Resistance ohms, how to intepret a reading that isn't the spec?

Question

The coil on a Honda CR 80h has a primary spec of about 0.4 to 0.6 ohms, the secondary circuit should be 10.6 to about
15.4 k ohms. My primary resistance checks out, but the secondary, plug lead to negative lead on coil, reads only 4 k ohms. Not the required 10.6 minimum. So my question is, this clearly shows a malfunction, but what is it actually wrong with the circuit, it can't be a broken wire inside or i would have no reading at all, if the needle was to shoot up or down, to the 0 and beyond indicates closed circuit of course. I know that, but at a lesser reading, the 4 in this case I take it that there is a continuation although with less resistance to pass the current, (or it volts? ) through the circuit, than the expected higher resistance of 10 .6 +.
so what conditions would indicate the lesser reading, damage? deterioration?
any ideas?

Answer 1

Think of it as a variable resistor or a rheostat with a wiper on a coil of wire. http://www.kpsec.freeuk.com/components/vres.htm
If the insulation has worn somewhere in the middle of the windings - since the windings are coiled around a core, if the insulation is melted, burned or worn somewhere between the two ends the windings will make contact in two parts of the winding. Which would be the equivalent of putting a short jumper across two places in the winding - which would decrease the resistance in the wire by reducing the length of the path - similar to the way a variable resistor works.

Usually a coil will go open but ocasionally the windings will shorten the circuit, or will only short or open only when they warm up and the the insulation or wires wires expand.

Answer 2

It's very simple to intepret. The reading is below the spec, so the coil is considered bad. I assume you are testing it because of a problem with the vehicle not running. If you are sure of your placement of the probes to the proper terminals and are sure of the reading you are getting........go buy a new coil and put it on. As far as the problem inside the coil, it has short circuited somewhere.

Answer 3

You have melted the secondary coil wires. They are insulated and the insulation has melted off causing a short between the wires. If the wires are touching then you have eliminated a lot of wire or "resistance" causing the lower resistance reading.

Answer 4

It is probable that manufacturers spec resistance were done at different temp than yours, as temperature can affect resistances. Try to check this out before taking any drastic or expensive actions.

Answer 5

It COULD be shorted turns in the secondary, but unless you are sure that the coil is faulty I would suggest that you try and borrow another one and measure that (or even try it in your vehicle).