12v coil test

[Lstpan65]

Hi fellows,

65-12v, bone stock
I know this has been covered in other treads but I'm still a little confused on the coil test with the ohm meter. I bench tested the primary I came up with 6 ohms, I believe thats to high but I don't know why? When I tried to test the seconday winding I got zero no mater which way I position the leads or which meter I used (analog-digital). I want to be able to understand the reading.

I'm assuming the coil is bad, and am going to go with a new one, but I'm not sure which would be better and why?

Thanks in advance
Mark

[kell]

I bench tested the primary I came up with 6 ohms
When I tried to test the seconday winding I got zero no mater which way I position the leads or which meter I used (analog-digital).Mark

Make sure you set the meter to the lowest resistance range on the dial when measuring the primary.

A lot of meters don't measure accurately at low resistances of just a few ohms (like a coil primary). The meters have resistance in their leads and banana plugs, etc. that shows up in the reading. Also, the people who designed the circuits in these meters had to compromise between making a meter that can read as accurately at five ohms as it does at a million ohms. Can't really be done without spending money, and you're not going to get that kind of performance in a twenty-dollar meter.

You can get a rough idea how accurate your meter is by setting it on the lowest resistance range and touching the leads together. Ideally you should see zero on the meter, but the average meter will not give a zero reading. Try it on your meter.

Of course, your testing of the secondary seems to indicate it is shorted, which renders the condition of the primary moot.

[Lstpan65]

Hi Kell,
Thanks for getting back to me. The test I ran was good, and my meter is accurate down at that range. I went with an Andrews 4.7ohms coil and the bike runs fine. I'm still not understanding why coils have different ohms? The parts house I go to told me the the point ignitions need a higher ohms then electronic systems. He was very helpful, knew exactly what what I was needing, but he to didn't know the science behind it.

Thanks again Kell.
Mark

[fourthgear]

Its all about the size and winding of the wire. Diff. thicknesses and length of wire will have diff. resistance readings( ohm's ) , basicly.

[Lstpan65]

Hmmmm.. Ok, so longer and thicker on the primary winding would make sence in getting higher resistence. So why would the older points ignition system need higher resistence then the new electronic systems? You would think it would be the other way around. So would I have to switch the coil if I went electronic ignition?

Thanks for your paients
Mark

[rigidpanman]

mark,i too am not sure of the science,but a lower ohm coil is supposed to burn up points faster.

[58flh]

Yes it will burn-up points faster & if you have elec. ig. a stock coil will burn-up the hall-sensor/ for electronic ig you need 3ohm max. on dual-plug heads you use 1.2ohm coils with electronic ig.(std-heads)--Dyna makes the best coils for Both 4-5 ohm app. & 1.2, &3ohm app.---Richie!--I have seen Accels come & go fast!--MSD is a good coil & $$$. IM still on a 27yr. old coil-12V-4.7ohm! Stock HD!.-----RICHIE /If possible stay away from V-TWIN!--There fitment is very bad!-(LOOSE after you tighten it up!)--Im talking stock looking & mounting in correct place! on pan!--Dont work without some ingenuity!.-Been there & done it -(more times then Id like to admit!)--Dyna makes a stock one that fits!-& MSD does to!