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Technical To Ballast or not to Ballast

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Technical To Ballast or not to Ballast

Bambino said:
The idea of a ballast resistor is to reduce the coil voltage during normal running. Most older coils were designed to give maximal output at 12V, which they did all of the time. However, when starting the engine, the starter pulls such a large current, with a coincident voltage drop (to around 9V), that the nominal 12V coil would under perform and generate a weak spark making starting difficult, particularly in cold weather.

The solution was to fit a 9V primary coil which would give the same secondary output as a 12V coil and add a resistor in series to drop the voltage from the coil to 9V during normal running. When starting the engine, the resistor is bypassed and the coil receives the usual diminished voltage (~9V) which is now sufficient to give full output. Once the engine starts, the resistor is back in circuit so that the coil does not overheat.

Modern coils are much more efficient and have more stable output voltage with a variable input voltage so external ballast resistors are not needed.

The ignition setup in the picture is the 'wasted spark' ignition common on later model Polish air-cooled Fiats. The small domed 'distributor' contains points and advance mechanism and only switches the primary current. The coil has a twin output that fires the spark plugs simultaneously - one on the top of the compression stroke and the other (wasted) on the top of the exhaust stroke. No rotors and caps to wear out, but the condensers were still a major weak point.

Chris

PS: See here https://www.fiatforum.com/500-classic/359053-650cc-engine-electronic-ignition.html for a recent discussion.
Click to expand...



Hi Chris !
Its been a while since your reply but hope you find time and interest to assist me.
I have recently bought a 500 with same ignition setup as Bleeding knuckles, so i guess i have a 126 polski engine.
Thing is my coil quit.
Got myself a new one, but added a ballast resistor, as this was recommended to me.
Compared to old coil it fells like engine runs a bit on the downside now.
I was told that with ballast i will not get 12 v but 9 v to sparkplugs , and that could explain why engine appears a little tired.
Should i at all have a ballast ?
Should i use ballast only during startup to save coil and add a switch in order to disconnect ballast after startup and get full effect on spark plugs ?


Coil is mounted right above exhaust on firewall and that is a bad place as it gets hot. Maybe i should move it to opposite side of fire wall ?
Thanks !


Per
 
Hello Per,
A coil receives anywhere from 14 to 9 volts depending on whether it uses a ballast resistor and the windings inside the coil. The sparkplugs receive 20,000 volts+ from the coil.

With your ballast resistor removed, remove all the wires on the coil and measure the resistance across the two electrical terminals of the coil. If you have 2.7 to 4.1 ohms you do not need a ballast resistor. If you have less you need a ballast resistor, if you have more than 4.2 then you need a new coil.

With the ballast resistor removed, check its resistance. It should be around 1.6 ohms. This is the recommended resistance for the wasted spark system.
John
 
Hi.


Many thanks for your advice and i will do some measuring once Christmas activities has settled.
Wish you all a merry Christmas.


Per
 
I will be probably be unable to conduct myself in the Fiat tomorrow due to mis-fuse of alcohol.
But if I have the capacitor and energy I will resist drinking until the afternoon.
Potentially I could have a positive post for you or a video of me doing a circuit of the local lanes.

By the way, the system has settled down now and miraculously it's steady at around 14.2v. I have no idea how that was achieved???? The miracle of Christmas!!!
 
Last edited:
Greetings all !






Jjacob and fiat500. i disconnected wires and measured the coil and got 1,3 - 1,4 ohm......on a brand new coil.
Enclose a picture.
Jjacob since Santa is visiting you today i hope you dont adopt to swedish alcohol traditions......a bit tired today
 

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Oh and another thing.
This ballast resistor came of a low price standard coil that i bought and i would imagine there are a variety of resistors on market.
How do i determine i have correct resistor or does it not matter ?


Thanks !
 
For the wasted spark coil, which you have, 1.4 ohms is normal. You would use a 1.6 ohm ballast resistor with that coil. I see in your picture that you have a ballast resistor. Take the ballast resistor out of the circuit and measure the resistance. It should be around 1.6 - 2.0 ohms.
John
 

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Hi John.


I have not measured resistance on my old coil as it is wasted, so the 1,4 ohm came up measuring on new coil as depicted in enclosed photo.


Can i determine ballast resistance with my measuring equipment or is more advanced methods required ?


Regards,
Per
 
I've got a crankcase somewhere without the hole for the distributor and the ignition control ECU.

What are the benefits of this over a standard 650 engine, with a 123 electronic ignition??

I guess the distributor has a bit of drag on the camshaft, but other than that??
 
nathanrobo said:
I've got a crankcase somewhere without the hole for the distributor and the ignition control ECU.

What are the benefits of this over a standard 650 engine, with a 123 electronic ignition??

I guess the distributor has a bit of drag on the camshaft, but other than that??
Click to expand...

Hi timing is not adjustable it relies on the flywheel sensors so once you set it, in theory forget it.
 
nathanrobo said:
Presumably, if you can access the ECU logically, you could map it??
Click to expand...

I don't think it is sophisticated enough to remap. There is a diagnostic pin if I recall but I don't think it is anything more than a few transistors inside to provide switching.
 
Per,
If you used your meter on your new coil and measured 1.4 ohms, then that is correct. Take the same meter and measure across the two terminals on your ballast resistor and you should measure something around 1.6 ohms. Connect the ballast resistor like the picture I attached on this page.
John
 
Hi John.


I now have received specifications on this ballast and it is 1.25 - 1,28 ohm.
Maybe its too low resistance as 1,6 ohm has been suggested, and not sure if i need ballast at all ?
Anyways engine runs great now with this setup.
 
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