DW400 to DW440?

[engineermike]

So help me/us understand, does the PWM use constant voltage and just vary the pulse width (current) to modulate power? I know others have said it varies voltage, but generally I thought in order to vary voltage it would need some sort of transformer assembly (which is generally tell-tale because it's larger and requires a heat sink/fins). I'm having a hard time believing that either the factory FPDM or the DW controllers have the physical infrastructure to vary voltage, so the only thing they must be using to vary total power is the current and varying the on/off (ground) length.

If you look just at the FPDM, it takes system voltage input and uses PWM to cut it down based on the fuel pressure and flow control system in the PCM logic. The output from the FPDM to the fuel pump is a 9600 hz square wave. The peak of the square wave is the supply voltage from the system, and the valleys are 0 volts. Since its alternating between 0 and 14v so fast, it acts as a constant voltage somewhere in between. The wider the peaks and narrower valleys, the more average power that makes it to the pump. If it turns into a constant flat-line at system voltage, then you are at 100% duty cycle. [One issue is that the stock tune sets a cap at 12-12.5 volts so they will never run 100% duty cycle, and most tuners leave this alone).

With a BAP. it has to create a higher voltage which is impossible in DC. So it has to invert it into an AC voltage, step it up through a transformer, then rectify it back to DC.

A variable output BAP combines the two above by first stepping voltage up using an inverter/tramsformer/rectifier, then using a PWM to pull output voltage back down when it’s not needed.

This being the case, one might wonder why you need PWM in the BAP and then another PWM in series in the FPDM. The answer is you probably don’t. However, the pcm calibration would need to be changed so the FPDM can control properly at the 18-22v input.

A brushless controller works totally different and is actually more like an AC motor.

Sponsored

 

[engineermike]

FYI top (green) trace is the signal from the pcm to the fpdm, 150 hz pwm. Bottom (yellow) trace is the fpdm output to the fuel pump.

 

[COYOTTMach1]

I did find that the dw400 does not have an internal check valve just fyi.

 

[HKusp]

I did find that the dw400 does not have an internal check valve just fyi.

The older DW400's don't have the check valve. The newer one's like 2-3 years old and newer, have a check valve. Reach out to Wengerd tuning. Tell him what you want to do and what you have. He'll get you straight. I can't remember, is your car an A10? If so, you will REALLY love what he does with it.

 

[COYOTTMach1]

No mines a manual

Sponsored