camd64
Remember Landy
does anyone remember the formula for figuring out voltage after you put in a resistor? say if i put a 0.8 ohm resistor and the input voltage is 14.0, what would the output voltage be? Johnny.
how many volts?
- Thread starter camd64
- Start date
-
adriver
Blazing Apostle
I can give you a quick answer. I'm sure you will get more "help". I might have time to check back. The best way I know to explain this is to think of the resistor as just a restriction. If you hooked one end of the resistor to your 14 volts and just check the potential at the open end, you would read 14volts. No drop. Now if you hooked the resistor up and completed the circuit the voltage drop across it would be 14 volts. In other words there is not an output "votage". A resistor is like a light bulb. Which is what a resistor is, sort of. If you put two resistor in the line, in series they would "split" the voltage drop. But it would be 14 volts across the two in total. Hope that help. Maybe you knew it already.
Robbie2734
Lambcharger
E=IxR E= voltage I = amperage and R= resistance...Thats the formula and adrivers got it right!
Demon 408
Well-Known Member
Go to the following link for Ohms Law and calculators that will help you answer your question.
http://www.the12volt.com/ohm/page2.asp
http://www.the12volt.com/ohm/page2.asp
camd64
Remember Landy
thanks for the help guys. the reason I ask is because the way I have understood it the ballast resistor in the ignition system is there to lower the voltage to the coil under the run position so it doesnt fry. on my car i changed to a unilite distributor and a msd coil but i still have a stock single ballast resistor. on the one side i have between 13.5 to 14.0 volts and the other i have about 5.8 to 5.9 volts? it runs ok but Im thinking part of my rich issue is possibly a weak spark. the mallory manual says to use a resistor about in the 0.8 ohm range. the stock one was about 1.6. wouldnt that 0.8 ohm slightly increase the voltage to the coil for more spark energy? shouldnt the voltage at the coil be more like 8 volts running? sorry guys its been about 10 years since i really messed with electrical math. :read2:
mopar head
DoD nuisance Alien/Squatch extermination team
If your experiment solves a ritch idle let us know. But if you have a long duration performance cam, you may have to resolve by modifying carb. Have a carb with choke horn? Your breather lid should have at least 3/4" clearance above blade.good luck
adriver
Blazing Apostle
Finding 5.8 to 5.9 tells me that you are checking the circuit once it is fully hooked up. That is what I was trying to explain when I said the voltage drop is "split" across what ever resistance a circuit has if it is a series circuit. That is what I assumed you were trying to figure out. Once you get past your resistor the coil is next in line I think? The rest of your voltage is "dropped" across the coil.
So to answer this question, yes decreasing the resistance of the resistor would provide a greater voltage available to the coil. As far as I know more voltage is always a good thing to get what ever mixture you have to ignite. It can "cover" up little flaws in a system like that. (Of course too many volts in electronic applications or certain other situations isn't good.)
Also be aware that according to the power formulas, increasing the voltage allows anything to use less current. (Pretty near always a good thing ) That is a good reason to change that motor on your table saw or compressor to 220V instead of leaving it at the 115 that it comes with. (check the wiring diagram on the label or under the cover)
Now just for giggles, and not to give T.I.M, I seem to remember reading that the real reason for a ballast resistors is to provide a stable current to the coil. As the car is driven at higher speeds more current would flow through the coil. The resister heats up and "chokes" off the current. At lower speeds the resistor cools and allows more current. Sort of a ballancing act.
But at start up the resistor is usually bypassed to allow "full battery voltage" to start the car.
camd64
Remember Landy
got it, thanks for helping me out with that one. i just ordered the msd 0.8 ohm resistor and I plan on going to my buddys shop where we can hook it up to a scope to see the difference in spark energy before and after. I'm thinking it won't be that much but ill see and post what i find. thanks.
camd64
Remember Landy
Wow Summit got my parts here quick! i ordered them at 4 yesterday and when i got home from work there they were. I just installed the msd 0.8 ohm resistor and took another voltage reading and now i sit right about 8.4 to 8.7 volts. it seems like it pulls a bit more cleanly through the rpm's. on a wierd side note i had recently installed a tach in the car and thought i might have a bad one, at around 1200 to 2000 rpm's the needle would flutter around and now its steady all the time. maybe i had a slight missfire i could not even hear? i still plan on hooking it up to the scope to see what the difference in spark output looks like.
dgc333
Well-Known Member
The ballast is there to limit the current flow through the coil. The coil can only disapate a certain amount of power in the way of heat so to protect it from over heating the ballast is installed.
The power handling capability is a know by the designers and the primary resistance is known so, V = sqrt of (P x R). That will give the voltage at the input to the coil to keep it from over heating.
Also, most rich issues at idle are the result of not enough initial timing. When dialing in an engine you always have to get the timing sorted out before you start playing with the carb. The stock timing requirements on apply to stock engines anything with more compression or more cam will require the timing to be modified from the stock specs.
-
Similar threads
