Anyone know the specifics of automotive wiring?

[Michael Yount]

stroth - baskin has saved my ass more than a couple of times on things electrical - he won't steer you wrong.

 

[baskin]

Thanks! I am just really confused by all of this electrical stuff.... I should just keep my mouth shut and stick to all things mechanical.

Ok, this is kind of a lame analogy, but it will work. Consider the battery a water pump, higher voltage equals higher pressure, the wire as a hose, the larger diameter wire, the larger the hose, and the water as current. Consider less conductive materials, such as carbon as a hose with baffles that block flow. Consider a pressure drop as a drop in voltage.

The water pump is connected to six equal size hoses, those are connected to a smaller hose (the starter), which runs through six other equal size hoses back to the water pump.

So, what limits the current (water flow) through the system? ; where is the voltage drop (pressure loss) in the system ? How is the current split between the wires?, Bonus question: what if one of the wires is smaller than the others, then how is the current split?

 

[srothfuss]

1)So, what limits the current (water flow) through the system?
2)where is the voltage drop (pressure loss) in the system ?
3)How is the current split between the wires?
4)Bonus question: what if one of the wires is smaller than the others, then how is the current split?

OK -

1) The blockage is at the Starter. Assuming 6 equal pipes feed into 1 pipe with less circumference

2) Pressure Drop (in this system) occurs after the starter. Assuming 1 pipe feeds into 6 pipes with more circumference

3) The pressures (current) should be equal unless there is blockage in one of the pipes.

4) My guess (I should read up on my Thermodynamics / EE notes before I post this): The current division is based on the folowing formula. Assume a simple circuit with 2 resistors in parallel.

I1=R2/(R1+R2) & I2=R1/(R1+R2)

If we knew the resitance (pipe size?) then we could determine the flow.


How'd I do?

 

[baskin]

OK -

1) The blockage is at the Starter. Assuming 6 equal pipes feed into 1 pipe with less circumference

2) Pressure Drop (in this system) occurs after the starter. Assuming 1 pipe feeds into 6 pipes with more circumference

3) The pressures (current) should be equal unless there is blockage in one of the pipes.

4) My guess (I should read up on my Thermodynamics / EE notes before I post this): The current division is based on the folowing formula. Assume a simple circuit with 2 resistors in parallel.

I1=R2/(R1+R2) & I2=R1/(R1+R2)

If we knew the resitance (pipe size?) then we could determine the flow.


How'd I do?

on q2, the pressure drop is across the small pipe, the analogy falls apart when you consider that the pressure difference across the pipe is square law with respect to flow instead of linear, but otherwise the analogy works pretty well.

With a BSME, you've obviously had enough EE courses that you don't need the analogy, but maybe it will help someone else out.

 

[srothfuss]

Cool! But that peice of paper doesn't make me (or anyone) smart... By no means am I trying to be an a$$. I am just curious


Thanks for the help!

 

[Saleen0679]

So if (2) 8-gauge wires are acting just like (1) 4-gauge wire, wouldn't it come down to surface area of the wire?

If you send voltage across 2 wires then you divide the current....But if the wires terminate on the same terminal, do you add the current back up? Forget about Voltage Drop.... I want to understand why it's a good idea to split wires into smaller bundles. The voltage thru 2 wires from 1 source is equal. So why don't more people do this? (like the power company)

With multiple paths you would have additional considerations when it comes to the design of a system. You would have to consider the additional weight, muliple points of failure, noise generated by the additional wiring (one reason you run your speaker wires down one side of the car and power wires down another with high power audio systems). In addition to the above, power companies will probably have to deal with corona effect created by the amount of power running through their lines and spacing between the lines to prevent arcing and also ease of repair.

As with most things you have to make some compromises with your design and prioritize your requirements.