1948 8n Front mount, 12v - resistor info / utter frustration

Eriklane · Jul 18, 2011

New 12V square coil (front mount) also measures .8 ohms. Why does everyone say 2.5 ohms?

Ballast Resistor 1 ohm hot, so 1.8 ohms resistance total in my circuit. Alternator output 12.8V / 1.8 = 7.11 amps WAYYYY too high. If I add another resistor in line, (end to end, right?), that means 2.8 ohms, giving me 4.5 amps, still an amp high.

Tonight the digital ammeter shows 1.8 ohms for the coil. My cheapie ammeter shows infinity.

UNCLE!

JMOR · Jul 18, 2011

(quoted from post at 20:54:41 07/18/11) New 12V square coil (front mount) also measures .8 ohms. Why does everyone say 2.5 ohms?

Ballast Resistor 1 ohm hot, so 1.8 ohms resistance total in my circuit. Alternator output 12.8V / 1.8 = 7.11 amps WAYYYY too high. If I add another resistor in line, (end to end, right?), that means 2.8 ohms, giving me 4.5 amps, still an amp high.

Tonight the digital ammeter shows 1.8 ohms for the coil. My cheapie ammeter shows infinity.

UNCLE!

hat is exactly why Bruce, Bob, myself among others tell all to measure current........much greater likelihood of getting an accurate measurement. Even 'ol Dell tells everyone that it is hard to get an accurate resistance measurement on low value resistors.....and it is difficult even with good instruments & technique.

KL-VA · Jul 18, 2011

Most of the cheap meters out there won't read zero ohms with the leads crossed and they don't have a zero pot. Changing batteries sometimes helps but not always. If you don't have a decent meter, do what the experts say and just read amps. Check your meter first on a couple of known loads even when reading amps.

Dell (WA) · Jul 18, 2011

Eric........pay attention, I don't care what TSC claims on the box, the OEM 6V-coil should read ABOUT 1-ohm. Didja know that 0.8-ohms is about 20% and well within tolerance of 1.0-ohms??? ...but... the modern 12V squarecan coil should read about 2.5-ohms. Do you realize that is 250% difference???

Can you tell the difference between 20% and 250%???

Iff'n not, go back to school or ask yer neighborhood grade school computer nerd. .....Sheesh!!!!......respectfully, Dell

souNdguy · Jul 18, 2011

ditto what the others said. check primary current, both resistor hot and cold. , post back

soundguy

Eriklane · Jul 18, 2011

Seems you posted almost this exact same text yesterday Dell. Hmm. You tell me. B.S. degree. Can I tell the difference? Hmm. You tell me. Your condescending attitude really stinks.

Eriklane · Jul 18, 2011

I measure 12.8V on the wire from my alternator, tractor running. I found the problem with the cheapo unit-when I put the leads together tonight-they didn't zero out and it does have a pot so I could zero it...problem is then, when reading the coil, it shows infinity. So, I got another ammeter and it shows 1.8.

You guys don't realize what those of us who don't do electric don't understand. "Measure primary current", meaning, what, the coil wire? Running?

KL-VA · Jul 18, 2011

Measure primary current means measure Amps in the low voltage ignition circuit going to the coil. There are two types of ammeters you could use. I prefer the clamp on type. The meter has jaws that clamp around the wire going to the coil. Turn key on with points closed and read Amps. Turn key off. If your meter only has test leads, you can use the meter to bypass the ignition switch. Leave key off, points should be closed and comnnect meter leads to the two terminals where the ignition key connects, read amps.

You must have a fully charged battery and clean wiring connections or these readings will be low.

KL

JMOR · Jul 18, 2011

(quoted from post at 23:20:43 07/18/11) I measure 12.8V on the wire from my alternator, tractor running. I found the problem with the cheapo unit-when I put the leads together tonight-they didn't zero out and it does have a pot so I could zero it...problem is then, when reading the coil, it shows infinity. So, I got another ammeter and it shows 1.8.

You guys don't realize what those of us who don't do electric don't understand. "Measure primary current", meaning, what, the coil wire? Running?

you guys don't realize...." ??????
How can you say that?? Bruce posted in response to your earlier post exactly how to measure current, even referenced my photo/diagram with instructions! Unless we come over & do it for you, I don't know how to make it any more simple & clear....but I'll try.....what don't you understand about this?

http://ytforums.ytmag.com/viewtopic.php?p=4483678&highlight=#4483678

Dell (WA) · Jul 19, 2011

Eric........you complain......"You guys don't realize what those of us who don't do electric don't understand. "Measure primary current", meaning, what, the coil wire? Running?".......there are 2-windings in yer squarecan ignition coil. The PRIMARY which gitts 12V from yer battery and is DROPPED thru enny resistors ...ie... ballast resistor and 12-to-6V converting resistor. Resistors are connected together in series, just like flashlite batterys. It does NOT matter which resistor is first or last. Do you understand that concept??? And then there is the SECONDARY winging. That winding makes the 17,000 sparkie volts. DO NOT try to measure that winding or you will be knocked on yer A$$. Understand???

Would it surprize you to learn iff'n you read "infinity" thru the coil......guess what??? You have an OPEN circuit. Its the LAW; Kirchhoff's Law. And with an open circuit, NO SPARKIES. How does that grab you??? ........respectfully, Dell sparkie-meister

Bob · Jul 19, 2011

"New 12V square coil (front mount) also measures .8 ohms. Why does everyone say 2.5 ohms?"

"My cheapie ammeter shows infinity."

1.) Likely 'cuz you have a cheapy Ohmmeter that's INACCURATE at low Ohms.

2.) It's REALLY unusual for an AMMETER to read "infinity", WHAT are you doing, powering the Superconducting Supercollider???

NOXJohn · Jul 19, 2011

I converted my 1949 front mount 8N to a 12 volt alternator system several years ago. I elected to gut out an old 6 volt square can coil and covert to using a real 12 volt round can no resister needed oil filled coil. This takes a little more work but I think it results in a much better job.

Eriklane · Jul 19, 2011

My tractor doesn't have the square resistor block, as I said. I did a reading this am and it shows 12.6V on the coil wire, I'll do an amp reading tonight.

Eriklane · Jul 19, 2011

I don't know how to gut a 6V.

Dunk · Jul 19, 2011

(quoted from post at 07:27:17 07/19/11) I don't know how to gut a 6V.

Now you do!!

http://www.polkcochat.com/hobo_dnn/Default.aspx?tabid=69

Eriklane · Jul 19, 2011

That's an interesting winter project. So am I correct in measuring amps on the coil wire with the points closed, key on, not running, and shooting for something < 4 amps?

Bob · Jul 19, 2011

Yes.

Take a look at the link below, as well.
Lets IMPROVE things

JMOR · Jul 19, 2011

(quoted from post at 08:09:58 07/19/11) That's an interesting winter project. So am I correct in measuring amps on the coil wire with the points closed, key on, not running, and shooting for something < 4 amps?

I give that a "conditional yes", as in, if less than turns out to be 1 amp. it very likely will not start and even at 2 amps may or may not run & if it does, it will run poorly. 4 amps, or a bit more, but not much less. 3.5 passable with all else in good shape...plugs, wires, mixture, etc.

Eriklane · Jul 19, 2011

Will check tonight and post. Tx.

Eriklane · Jul 19, 2011

I measured 14.8V on the alternator wire tonight. Can't get an amp reading on the coil wire, sorry.

JMOR · Jul 19, 2011

(quoted from post at 20:32:00 07/19/11) I measured 14.8V on the alternator wire tonight. Can't get an amp reading on the coil wire, sorry.

can't think of anything nice to say, so........silence.......

Hobo,NC · Jul 19, 2011

(quoted from post at 13:09:58 07/19/11) That's an interesting winter project. So am I correct in measuring amps on the coil wire with the points closed, key on, not running, and shooting for something < 4 amps?

Put cher elcheapo battery charger on the bat while check'n :idea: ... That should get ya in the 14V range for check'n... simple he!

I got all this chit started,,, i don't waist much time fudgen with get'n it dead nuts on any more,,, I gut'em and move on... are use a 2.5ohm coil and the OEM ballast... You can not buy a good front mount coil any more 6 are 12v so gut one are do a Bob conversion 8) ...

Eriklane · Jul 19, 2011

I figured the meter out-it's a clamp on and you have to take the leads out to use the clamp. Now, once the tractor starts, which it don't, and I DO have spark, and gas, I'll get a real reading.

Infuriating. Turns over and over and won't start. Effit.

I can't think of anything positive to say, so, silence here too...this tractor has done so much for me, even tonight, after cranking forever, if finally started, and I disked for an hour. 2 hrs sitting, and then it won't run? DUMB.

And if no 12V coils are 2.5 ohms, then, were talking about having, what, 3 resistors inline? CRAZINESS. And yes, I WILL gut a coil. Got one sitting right here.

1948 8n Front mount, 12v - resistor info / utter frustration

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