Home made Megajolt type ignition.

DEVONMAN · Post by **DEVONMAN** » Thu Sep 12, 2013 5:55 pm

Going back to the OP, can someone please explain how you would get a dizzy to tell the ign system that the engine is at No 1 TDC?

I understand how the 36-1 trigger wheel does it, but with an 8 toothed reluctor in the dizzy moving at half engine speed it must be more difficult to achieve.

I can imagine when the battery is low and cranking speed is down, the the ignition brain would take time to sort a reliable pulse pattern to allow fire up.

DaveEFI · Post by **DaveEFI** » Thu Sep 12, 2013 10:37 pm

You'd have to remove a tooth from the reluctor - otherwise it has no way of telling. If doing wasted spark, remove two teeth opposite one another. But I dunno how well this would work in practice, given EDIS used 36-1, and later systems even more teeth. And I also dunno if any of the commercial systems could work with so few teeth.

kiwicar · Post by **kiwicar** » Fri Sep 13, 2013 9:50 am

Hi
Did I miss something here, as far as I know the primary advantage of wasted spark is you can dump the distributor and all it's associated spark scatter and horrible gears, so why would you want to make a wasted spark set up that required a dissy to drive it and retains all the inaccuracy? If I want mappable ignition and don't mind retaining the dissy I can buy that sort of thing from the likes of MSD with their crank trigger wheel set up. Sorry I just don't understand this one.
If you want wasted spark cheaply do it like the set up I have on my motorbike, wheel and sensor on the crank, 8 magnets on the wheel a simple 8 way ring counter plus a single magnet/sensor pair to give you a TDC no1 cylinder reset for the ring counter, 8 x 50p power FETs, 8x 2p diodes and 8 coils, you might want some simple frequency driven delay line on the input to the ring counter to give your an advance curve for starting, worked on the Laverda.
Best regards
Mike
PS you could do it like Mr Honda and have 8 pickups and 1flying magnet, a lot more wire though

DaveEFI · Post by **DaveEFI** » Fri Sep 13, 2013 12:54 pm

You don't need the bother of magnets - a simple toothed steel wheel with either a VR or hall effect sensor will work just fine.

kiwicar · Post by **kiwicar** » Fri Sep 13, 2013 7:18 pm

Hi Dave
True, but with magnets you need less processing to get a nice big fat pulse chain

Best regards
Mike

DaveEFI · Post by **DaveEFI** » Fri Sep 13, 2013 11:16 pm

kiwicar wrote:Hi Dave
True, but with magnets you need less processing to get a nice big fat pulse chain
Best regards
Mike

A hall effect sensor will give you rail to rail switching at (near) any speed. Like up to 18,000 rpm on a 36-1 wheel.

markypug106 · Post by **markypug106** » Fri Sep 13, 2013 11:20 pm

Hi guys, as its not a digital system I cannot do the usual 36-1 but I can do 8 or a multiple trigger wheel and have a separate reset trigger like mike said. Since you guys said about the disadvantages with using the dizy I've reconsidered the idea and now going to use a crank trigger wheel. I've also worked out how to add in advance.
In regards to the the EMF feedback from the coil, I've got some veristors that will drop the voltage to a max of 160. Which is within the safe range.

markypug106 · Post by **markypug106** » Fri Sep 13, 2013 11:30 pm

Also as mike said, a magnet adds signal strength and you basically have on you bike what I'm doing. But this will be a little more in depth.

markypug106 · Post by **markypug106** » Mon Sep 16, 2013 2:24 pm

Last night I had a chance to have a quick fiddle and managed to drive the coil without blowing the fets, also had a look at working out how to manage advance.

Due the complicated nature of the mechanical advance starting at around 1000-1500rpm and ending around 3000-4000rpm it will be rather difficult to replicated it in analogue terms, the megajolt ect systems are digital so rather easy to work out due to a digital map and a programmable chip!
So for now I'm going back to building it up on the dizy as it wont be hard to change to a trigger wheel at a later date once I'm happy with it, will only take a few wires and an additional cmos to modify it.

Cheers Mark

Eliot · Post by **Eliot** » Mon Sep 16, 2013 3:13 pm

Whilst rolling your own system is commendable, you will find that Megasquirt 1 will do you want and will get you into a whole new field of understanding of how modern ecu's work and your enthusiasm will thrive.

What if you still get mis-fires after building your own system? - With megasquirt you could take a datalog and share it with thousands of people around the globe for an opinion.

If you like soldering, buy a Megsquirt kit and assemble it yourself. As an ex-electronics guy, building and installing MS was one of the most rewarding things I've ever done.
From this:

to this:

In a few hours.

DaveEFI · Post by **DaveEFI** » Mon Sep 16, 2013 3:49 pm

Is that a genuine B&G MS kit? Not seen that case design before.

markypug106 · Post by **markypug106** » Mon Sep 16, 2013 6:01 pm

I must admit, all the positives you get from ms are appealing, its just the initial outlay that puts me off, If I can do something similar for myself.. why not!

In regards to the misfire, it has been sorted! it was the alternator after all this time! felt good to be able to drive it without the nasty jerking!

ChrisJC · Post by **ChrisJC** » Mon Sep 16, 2013 9:23 pm

Don't get carried away with MS if you only want ignition. The MegaJolt is what you need for that.

Chris.

DaveEFI · Post by **DaveEFI** » Mon Sep 16, 2013 10:47 pm

markypug106 wrote:I must admit, all the positives you get from ms are appealing, its just the initial outlay that puts me off, If I can do something similar for myself.. why not!

In regards to the misfire, it has been sorted! it was the alternator after all this time! felt good to be able to drive it without the nasty jerking!

But you've already said you can't do something similar. Like fully mapped ignition.

Eliot · Post by **Eliot** » Tue Sep 17, 2013 6:19 am

DaveEFI wrote:Is that a genuine B&G MS kit? Not seen that case design before.

This is back in day fella....just after the "2nd group buy".. turn-key kits with cases were expensive, I saved a little by using a case is from Maplin.

Back then 4 barrel throttle bodies in UK were unheard off and from the US they were like £500 + import. So I bought a brand new holley carb from real-steel and converted it into a throttle body:

Turbocharging chevy V8's is almost common place now, but back in 2003 few people were doing it. I remember a certain Mr Andy Frost of twin turbo red victor fame telling me I should be putting a supercharger on my engine.