Stop guessing on coil amps.

[MikeZ]

I have an early 48 N. Five years ago I installed an electronic ignition, 12V, coil, and alt. Recently I replaced the 12V coil, after apprx 6 years of use, and also the ballast resistor. Before starting the tractor, I temporarily hooked up a 5 amp DC meter,between the coil and the resistor. I just have the ballast resistor.(2-1/2 ohm coil)

The 5 amp DC meter installed between the coil and the ballast resistor reads 3-1/4 amps with the ignition switch on, and the tractor not running, the instant the tractor starts the reading drops down to 2 amps. after approximately 5 to 10 minutes (80 degree temperature) the amp reading on the meter drops to 1-3/4 amps,where it remained for appox 20 minutes,when i turn it off.

The meter that I purchased, normally is used for monitoring electronic equipment. I am using it
as a temporary hook-up, I have 2 leads coming off the amp meter, with connectors on the ends of the leads, which I attach to one side of the coil and one side to the resistor. Be aware of polarity.


I purchased the 5 amp DC meter for $6.00 plus shipping,(sourcingmap)


The 5 amp DC meter eleminates the guess work.

Mike

 

[Jock (OR)]

Great post Mike!

The hookup can be made on either end of the wire to the coil, after the last resistor in the system. Emphasis on the after.

 

[Dunk]

Just for the record....

I don't think Ohm's Law is "guessing".

 

[souNdguy]

I agree with dunk.. ohms law is a calculation not a guess.. AND.. yer N came fromt he factory with an ammeter. if it isn't working, nno need to scab one in at the coil.. just replace the one on the dash.

If you like the new digital stuff, you can get them to fit that OEM hole and be just as accurate .

soundguy

 

[Bob]

"after the last resistor in the system. Emphasis on the after."

I guess you didn't get the memo that current measured ANYWHERE in a series circuit is the same???

 

[Dell (WA)]

Mike.......congratulations on discovering the inherent accuracy of using the correct scale meter to read enny thang.

Realizing of course the the OEM amp-meter (30-0-30).....(thats 60-amps FS) and the meter is 20% accuracy with a wide needle, its amazing that you can even read 3-amps indicated. And yer comparing it to a 5-amp FS meter at 5% accuracy with a needle that is a skinny RCH.

And definitely be aware of meter polarity. While it won't "kill" yer meter to incorrectly hook-it up, you can't read the backside of the meter 0-5 scale can you?

3-1/4 amps is kinda typical of closed circuit ignition before start-up. And the moment of start-up you now have a pulsating DC that averages about 2-amps. This is normal.

And after 10-mins of running the ignition current drops to about 1-3/4 amps. That is the effect of the mandatory "infamous ballast resistor" heating up and increasing its internal resistance, thus reducing the total circuit current flowing. Its the LAW; Ohms Law. .......Dell, ret Electronics Calibration Lab Engr

 

[Crem]

Mike,
That is a great idea using that meter with a 5 amp scale. I like how you can see the start up amps and then watch the current draw change as it is running. I think that I am going to try that just for the fun of it.

 

[Bob]

It's not just that the current changes, it goes from pure DC to a pulsed waveform with a duty cycle in the 45% range... the time the points are closed relative to the time they are open.

(Dwell of roughly 40º X 4 cylinders / 360º.)

(IF I'm thinking clearly at the moment!)

 

[JMOR]

(quoted from post at 12:01:56 06/27/10) I have an early 48 N. Five years ago I installed an electronic ignition, 12V, coil, and alt. Recently I replaced the 12V coil, after apprx 6 years of use, and also the ballast resistor. Before starting the tractor, I temporarily hooked up a 5 amp DC meter,between the coil and the resistor. I just have the ballast resistor.(2-1/2 ohm coil)

The 5 amp DC meter installed between the coil and the ballast resistor reads 3-1/4 amps with the ignition switch on, and the tractor not running, the instant the tractor starts the reading drops down to 2 amps. after approximately 5 to 10 minutes (80 degree temperature) the amp reading on the meter drops to 1-3/4 amps,where it remained for appox 20 minutes,when i turn it off.

The meter that I purchased, normally is used for monitoring electronic equipment. I am using it
as a temporary hook-up, I have 2 leads coming off the amp meter, with connectors on the ends of the leads, which I attach to one side of the coil and one side to the resistor. Be aware of polarity.


I purchased the 5 amp DC meter for $6.00 plus shipping,(sourcingmap)


The 5 amp DC meter eleminates the guess work.

Mike

ood plan, Mike, as the dash ammeter is far too coarse or high current scale to read, with any degree of accuracy the 2 to 3 amps in question, you did the right thing. More folks should do the same, as you can calculate all day long , but unless you have all the inputs to the equation right, you still end up with a result that is in question. Most have a hard time knowing the correct numbers to plug in for coil resistance, 'warm' ballast resistance, or even battery voltage. Your amperes reading is an end to end measurement that encompasses everything, even a good/bad ignition switch, faulty connections, wiring, etc. An all around good plan!

 

[DollarBill]

For the graphically oriented - is this what you're referring to Mike??

 

[MikeZ]

Bill, yes, it takes about 2 weeks for delivery. I installed mine in a small plastic parts container, which I hang with a wire on the tractor. I also cut the wire between the coil and the resistor and install connectors. I install the same connectors on the meter leads so that I can pull the connectors apart on the coil wire and the resistor and plug those into the meter connectors.

I hope this helps.

Mike

 

[Dunk]

Man, I sure would like to have a "hit" offn what yall are having....

 

[Hobo,NC]

I gave up waisting my time on this along time ago,,, 2.5 ohm coil and the original ballast run it and forget it,,, are gut the P.O.S. front mount coil,,, I would not put much faith in the amp reading while run'n with a analog gauge....

 

[JMOR]

(quoted from post at 21:59:44 06/27/10)
I gave up waisting my time on this along time ago,,, 2.5 ohm coil and the original ballast run it and forget it,,, are gut the P.O.S. front mount coil,,, I would not put much faith in the amp reading while run'n with a analog gauge....

hat's OK........faith will get you nowhere anyway. Facts will serve you better & I bet you already knew that.

 

[Crem]

Bob,
Yeah that pulsating DC current. I forgot about that. I see that Dell also mentioned it. I think that I had that in an Electronics Class back in the 60's. That is good to know but I guess that I don't really need an oscilloscope for this application. )

 

[Jock (OR)]

Except for the current that is consumed making heat in the resistor(s)!

 

[JMOR]

Sorry, there is no "except"........I'll leave it to Bob to spank your typing fingers.

 

[Crem]

Dunk,
We are getting high on amps. )

 

[Bob]

Aw, c'mon Jessie! You KNOW it's NOT "PC" to spank the ignorant!

 

[souNdguy]

ditto what the other two electrical compentent people are telling you.

current in a series circuit is the same in all 'series' portions. This is a first day, 9th grade beginning electronics issue.

soundguy