62-C1

My 62 327/340 windshield wipers won't operate. two questions what Voltage should I see on the High side of the Ballast resistor, What on the Low Side? Which side should the wipers be attached?

Presently attached to low side. Voltage on high side is 8.5V on low side 3.0V.

Any answers?

Marty

jim lockwood

The "high" side, as you call it, is where the wiper motor should be connected and the Voltage there should be full battery/generator voltage.... 12-ish Volts with engine off, 14-ish Volts with engine running.

Jim

cardo0

What your asking for is a number for the voltage as if the it doesn't change. Voltage across a resistor is dynamic and changes as the current through it changes. So the voltage when current flow is low like during idle w/o accessories running and the generator/regulator has not picked up the voltage drop across the ballast resistor will be smallest. When the loads are high the voltage drop can be much greater. Issue with the '62 corvette wiring diagram I'm looking at is that load side/brown wire of the ballast is electrically connected to the "B" terminal of the voltage regulator so when that "picks up" the voltage on the load side/brown wire should be greater than the supply side/dark green wire side of ballast resistor.

What I'm saying is your pretty much chasing your tail trying to measure a constant/static/steady voltage across the ballast resistor.

Hope this helps.

GearheadJoe

I agree. If you have 8.5 volts on one side of the ballast resistor and 3.0 volts on the other side, something is wrong with the high side feed.

Also, the only load connected to the low side should be the coil.

The sole purpose of the ballast resistor is to reduce the voltage at the positive input to the coil to help the points last longer. The ballast resistor is bypassed by the starter solenoid during cranking so that the coil gets full battery voltage during cranking. This temporarily provides a hotter spark to help get the engine started.

Once the engine is running, the ballast resistor reduces the coil voltage by a few volts.

Frankie the Fink

The ballast reduces the stress in the system and keeps the coil from overheating during normal running but bypassed when starting.
I've "limped home" several miles jumpering past a faulty one but I wouldn't do it for kicks..

The 'high side' should be as Jim has indicated whereas the low side voltage may vary.

69427

The sole purpose of the ballast resistor is to limit the current through the points and coil. It is not there to function as a voltage "regulator".
The points have 12 volts across them when the points are open, and zero volts across them when the points are closed. The ballast does not change those readings. Also, when the points first close (at the start of dwell) the voltage across the coil is 12 volts. The ballast does not limit it to some arbitrary lower level at the start of dwell.

During cranking, the ballast is bypassed to restore the current level through the coil despite the battery voltage being lower than when the engine is running and the alternator/generator is charging.

GearheadJoe

Okay, but I think this is just a semantics issue. I'm and electrical engineer and I work with voltage and current relationships every day.
Ohms Law is sort of hard-wired into my brain.

For a fixed resistance, there is a one-to-one relationship between voltage and current, so you can describe the important parameters of the circuit either in terms of voltage or current. I find that for non-engineers, it is usually easier for them to understand something in terms of voltage rather than current.

However, in terms of the underlying physics, it's probably more technically correct to describe the operation of the primary circuit of the coil in terms of current.

jim lockwood

Absolutely, positively true. But good luck getting that point to sink in with anyone.

65GGvert

Semantics indeed. But it limits the current by dropping some of the voltage across the ballast resistor leaving less voltage available at the coil. Less voltage equals less current through the coil. So, semantically it restricts current by dropping voltage. Also semantically, it restricts current because the ballast resistor adds resistance to the total resistance of the circuit. Take your pick, either way it does the same thing.

Frankie the Fink

Sigh....another semantic felony committed under Ohm's Law...

jim lockwood

Indeed.

dplotkin

I have argued this many times on this forum. That's why it's called a ballast, a ballast is a stabilizing influence just as it is in a boat, it limits current to prevent the needless consumption of contacts and coils.

It isn't semantics either. Its more like improper use of technology. When ever the purpose of the ballast is explained as to effect a reduction in voltage it is the wrong explanation. It is forgivable. There's plenty of technical crap in the world I don't know.

Dan

69427

The ballast limits the peak current through the coil. It doesn't limit the peak voltage across the coil. The coil and points still withstand/contend with 12 volts every dwell cycle (not to mention the hundreds of volts each time the points open).

It's not just semantics to an electrical engineer.

GearheadJoe

I think this discussion has wandered pretty far from the actual question posed by the OP.

Please rest assured that I thoroughly understand the fundamentals and the nuances of the circuit under discussion.

However, my goal here was not to provide a tutorial on how to best describe the operation of the ignition circuit. Rather, my goal was to help the OP troubleshoot a problem.

The OP stated his measurements in terms of voltage, and I responded using the same terminology. And, the advice I offered will allow the OP to readily make progress in his troubleshooting.

Hopefully we will hear back from the OP after he has double-checked his voltage measurements and the power supply connection to his wiper motor.

65GGvert

That's correct. Ohm's law isn't suspended because it's a Corvette (or any other car). He will get 12V plus (battery or alt) to the ignition side of the ballast, and less than that on the coil side of the resistor, because the resistor drops voltage as current passes through it. So all he needed to know in the first place was as you said, ignition side of resistor for supply to wipers.

69427

I wrote post #6 because I disagreed with your technical statements there. I still do.

69427

Ohm's law is for resistive circuits. An ignition coil is an inductor. The formula for figuring out the voltage across an inductor is not Ohm's law.

Do you disagree that the coil will have 12v across it at the start of dwell?

GearheadJoe

Yes, I agree that at t=0 (the instant the points close), the voltage across the coil primary starts at 12 V, but this initial condition does not last very long.

As you apparently know, this is a reactive circuit that has R, L, and C elements. The actual behavior is rather complex at the instant that the points close and the instant that they open. So, it is an oversimplification to describe the circuit only in terms of Ohm's Law. I'm sorry if my description bothered you.

However, I favor oversimplification when the transient details are not relevant to the question at hand, particularly if the person I am trying to help is not familiar with transient circuit analysis of R-L-C circuits.

At idle speeds, the coil current stabilizes soon after the points close and the reactive elements L and C become momentarily invisible in terms of the circuit analysis. At that point in the cycle, the primary current is established only by the battery voltage, the resistance of the ballast resistor, and the resistance of the coil primary winding.

So, at that point in the cycle, the current in the primary becomes subject only to Ohm's Law. This condition would continue indefinitely if the points remained closed.

The situation changes again when the points open and the coil field collapses, which induces a very high voltage on the coil secondary. Then for a brief period we are back to transient analysis of an R-L-C circuit.

All of this detail can be quite interesting to electrical engineers like me, but it is not particularly helpful to someone who is trying to troubleshoot a problem by connecting a volt meter to the ballast resistor.

62-C1

GearheadJoe,
Thanks for the information, I'm a mechanical / Industrial Engineer and the only thing I remember from school is if you have an electrical problem, get yourself an electrical technician. I had picked up the car from a fabricator and was test driving it when it started to rain. turned on wipers, engine quit.

Turns out the engine had been out of the car twice and on second install, the wiper was attached to the wrong side of Ballast resistor. Speaking as a non-electrical I think its a dumb place to power the wipers.

Thanks to everyone for the education.

Marty

65GGvert

No I don't. Any series circuit will read source voltage at any point in that circuit when no current is flowing (points open). No current flowing through ballast, no voltage drop, so 12v Ohm's law. When current starts flowing, (points closed) ballast will drop its portion. The coil does it's own thing with inductance and collapsing fields, but the ballast RESISTER drops voltage according to Ohm's law any time there is current flowing.
​​​​​​.It all ties together with Ohm's law since adding resistance in series increases total circuit resistance reducing current flowing when source remains constant and path is complete. Voltage drop can be read across ballast with points closed, but you get source when open. I realize you know how it works, and explained it well, but I don't understand your disdain for Ohm's law. They didn't name it " Ohm's incorrect theory.

Regardless, you still connect wipers to ignition side of ballast to get 12v.