Re: hornet wire wanted

[Tom Jennings <tomj@xxxxxxx>]

In general, resistors don't (intentionally :-) change resistance.  
Ballasts are resistors that change resistance with temperature, or  
the amount of current through them, which heats it up (causing temp.  
change causing resistance change).

There can be negative and positive temp. coefficient resistors too;  
decrease or increase of resistance with temperature. Car ballasts are  
positive T.C. -- as the coil draws current, the ballast heats up,  
causing the resistance to go up, limiting the current, etc.




On Nov 8, 2005, at 10:10 AM, <mail@xxxxxxxxxxxx> wrote:

> DUH!!! Joe, Pete, I accidentally typed the EXACT OPPOSITE of what I
> meant!! Both are correct. The ballast resistor doesn't usually have a
> bypass wire, it IS the bypass, working as Joe explains -- it passes  
> 12V
> when cold, increases resistance to the stated value and only  
> passing 6V
> as it heats up, which usually just takes a few seconds (I'd guess  
> 15-30?
> Never saw any specs or tested one.). Outside temperature affects
> heating, so on colder days the ignition will get more voltage for a
> slightly longer period. I'm pretty sure the resistance wire works the
> same way. Otherwise a relay and timer would be needed. This heat/cool
> cycle is what causes them (resistor or wire) to eventually fail.  
> That's
> why I like a ballast resistor better -- easier to check and  
> replace. The
> resistance wire usually lasts 20 or so years and is easier for the
> manufacturer to install. One less thing on the firewall also.
>
> Joe Fulton wrote:----------------
>
> Uh, I may be all wet here, but I seem to remember from general physics
> class and electricity and magnetism classes that resistance (like in a
> wire) increases almost linearly with temperature). Therefore a
> resistance wire (or ballast resistor) will pass a decreasing amount of
> current as it heats up, ie. voltage will drop.
>
> Joe Fulton
> Salinas, CA
>
> Pete Savage wrote:----------------
> Frank,
>
> I hate to disagree with you, but placing a resistor in-line any
> electrical circuit will always reduce voltage, whether the resistor is
> hot or cold!
>
> The reason you need a voltage reduction to the coil in historical.   
> When
> cars had 6 volt systems coils were designed for 6 volts.  With the
> advent of 12 volt car electrical systems there was a need to reduce  
> the
> voltage to the coil from 12 to 6 volts and as such ballast  
> resistors and
> resistor wires were invented.
>
> When a car is cold and starts the ballast resistor is bypassed and a
> full 12 volts are made available to the coil to aid in a hotter  
> initial
> spark for starting.
>
> later
> Peter
>
>
> ----- Original Message ----- From: <mail@xxxxxxxxxxxx>
> To: <mail@xxxxxxxxxxxx>
> Sent: Tuesday, November 08, 2005 4:49 AM
> Subject: re: hornet wire wanted
>
>
> Eddie, www.amcgremlin.com blanks out the e-mail address in  
> messages, so
> please forward this to Hornetracr!
>
>
> The wire he needs is the resistance wire. It's pretty generic -- it  
> can
> be found on the electrical isle of any auto parts store. It will be
> marked "resistance wire" and may or may not have the ohms, and may not
> be pink. An alternative is to use a ballast resistor. They range from
> 1.1K-1.5K ohms. Value shouldn't make much difference as long as  
> it's in
> that range. All resistance wires/ballast resistors are designed to cut
> voltage to 6V until they warm up, then they will pass 12V. The actual
> resistance just means it will warm a little faster or slower (1.1K  
> will
> warm a little faster than 1.5K). We're only talking seconds  
> difference,
> so it shouldn't make a difference in the exact value, but I bet  
> 1.35K is
> a common value.
>
> Frank Swygert
>
> MSgt Frank Swygert
> 436 CES/CECM (MilCon)
> 302-677-6436, Cell 302-363-0530