Ohm reading jumps

[BreilaRose]

I know that when the resistance reading jumps wildly, it indicates that there might be a short or other problem.

But what about when a coil that has been successful and stable for awhile suddenly starts jumping minutely, in this case from .7 to .8, but repeatedly?

I built a new coil just out of precaution, and it is working fine, but I'm curious as to cause. Loose screw? juice gunk? Theories?

 

[sacullen]

A screw has usually worked itself loose, often because of all the heating/cooling cycles it goes through. Some are more prone than others, likely as a result of machining. Sometimes the 510 has become loose, so just another small thing to check.

 

[WindyCityJoe]

Usually just gunk building up on the coil.

 

[AzPlumber]

Usually just gunk building up on the coil.

^this^ and temperature

 

[Alien Traveler]

0.7 to 0.8? It could be just that your coil has resistance somewhere about 0.75 and built-in ohm-meter is not sure what to show. I would not bother if everything else is fine with the coil.

 

[IMFire3605]

coils do change in reading over time with abuse, listed above are the majority of candidates, also as the coil ages the wire crystalizes, increasing gradually over time in resistance, 0.5 initial resistance, month later 0.65, next month 0.8, this is normal wear and tear, what would alarm me is from one day you are 0.8, then next time you fire it, it drops down to 0.3, then there would be a problem of a loose screw or a short somewhere.

 

[Big Me]

I know that when the resistance reading jumps wildly, it indicates that there might be a short or other problem.

But what about when a coil that has been successful and stable for awhile suddenly starts jumping minutely, in this case from .7 to .8, but repeatedly?

I built a new coil just out of precaution, and it is working fine, but I'm curious as to cause. Loose screw? Juice gunk? Theories?

It could be that your coil is actually 0.74Ω and so a small fluctuation (to 0.75Ω) will send the reading from 0.7Ω (rounding down from 0.74Ω) to 0.8Ω (rounding up from 0.75Ω)

ETA: Sorry, Alien Traveler, didn't see your post saying the same thing already

 

[The Torch]

Anything in the way of current is resistance; clean your threads, check your screws and dry burn your coil clean. Some ohm meters will also have a varying reading when the battery is low. Else, your coil is aging. It is sad, but coils age much faster than we do.

 

[Ryedan]

I know that when the resistance reading jumps wildly, it indicates that there might be a short or other problem.

But what about when a coil that has been successful and stable for awhile suddenly starts jumping minutely, in this case from .7 to .8, but repeatedly?

I built a new coil just out of precaution, and it is working fine, but I'm curious as to cause. Loose screw? Juice gunk? Theories?

I agree with Alien Traveler, the difference between a resistance meter reading of 0.7 and 0.8 could be the rounding error between 0.74 and 0.76 ohms. It depends on how many decimal points your meter reads.

OTOH, if your resistance jumps wildly, say +-0.2 or 0.3 ohms you've likely got a problem with the build.

A loose screw will always mess with your resistance. What I do is put the atty on a 'black box' ohms checker after I figure I have built it as well as I can and before I put it on a mod. I turn the tester on, read the ohms and then give each coil a gentle nudge with a fingertip and check if the resistance changes. If the resistance changes by say +-0.01 ohms that's not bad. If it changes by more than +-0.1 ohms I have a weak connection that can become a problem. More than 0.1 and I definitely fix it before I continue.

Juice gunk doesn't make any difference that I could ever tell and if you ask around folks will tell you that I sometimes run some pretty gunked up coils

 

[edyle]

10% (or less) I'd call a fluctuation.
50%+ I'd call a jump.

 

[roxynoodle]

Usually just gunk building up on the coil.

0.7 to 0.8? It could be just that your coil has resistance somewhere about 0.75 and built-in ohm-meter is not sure what to show. I would not bother if everything else is fine with the coil.

I agree with these guys. Either or both situations.

 

[Bunnykiller]

its the flux of magnetic fields From the Van DeGraff Belts causing inductance issues in your coils or... you live near a plant that is secretly emmitting EMP waves and its messing with your coil

 

[The Torch]

its the flux of magnetic fields From the Van DeGraff Belts causing inductance issues in your coils or... you live near a plant that is secretly emmitting EMP waves and its messing with your coil

You forgot neighbors vaping on a Tesla coil.