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Short circuit protection from back EMFs on inductive loads such as injectors and coil-on-plug ignition


Ian Hendra
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Hi, I've heard of a case where an injector on  a Link ecu spontaneously pumped enough fuel to fill a cylinder.  It's not unheard of, apparently.  Obvious causes include wiring damage but semiconductor failure and track damage on the motherboard are other culprits that could be down to back-emfs from inductive loads like injectors and coil-on-plug arrangements.  Is there any suppression in the Link itself, or is it a good idea to install reverse diodes across the loom wiring? I believe 1N5366 is a good option? 

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  • Ian Hendra changed the title to Short circuit protection from back EMFs on inductive loads such as injectors and coil-on-plug ignition

You generally don't need back EMF protection for low current inductive loads such as injectors (high impedance, switched low side).
Ignition drive triggers won't really need a back EMF protection as they are switched to high (to trigger external igniter or 'smart' coil-on-plugs).

Back EMF protection is mostly needed for injector drive or ignition drives repurposed to control higher current inductive loads on PWM (like solenoids).

For more info, you can refer to the help file under 'Wiring Information > Output Wiring > Auxiliary Output Wiring'.

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Very, very rare to damage an injector drive in a Link ecu.  The fet for each drive is rated for 60A continuous. Flyback is clamped at 80V like most good ECU injector drives.  You need to clamp it high to get good injector performance.  You will generally melt the connector or burn the track off the PCB first before you damage an injector drive. 

Ignition drives have no flyback protection but that's why you have an ignitor, it is meant to handle the current and primary flyback, it doesnt make it back to the ecu.  

Aux outputs are flywheeled.  

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