coil check values

[carolina gator]

This Mercury coil reads correct values at all check points. But also shows connectivity between + and - terminals for primary. Would this make it a good or bad coil?
Secondary 9.5
Primary 0.0

 

[carolina gator]

Strange that with the "experts" on here that no one has the answer.
But, thanks for looking.

 

[Chris1956]

OK, let me guess what kind of motor and coil you have.

On my mercury motor (year and HP intentionally left off), the primary winding of an ignition coil is .02-.04 ohms resistance. The secondary winding is 800 - 1100 ohms.

 

[dingbat]

Resistance testing a coil rules out an outright (open) failure of the coil. It does not mean the coil will perform to specification under load

 

[carolina gator]

Sorry, there was supposed to be a picture and part # in the post. Didn't notice it was missing. It was stated that the specs shown were correct as tested. Only question is the + and - primary posts show 0 ohms but do show continuity. Should that be so, or a short to ground? Maybe it is supposed to work that way. I don't know, that's why I ask.
Tested coils on a known running engine and they check the same, so must be correct. Thanks

 

[Chris1956]

The specs I gave were for that coil. It takes a decent ohmmeter to measure the difference between a dead short (zero ohms) and .02 ohms.

What issue are you having? The coils must have a good ground to the block, and clean connections from the switchbox.

 

[carolina gator]

Using Fluke 110 meter. Just running through the procedure for checking electronics on this engine before trying to start it. Seems some one pilfered parts off it while it was in shop to be sold. Just want to determine what parts were taken and replaced with old ones. Beginning to think they may have changed powerheads. The lower cowls are loose.

 

[CaptnKingfisher]

Using Fluke 110 meter. Just running through the procedure for checking electronics on this engine before trying to start it. Seems some one pilfered parts off it while it was in shop to be sold. Just want to determine what parts were taken and replaced with old ones. Beginning to think they may have changed powerheads. The lower cowls are loose.

So you think a thief stole the power head and went through the trouble of installing their old power head on when they were done? Fat chance!

 

[carolina gator]

So you think a thief stole the power head and went through the trouble of installing their old power head on when they were done? Fat chance!

Not just any thief. This was a Yamaha dealer, that admitted to pulling parts off to test customer's motor, so he said. He only had this motor in to sell for a friend. I had just redone carb and water pump kit for him . This was an 85 18XD with only 30 hours on it. Paint wasn't even scratched. Had been in storage for years. Ran like a top. So, don't tell me I am an idiot for thinking this.

 

[Texasmark]

The coil has to transfer watt seconds of power to the spark plugs to fire them. Thats volts x current x pulse width. Being a product, and the fact that you are upping roughly 200V to 40kv (open circuit in todays engines), normally plug fires around 18kv and the gap drops to a low voltage while the current is delivered, there is a large turns ratio and the primary current has to be larger than the secondary to support the energy requirement.

Therefore the primary will be larger wire and fewer turns by the magnitude of the difference in input vs out VI.

On checking the primary, zero your meter leads first and record the number....my Digital MMs run about 0.4 Ohm lead resistance. When you measure the primary and get a number, subtract that lead resistance number to determine the primary resistance. Remember Copper has a pretty good temperature/resistance profile so numbers you get will be lower when the wire is cold vs hot and is part of the reason for the variance in the spec data.

 

[carolina gator]

The coil has to transfer watt seconds of power to the spark plugs to fire them. Thats volts x current x pulse width. Being a product, and the fact that you are upping roughly 200V to 40kv (open circuit in todays engines), normally plug fires around 18kv and the gap drops to a low voltage while the current is delivered, there is a large turns ratio and the primary current has to be larger than the secondary to support the energy requirement.

Therefore the primary will be larger wire and fewer turns by the magnitude of the difference in input vs out VI.

On checking the primary, zero your meter leads first and record the number....my Digital MMs run about 0.4 Ohm lead resistance. When you measure the primary and get a number, subtract that lead resistance number to determine the primary resistance. Remember Copper has a pretty good temperature/resistance profile so numbers you get will be lower when the wire is cold vs hot and is part of the reason for the variance in the spec data.

Thank you, my coils match all necessary specs, but I just could not understand why there was continuity between positive and negative posts. I just do not understand electricity. But they work, so I am satisfied.