what is the ohms reading for a ballast resister on 67 vette?

[Michael F.]

need ohms reading for 67 ballast resistor....thanks.

[Duke W.]

Re: what is the ohms reading for a ballast resister on 67 vette?

...should be about 1.8 ohms at room temperature for all '67 single point distributor systems.

The last time the 0.3 ohm ballast was used in production was 1964 and only on single point mechanical lifter engines.

Duke

[Gene M.]

Re: what is the ohms reading for a ballast resister on 67 vette?

...should be about 1.8 ohms at room temperature for all '67 single point distributor systems.

The last time the 0.3 ohm ballast was used in production was 1964 and only on single point mechanical lifter engines.

Duke

I understand that is the nominal value. But I have a question. I've checked a few ballast resistor I have and values on them were lower some I recall were 1.5 - 1.6 ohm. I verified on different meters all showing same values. Are these ok? I have one in my 65 measures 1.5 ohm. I have no issues with point life and the same coil has been in use for years. Is there any reason for 1.8 vs 1.5 ohm? How low ohmage can this go before point life or coil is affected? thanks

[Duke W.]

Re: what is the ohms reading for a ballast resister on 67 vette?

It's difficult to get two digit accuracy when measuring low resistance devices. You need a high end meter and very good connections. Measuring from the screw terminals versus the wire ends on the backside may make a difference of a tenth or two.

As long as resistance is over about 1-1.2 ohms I don't think there's much chance of burning points. It occurred with the 0.3 ohm ballast (incluidng my SWC back in the mid-sixties), and it was more typical in cold weather since resistance decreases with decreasing temperature and vice versa.

So there's not need to worry IMO.

Duke

[Richard M.]

Re: what is the ohms reading for a ballast resister on 67 vette?

Duke, did you ever see a tolerance spec on these ballasts? I never have.

I'd imagine likely 10 to 20 percent. If 20%, then the range would be +/- .36 ohms, yielding around 1.4 to 2.2 ohms. Speculative, but possible. However, I rarely see more than 1.8 ohms over the years on those I've measured.

Gene, when using a basic ohmmeter before testing, short the 2 leads together. Likely about .1 to .2 ohms just in the leads. Then subtract that from the actual resistor measurement. In order to get very accurate measurements one would need a very accurate(expensive) meter. A Kelvin 4 wire measurement system can used for this purpose. There are 2 pairs of test leads.

380580.jpg

Example....

http://www.grainger.com/product/1XU18?gclid=CjwKEAiAmuCnBRCLj4D7nMWqp1USJABcT4dffaw3pb3bXur773MoCLpvh_xzhGhCof5eKh-7Nnft6BoCStjw_wcB&cm_mmc=PPC:GOOGLEPLAA-_-Test%20Instruments-_-Electrical%20Power%20Testing-_-1XU18&ef_id=UpZPGQAABNDrHgwB:20150305113719:s

Rich

[Joe R.]

Re: what is the ohms reading for a ballast resister on 67 vette?

Hi Rich,

I knew you would have some answers on this one! Also, there is one other fact I don't believe has been mentioned yet. The resistor needs to be disconnected to ensure an accurate reading. The reason is the Ohmmeter will see any other loads in the circuit that are in parallel with the resistor, thus giving a false reading that is lower than what the resistor's actual value is. Disconnecting one leg of the resistor will do it. This does not effect every resistance measurement (it depends on the circuit), but can fool you if you're not careful!

Joe

[Richard M.]

Re: what is the ohms reading for a ballast resister on 67 vette?

Right Joe. You'd need an In-Circuit tester for that.

Rich

[Duke W.]

Re: what is the ohms reading for a ballast resister on 67 vette?

The 1963 Corvette Shop Manual lists a range of 1.4-1.62 ohms, which is interesting because all Corvette engine ballast resistors in 1963 were the 0.3 ohm type at the time the manual was published. The change to the higher resistance ballast for 250/300 HP engines didn't occur until about mid production.

If they're in the ballpark of the nominal spec, good to go IMO.

Duke

[Gene M.]

Re: what is the ohms reading for a ballast resister on 67 vette?

Duke, did you ever see a tolerance spec on these ballasts? I never have.

I'd imagine likely 10 to 20 percent. If 20%, then the range would be +/- .36 ohms, yielding around 1.4 to 2.2 ohms. Speculative, but possible. However, I rarely see more than 1.8 ohms over the years on those I've measured.

Gene, when using a basic ohmmeter before testing, short the 2 leads together. Likely about .1 to .2 ohms just in the leads. Then subtract that from the actual resistor measurement. In order to get very accurate measurements one would need a very accurate(expensive) meter. A Kelvin 4 wire measurement system can used for this purpose. There are 2 pairs of test leads.

[ATTACH=CONFIG]59063[/ATTACH]

Example....

http://www.grainger.com/product/1XU18?gclid=CjwKEAiAmuCnBRCLj4D7nMWqp1USJABcT4dffaw3pb3bXur773MoCLpvh_xzhGhCof5eKh-7Nnft6BoCStjw_wcB&cm_mmc=PPC:GOOGLEPLAA-_-Test%20Instruments-_-Electrical%20Power%20Testing-_-1XU18&ef_id=UpZPGQAABNDrHgwB:20150305113719:s

Rich

Rich,
Thanks for the tip. But I have always checked lead resistance. An electrical tech showed me that technique many years ago. I have some quality meters that have multi scales for range selection. And yes the check needs to be off the car or at least without any connections to the resistor. That is a good point.

But I was also interested in the effects of lesser ohm resistor has on the coil. I would think the voltage to the coil would be higher with a lower ohm ballast resistor. Discounting the point life, (if less than 1 ohm) is there any ill effects to the 202 coil?

[Richard M.]

Re: what is the ohms reading for a ballast resister on 67 vette?

Rich,
Thanks for the tip. But I have always checked lead resistance. An electrical tech showed me that technique many years ago. I have some quality meters that have multi scales for range selection. And yes the check needs to be off the car or at least without any connections to the resistor. That is a good point.

But I was also interested in the effects of lesser ohm resistor has on the coil. I would think the voltage to the coil would be higher with a lower ohm ballast resistor. Discounting the point life, (if less than 1 ohm) is there any ill effects to the 202 coil?

Gene,

I don't have the answer to that regarding the 202 coil as I'm not familiar with the specs on that. There may be specs here in the archives or in the AMA specs at gmheritagecenter.com .

Rich

[Timothy B.]

Re: what is the ohms reading for a ballast resister on 67 vette?

I bet the low OHM resistor would not effect the #202 coil. I think it's the best HP coil of all, somewhere I read the 202 eliminates the need for dual points because of it's fast recharge time. I can't speak to that or give any facts to support my opinion.