Megasquirt Build

If you have the flyback circuit, you can connect them directly. This is the 3.0 board, right? And you bought the DIY Autotune kit?

The 3.0 board has the flyback protection built in. It also has current limiting that will protect the board from low impedance injectors, or even shorting the injector leads together. Read here - V3 Main Board

"Injector Driver Circuit Protection: The new V3 MegaSquirt® board is much more resistant to wiring errors and component problems. There is new circuitry incorporated which protect the injector drivers from short circuits. This circuit, a board build-option during construction, limits the maximum current to 14 amps, at which point the driver FETs will transition into a "linear" region and start direct limiting current. In fact, the outputs can be shorted together for an short period of time without any damage to the driver or FETs."

and

"PWM Flyback On-Board: The flyback and synchronous rectifier (flyback damper) circuits are now on the V3 board, so no external flyback board is required as was the case with version V2.2 MegaSquirt. This is a build option, so if you are using high-impedance injectors and no PWM current limiting these components can be omitted to reduce assembly cost."

As I understand it, the flyback board damps the high voltage peack due to the turn-of of the injectors. The injector has an inductance and stores energy as magnetic field when it is on. When the circuit is broken, the magnetic field collapses and makes an inductive kick that is higher voltage than when the injector is on. How high and intense this kick is depends on the inductance of the injector.

JMO - I would build the board with every possible option that comes with the kit. There's no reason to leave off the parts that you expect not to use (like the VR circuit). The additional power consumed won't matter, and you have the parts. I'd build it fully and then configure it to the purpose I needed.

Re simultaneous vs bank firing, the instructions tell you to connect them for bank firing - Assembly Guide - MegaSquirt(R) V3.0 Main Board "Note that MegaSquirt® is a bank fire injection system, you connect half the injectors to the driver for one bank (pins 32/33), the other half to the other driver (34/35) [4 are shown]." I would reason that connecting them this way distributes the load over two driver circuits, and halves the heating for any single component. This will be true whetehr the banks fire together or alternately.

 

This version of the manual is somewhat more clear -
MS2V30_Hardware-3.4

You can connect the injectors directly to the board using the PWM option, or you can disable PWM and use resistors. I expect that if you do disable PWM and do not use resistors, the injector driver circuit protection will kick in. Unknown what the injector performance will be in that case - likely sub-optimum.

 

Yea I got the adapter designed, hoping to cut them on a buddies CNC next week while I'm off of work for 7 days.