Excitor coil signal conversion

Thread Starter

Vforce94

Joined Jan 11, 2023
21
So why not get a Hall sensor as your pick up? Get one made for acting with a single polarity (Ithink they most commonly use magnetic south, but may be wrong) This would allow you to use the existing magnets in the flywheel to get a DC pulse to the ignition rather than the AC pulse that it normally makes. They are normally AC because the magnets in the flywheel has both N and S poles, and that generates the AC output.
Because there is not enough room to install a new sensor to a certain spot that can read the rotor. The only option would be to add a new piece to the rotor and that causes a series of other problems, it is much better to just convert the signal as MisterBill2 said.
 

MisterBill2

Joined Jan 23, 2018
18,176
Because we do not have any information about that exciter winding output voltage or source impedance, nor any information about what the original trigger pickup coil delivered, I see no way to determine the component values for the circuit in advance. .
 

shortbus

Joined Sep 30, 2009
10,045
What exactly is the ignition system your wanting to use? You gave a name in an earlier post and it seemd to do everything you want but wasn't "programmable". So if the igniton you named isn't what your using, how about some help in letting use look at it's requirements. Doing that would keep this from being a guessing game.
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
I have the original ignition from Aprilia rs 125 and the new retrofit MVT ignition for scooters and mopeds. The reason why I'm doing all this is that you don't have the racing Ignition for Aprilia RS 125 that has Lighting output, this one for scooters has and I want to keep this bike street legal. So the difference between the original ignition and MVT is that it uses different type of signal to communicate with CDI. So the easiest way to convert the signal is via external electronic circuit that will convert the signal from the excitor coil to the inductive pickup like signal. Right now I'm trying to get readings from both ignitions in order to be able to design a circuit with components that have proper input/output values. I know the values approximately but it will take some time to measure everything precisely because I don't have access to the scooter that has MVT ignition installed and ready to be measured with oscilloscope.
 

shortbus

Joined Sep 30, 2009
10,045
Again it doesn't make sense. What your calling an "inductive pickup" has an AC output, exactly the same as an exciter coil. Sorry but that's just a fact. If the MVT will fit you engine it will fire your CDI. But the real thing is, are a Aprila50 and 125 rotors and stator the same? If not then the "inner rotor" won't even work for your engine. Aprila isn't sold here so I know nothing of the engines and parts. You need to do some research to find out if parts interchange. My guess would be the 125 will have a different size crankshaft diameter than the 50, but that's just a guess.

 
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Thread Starter

Vforce94

Joined Jan 11, 2023
21
Again it doesn't make sense. What your calling an "inductive pickup" has an AC output, exactly the same as an exciter coil. Sorry but that's just a fact. If the MVT will fit you engine it will fire your CDI. But the real thing is, are a Aprila50 and 125 rotors and stator the same? If not then the "inner rotor" won't even work for your engine. Aprila isn't sold here so I know nothing of the engines and parts. You need to do some research to find out if parts interchange. My guess would be the 125 will have a different size crankshaft diameter than the 50, but that's just a guess.

Ahh... Excitor coil has 305 VAC output at peak RPM, induction pickup has maybe 5V peak, it still needs to be converted.
 
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MisterBill2

Joined Jan 23, 2018
18,176
INDEED!! The exciter winding output does not look at all like the ignition timing signal. And neither one looks like a sine wave at normal engine speeds. That is because the profile of the magnetic paths are rather different. Likewise the pulse shape of the original magnetic timing pickup is not a sine wave. It would be useful to know if the intended igntion triggrt spark advance system could also trigger from a nice square edged pulse, because that would be simpler to produce, given that the exciter pulse is intended to deliver power to a capacitor discharge system.

And that video on yootoob is not representative of quite a few models and installations of inductive pickups, although certainly there are some instances where the output may approach a sine wave. But not even close for a typical ignition trigger pickup.
 

shortbus

Joined Sep 30, 2009
10,045
Ahh... Excitor coil has 305 VAC output at peak RPM, induction pickup has maybe 5V peak, it still needs to be converted.
Both you and mr billy don't understand this unless it works different than other small 2Cycle moped/scooter engines. The rotor doesn't have magnets all around it, like say one in a real motor cycle, say a Harley or any other make. The rotor only has a small segment of magnets and it includes both poles of the magnets, N and S. this gives the stator AC output, both in the lighting and exciter coil. When the last edge of the magnet segment passes the exciter coil iron core edge the voltage stops. That stop point is what provides the timing point for the ignition. If you look carefully at the mounting plate of the stator it will have a slot, not just a hole, for the attaching bolts. This slot allows the adjustment of the timing, just enough adjustment to make up for any manufacturing miss alignment.

You say, "induction pickup has maybe 5V peak" where is this 5V coming from?

Just because the advertising for something like this MVT ignition says "racing" in it doesn't mean anything more than the stripes on a car being "racing stripes". It's all in a name.
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
Shortbus, man, what are you talking about, we have no problem in understanding how motorcycle ignition works. I do understand how the ignition gets pulses BUT! It is not the same principle on both of the ignitions. The original ignition has separate inductive pickup and only one magnet attached on the outer side of the rotor.(Lighting generator has different sets of the magnets) So it gets only one pulse per rotation when the magnet is leaving the coil. The stator has four wires, three of them are three phases from lighting generator and one is ground. Pickup tells the CDI when to energize the ignition coil.
Now, MVT ignition is called racing ignition because it has 50% lighter rotor so it picks up RPM much faster. Also, MVT ignition has four wires coming from the stator. Two of them are for single phase generator lighting output and the other two are ground and exciter pickup wire. KEY difference: MVT rotor has two pairs of magnet poles or four poles total. Each pole produces a pulse when it passes over the excitor pickup. That means that the frequency of the MVT ignition timing is four times greater per rotation than with the original ignition. Also excitor coil produces 305 VAC amplitude at peak RPM while Inductive pickup from the original coil produces maybe 5-12V amplitude at the same RPM. To conclude everything, those two ignitions are not even remotely the same. Did that clear any of your dilemmas ?
 

shortbus

Joined Sep 30, 2009
10,045
Vforce94, Finally it took you getting mad to fully explain what your working with. At the very first of the thread I said I have never heard of an inner rotor type of ignition. So then, tell me how MVT gets their timing?

How without adding another magnet or pickup and magnet, how are you going to get the correct timing? 4 magnets giving 4 pulses per revolution and your expecting to get the correct timing? Just dropping the exciter coil voltage to 5V isn't going to work, since it won't be timed to the firing point of the motor. Can you post a picture of your engine with the rotor and stator mounted.

And you've said you want this for the street. Using a lighter rotor will allow the motor to rev faster but just like using a very light flywheel in a car, they don't retain as much momentum for good street driving. Your rotor like any motor cycle alternator rotor also acts as a flywheel, to store energy ,something much needed on street driving but not much needed in racing.
 

shortbus

Joined Sep 30, 2009
10,045
To conclude everything, those two ignitions are not even remotely the same. Did that clear any of your dilemmas ?
Yes it did. You want to mix things that shouldn't be mixed, or maybe can't be mixed. I still don't understand the refusal to simply use everything that comes with the MVT, it will and can do everything you need.
 

MisterBill2

Joined Jan 23, 2018
18,176
Many posts back I suggested two different ways of avoiding the need to mount a magnet on any rotating part. Both a variable reluctance pickup or an optical pickup can do it quite well. But neither would be invisible like triggering off of the CD exciter charging signal would be.
But really, unless the scooter has gear shifting, the added inertia of that flywheel relative to the inertia of the rider does not seem worth the effort. I am not familiar with racing low powered light weight scooters so it is a bit of a puzzle.
 

shortbus

Joined Sep 30, 2009
10,045
The reason for the low mass rotor is because racing bikes spend most of their time at or near full throtle. A street machine doesn't so in stop and go or trafic there is no need or want for the high RPMs.

After doing much reading on both the original equipment and the MVT ignition, it comes down to the type of CDI they use. The OEM version is a DC- CDI, and needs the inductive pickup which is powered by the battery. The MVT is an AC-CDI, needs no inductive pickup and fires after counting the number of times the rotor magnet passes the exciter coil pole shoe. Similar to what and how chain saws, lawn mowers and other small electronic ignitions work, like I explained earlier.

They both have a variable timing curve built into the "black box". Full ignition retard at start up, advancing to a certain set mid range RPM, then a partial retard of ignition beyond that point. Unlike 4 cycle engines a 2cycle makes more high RPM power when ignition is slightly retarded.

And according to people that build these scooters and moped type bikes you CAN NOT mix the two types of black boxes. Until getting into this thread I never knew there was such a large community of people doing this stuff.
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
Where I live, there is no laws about motorcycle modification as long as you keep it street legal, since Aprilia RS 125 is practically a motorcycle with gear shifter, and you have to keep it in high revs in order to produce power, it would still be beneficial during coutryside cruises. Other than that, this is a fun project and I just wanted to make something that nobody has so far.

MVT CDI has different ignition curve because it is made for scooters, so this motorcycle won't rev to the max rpm with the MVT CDI. Somebody has mounted MVT ignition to the APRILIA RX 125 dirt bike and it was picking up RPM like crazy but did not rev all the way to the top. Also Aprilia RS 125 has exhaust solenoid power valve that operates through programmable CDI.

I mean you can even reduce the frequency four times to get the desired product but how precise will it be. I could convert sine vave to square wave, reduce the frequency four times and conver it back to sine wave. But that is adding too much complexity.

So the second best option would be to add some kind of optical pickup, do you think it would read that red mark in the picture below precisely ?mvt-dd_12-54477-01.jpeg
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
If this rotor gives cca. 866 Hz on 13000 RPM, The original pickup would give 216 Hz, so if the optical pickup would be able to read that red marking precisely, i could 3D print the new cover for the stator and just mount the pickup.
 

MisterBill2

Joined Jan 23, 2018
18,176
Reading a mark at high speed can be a challenge,but the good news is that there is a simple solution. The trigger function is based on one edge of the mark, either the leading edge or, more likely, the trailing edge. So the mark can be much larger with only one edge needing to be precisely located.
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
The original pickup triggers at the trailing edge of the magnet. What kind of the material would be good for the mark ? Does it needs to be reflective ? I haven'tdone a lot of projects with optical pickups.
 

shortbus

Joined Sep 30, 2009
10,045
@Vforce94 Probably my last post in your thread, but think I should warn you. The one who is encouraging you in the project has a bad reputation of helping until the person actually starts spending money, then once that happens or he hits a wall in his knowledge he will leave you high and dry.

But if you are going to continue with the project why not start looking for an AC type CDI black box from a real motorcycle? The MVT has a built in rev limiter to keep the very small engines it's made for from throwing a rod.
 

MisterBill2

Joined Jan 23, 2018
18,176
The original pickup triggers at the trailing edge of the magnet. What kind of the material would be good for the mark ? Does it needs to be reflective ? I haven'tdone a lot of projects with optical pickups.
The optimum material surface for an optical pickup will depend on which pickup is selected, and that will depend on:First, the trigger input requirements of the CD system, and second, how it will be able to be mounted on the engine. Mounting could be a big challenge because high-reving-2-stroke engines vibrate a bit.
 

shortbus

Joined Sep 30, 2009
10,045
@Vforce94 Since I have been reading more and more about AC and DC CDI units and you said you inner rotor is an AC one here is the pin out of evidently all AC CDI ignitions, no matter the brand. AC type use a 6 pin connector and the wiring has been from every thing I've read been standardized in the industry.

The AC type has it seems a built in pick up in the stator, where the DC ones use a raised "lump" on the rotor for the pick up to read. So then I'm assuming the signal from the AC stator should be what you need to connect to your DC as the firing pulse. But I'd find a way to mechanically rotate the engine and measure the output before wiring directly to your DC CDI.

The six pin connector has a pulse and two ground wires plus the AC output. You will need to use a multimeter to find which of the grounds goes with the pulse/trigger out put. This picture is from - https://itistheride.boards.net/thread/788/cdi-dc-wires-connected-why There are many Youtube videos showing the same thing but they are in a language I don't know. There were many more ictures on other sites, but this was the best one that I found.

cdi.jpg
 
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