testing for ohms
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testing for ohms
When you use your multi-meter for checking for resistance, are you supposed to subtract the resistance in the probe testing wires to calculate your ohm reading? When I touch the two probes together I get about a half ohm reading. That's enough to make or break the circuit I'm testing.
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From: Bel Air USA
testing for ohms
Why do you say that will make or break the circuit you're testing? If you're testing a circuit and get .6 ohms, subtract .5 and the ohms in the circuit would be .1 ohms. If you read .5 ohms, subtract .5 ohms and that would mean you have 0 ohms resistance. I miss the days when meters had zero adjustments. Now they are suppose to be auto zeroing.
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From: Laveen
testing for ohms
A lot of the good digital meters do have a zero feature at least the two Flukes and the Radio Shack one I have do ( the RS has a HUGE readout easy to see at the far end of the vehicle) But if not yes subtract the lead resistance from the circuit measurement.
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From: Central Kali
testing for ohms
Low values of resistence is hard to measure with precision. Another way to do it is to hook up a variable power supply to the resistence with an ammeter in series. Increase the voltage until you have some current flowing. Measure the voltage drop across the resistor. Calculate the resistence by dividng the voltage by the current. If you have 1 amp of current and a voltage of .5 volts, the resistence is .5 ohms.
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testing for ohms
I was using the ohm meter to test some coils for my truck. They require a range of 1.05to 1.27ohms to meet specifications and the new coils I purchased were reading 1.8 to 1.7 ohms not discounting the resistance in the probe wires. Would this small of a difference really affect the performance of the ignition system and the output of the coil? I see from my catalogs that the Accel coil has .7 ohms resistance, would this extra current hurt my ignition module? 
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From: Bel Air USA
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testing for ohms
The specifications call for 1.05-1.27 and the Accel has .79 ohms resistance so it would draw more current, correct? And if it does do you think it would damage the module? As you can tell, I'm no electronics guru so how much would the current vary and how much does it take before it makes a difference?
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From: Central Kali
testing for ohms
I need to know what the ballast resistor value in ohms is to give you an exact answer. I assumed 1.3 ohms for the ballast. With a 1.27 ohm coil at 14 volts the current is 5.45 amps. The coil has 6.9 volts, 37.7 watts. The ballast resistor is running at 38.6 watts.
If you change to the .79 ohm coil, the voltage on it is 5.29 volts(kind of low). The coil wattage is now 35. The current flow is 6.7 amps. The ballast is now running at 58.3 watts.
To get the coil voltage at 7 volts, you would need a .79 ohm ballast. Now you would have 8.86 amps of current and 62 watts in both the coil and the ballast. You may exceed the ignition module's rating with an extra 3 amps.
Handy formulas: volts\ohms=amps volts\amps=ohms amps*onms=volts
volts*amps=watts amps*amps*ohms=watts
If you change to the .79 ohm coil, the voltage on it is 5.29 volts(kind of low). The coil wattage is now 35. The current flow is 6.7 amps. The ballast is now running at 58.3 watts.
To get the coil voltage at 7 volts, you would need a .79 ohm ballast. Now you would have 8.86 amps of current and 62 watts in both the coil and the ballast. You may exceed the ignition module's rating with an extra 3 amps.
Handy formulas: volts\ohms=amps volts\amps=ohms amps*onms=volts
volts*amps=watts amps*amps*ohms=watts
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testing for ohms
Geez, I guess it is rocket science after all! I can't locate any ballast resistor in the engine compartment and don't see one listed on the schematic. It looks like I'm going to have to go with the factory coils. I hate to spend $56 on a coil that looks like a standard oil filled unit especially since I need 2 of them. Thanks again.
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testing for ohms
Ballast resistor actually means a *resistance wire* that feeds the coil.
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