CT70 Lighting Coil Exposed

Time for a new series of “stators & flywheels”. This time around, at Kirby’s request, is the lighting coil used on Z50’s from K2 - K6 (71-75). The coil matches the schematic. It is a continuous coil with 2 taps along the way – Grey & Blue. The gray winding has the lowest resistance, least number of turns, and the voltage is lower than the other 2. Next up is the blue winding – more turns than the grey and a little more voltage as well. The red is one end of the coil. The other end of the coil connects to ground. Just like shown in the wiring diagram. No surprises here.

The K2 is unique between the Z’s that use this particular set up. No battery, but it has a HL, TL and a brake light. When the key switch is in Position 1, AC from the blue winding is supplied to the brake switches. Makes perfect sense to use the blue because it supplies the least amount of voltage when the HL or TL is not on. Still yet, the voltage gets a little too high above about 6500 RPM. But again, who cares about popping a BL if you need to stop in a hurry.

When the key switch is in Position 2, the “red winding” supplies AC to the HL & TL but the “Grey winding” supplies power to the brake light. The blue winding does not supply enough AC when drawing power for the HL & TL. No surprises here.

I also simulated a blown TL so you can see how high the AC goes with a burnt out TL. If either one goes out, the other one is soon to follow. If the HL goes first, the TL will follow…and quickly.

K3 – K6 is easy – Just look at the section for Test #3. No brake light from 73 ~78. The grey and blue windings are not used thru 1975 - only the red winding. Things change a bit from 76 thru 78. More on that later.

I condensed the results to show what I think most will want. If you want to see current, watts, etc., just drop me a note. This time around, I’m trying to show what time it is more so than how to build a watch

Roy Chambers said:

Hi, Allen. the wire I has is .043 thousands thick, it's on a 7 pound spool.

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Assuming that is the wire diameter, it's too large. That is close to 18 gauge. Thanks for checking. I'll get a few feet of what I think we need on order.

Kirby was kind enough to send me a box of goodies to test. The first item that caught my attention was a K0ish stator with aftermarket coils. It looked weird at first glance. Then figured out both coils were mounted upside down, and the common connection to ground (lighting coil) had been cut down (too short). Still looked odd, then it slapped me upside the head. The PO had also cut the flange off the top coil plate so they could be mounted upside down. The PO did a really nice job cutting it off. Wasn't sure exactly what to expect other than output would be down. Please see pic where I aded in red circles, and a comparison pic.

Anyhoo, all 3 tests showed about 12-15% drop in output on both windings. No need to post a file on this one.

Assuming this one is from TBparts, they did a fine job cloning the OEM honda coil. Spot on resistance readings to an OEM Honda. Wire size looks to be the same as well, which means turns & wire length should be same as well.

Judging based on your test results, flipping the coil increased the airgap(s). If I understood this correctly...why would anyone want to invert/flip the coil(s)? Assuming that the principles involved here are the same as with permanent magnet motors, the ideal would be the absolute minimum gap between the rotor(flywheel) magnets and the exposed ends of the armature lamination stack.

racerx said:

Judging based on your test results, flipping the coil increased the airgap(s).

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Just by my eye ball, flipping the coil did not change the air gap. As you mentioned, that would have been a disaster. I really can't fathom why the PO did this, other than maybe he though the lip/ridge was to protect the curvature of the mounting pad? When it did not fit, and it should not, he cut off the ridge.

My concern was that it reduced the effective pick up area for the magnets in the flywheel.

Just started testing some a couple of coils I wound myself. It took a little "cyphering" to figure out to do wind them and keep the windings tight and uniformly wound. I finally ended up with a Rube Goldberg method to apply pressure to both side of the reel so I was pulling against a light tension. Here's what I have tested thus far, a brief summary of results, and where I'm going next. Any and all feedback and thoughts are welcome. I plan on hooking up a FWB with a 12v battery and correct load once I nail down 1 or 2 that look the best just to be 100% it will do what I see with fixed loads.

For 12 volt Operation.
I wound 2 coils with a continuos run of magnet wire putting as many windings as possible on the core and it still fit, and clear the points cam.
Fat Boy (large wire):
2,000 RPM - Estimate a few watts of usable 12v power.
4,000 RPM - ~ 28 watts of usable 12v power
6,000 RPM - ~31-33 watts
8,000 RPM - ~34-36 watts. Maybe a touch more

Skinny Mini (smaller wire): Skinny mini was not always skinny. Skinny was fat and until I saw identical results.
2,000 RPM - Not enough E to for any charging
4,000 to 8,000 range: No difference at 4,000 but a couple watts more at 6k & 8k as compared to fat boy.

Interesting point but not too surprised - You reach a point of where additional turns add no value. I went to that point

I still believe there are a few more watts that can be extracted. A few more tests will confirm if I right or wrong.

I plan on making skinny a bit smaller so I'll know the min turns needed. Fat Boy will also get the same spa treatment as skinny in the next few days.

Testing continues. I think I have found out why so many have seen acid corrosion inside the frame and on the battery box. At higher RPMS even with a half wave rectifier, the battery is being overcharged....a lot. Not uncommon to see 7.5 vdc to 8.5vdc on the battery. Since the battery is the voltage regulator, it takes a beating at higher RPMS. The voltages I have seen are close to what I saw in Clymers Manual for a 80-81 CT70.

With the 77 flywheel, I have seen up to 9 volts on the battery. That's a lot of juice and is way beyond the recommended charging voltage. I think Bob mentioned that the AGM battery was more tolerant of being over charged as compared to a standard lead acid, Based on what I've read, I believe this is correct. However, long term over charging is not good for with any battery type.

Regardless, it is what is and obviously works better and last longer than is expected. But again, it all comes down to how many CT70 riders keep the throttle at 6500 - 8000 for hours on end.

I guess the closest analogy I can think of is the heavy duty battery charger at most auto repair shops. They leave in on a few hours and then you're good to go. If left on for several hours at max current/voltage, suspect you would be getting a new battery.

I have just completed one round of testing a coil wound for 12 vdc. Honestly, better than I expected, and still think I might squeak another a watt or 2 out of it by changing the windings a bit. Don't know how much more fiddlin' I'm going to do, but here are the results.

A points about how I connected everything and why:

Since I'm trying to stay on the cheap, I used a generic/cheap/china Rectifier/regulator. It is one that Fatcatt has experience with and at $10, no big loss if went up in flames. Feel certain the TraiL Tech 7004-RR150 is much nicer, better built, etc., but trying to keep check on my hobby budget.
https://www.ebay.com/itm/Universal-4-Wire-2-Phase-Motorcycle-Regulator-Rectifier-12V-Quad-Bike-Scooter/333019531481?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m2749.l2649

As a first step, I wanted to know precisely (within reason) when the battery was being charged or discharged, So I did something similar to what is used on old farm tractors. An ammeter for the battery, but I used an 0.1 ohm resister in series with the positive wire from the regulator. The other end of the resistor connects to the Battery +. The load connected at the same connection as the stator.

I put a DVM across the 0.1 ohm resistor and could easily see when the battery is being discharged or charged and by how much voltage is dropped across the resistor. As a sanity check, I had a 2nd DVM monitoring battery voltage.

I did not have 3 or 4 AH battery (12v) but I did have a spare 18AH. Overkill I know, but for what I wanted to know, would be just fine.

Initially, I made sure the battery was fully charged using a Battery Tender that I have.

Then I hooked up a 5.1 ohm resistor as the load. This value puts the equivalent of of 30-34 watts load depending upon battery charge level.

Used a standard K0-76 Flywheel

Then made a a few measurements, repeated them to be sure, and here's what I see.

In a nut shell, you can see the total capacity of the stator. You can spin it anyway you like between charging current and capacity for lights etc. Just to state the obvious, it the battery is weak, less power is available for lights & accessories. A lot rides on battery condition and charge level when EVERYTHING is powered from a single source.

All in all, I am pleased. Think it's a reasonable assumption at this stage that it can supply 25 watts of lights, maybe 30, all day long and still keep the battery charged.

If I can find a reasonably priced LED version of headlight bulb in a PX15D base, less than 48mm in length, then you can do what you want with the other lights. Problem solved if I find this.

A few things to keep in mind when you look at the PDF: 1) The table has ~30 watts load connected;, the last line shows the 12 volt load capacity for each of the RPMS. I would expect some error in my measurements but not much more than a couple of watts.

Doc Brown and Michael J. Fox have sold out of Flux Capacitors for their Delorean so this is all I could do.

allenp42 said:

Doc Brown and Michael J. Fox have sold out of Flux Capacitors for their Delorean so this is all I could do.

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Slightly off-topic, but my neighbor at the end of the block is a big Back to the Future fan. Owns a minty Delorean along with the black Toyota truck and Biff’s car. Also mint. And the sleeveless jacket. Only problem is he’s a 6’3” redhead and 300lbs. You can’t win ‘em all...

airblazer said:

Slightly off-topic, but my neighbor at the end of the block is a big Back to the Future fan. Owns a minty Delorean along with the black Toyota truck and Biff’s car. Also mint. And the sleeveless jacket. Only problem is he’s a 6’3” redhead and 300lbs. You can’t win ‘em all...

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Lol

Outstanding, Mr. P.!!

I'd call this one an unqualified success. You're into 30W output territory...~20W should do the job, with just a little planning. I'm running a 16/24W LED headlight, output is very good...by current (2019) automotive standards. The brightest 1157 LED array I could find, prior to the aftermarket TL I now have (which pulls less than 5W) sipped current at the dainty rate of 1W continuous. I think you may be a little surprised to see how much time your motor is spinning above 5,000rpm. Even with your 54mm stroker tune, that's gonna be around 35mph, in top gear. Around town, you're going to be running through the gears following every stop...upshifting north of 6K, pretty much every time. That, essentially, defines the critical operating parameters...guesswork removed.

Yes, I had very good luck with my first AGM battery...it reached its teens, with no maintenance of any kind. That said, there comes a point where it's time to consider cost vs price. I "sacrificed" that battery to get an idea of how viable the electrical system was, overall. Turned out to be no sacrifice; IMHO, anything beyond 5 years is decent battery life. You are 100% correct in saying that cooking a battery as a voltage regulator is cheeezeee, especially when there are real voltage regulators available.

Cutting to the chase...
What's an extra $50 bill, up-front, to get the TT reg/rec unit? It's proven reliable and allows system control that's not available any other way, for anywhere near the price. There are plenty of 12V LED headlight options out there and the number is growing, some are considerably below 16W/24W. It's not terribly difficult to adapt an LED bulb, some are sold as "universal kits" with adapter rings. There are also aftermarket reflector assemblies available, in 5, 6 & 7-inch flavors...some with LEDs included. Bottom line, ditch the goofy HL base, in favor of a garden-variety H4, source the reg/rec unit and an 1157 array for the TL and enjoy real-bike lighting...whilst breezing through the countryside at 50mph.

Thanks for the kind words. Yes, I am pleased with the results. From what I had read and been told, 40 watts is the upper limit for a single core. After this exercise, I believe it.

I too like the features of Trail Tech regulator, and you don't have to worry about the Quality. I just did not want to spend the funds upfront knowing that a slip up and it would be toast.

The one that I am using for testing seems to do ok. It throttles back once battery voltage reaches 14.4 vdc. In the data that I posted, battery voltage was climbing anytime the load was not connected, or anytime beyond ~5,300 RPM with 30ish watts of load. I just did not run it long enough under load to see the 14.4 water mark.

I did a quick test with the 77 Flywheel and got interesting results. So much so, that I'm going to have re-think how to test. Max current (and watts) will likely exceed the capability of the Rec/Reg unit and probably the coil as well....and the load resistors I'm using. It is sending a healthy charge to the battery at 2,000 RPM and can sustain 5 amps plus at 4,000 RPM. Not going any further until I noodle this one around for a day or 2.

Got plenty to do anyway. I noticed that DRATV has a socket for LED bulbs. Will be poking around a over the next few days to see what options I have.

5 amps @ 12 volts = 60 watts. That's getting into new-gen/6-coil radial stator range...sufficient to power any practical lighting setup on a bike this size. That's enough to power a conventional 45/55W H4 bulb, but I'd advise against that due to the extreme heat.

Kinda sounds like the TT 150 reg/rec unit is going to be the cheapest solution.

Sounded too much to me too. I double checked the R value and I was off a bit. However, it's still pretty stout with a 77 FW.

4,000 RPM - 58 watts (4.4a @ 13.2)
8,000 RPM - 64 watts (4.89 @ 13.2)

Also, I'm pretty sure I have reached the maximum current even if I ran at 10,000 RPM. One thing I have learned, every coil has a max current (Imax) no matter how much load you have or how fast you spin it for a fixed magnet strength.

Honestly, not sure if the rating should be based on 12v or actual battery voltage. Regardless, it's almost a moot point. It's a lot of juice from a single coil.

I still need to read back a little, and read thru this a couple times to get all caught up and straight.
But,
You took a run of the mill Hitachi 3 speed flywheel and lighting coil and rewound the coil...with larger gauge wire, to make it into a 12 volt lighting coil??? That would run in any CT or Z engine?? AND it's making a buttload of juice?
This is good shit.

AND you're telling us that the Hitachi coil(s) in the 3speed stators are the same as the ones in the 4speed version, that uses the mechanical timing advance flywheel..?

So...the coil that you're testing right now could be screwed on to any Hitachi stator plate, on any of our bikes, and convert it to 12v..?
12v lighting, while maintaining the 6v, points ignition system???
This is good shit.

allenp42 said:

Honestly, not sure if the rating should be based on 12v or actual battery voltage. Regardless, it's almost a moot point. It's a lot of juice from a single coil.

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At this output level, it is a moot point. Consider, a typical automotive HL bulb will be 55-65W. Thus, 70W becomes the "gold standard" IMHO...enough to power anything one could reasonably want to have on a CT70.

kirrbby said:

So...the coil that you're testing right now could be screwed on to any Hitachi stator plate, on any of our bikes, and convert it to 12v..?
12v lighting, while maintaining the 6v, points ignition system???
This is good shit.

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The takeaway from all of this is the fact that once you have 12VDC, you also have lots of lighting & gauge options...an ever-expanding list of them. You can also power things like phones & cameras...nice capabilities to have, especially if you want to ride any distance.

Keep in mind that the lighting coil is completely separate from the ignition circuit. We refer to breaker point ignition as "6 volt" and CDI as "12 volt" even when those engines don't have lighting coils...like the `90s-later motors, other than the CT70 version. The whole point is that it is possible to get 12 volt output by re-configuring the coil & using the proper reg/rec unit.

Now, think of watts as horsepower...the terms are interchangeable, just unwieldy to use that way. One horsepower = 746 watts. Thus, in the same way that horsepower is horsepower, watts is watts...kindasorta. With engines of the same horsepower, there's the torque curve to consider. With, say, 10hp output, 110cc might need 8500rpm...72cc would need ~13000rpm vastly different torque numbers. Now, think of torque as being analogous to amperage. With an engine, it comes down to cam & gearing (sprocket combo) choices. With a stator coil, it comes down to wire gauge and number of turns. That's oversimplified but, hopefully, sufficient to illustrate what's being done here.

Bottom line is that any of these lighting coils can be rewound. It's just a question of determining the best wire gauge and overall quantity of wire, i.e. provides enough watts (volts x amps) with the existing flywheel (rotor) and stator armature. The 12v-era 5 & 6 pole armatures, as found in any "12 volt" era 49cc or 72cc motor can be series-wound, from scratch. As for the single coil "6 volt" coils, there's nothing remarkable about 3 speed or 4 speed flavors, it's only a matter of fitment.

racerx said:

With a stator coil, it comes down to wire gauge and number of turns.

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racerx said:

Bottom line is that any of these lighting coils can be rewound. It's just a question of determining the best wire gauge and overall quantity of wire, i.e. provides enough watts (volts x amps) with the existing flywheel (rotor) and stator armature.

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racerx said:

As for the single coil "6 volt" coils, there's nothing remarkable about 3 speed or 4 speed flavors, it's only a matter of fitment.

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You stole my thunder Those statements are spot on accurate. The only thing I can re-confirm - Is there a difference between a H coil and 3 speed coil. I have made accurate electrical measurements of both, including a NOS version of each flavor, and the electrical specs are the same...down to the 3rd decimal point. Physically, based on the NOS ones I have,and several used K0 and K1 coils in my stock pile, I can find no physical difference either. Maybe a slight difference in wiring harness length, but would not bet the farm on that. I even went as far as to measure the cam diameter on a 3 speed vs. H flywheel - no difference. I was trying to find a physical reason the coils were not interchangeable. Thus far I haven't found it.

Now with that said, Kirby has a NOS K1 coil that is different my from NOS K1 coil. So purely as a guess, maybe there was a difference at one time. For sure, my NOS stock is the same as several used ones I have and it is the same as a NOS H coil I have. Kirby is sending it to me just so I can measure it and make some sense out of this.

kirrbby said:

You took a run of the mill Hitachi 3 speed flywheel and lighting coil and rewound the coil...with larger gauge wire, to make it into a 12 volt lighting coil??? That would run in any CT or Z engine?? AND it's making a buttload of juice?

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Yes. I'm attaching a pic of the actual 12v coil still mounted to the plate and the flywheel. Please ignore the sub standard wiring leaving the stator plate. After about test no. 3, I stopped being so picky and just ran the magnet wire out far enough to attached test leads to it. Also, I did not cherry pick the best looking lighting core of the lot. It had some rusty spots on the ends, but about average from what I've seen.

Here's my opinion on the standard flywheel and this coil - It's not making a ton of power and I would suggest limiting the load to 25-30 watts just to keep enough reserve to charge the battery. Off the cuff, would need to use a LED headlight bulb and whatever for the remaining lamps, or use an Eiko A-3603 for the headlight (25w) and LED for all remaining lamps. Right now, I'm in the LED HL camp. Leaves more power available for other stuff. There are a few tricks you can do to drop the wattage of the 25 watt bulb a bit as well. But again, LED HL is my preference.

Yep, I can find no difference in the H or 3 speed coils. Now of course, the harness length is different for a Z50-K1 as compared to any CT70, HKO does not have the neural wire, etc. Honestly, I can't find a difference in the e-specs for the coil, physical measurements are the same and so on. Now the plate is different between a 3 speed and any 4 speed I've seen. The points mount on a 3 speed is a lot higher than a 4 speed. Go back to Post #13 for the differences.

Very soon, I will summarize all the key points, do's and don''s, what I know and don't know, etc. into a single document. I think that will help anyone who is interested cloning what I have done.

I hooked up a DRATV 12v to 6V rec/reg that Kirby had to the test fixture and ran it through a few tests. I tried it with both a partially discharged 6V AGM battery and after a full charge. I connected it per the drawing on DRATV's site checked to see how well it maintained the DC voltage to the battery and the AC to the lamps. I even simulated a blown fuse on the battery to make sure the HL voltage did not shoot thru the roof (it does not).

http://dratv.com/6voregre.html

Easy stuff first. The HL voltage never went above 6.3 volts no matter the RPM or if the battery was connected or not. I used a 2.5 ohm resistor, which is very close to the load of a standard 15 watt bulb.

DC Side - Used a 5 ohm resistor as the load, which is a little more load than a TL places on the circuit. The battery started to "tricked charge" at about 3600 RPM and was suppling the load and charging the battery with ~0.14 amps at 4,000 RPM. Charging current never went above 0.28 amps even at 8,000. With a 5 watt TL, more current would be available to charge the battery. All in all, seems to work fine.

I added a little more load just to see how much the regulator could support, and it appears it current limits at ~1.5 amps.

With the current limiting going on, the DC load (battery charging + TL) can not exceed about 9.5 watts.

Should work fine on a bone stocker K0 or K1 with a decent battery, but the regulator won't support additional DC load.

Another really well-done test session & write-up.


I have to assume that these results would only matter to someone wishing to retain 6V bulbs & battery and the original-type balanced/half-wave alternator, correct? The head-scratcher, for me, would be the reason for wanting to retain a 6V system, when a 12V engine has been installed...which is non-purist and easily reversible. 12V flavor components are so much easier to source than 6V, a trend that's not going to reverse. Not knocking anyone here, just want to be clear about what is being presented in post #119.