Calculate Ohm without a meter!

[Pyxt]

WARNING! THIS ISN'T PERFECT, DO YOUR RESEARCH, CHECK CALCULATIONS TWICE, MAKE SURE IT IS ALL CORRECT! PLEASE HAVE AN OHMS METER, ESPECIALLY FOR BEGINNERS! THIS CAN NOT FIND IF THERE IS A SHORT OR ANYTHING! DO NOT USE FOR SUB OHM coils EITHER






HELLO THERE! Now if you're looking into building coils, but lack an Ohm meter, or yours has broken, or anything of the sort, I have come up with a Mathematical formula for figuring out!



PLEASE NOTE! I use Parenthesis to show order of operations! (Because PEMDAS can be mathematically incorrect, also the x's are multiplication symbols)






Ohms=((Opc x ((Wc x c)+(El+.5)))-((.1 x OPC) x mml))


We'll go over everything that was stated here!


Ohms = Well ovbiously Ohms


Opc = This is Ohms per Centimeter, depending on where you get it off of, many websites will tell you the ohms per centimeter rating. The personal wire I have is a .45 Nichrome.


Wc = This is wrap count, this is how many wraps you intend on doing.

C = This is circumference, of whatever you are coilng on on (Yes this was made for wraping coils and then threading wicks through) Keep this all in Metric centimeters.

EL+.5 = well this is for the extra wire that is going inside of your posts, and that may be a bit extra on the extra coil, it is kind of a error corrector. EL is equal to how much wire you meausre that isn't actually coiled it's self.


.1 x OPC = Well this is for figuring out Ohm per millimeter


mml = This is how many millimeters were lost when cutting the ends off the posts.




There are a very variants of this Formula for different applications..






Having a certain length of coil already precut (wl being wire length)


Ohms=((Opc x wl)-((.1 x OPC) x mml))


With basic algebra and a bit of problem solving this can be applied to figure out


Length to wraps (c/wl-(El+.5))=wc


Etc!


Play around with some of the stuff I've presented

This Formula tends to be correct by about to .05 ohms off at most, due to outside variables, if you don't have proper equipment for exact measuring, etc. But play around with it. I've tested it myself with some of my builds, and it seems to work pretty damn well.




If I've made any mistakes in typing this up, please point it out, and we can correct it. I don't want to leave the public with a botched formula!

 

[nostinkies]

yup. that looks too much like work. Harbor freight give OHM meters away for FREE. Just find a coupon and pick one up.

 

[State O' Flux]

I'm no electrical expert, nor do I play one on TV... but please explain to me Pyxt, how the number and/or diameter of coils has an effect on the resistance value of a length of wire, with a known resistance.
I've measured the resistance of a wire with a DMM, and the resistance again after coiling that same wire... it doesn't seem to change much, if at all.

This would make some degree of sense if a magnetic flux inductance were your goal value... but basic resistance, I don't follow.

 

[Nataani]

The formula seems to work with a reasonable degree of accuracy, for me its +/- 0.2 ohms. As far as I am concerned that's ok for building coils in a pinch, but I would never consider nor condone its use for sub ohm builds.

I would recommend changing C to [pi]D instead. Then again, anybody using this formula probably knows how to calculate the circumference of a circle.

edit. Another point, a 'wrap' is rather ambiguous, and I dont see a correction for the fact that you always have one incomplete wrap in a coil.

 

[Stosh]

Building a coil without an ohm-meter is like driving past a cop in a speed trap without looking at your speedometer, 'cause you're only in 4th gear and can't be going that fast....

 

[WattWick]

Not to take anything away from Pyxts work...

No amount of calculations will tell you if you got a short or not. Be safe. Check for shorts.

 

[State O' Flux]

Not to take anything away from Pyxts work...

No amount of calculations will tell you if you got a short or not. Be safe. Check for shorts.

I so want that to say, "be short - check for safes". Really... I do. ;-)

 

[Nataani]

I'm no electrical expert, nor do I play one on TV... but please explain to me Pyxt, how the number and/or diameter of coils has an effect on the resistance value of a length of wire, with a known resistance.
I've measured the resistance of a wire with a DMM, and the resistance again after coiling that same wire... it doesn't seem to change much, if at all.

This would make some degree of sense if a magnetic flux inductance were your goal value... but basic resistance, I don't follow.

Considering that mutual inductance is calculated via double integrals involving radial vectors and inclination, and flux is calculated based on area and magnetic field strength... No, that wouldnt make sense.

Instead, Wc, the number of wraps, and C, the circumference of said wraps, multiplied together would result in the total length of the wire in the coil (give or take), which is then multiplied by the resistance per cm.

 

[Pyxt]

Considering that mutual inductance is calculated via double integrals involving radial vectors and inclination, and flux is calculated based on area and magnetic field strength... No, that wouldnt make sense.

Instead, Wc, the number of wraps, and C, the circumference of said wraps, multiplied together would result in the total length of the wire in the coil (give or take), which is then multiplied by the resistance per cm.

He understands it

The formula seems to work with a reasonable degree of accuracy, for me its +/- 0.2 ohms. As far as I am concerned that's ok for building coils in a pinch, but I would never consider nor condone its use for sub ohm builds.

I would recommend changing C to [pi]D instead. Then again, anybody using this formula probably knows how to calculate the circumference of a circle.

edit. Another point, a 'wrap' is rather ambiguous, and I dont see a correction for the fact that you always have one incomplete wrap in a coil.

True true, the wrap count was intended for complete and total wraps in the coil it's self. The .5 added to El was intended to cover for the incomplete wrap it's self, and the extra wire on the coil, because instead of forming perfect circles, it is wrapped around something, not following perfect diameter.

And yeah, it wasn't intended for sub-ohm at all. For more basic building and just something to play with, and give yourself ideas of what ohms you're looking at with the materials, and what you could do to get a more desired ohm reading.

 

[State O' Flux]

Instead, Wc, the number of wraps, and C, the circumference of said wraps, multiplied together would result in the total length of the wire in the coil (give or take), which is then multiplied by the resistance per cm.

So, if you know the (pre-coil) length of wire to be used, from terminal to terminal and it's resistance, then Wc and C... serve what purpose?

 

[Pyxt]

So, if you know the (pre-coil) length of wire to be used, from terminal to terminal and it's resistance, then Wc and C... serve what purpose?

You don't need it then. As stated later in the post I actually posted a formula for that specific circumstance

Ohms=((Opc x wl)-((.1 x OPC) x mml))

 

[Pyxt]

Not to take anything away from Pyxts work...

No amount of calculations will tell you if you got a short or not. Be safe. Check for shorts.

Building a coil without an ohm-meter is like driving past a cop in a speed trap without looking at your speedometer, 'cause you're only in 4th gear and can't be going that fast....

Yeah, as stated at the beginning I had pre-warned about it, I had actually tossed this formula together for more of the purpose of seeing what type of materials, coil counts, and whatnot you'd need to get a desired Ohm Output. It shouldn't be used for builds without a meter, especially sub-ohm ones.

 

[State O' Flux]

You don't need it then. As stated later in the post I actually posted a formula for that specific circumstance

Ohms=((Opc x wl)-((.1 x OPC) x mml))

Ah... apologies. I did not get to that point... only paused to think "ah... hold up there, what's wrong with this picture".

What was wrong with the picture... my poor manors of not reading through to the end.

 

[Pyxt]

Ah... apologies. I did not get to that point... only paused to think "ah... hold up there, what's wrong with this picture".

What was wrong with the picture... my poor manors of not reading through to the end.

Haha it's quite alright. I'm never one to hold a grudge

 

[BardicDruid]

After 23 years as an electronics tech I can tell you for a fact that you don't calculate ohms, you measure them with a multimeter. The wire isn't perfect and will vary from batch to batch, especially when dealing with single ohms.

 

[Pyxt]

After 23 years as an electronics tech I can tell you for a fact that you don't calculate ohms, you measure them with a multimeter. The wire isn't perfect and will vary from batch to batch, especially when dealing with single ohms.

I've grown quite tired of repeating myself

This was intended for people to just general ideas of what they want to do for a coil build. It was never intended to be used to find ohms. Yeah you do need a meter for it. It was for ideas on coil builds, not a reliable source of ohm reading. As stated it is typically .5 to .15 off. It's only for ideas on future builds, so you can land up somewhere in the ballpark. Makes building more complicated coils (like quads) easier to set up and figure out what you need.


Sent from my iPod touch using Tapatalk

 

[Dampmaskin]

Is the coil inner diameter the most accurate measure of the length of a single coil wrap? I currently use (inner diameter + (wire gauge * 1.25)) in my calculator, but I have to admit that I pretty much picked that 1.25 factor out of thin air. I imagine it will be significant with nano coils, since the wire gauge to inner diameter ratio can be quite high.

 

[Kemosabe]

big props to the OP for discovering this.
that being said, im more comfortable with a meter. way too much user error possible me lol

yup. that looks too much like work. Harbor freight give OHM meters away for FREE. Just find a coupon and pick one up.

agreed. Maxim magazine often runs Harbor Freight ads and it seems that every other month is a free Cen-Tech multimeter. theyre only $5 even if you dont find a coupon. my advice is to baby the leads. the lead tip can dislodge from teh lead wire very easily. but they do work just fine if you dont break it, which isnt hard.

 

[BobC]

Sorry, I still don't get the work effort required, when all you have to do is measure your wire