HPI Experimentation: First Blood

So a lot has happened since the last time I posted too! Unfortunately, I still don't have an ignition with a significant fun curve for less than $300 that has lights, but here's my progress.

There is no trigger coil for HPI. HPI is a TCI ignition. It fires based off of peak exciter coil voltage not from a trigger. Don't believe me? Check out the resistance/continuity readings from the stator.
Blue and white are both ends of the exciter coil and black is just frame ground for the box. If the stator had trigger AND exciter coils, then there would be continuity to ground for blue and white. With one having a 300-400 ohm reading (exciter) and one with 30-70ish reading (trigger).

Black and blue continuity test - overload (no continuity) 

Black and white continuity test - overload (no continuity)

White and blue continuity test - continuity 367ohms resistance over the coil no continuity with ground

From left to right: pin1 Blue (one end of exciter coil), pin2 White (other end of exciter coil), pin3 Black (frame ground)

From there, I generated a spreadsheet to calculate/play with coil dimensions and gauge to estimate wire gauge on existing coils. It assumes ideal winding, but like I said, it's just for estimation to get you in a ballpark. You can download that spreadsheet here.

Important Note: When you use the spread sheet, whenever you change the coil dimensions or the wire gauge, you have to manually enter the nearest whole number from "ideal turns" into "actual turns" and maybe put it a bit lower since you aren't going to perfectly wrap the coil.

Keep in mind we're trying to match existing resistances and dimensions to find a length and gauge of wire suitable. Resistance has no effect on voltage, it's only for guesstimating a size. If you choose too small of a gauge it may not be able to supply ample current, but I haven't encountered that yet.

I emailed HPI and got the ballpark voltages off of the stator we are shooting for, Here's how their email reads:

hello Ryan
the resistans off 370 looks Ok
the voltage AC is going from 50 til 380 V on bleu and white til 12000 rpm
please look with a strobe to see the advance and after the retard from about 20° til 12000
regards
willy

So your goal should be 50VDC at no more than 380VDC.

I used a drill and spool setup. I went with 38gauge and wound near all of the 1200ft I had. First time I wrapped it, the wire fatigued at the point of entry to the coil. To get around that, I used the smallest heat shrink I have to go over the winding wire about 1cm onto the coil and stick out a good bit from the coil.

 

  





Then like the awesome person I am, I worked with the connector manufacturer to find the connectors for the HPI box in the states and through lots and lots of phone calls and emails, I have a source for these connectors. I'll start selling them if I get this mod dialed in.

Like a n00b, when I got the bike started I hopped on it and rode it around. It cut out after about 5 minutes. When I went through checking for what it could be, I pushed it with the stator spinning and just at a PUSHING speed - voltage was well into the mid 300VAC. So right now I'm assuming my box is fried, but I'm going to wait to call that until I hook it up to an HPI stator on a bike.

This is super depressing it broke, but also exciting because it seems 300VAC isn't so hard to generate.

Crazy Wayne from MA stepped in and informed me that with a rotor over coil ignition, my magnets were going to be moving at a higher velocity - which is obvious now but I totally hadn't thought of it. This make sense because I was using a comparable length of wire to what I had calculated was in the HPI coil on the inner rotor. So instead of being less efficient, the rotor OVER coil systems are actually more "efficient" powerful, whatever - it doesn't take as much to generate voltage on them.

So it does run, whether or not well or with a curve or not, I don't know...

The next magic step will be dialing in gauge for resistance after I get the voltage right.

I'm currently waiting on boxes to be restocked at treats or 1977 mopeds and for final exams to be over with... I have a diffeq exam tomorrow and a very crucial ME exam that I need to do well on.

Wish me luck! Tons to come starting the 15th when I get back to my garage and all my bikes!

the 80cc sachs 3 speed
the UPS polini HPI homoet 6p magnum
the vespa gets an HPI cdi box?
transmission cooling on a ZA50

I can't wait to post about all those! I've got the parts stowed and the enthusiasm mustered!