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12V battery-12V coil
:

Why a ballast resistor?

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Terry Alexander

08-05-2002 11:07:17




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My side mount 8N was converted to 12 volts before I got it. I read dang near everything posted here. I just reviewed the steps required to convert the 8N to electronic iginition.

I just get confused over different "slants" (for lack of a better adjective) regarding the ballast resistor.

I have a 12V battery and a 12V coil.....AND upon advice from the New Holland Dealer (who is an 8N owner), I have a ballast resistor.

Do I need the resistor? If so....why?

TIA

I'll sit back and listen.

Terry A. 1950 8N

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Canadianiner

08-05-2002 16:15:11




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 Re: 12V battery-12V coil - Why a ballast resistor? in reply to Terry Alexander, 08-05-2002 11:07:17  
The big problem with ignition coils in automotive use is that they take a fixed amount of time to charge the magnetic field. However the engine runs at many different speeds and so the dwell time (time that the points are closed or the time available for the coil to charge) keeps changing. In other words the faster the engine goes the less time to charge the coil. The designer has to design the ignition circuit so that the coil charges adequately at maximum operating speed. This of course means the coil will overcharge at lower speeds when the charge time is longer. Just like overcharging a battery this shows up as heat. The time honored solution to this overcharging has been the use of the ballast resistor which limits the maximum amount of current that can flow in the circuit.
To answer your question � if it runs properly with the resistor wired in then leave it. Even if it was designed to not have a resistor you are better off with the resistor as it will reduce the load on your points and condenser.

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Danny in CO

08-05-2002 14:18:39




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 Re: 12V battery-12V coil - Why a ballast resistor? in reply to Terry Alexander, 08-05-2002 11:07:17  
It is my understanding that front mount distributors need and use the ballast resistors, side mount don't. If I'm wrong I'm sure someone will correct me.

Therefore, in my opinion you don't need the ballast resistor.

Danny



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Phil (NJ-AZ-SK)

08-05-2002 14:07:14




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 Re: 12V battery-12V coil - Why a ballast resistor? in reply to Terry Alexander, 08-05-2002 11:07:17  
Terry, >>I have a 12V battery and a 12V coil<<<
Yes! but you have an alt putting out 14.5 V

(Simple Math) Wattage = V X V /r The normal Automotive 12V Coil needs to be of a lower inductance because it fires 8 cyl @ high RPM. The Coil resistance is ~.5 Ohm.. So if you have an automotive Coil you must always have a ballast because without it.. The WC (worst Case) 12.5 X 12.5 /.5 = 312 Watts
Alt 14.5 X 14.5 /.5 = 420 Watts

As a comparison the Side Mount 6 Volt Coil is ~1.3 Ohms and operates without a ballast on 6V 6.5 X 6.5 /1.3 = 32.5 Watts
Gen 7.5 X 7.5 /1.3 = 43.2 Watts


SO measure your coil and if its > 4.0 ohms the side mount (coil in a can) may not need a ballast
(You probably don't want more than 52 Watts MAX)

Hope this Helps,

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Ah, okay.... Evil Steve

08-05-2002 13:19:17




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 Re: 12V battery-12V coil - Why a ballast resistor? in reply to Terry Alexander, 08-05-2002 11:07:17  
I just posted to your ? on points replacement and asked if you had a 12v conversion. There's your problem.

First, realize that alternators actually put out 13.4 (?) volts and that batteries are also 13.4.

Your new coil gets this voltage and doesn't know what to do with the excess other than send it right on to your innocent, non-suspecting points and condensor. They weren't designed for the extra. Your coil probably isn't either.

The resistor puts the voltage to your coil and points/condensor where it needs to be. I don't know the exact amount of resistance you need, but Dell's written on this subject countless times, so check the archives.

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Mountainman

08-05-2002 12:18:21




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 Re: 12V battery-12V coil - Why a ballast resistor? in reply to Terry Alexander, 08-05-2002 11:07:17  
I don't know why but every car I've ever owned, 6 or 12 volt, that had points type ign had a resistor or a resistor wire (in the harness) to the coil. It has to do with coil heat and the ability of the points by design to handle the voltage/amperage. I'll be looking forward to what the experts here have to say.

N - joy.

Mountainman...CA



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Dave OH

08-05-2002 16:18:58




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 Re: Re: 12V battery-12V coil - Why a ballast resistor? in reply to Mountainman, 08-05-2002 12:18:21  
Do what "Evil Steve" said and go to the archives and check out Dell's answers.
Dave OH



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Dave OH

08-05-2002 16:18:49




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 Re: Re: 12V battery-12V coil - Why a ballast resistor? in reply to Mountainman, 08-05-2002 12:18:21  
Do what "Evil Steve" said and go to the archives and check out Dell's answers.
Dave OH



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