Hey everyone. I am interesting in using my PMU to control the duty of my Walbro 485 lift pump. Currently the PMU simply turns it on. This pump feeds a surge tank which contains a speed controlled Fuelab pump. My issue is that the 485 supplies more fuel than needed for idle and light loads so I want to use the PMU to duty it via PWM. I am not clear if this ideal to do directly with the PMU. It seems like being able to use higher frequencies, closer to 1000Hz is better but the PMU output appears limited to 400Hz max. I see people suggest a flyback diode, others do not.
So - can I safely and effectively duty this pump directly from the PMU at 400Hz? Should I use a flyback diode or is that not necessary?
Thanks
The PMU can PWM on the 25amp outputs only. That 400hz will likely be too low for what you want. You would likely need to use the PMU to control a SSR that can then be wired to the lift pump.
I’m running the fuel pump without any duty right now on a 25a output on the PMU without any issue. It seems to pull about 14 to 15 amps max.
Given that, do you think it would be okay or is the 400 Hz still an issue?
I may not understand how the frequency and the amperage, when trying to duty a pump like this, affect each other so please let me know if I’m not understanding something in that regard.
I’m a little confused how a solid state relay would help because that relay would still have to get power from the PMU and then I think you’re suggesting that the PMU would still provide duty to that relay?
Either way thanks for chiming in and let me know if you can provide some more information about what you’re suggesting here so I can understand this better.
Well the amperage is not the issue of your original question. You said You are over feeding your surge tank which is the issue. The way you have it will work forever for sure. The problem is you are saying the PMU can only go up to 400hz this may not even be enough to get the pump to do much (flow enough fuel for your needs) This doesn’t mean it’s impossible but not very efficient.
If I may make a suggestion. If you are running any stand alone ECU now, use an available output and PWM a SSR (made for DC current) to control the lift pump. I just looked at the PMU manual and you are certainly correct it can only go up to 400hz and that’s likely not gonna be high enough to operate the pump at full tilt when you do need it.