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Author Topic: Electrical 101 - Read This First  (Read 23403 times)

Offline Qawls

  • Posts: 131
Re: Electrical 101 - Read This First
« Reply #10 on: Feb 24, 2013, 00:03:09 »
Very cool, will probably have to read through it a few times before I fully comprehend what you're talking about.

Cheers mate!

Offline gregajo

  • Posts: 207
  • wrenching in the bad oil garage
Re: Electrical 101 - Read This First
« Reply #11 on: Feb 27, 2013, 15:16:34 »
Thanks!  Keep it coming in read this second!!  Cheers, Greg

Offline AbbyRider

  • Posts: 100
Re: Electrical 101 - Read This First
« Reply #12 on: Mar 05, 2013, 20:06:11 »
What a great sticky.

Offline Qawls

  • Posts: 131
Re: Electrical 101 - Read This First
« Reply #13 on: Mar 24, 2013, 06:13:52 »
This still seems like black magic to me, how do you know what currents are running to and from different components and what wires to use.

Offline biggiesmalls

  • Posts: 141
Re: Electrical 101 - Read This First
« Reply #14 on: Apr 03, 2013, 01:09:13 »
It's never a bad thing to go over the basics. And over, and over, and over...
1987 Suzuki GS 450 Build Thread - Just gettin' started.

Offline Sonreir

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  • Posts: 10293
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Re: Electrical 101 - Read This First
« Reply #15 on: Apr 03, 2013, 01:14:34 »
This still seems like black magic to me, how do you know what currents are running to and from different components and what wires to use.

Current, Voltage, and Resistance are all related due to Ohm's law.

Current = Voltage / Resistance.

You know voltage is set at 12V (or in some cases 6v if your bike is old enough), so measuring the resistance across a component will tell you how much current will be drawn.
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Offline Fab 5 Freddy

  • Posts: 45
Re: Electrical 101 - Read This First
« Reply #16 on: Jul 02, 2013, 18:14:10 »
Whew! I feel like i just took a college course!
Definitely NOT a "hardcore mechanic" like most of you guys. Just a regular plumber/welder from NY that does not have the luxury of a garage. (So all my work is done either in my apartment or right on the street.)

Offline Mydlyfkryzis

  • Posts: 3062
  • 当有疑问时踢你的敌人在生殖器上,你可以道歉后
    • CB360 Build
Re: Electrical 101 - Read This First
« Reply #17 on: Jul 04, 2013, 19:14:13 »
Add to Your excellent post Sonreir:

Watts = Amps x Volts

Amps = Watts/Volts

Volts = Watts/Amps

So to determine the Amps a 60 Watt headlight bulb needs:

60/12 = 5 Amps

Your ignition coil is 5 Ohms (Stock)
Using Ohm's Law,  12V/5 = 2.4 Amps

Now, put one of those fancy 3 Ohm Coils in:

12V/3 = 4.0 Amps.

Better yet, remember, the alternator runs the bike at 14.5 volts when running properly.

14.5/3 = 4.8 Amps  -

Wonder why your CB350 with a 110 Watt alternator is losing its charge?

110 Watts at 12V = 9.2 Amps
110 Watts at 14.5 Volts = 7.6 amps

So what happens with a 60 Watt / 5 amp Lamp and a 3 amp Ignition?  8 amps leaving 1.2 amps for the other lights and charging the battery.

  Now do 60 Watt lamp and 3 ohm Coils: 5 amps and 4 amp = 9 amps...nothing left from the alternator to charge the battery.

Keep in mind, the resistance of bad connections, wire length, all contribute to current use, and these numbers are based on a NEW CB350, not a 40 year old one. 

Another note, the ignition does not draw the full amps continuously. It has about a 25% duty cycle, so 75% of the time, it is drawing nothing.

However, your 40 year old alternator probably isn't producing its full wattage either.

Some food for thought.
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Offline bud.

  • Posts: 106
Re: Electrical 101 - Read This First
« Reply #18 on: Jul 07, 2013, 16:46:03 »
Mind blown. This is SO helpful... thanks sonreir (and mydlyf)

Offline shutupthepunx

  • Posts: 2
Re: Electrical 101 - Read This First
« Reply #19 on: Nov 04, 2013, 16:03:31 »
I have a '75 Honda cb125 that needs a new ignition coil. It has proven rather difficult to find a '75 honda cb125 coil. There has to be something else I could use, right?