Ballast attached to Coil

Hi RAMVA!

My '73 SB has a ballast resistor attached to the coil (rectangular ceramic part with one conector on each end). It has two connectors, but only one is plugged to the coil. Experience with ballasts tells me it's not working like that. How is that suposed to help me? Why did the PO install it? Can I plug in a current triggered tach there? I'll replace the whole ignition soon, and I'd like to know what to keep and what to give/throw/brake.

BTW, is it my imagination, or lately all my post are ignition/electrical related?

TIA, Karls

Reply to
Karls Vladimir Peña
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Reply to
Shane

The pulpose of a ballast resistor is to limit the current through the primary of the coil and the points, to prolong points' life. If needed, the balast resistor is connected in series with the coil, that is the ignition wire goes directly to the one end of the resistor, and the other end of the resistor feeds the (+) side of the coil.

The stock VW coil, has the ballast resistor incorporated, no need for an external resistor. Coils that need an external ballast resistor, usually have that provided with the coil from the manufacturer (with the exception of high energy coils). If you do not have the stock coil, you can use an amp-meter to check if you need the external ballast resistor. To do so, connect the (+) side of the coil to the ignition wire, and ground the (-) side of the coil through the multimeter, set to the 10Amp or more range. Turn the ignition on, and record the currect value. If the current is in the range of 2.5 - 3.5A, you do not need an external ballast resistor.

Bill, '67 Bug.

Reply to
Bill Spiliotopoulos

He said it looked disconnected. Yes the coils have built in ballast resistors but, if you are running, lets say a Mallory Unilite Distributor, it needs a ballast resistor. Or it can fail from overvoltage. I have to use one on my bug. Did you know if the last owner had some solid state device or dizzy.

Joe Cali - Next Generation - USA.

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Reply to
Joe Cali - Next Generation-USA

I remember he said something about some electronic ignition. But I have a stock brazillian vacuum dizzy and coil...

Reply to
Karls Vladimir Peña

You may not necessarilly need an additional ballast resistor to run a Unilite distributor, if you are using a stock coil / wire loom. Mallory recomends using a ballast resistor of 1.5 Ohms, with coils that have a primary resistance of under 1 Ohm. So, in the worst case, the Mallory Unilite module must be able to at least drive 2.5 Ohm primaries, which correspond to primary current of about 5 Amps.

The resistance of the stock coil's primary in addition to the resistance of the wire from the ignition switch to the coil, is at the range of about 4 Ohms (at least that is what I measured in my bug), far adequate to limit the current that passes through the coil and the Unilite module (to about 3 Amps).

Anyway, you should measure the current drawn by the coil in your application, to determine if you need an external ballast resistor. Using additional resistance to the coil's primary weakens the spark, so a ballast resistor should only be used if necessary.

Bill, '67 Bug.

Reply to
Bill Spiliotopoulos

Bill, correct me if I am wrong. The Mallory Unilite plus wire goes only to the 12v terminal on the coil. Just as if the coil was not in the circuit, so the Dizzy is getting hit with a full 12volts. The wire goes to the coil from the battery, so the coil gets full voltage, then to the Dizzy. The ballast is placed between the coil and the dizzy to drop the current and act as overvoltage protection.

Joe

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Distributor,

Reply to
Joe Cali - Next Generation-USA

Normally, the ballast resistor goes between the +12V and the (+) side of the coil, but if you put it between the coil and the distibutor you obtain the same results, and it is easier to do the connections. In the early days, the ballast resistor's purpose was to reduce the current trough the points, to prevent burning them. Limitting the current though the coil's primary also reduces the overvoltage on the coil's primary when the points open (which should normally be in the range of 400V). This also reduces wear on the points because it reduces arching.

With an electronig ignition module in place of the points, the ballast resistor still protects against overcurrent and overvoltage.

Anyway, the point is that you should not increase the primary's resistance beyond what is necessary to protect the contacts. Reducing the overvoltage or spike when the contact opens, reduces the high voltage that is sent to the sparks. The coil acts like a transformer that amplifies by 50 (stock coil) that overvoltage (the 400V spike), creating the 20000V in the HT lead.

The only accurate way to determine if you need an external ballast resistor and of what value, when you switch to an electronic ignition, is to use an osciloscope to moitor the voltage on the primary of the coil and to have the accurate specs of the electronic ignition module (how much current can it drive and which is the overvoltage you must set the coil to produce).

Unfortunatelly, most of us do not have access to an osciloscope and probably can't either find the electronic ignition's specs. The only easy thing we can do is to measure the current through the coil when it's (+) terminal is connected to +12V and the (-) terminal is connected to the chasis, through an Amp-meter. Be carefull when finishing the measurment to break the circuit from the (+) side of the coil (e.g turn off the ignition switch) and not by disconnecting the Amp-meter, especially if you use a digital multimeter, because the overvoltage will appear at the point where the circuit is bloken and it may destroy your multimeter. This way we can get a rough calculation of the resistance of the coil's primary ( Res. = 12 / Amps). In the case of the Mallory Unilite, if the Resistance is more than about 3 Ohms, you don't need an external ballast resistor. The value of 3 Ohms is a rough estimation based on worst case assumptions. I couldn't find any real specs about the mallory Unilite module. By the way, I run a Mallory Unilite distibutor with the stock coil for allmost a year now (15000km) without an external ballast resistor and it is doing ok.

I hope I didn't confuse you more...

Bill, '67 bug.

Reply to
Bill Spiliotopoulos

Bill I did not tell you what I was running, thus some confusion from my faults information. I am running a Jacobs Bug Pac with the Mallory Unilite. By placing the Ballast between the coil and the Unilite only the Unilite gets the protection, the coil get full voltage and current. Thus providing max. to the Jacobs. My coil only acts as a trigger to the Jacobs. The high voltage wire from the coil goes to ground. The Jacobs goes to the Dizzy.

Thanks for the info. that you have been using the Mallory without the ballast, it is comforting.

Regards,

Joe

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Reply to
Joe Cali - Next Generation-USA

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