Coolster 3125XR8 Ignition Coil Resistance

Taylor · 06-07-2024, 07:21 PM

For a little bit of context, I own a Coolster 3125XR8 ATV that had been sitting for a long time, and it has no spark. The first time I tested it, it sparked up well, but the next day, after I replaced the carburetor, It wouldn't spark. Today, it sparked on the first crank of the starter, and stopped sparking completely after that.

I think I have narrowed it down to a bad Ignition Coil, but I want to make sure by testing the resistance of different parts of the coil. What are the resistance values supposed to be for this model?

Any answers or advice are appreciated.
Thank You,
Taylor

Taylor · 06-09-2024, 02:59 PM

I bought a cheap new Ignition coil, and, upon testing it, I found that across the prongs, it had almost no resistance(.5-.7 Ohms) , and from the spark plug end to the negative prong, it was very high resistance (>20M Ohms). This is the same on my old ignition coil, except for that the old one had an open loop from the spark plug end to the negative side. I've replaced the CDI and tested all the other parts and wiring harness, but I don't want to chalk it up to a faulty Ignition coil until I know what the Resistance is supposed to be.
If anybody knows, please help.

Thanks,
Taylor

cwright53 · 06-09-2024, 05:36 PM

The ohmic resistance of the coil is around 0.2–3.0 Ω on the primary side and around 5–20 kΩ on the secondary side. The winding ratio of primary to secondary winding is 1:100. The technical structure may vary depending on the ignition coil's area of application.
20 meg seems a bit high. The CDI just delivers a 12 volt pulse at the right time to step up the voltage on the primary to induce the secondary. Low Z to High Z.

Strange that both coils read the same one new and one old.

I would suspect the other safety features like start stop switch, neutral switch and brake switches and how they interconnect. Something in that loop may be killing the spark from the CDI.

Taylor · 06-10-2024, 10:31 PM

Thanks for the information.
I just tested the CDI according to this forum , and, using a multimeter from the stock CDI's coil output wire to ground, read .5V. Then I tested a cheap CDI that I bought off Amazon, and read even less, .15V Does this mean that both the CDI's are bad, or could it be a component closer to the battery?

Thank You,
Taylor

06-07-2024, 07:21 PM	#1
Taylor Join Date: Jun 2024 Posts: 7	Coolster 3125XR8 Ignition Coil Resistance For a little bit of context, I own a Coolster 3125XR8 ATV that had been sitting for a long time, and it has no spark. The first time I tested it, it sparked up well, but the next day, after I replaced the carburetor, It wouldn't spark. Today, it sparked on the first crank of the starter, and stopped sparking completely after that. I think I have narrowed it down to a bad Ignition Coil, but I want to make sure by testing the resistance of different parts of the coil. What are the resistance values supposed to be for this model? Any answers or advice are appreciated. Thank You, Taylor
	0

06-09-2024, 02:59 PM	#2
Taylor Join Date: Jun 2024 Posts: 7	Update: I bought a cheap new Ignition coil, and, upon testing it, I found that across the prongs, it had almost no resistance(.5-.7 Ohms) , and from the spark plug end to the negative prong, it was very high resistance (>20M Ohms). This is the same on my old ignition coil, except for that the old one had an open loop from the spark plug end to the negative side. I've replaced the CDI and tested all the other parts and wiring harness, but I don't want to chalk it up to a faulty Ignition coil until I know what the Resistance is supposed to be. If anybody knows, please help. Thanks, Taylor
	0

06-10-2024, 10:31 PM	#4
Taylor Join Date: Jun 2024 Posts: 7	Tested CDI Thanks for the information. I just tested the CDI according to this forum , and, using a multimeter from the stock CDI's coil output wire to ground, read .5V. Then I tested a cheap CDI that I bought off Amazon, and read even less, .15V Does this mean that both the CDI's are bad, or could it be a component closer to the battery? Thank You, Taylor
	0

06-09-2024, 05:36 PM	#3
cwright53 Join Date: Nov 2022 Posts: 4	The ohmic resistance of the coil is around 0.2–3.0 Ω on the primary side and around 5–20 kΩ on the secondary side. The winding ratio of primary to secondary winding is 1:100. The technical structure may vary depending on the ignition coil's area of application. 20 meg seems a bit high. The CDI just delivers a 12 volt pulse at the right time to step up the voltage on the primary to induce the secondary. Low Z to High Z. Strange that both coils read the same one new and one old. I would suspect the other safety features like start stop switch, neutral switch and brake switches and how they interconnect. Something in that loop may be killing the spark from the CDI.
	1