What is the purpose of a ballast resistor in a '72 510?

[rosso]

I will be removing the ballast resistor in my 510 VG33 conversion project since I am using a carburetor and Saudi electronic distributor. I also have an epoxy filled coil.

 

What is the purpose of the ballast resistor? What exactly did it do?

 

Just trying to understand so I make sure I don't damage anything in the VG.

[datzenmike]

The long story..

 

There are certain physical limits to how much current can pass through a set of points* before they just erode away from the arcing. Say about 4 to 6 amps. To limit the current, the coil resistance in the windings are kept to about 1.5 ohms. A ballast resister of another 1.5 ohms is added in line and the combined resistance of 3 ohms (12v/3 ohms = 4 amps) and everything works and the points happily last thousands of miles. Oh yeah, why the ballast rather than running a 3 ohm coil??? Well on the ignition switch is another output of 12v only in the start position. This wire runs directly to the coil (by passing the ballast) and 12v / 1.5 ohms of the coil = 8 amps and a much hotter spark is produced while starting the engine. The engine may be cold and the battery low and while the starter is cranking the voltage is also lower so connecting 12v to the coil is a good idea. When the engine starts and the key released, this 12v directly to the coil disappears and it only gets what flows through the ballast.

 

Running 12v constantly to the coil would over heat it and the points would last maybe 150 miles*.

 

 

If running an EI ignition you really need the EI coil which does NOT need a ballast and is less than 1 ohm. The EI module can easily handle this current. (12v/1 ohm coil = 12 amps and a huge increase in spark. If you plan to run your points coil you HAVE to keep and use the ballast resister or the coil will burn up. No increase in spark power either.

[rosso]

Thanks DMike,

 

I have an MSD Blaster high vibration coil and MSD said I did not need a ballast resistor with the electronic dizzy. Here are the specs for the coil does that all look okay?

 

Emission Code	1
Inductance	8 mH
Maximum Voltage	45,000 Volts
Peak Current	140 mA
Primary Resistance	.7 OHMs
Product Type	Ignition Coils
Secondary Resistance	4.5K OHMs
Spark duration	350 uS
Turns Ratio	100:1

[datzenmike]

That'll work. The EI coils are 0.7 to 1.0 ohms.

[rosso]

	Whew, thanks Mike. So it looks like I can connect the BW wire from the ignition switch to the + terminal of coil, then run a new wire from the - terminal of the coil to the distributor. Does that sound right. I posted this question about wires on my project page if you had not seen it.  ('72 510 Goon - Prova )   <big sigh of relief>

[datzenmike]

Sounds right. I just join the START and the ON signal from the ignition switch to the + coil and the EI module. One less loose wire laying around.

 

Below... ignore the coil resistance. This is how to wire the matchbox. Definitely try the MSD separately and compare them.

[rosso]

Okay Mike, within the next week I will be working on wiring again and cleaning up connections and removing extraneous wires.

 

As you suggested, I will join the BW and BL wires together and connect to the plus terminal of the coil. Much cleaner than having another loose wire hanging around.

 

Speaking of loose wires hanging around (in this same coil/windshield washer bottle area) - I have 2 or 3 solid black wires that are cut off with no connectors that are maybe 18ga. I was planning to wrap them altogether and make one lug connector to a new or existing ground point. Do you see any problem with that? These are probably for things that have been removed and rather than having 3 loose singe wires it would be tidier to group them into one connector and ground to body/frame somewhere.

 

That will only leave one loose wire in that area - yay! And it is R/L and hot all the time so it's probably the engine room lamp - which I don't have and probably never will since I think they are really ugly. Does anyone know of a really pretty light?

 

Thanks Mike and all other electrical gurus.

[datzenmike]

 

This was an optional lamp for many Datsuns, The lamp end twists off and there is a coil of wire inside so it's mobile and even a hook on the bottom of the lamp so it can be hung on something.

 

 

[rosso]

Yep, that's the one I know about - that I think is rather ugly. However; after searching the interwebs for about an hour - it's starting to look better. 🙂

 

[rosso]

Okay, I wanted to make some progress today so I cleaned up wiring and connected the coil wires. Both BW and BL are connected to the coil plus terminal. The rest of the ballast resistor wiring is folded back and zip tied to the harness. Once the car is running and everything working I can go back and decide what to do with all the extra stuff and wrap the whole harness. Thanks again DMike. There is a current picture of my engine bay on my project page.

 

 

EDIT: 12V at battery and 11.9V at coil.

 

Edited October 6, 2020 by rosso