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Need Help - Coil voltage values?
Posted by: BobV66Vair ()
Date: June 14, 2018 07:51AM

I replaced the coil on my 65, 140 engine. I bought one that says right on it, needs 12V. The car does not appear to have an external resistor so it may have a resistor wire in the loom. I connected the coil and the engine runs OK but then I tested the voltage with the key in the run position to the + side and to ground. It only reads 4.7V DC. That seems low. Anyone have required voltages and the best method for testing? I just used a multimeter set onto DC volts X 20. I check it on the battery directly and it reads 12V so it is working correctly.

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now



Edited 1 time(s). Last edit at 07/03/2018 04:27PM by MattNall.

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Re: Need Help - Coil volatage values
Posted by: cnicol ()
Date: June 14, 2018 07:57AM

Factory harnesses (except a few years of Spyder) all had built-in ignition resistors. Your measured voltage is a little low but not crazy low.

What are the specs for the coil? Is it a factory or aftermarket coil? It might be the coil resistance is too low for the system and that's dragging the voltage down. What are you running for a trigger? Points? Pertronix-1? Pertronix-2? Something else?

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
61 Seamist Jade Rampside 140 PG
60 Monza coupe (sold, sniff sniff)
66 Sprint Corsa convt - First car! Re-purchased 43 years later
2+2 gnatsuM 5691

+17 Tons of parts

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Re: Need Help - Coil volatage values
Posted by: 66vairman ()
Date: June 14, 2018 10:09AM

You can remove both wires from the coil and measure for ohms from the "+" terminal to the "-" terminal. The original coil is about 1.35 ohms (note most meters aren't that accurate at such low ohmic values).

With the key on and the engine not running your battery should be about 12.8VDC. With the original GM coil and 1.8ohm resistor wire in the harness AND THE POINTS CLOSED the coil "+" terminal will read about 5.5VDC.

Some aftermarket coils are 1.5ohms and will read about 5.8VDC.

"12VDC" on the coil usually means it's for a 12VDC system, it does not indicate if a ballast is needed. Non ballast 12VDC coils are usually 3.0ohms.

Today coils are not produced in the variety GM used, but a new coil for a 1955 - 1966 Chevy V8 will be acceptable. My experience is they are typically 1.2ohms and at 12.8VDC battery the coil "+" terminal will be about 5.0VDC with the points closed.

NOTE: if you have an electronic ignition disconnect the coil "-" lead and connect the coil "-" side to ground BRIEFLY to check the coil "+" voltage. Engine not running of course. Also works if you don't want to rotate the engine to close regular points.

Keep in mind these numbers assume good connections from the battery to the ignition key and back thought the bulkhead connector. So don't try different coils until you are sure ALL the connections are good.



Edited 3 time(s). Last edit at 06/14/2018 10:19AM by 66vairman.

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Re: Need Help - Coil volatage values
Posted by: Gregory_Miller ()
Date: June 14, 2018 10:31AM

What 66Vairman said about checking coil voltage in the note area. Even if you don't have electronic ignition disconnect wire to points and do all else the same.

Greg Miller
Eugene, Oregon

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Re: Need Help - Coil volatage values
Posted by: BobV66Vair ()
Date: June 14, 2018 02:09PM

Thanks to all. I will print this and go back to the garage.

FYI, it is an aftermarket coil with stock points distributor. I'll post after I get to check it all. Probably Saturday as I have dialysis Friday.

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now

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Re: Need Help - Coil volatage values
Posted by: Seth Emerson ()
Date: June 14, 2018 02:28PM

The MSD Blaster 2 Coil, as well as the coils I provide for my HEI style distributor measures 0.7 Ohms across the primary. It is designed to use a 12 Volt feed with no dropping resistance.

Seth Emerson

Check my new Performance Corvair Web site [www.perfvair.com]

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Re: Need Help - Coil volatage values
Posted by: 66vairman ()
Date: June 16, 2018 06:48PM

The coils Seth mentioned are for specific electronic ignitions like HEI type or Petronix II module. They don't use a ballast and are NOT meant to be used with points or a Petronix I module

Occasionally I get a call about a HOT ballast wire and points burning up and find a low primary resistance coil installed like Seth referred to.

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Re: Need Help - Coil volatage values angry smiley
Posted by: BobV66Vair ()
Date: July 03, 2018 11:11AM

Follow Up.

I replaced the coil with a good stock coil. I get 4.7 VDC with the key on but not running. I get only 1.97 VDC with the engine running. It seems really low to me. Any thoughts?

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now

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Re: Need Help - Coil volatage values
Posted by: oldqmguy ()
Date: July 03, 2018 11:25AM

Bob,

You should see +12 Volts (ie: Current Battery Voltage, which may be higher or lower than "12") with the KEY ON and POINTS OPEN.

You should see ~ +6 volts with the KEY ON and POINTS CLOSED.

When the engine is running the voltage on the + Terminal will be "Pulsed" by the rapid opening and closing of the points so it is difficult to get a reliable reading on a any meter.

The "resistance" in your ignition wiring should be 1.8 Ohms (a RESISTOR or RESISTANCE WIRE) and the Coil should measure 1.3 to 1.5 Ohms from the + Terminal to Ground (the case of the Coil).

This is based on a "standard" Corvair ignition system.

I hope this helps! confused smiley

Dale cool smiley

Dale E. Smiley CPBE
Life Member The Society of Broadcast Engineers
RETIRED Broadcast Engineer
CERTIFIED CORVAIR NUT
CORSA/Circle City Corvairs/Corvair Performance Group
Avon, Indiana
WB9SFF
1967 4-Door Monza PG!

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Re: Need Help - Coil volatage values
Posted by: Spectre ()
Date: July 03, 2018 11:27AM

If the car is running fine, I wouldn't be worried. What prompted you to check voltages?

David Clamp


1965 Corsa convertible - 140 4spd/3.55/AM-FM

2013 Mustang GT convertible - 5.0, 6spd auto, Procharger i-1

2003 Miata SE - 6spd manual (wife's toy)

"Victory is mine!" - SG

Oklahoma City, OK

Click for Oklahoma City, Oklahoma Forecast

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Re: Need Help - Coil volatage values
Posted by: MattNall ()
Date: July 03, 2018 11:28AM

Put new coil back on!


Coil says 12 volts... Run a new wire from Harness connector to Coil positive...





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Need Help - Coil volatage values
Posted by: BobV66Vair ()
Date: July 03, 2018 01:38PM

Matt, the wire is in the harness that goes/comes from the starter. I assume the solenoid there affects the voltage the coil gets. Also keeps the coil from getting any voltage when the car is off.

I started checking because the spark on a removed plug was kind of blue and didn't seem that strong. I may just give this up since it seems to be running alright.

Thanks for the advice. I'll check more Thursday.

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now

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Re: Need Help - Coil volatage values
Posted by: MattNall ()
Date: July 03, 2018 04:00PM

Bob, the Yellow wire only has voltage when Cranking...to give the Stock 6 volt coil a boost...

Leave the original wire at the Coil + disconnected...tape it....

Put in the 12 volt coil and run a new wire from the harness connector to the Coil +

It's the pin with the cloth wire [ resistance wire ].





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Need Help - Coil voltage values?
Posted by: 66vairman ()
Date: July 03, 2018 06:26PM

Some incorrect info here.

The "12 VDC" on the coil means it is for a TWELVE VOLT SYSTEM. The GM/DELCO coils used with a ballasat often had "12VDC" on them. It DOES NOT mean hook the coil to 12VDC WITHOUT a ballast. Even more confusing non ballast coils also are labeled "12VDC".

If you car has the correct ballast wiring harness and you need a new coil then use a coil specified for a 65 Chevrolet V8 (not much to choose from now and as Bob Helt documented some of the hyped aftermarket coils are no better).

On a 65 there is ONLY one yellow wire to the coil "+" terminal. The ballast is in the harness and goes to the solenoid plug for the starter. While starting power goes directly from the solenoid "R" terminal to the coil via the yellow wire.

When the starter is released (key on) power goes through the ballast wire TO THE SOLENOID PLUG and THEN to the coil via the SAME yellow wire.

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Re: Need Help - Coil voltage values?
Posted by: red monza ()
Date: July 03, 2018 06:28PM

FROM MEMORY.....and that is a disaster ready to happen.

On my 66 140/pg car I get about 8 volts on the pos side running and 5 or so on the neg side....IDLING.

On the 283 in my 49 chevy....repeat those numbers....both run great...the 49 has a ballast resistor wired in by me as all the wires were...the corvair a cloth covered factory wire that is hidden in the wrapping.

Photo of the 49 283 engine I built still had the HEI in this photo...Points dist was installed before the first outing due to the elec speedometer problems.



Edited 1 time(s). Last edit at 07/03/2018 06:34PM by red monza.

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Re: Need Help - Coil voltage values?
Posted by: oldqmguy ()
Date: July 03, 2018 06:40PM

Matt,

Until we know the resistance of the coil we can not tell if it needs a "resistor" or not.

I did make a mistake in my last post!

Resistance should be measured from left + terminal to the - terminal, not ground!

A 3 ohm coil needs your 'new wire' for direct +12 Volts.

A coil with 1.3 to 1.5 ohms resistance needs the resistor or resistance wire!!

Dale cool smiley

Dale E. Smiley CPBE
Life Member The Society of Broadcast Engineers
RETIRED Broadcast Engineer
CERTIFIED CORVAIR NUT
CORSA/Circle City Corvairs/Corvair Performance Group
Avon, Indiana
WB9SFF
1967 4-Door Monza PG!

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Re: Need Help - Coil voltage values?
Posted by: MattNall ()
Date: July 03, 2018 06:43PM

New Coil

Dale it says 12 volts on it!! Internal resistance will be 3 ohms.....





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Need Help - Coil voltage values?
Posted by: oldqmguy ()
Date: July 03, 2018 07:01PM

Matt,

Just because it's marked "12 Volts" does not mean it is "automatically" a 3 ohm coil.

But then I am just a suspicious SOB and I have plenty of VOM's sitting around!!

Dale cool smiley

Dale E. Smiley CPBE
Life Member The Society of Broadcast Engineers
RETIRED Broadcast Engineer
CERTIFIED CORVAIR NUT
CORSA/Circle City Corvairs/Corvair Performance Group
Avon, Indiana
WB9SFF
1967 4-Door Monza PG!

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Re: Need Help - Coil voltage values?
Posted by: MattNall ()
Date: July 03, 2018 07:06PM

55 years...never seen different. on stock style coils





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Need Help - Coil voltage values?
Posted by: JimBrandberg ()
Date: July 04, 2018 06:06AM

I think oldqmguy is correct in what he's saying. With points and condensor ignition, you want to add up to about 3 ohms, usually about half from the coil and half from the wire or ballast.
I keep forgetting to get another ohm meter, I plan to get one at Harbor Freight. the one I had seemed to need a battery every time I went to use it. I went to my usual auto parts with some coils and they let me use their meter. If your coil is roughly 1.5 leave the resistor wire, if it is roughly 3.0 bypass the resistor wire.
MattNall could very well be correct about the markings, I don't know.
I've never checked voltage at the coil with the engine running. With the rapid pulsing, is it hard on the volt meter?
I guess I'm not really adding content, just trying to verify my understanding.
Jim Brandberg
Isanti, MN
CorvairRepair.com

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