Multimeter issues with coil readings-resistor questions

Eriklane

Member
Have a cheapo dial meter, and, a Craftsman professional 73756 clamp meter. I can't tell which is right.

I had a coil that I'd removed years back and I think now I understand what's wrong.

Spare coil.
Craftsman:
I touch the top of the coil to the pigtail and get 1200 ohms (1.2k)
I touch the top to the inner tang and get about 1300 ohms
I touch the pig to the inner tang and get about 1300 ohms

Cheapo meter:
I touch top of the coil to the pigtain and get 0.
I touch the pig to the inner tang, and get 800 ohms
I touch the top to the inner tang, and get 800 ohms

Current coil.
Craftsman:
I touch the top of the coil to the pigtail and get 1800 ohms (1.8k)
I touch the top to the inner tang and get 1200 ohms
I touch the pig to the inner tang and get 1200 ohms

Cheapo meter:
I touch top of the coil to the pigtain and get 0.
I touch the pig to the inner tang, and get 550 ohms
I touch the top to the inner tang, and get 550 ohms

Based on the current coil at 1.8, assuming 7.5V operating, with 1 resistor, I'm showing 2.67 amps. Operating without a resistor puts me at 4.166 amps.

Using the old coil, with 1 resistor 7.5v/(1+1.2)=puts me at 3.4amps.

What should I do?
 
(quoted from post at 21:54:31 01/19/13) Have a cheapo dial meter, and, a Craftsman professional 73756 clamp meter. I can't tell which is right.

I had a coil that I'd removed years back and I think now I understand what's wrong.

Spare coil.
Craftsman:
I touch the top of the coil to the pigtail and get 1200 ohms (1.2k)
I touch the top to the inner tang and get about 1300 ohms
I touch the pig to the inner tang and get about 1300 ohms

Cheapo meter:
I touch top of the coil to the pigtain and get 0.
I touch the pig to the inner tang, and get 800 ohms
I touch the top to the inner tang, and get 800 ohms

Current coil.
Craftsman:
I touch the top of the coil to the pigtail and get 1800 ohms (1.8k)
I touch the top to the inner tang and get 1200 ohms
I touch the pig to the inner tang and get 1200 ohms

Cheapo meter:
I touch top of the coil to the pigtain and get 0.
I touch the pig to the inner tang, and get 550 ohms
I touch the top to the inner tang, and get 550 ohms

Based on the current coil at 1.8, assuming 7.5V operating, with 1 resistor, I'm showing 2.67 amps. Operating without a resistor puts me at 4.166 amps.

Using the old coil, with 1 resistor 7.5v/(1+1.2)=puts me at 3.4amps.

What should I do?
ust install a coil a run it..........your readings are not any value, as there is not a chance in h3!! that the primary of those coils will be 1800 or 1200 Ohms. Your zero Ohms readings are closer.
 
Come on. If my coil had 4000 ohms, would you say that? If it had 20 ohms, would you say that? I'm trying to understand what's best here, and how to do this. Just telling me to ignore the details doesn't seem the way to go...
 
(quoted from post at 22:22:32 01/19/13) Come on. If my coil had 4000 ohms, would you say that? If it had 20 ohms, would you say that? I'm trying to understand what's best here, and how to do this. Just telling me to ignore the details doesn't seem the way to go...
easuring low resistance values "accurately" is not simple or easy. Just your test leads, the resistance of the contact between probes & coil terminals can swamp the low number that you are trying to read. A very good reading can be made by using a power source and two meters. Power the primary through an ammeter with one set of leads and connect a voltmeter with a second set of leads directly to coil primary terminals and read amps & volts. Divide , V/I to obtain Ohms.
 
Jmor's telling you correct.

your readings are erronious or you are taking the measurements wrong.. or the meters are malfunctioning.

primary resistance on a front mount coil will be a little less than an ohm up to 2.5 ohms if it is a 12v coil.. no way it is 1.2K ohms,. sorry.. just not possible on a running machine. primary is what purrent passes thru to the points. if it wqas 1.2k the tractor would never ever start.

top or pig tail to the flat tang.. now that WILL be in the 'K' range. exact amount may vary. i'd say 4k on that coil may be reasonable.

you can believe 2 engineers.. or you can choose not to. don't matter to me. my tractors all start and run, and I understand how a kettering ignition system works...

ball in your court...
 
(quoted from post at 22:57:47 01/19/13) SORRY! I do mean 1.2 ohms...not 1.2k and not running obviously...coil in hand.
would go with the 4.1 or 3.4 as 2.6 is low-marginal.
 
Did a bunch of reading tonight. Sounds like 2.7-3.3 ohms is best. And also sounds like 1.7 is about the normal HOT resistance for a ballast resistor, I was using 1.0 in my calculations...

1.2 ohm coil with 1.7 resistor puts me at 2.9 ohms.

1.8 ohm coil with 1.7 resistor puts me at 3.5 ohms, a touch high.

I'm going to to with the 1.2+1.7 and see how it goes...

Also going to check the alternator charging.
 
(quoted from post at 23:37:21 01/19/13) Did a bunch of reading tonight. Sounds like 2.7-3.3 ohms is best. And also sounds like 1.7 is about the normal HOT resistance for a ballast resistor, I was using 1.0 in my calculations...

1.2 ohm coil with 1.7 resistor puts me at 2.9 ohms.

1.8 ohm coil with 1.7 resistor puts me at 3.5 ohms, a touch high.

I'm going to to with the 1.2+1.7 and see how it goes...

Also going to check the alternator charging.
ou will not normally see 1.7 ohms hot for the 12250 ballast........when it is at 1.7 it is glowing red & will set paper on fire if in contact. 1 ohm is reasonable to use for operating-hot resistance. BTDT
 
Picked up a new multimeter, and, the coil I had been using reads 2.6 ohms, the old one reads 1.2. I'm going with the 1.2 and 1 resistor...
 
Update-after finding my alternator putting out 8-11 v when running, and, after putting the 1.2 ohm coil back in, and taking out 1 resistor, so now I just have the 1, tractor starts right up and runs great...Love it.
 
(quoted from post at 20:17:24 01/27/13) Not sure what you mean. I just manually checked it with a hand held multimeter.

Remove that useless dash amp meter and install a voltmeter in its place...
 

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