Accel 3 Ohm Coil from a Harley (Do I need a Ballast Resistor?)

S

slushie07

Been Around the Block
I recently bought an Accel 3ohm Dual Output Coil from another DTT member. The 1976 KZ400 that I am going to use it on uses a 4ohm coil. According to http://chrislawson.net/kz/repairmaint.shtml under the electrical system heading, I will need a ballast resistor. Can I just buy a ballast resistor that is about 1 ohm like this one,

http://cgi.ebay.com/ebaymotors/MSD-Ignition-8214-Ballast-Resistor-0-8-Ohm_W0QQcmdZViewItemQQhashZitem563a875bd4QQitemZ370349136852QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

or do I need to do some calculation to figure out the correct resistance of the ballast resistor. Also do you guys think this is even necessary. And do I just connect it in series right before the power cable in to the coil. What exactly does a ballast resistor even do, protect the coil from voltage spikes, why do different coils have different primary resistances?
 
rule of thumb..3 ohm electronic ignition....5 ohm points....plus or minus for both values.Is your kz points or electronic???????
 
not sure why you'd need a "ballast" resistor, the inductance of a 3ohm vs 4ohm coil is probably lower, the function of a resistor in series with a coil is to reduce the apparent inductance of the circuit. I think they might be suggesting a resistor to limit the current flowing through the points and prevent them from being destroyed, but with that setup, you effectively lose any benefit of the lower resistance coils. You might want to just run them as is, you will probably go through them faster, but not by a lot, or move to a transistor (mosfet) assisted booster box, or just go electronic.
 
fitting low impedence coil(s) to points system is not advised.Points stay closed for most of the 4 stroke cycle,these coils can overheat, producing a weak spark........try them they might work :o
 
Wee Todd said:
fitting low impedence coil(s) to points system is not advised.Points stay closed for most of the 4 stroke cycle,these coils can overheat, producing a weak spark........try them they might work :o
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kz400's have several specs of coils. some with 3, some with 4 and some with 5. my 78 stock was 3ohm. They were moving things around a lot. a lot of people run dc-3's and accels on kz's...
 
Wee Todd said:
rule of thumb..3 ohm electronic ignition....5 ohm points....plus or minus for both values.Is your kz points or electronic???????
Click to expand...

I heard it's the other way around?
 
DrJ said:
I heard it's the other way around?
Click to expand...

I wasn't going to call him out, but yes, it's usually higher for electronic, but not always. carbed monsters and ss's use dual 3 ohm coils.
 
I have fabricated and tested(raced) two types of igntions based on Yamaha componets,,and being electronic, coil specs were 2.8- 3.2......points coils are higher because they have to asborb the current,..this applies to most 180 degree crank, cam driven systems,,, as for crank driven wasted spark design.....maybe the impedence is less
 
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