Injector timing

[Circlotron]

... so what do they use for the injector switch: MOSFET, BIPOLAR, SCR ??? How do they protect from inductive kickback diode/resistor/coil .. in other words what do the injector switching circuits look like ??? So far I have not been able to find out ...

I haven't played with injectors but I have messed an awful lot with ignitions. For a high impedance type injector driver I'd use a mosfet (low "on" voltage, not like an IGBT), and a zener connected from source to drain, rated a just a little less than VDSmax. The higher the kickback voltage is allowed to rise, the faster the injector will close, up to a point. An ordinary diode directly across the injector like you do with a relay is a disaster. Very slow injector closing. Low impedance injector driver is more complex. You need to open it will full voltage then back off to a PWM voltage for the duration of the open time. I'd try using a high impedance injector first.

[mk e]

So I have to do my own .. The above info was really good re timing but if I knew what sort of circuits the ECUs use I could do a really quick one now with an Arduino board ... so what do they use for the injector switch: MOSFET, BIPOLAR, SCR ??? How do they protect from inductive kickback diode/resistor/coil .. in other words what do the injector switching circuits look like ??? So far I have not been able to find out ...

Go to the rusefi site and look at the hardware. It's all open source, and the schematics, gerbers, boms can be downloaded, they are happy to answer any questions you have....heck you could probably use the whole ecu with a few light code changes perhaps. Everything you need is there, it's all tested. That is where I'd start.

[icedvolvo]

... so what do they use for the injector switch: MOSFET, BIPOLAR, SCR ??? How do they protect from inductive kickback diode/resistor/coil .. in other words what do the injector switching circuits look like ??? So far I have not been able to find out ...

I haven't played with injectors but I have messed an awful lot with ignitions. For a high impedance type injector driver I'd use a mosfet (low "on" voltage, not like an IGBT), and a zener connected from source to drain, rated a just a little less than VDSmax. The higher the kickback voltage is allowed to rise, the faster the injector will close, up to a point. An ordinary diode directly across the injector like you do with a relay is a disaster. Very slow injector closing. Low impedance injector driver is more complex. You need to open it will full voltage then back off to a PWM voltage for the duration of the open time. I'd try using a high impedance injector first.

Thanks for that info.
I have to use what is in the bike atm so I will have to do some measuring first (5V Vs 12V ??? Current ?? LC constant ?? kickback V ?? etc) ....

Why the PWM ?? Isn't the injector coil just like a relay coil: magnetise to move against a spring and then demagnetise to close ??

[Circlotron]

High impedance injectors are like the relay coil you suggest. Low impedance injectors are in effect a low voltage injector. You apply full battery voltage for just the briefest moment to make it open really fast then back off the effective voltage once it has opened. If you maintain full voltage while open they will burn out. Measure the resistance of the existing injector to determine what type it is.

[icedvolvo]

High impedance injectors are like the relay coil you suggest. Low impedance injectors are in effect a low voltage injector. You apply full battery voltage for just the briefest moment to make it open really fast then back off the effective voltage once it has opened. If you maintain full voltage while open they will burn out. Measure the resistance of the existing injector to determine what type it is.

Ok will do thanks, the injector is a Denso if that makes any difference ...