this for decades, and recommend it...see: https://www.sw-em.com/anti_corrosive_paste.htm
...including for making an encapsulated Gas-Tight-Joint when making crimps...see: https://www.sw-em.com/Wiring%20Notes.htm#Makin_a_Proper_Crimp

Cheers
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PostPosted: Fri Feb 05, 2021 3:03 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

I lost the link, but a scientific study pointed out that many misconceptions in electricity among high school students were due to the comparison between water and electricity. The comparison just doesn't really work, and it confuses a lot of students.
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PostPosted: Fri Feb 05, 2021 3:34 pm    Post subject: Re: Electrical Misconceptions?? Reply with quote

Ronzo_volvo_guy wrote:
...There NO SUCH THING as a "Conductive Grease"...

Yeah...I think we're on the same team here... Wink

- Dave
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