Front mount coils

Guys I need some electrical help again.
I'm using an el cheapo meter to check ohms on the 12v and 6v coils.Measuring from the primary stud on top of the coil to the tab that would go to the dist.cap.I'm reading 2.7 ohms on the 6v coil and 4.0 on the 12v coil.I also have another coil from a diff manufactor that reads 3.3 ohms.I suspect the 3.3 is a 12v coil attempt.All coils are new out of the box.What is correct for both 6 and 12v coils?Does this measurement have anything to do with voltage goinig to the coil and if so,how much MORE resistance does the system require to keep either 12v or 6v coil and resistor from burning up?Thanks for all help. don b

How about making up a simple test circuit to power the coil with a 6 or 12-Volt battery, as needed.

Start with a 6-Volt setup, with the OEM ballast resistor in the circuit, and measure the AMPERAGE draw.

Then, a 12-Volt setup, using the 3.3 Ohm coil AND the OEM ballast resistor, then swap in "Dell's Trick Resistor".

Lastly, a 12-Volt setup, with NO resistor and the 4 Ohm coil.

Give it a try, and see how the actual MEASURED amperage draw compares between the 4 "setups".

I believe it's fair to say you don't want to see much over 3 Amps, and certainly NOT over 4 Amps of primary current flow for a given set of primary ignition components, or coil and point life are gonna go right into the dumpster.

What you are seeing so far seems to confirm what some of us have been saying about the variations in primary resistance between various "aftermarket" so-called 12-Volt coils, and the need to use the appropriate ballst or current-limiting resistor with a given coil.

If you don't want to take the time to do this, how about loaning me a a couple of coils for a day or two, and I'll make the measurements?

It's about time this gets "quantified". There's NO REASON for all the guesswork and cooked coils folks go through with these things!

It would also be interesting to run each "combo" on the distributor machine, and get a secondary KV reading on each setup.

Measuring from the primary stud on top of the coil to the tab that would go to the dist.cap.I'm reading 2.7 ohms on the 6v coil and 4.0 on the 12v coil.

Click to expand...

The Top of the coil to the TAB (dist cap) is the secondary winding. The
correct measurement is from the TOP of the coil to the PIGTAIL (coil) spring (primary winding)

BTW the Secondary winding measures in the 1000's, so make sure you are reading your meter correctly.


BOB & you have the right idea because nobody really Knows the
Primary value of the 12V coils. The 6v is ~1.0 ohm

JMHO

If you apply ohms law and a little math and don't figure any resistor into the circuit I came up with:

6 volt and 2.7 ohn will draw 2.2 amps and create 13.2 watts of heat

12 volt and 3.3 ohms will draw 3.6 amps and create 43.2 watts of heat

12 volts and 4 ohms will draw 3 amp and create 36 watts of heat

This explains why we need the right resistor in the circuit for each coil.

This is not considering the rising voltage of either system as the generator or alternator starts charging. That of course would create even more heat. I had never taken the time to calculate this before and hadn't thought about how much more heat 12 volts was going to create. No wonder we have problems with 12 volt coils with improper resistors.

Phil caught the way it was being measured and I just didn't read it right - scratch my figures for heat - Thanks Phil! and you type faster that me too

Don.........dunno why I'm responding 'cuz last electrical technical question I responded to, I got jumped on all-over by super-engr Phil with his college level drivel of Vx and Vy. (grin)

As a former electronics calibration lab engr, I've measured a few resistances in my time. My personal meter is a hi-quality Fluke-78 digital. First thing when measuring LOW resistances is make certain the meter reads ZERO by shorting the leads together. Iff'n it don't read ZERO, zero the meter ...or... SUBTRACT that excess lead resistance from yer final resistance measurement.

Case in point; my Fluke-78 leads shorted read 0.2-ohms. (I may need to change batterys) I have an unused 12-volt frontmount coil that is labeled 2.5-ohms. I just measured the coil primary (springy-thingy) and get 2.3-ohms. This means this coil primary is really 2.1-ohms. Is this a realistic 12-volt squarecan coil primary reading? Well its gonna OVERHEAT, thats fer shure iff'n don't limit the current (amps).

Usually lead resistance is immaterial since most resistances in normal electronic circuits are in the 100-ohm and up range.

After you've checked and adjusted the meter ZERO (some quality old fashioned analog (needle) ohm-meters actually had a meter-zeroing volume control thingy)

Right now, I don't trust enny of yer coil resistance readings. Why? 'cuz yer 6-volt coil reading is WAY TOO HIGH, shud be about 1.4-ohms. (yer off by factor of 2)

I know this doesn't answer yer question but I'm glad yer onna quest.......Dell, retired Electronics Engr

Jack,

You posted:

"This is not considering the rising voltage of either system as the generator or alternator starts charging. That of course would create even more heat. I had never taken the time to calculate this before and hadn't thought about how much more heat 12 volts was going to create. No wonder we have problems with 12 volt coils with improper resistors."

Once the engine starts, the "duty cycle"... the % of time the points are CLOSED, and primary current is flowing (dwell) is in the 40% to 50% range, making for a LOT less coil heating than if uninterrupted DC were involved.

I suppose, though, in operation (engine running), the coil secondary winding gives off a certain amount of heat, as well, ADDING to heating of th coil.

With too little resistance, though, the coil will still get "cooked", whether the engine is running or stopped.

I'm thinking don was measuring correctly, as the numbers don't make sense (even changing the "range" to "K" Ohms), if he was including the secondary winding in the circuit by measuring from to top terminal to the FLAT spring tab, rather than to the "coiled spring thingy", as it usually gets referred to around here.

Well....I guess the measurements I gave were wrong.Meter plainly says x1000.If I was measuring in the wrong place, those measurments are null and void.Sorry for my stupidity. don b

I'd deffinately like to see those results. And Ditto on the variations in coils. I've seen at least 3 different styles of 12v front mount coils... all bought as 12v.. etc.. black and brown plastic cases, as well as black metal cans...again.. all sold as the 12v version.

I'd love to see the kv trace on each in each ressitor / combo setup.. including the 6v coil with a dropping ressitor and oem resistor in line.

Perhaps an expirement with larger gaps on the 12v unit might be a good test set as well.

Soundguy

Thanks Dell....like I said in my other post,I was measuring in the wrong place and still gave wrong info.My el cheapo meter won't measure that small.Thanks guys, back to the drawing board.
Bob.....if you have the equipment to make these measurments,I'll be glad to furnish the coils if you would do the tests.Shoot me an address. don b

I agree Bob - my figures were to be with a dead engine/ignition on/points closed. Was thinking primary ohms rather than the secondary. I have a lot of those "Senior Moments" anymore along with not paying attention to how it was written.

If Bob tests them for you, I think you will be happy with the results. That nice piece of equipment he has would look great in my garage!

Soundguy

Sounder.....I'm sure Bob can do the test right.I didn't mean to imply that he didn't have the equipment.Sorry if anyone thought I did. don b

Oh no.. not at all. I didn't mean to imply that you meant to imply that ( sounds like a laural and hardy line there! ).

Just that that tester Bob has is a real nice piece of work. Reminds me of the vacume tube tester i used to have.. wish i still had.. etc..

Soundguy

This post looks more like a meeting of the minds.
Almost warm and fuzzy.
Normally When I see these names together in one post there be storm clouds and a hint of lightning.
Good to see we're still all learning from one another.

Ultradog,
Who never went to law school and never learned a thing about Mr. Ohm or any of his legal theories...

I think this is GREAT... there shouldn't be SO MANY problems with these coils, and how to use them... it ALL can be "quantified". Hopefully, SOMEONE will get it done!

BTT