Red 6-volt DC Coil compared to Green 6-volt AC Coil

[JimF]

I've been asked what the static resistances are for both the Ducati AC green coil and DC red coil.

I was able to find both style coils among my spare coils. I have coils with Ducati labels assuring me that two types of coils and I am not reading coils made for another brand.

I have no way to assure these coils are good, but given that there is measurable resistance through both internal coil windings it is likely that the coils are good.

I checked my multimeter by measuring a known resistance before making these measurements.

two coils.jpg

Each "coil" has two coils inside the can, The first coil winding (the primary) is measured across the two threaded terminals on opposite sides of the Bakelite top.

My green coil measured 3.8 ohms of primary winding resistance across the two threaded terminals. The secondary winding is measured from the terminal that the black wire connects to and the center contact under the cap, where the high voltage wire connects. The secondary winding measured 11K ohms (That's 11,000 ohms.)

Green.jpg

My red coil measured 1.7 ohms of primary winding resistance across the two threaded terminals. The secondary winding measured 600K ohms (That's 600,000 ohms.)

Worth noting is that the black wire's terminal on either version exhibited no resistance to the coil's metal can. This is why it is necessary to ground the black wire to the frame. Clamping the coil's metal can to the frame does not provide the required electrical connection to the frame.

[Ventodue]

Good stuff! Thanks Jim.

[mrkprsn]

I want to add this from another post so if someone is searching for this answer they will find it here.

Originally, the AC coils had a green sticker and the DC ones a red sticker. Then later on again they moved to stamping the bottom of the coils. AC in Italian = CA (corrente alternata), DC = CC (corrente continua).

I checked one of my "4 ohm" coils and sure enough 6Vca was stamped on it.

[JimF]

Thanks for the good information on the stampings. I have at least two coils that have no remnants of the stickers. It's good to know that they are still identifiable.