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PDM Output

Practical Motorsport Wiring - Club Level

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Hello everybody. My name is Ignacio and this is my first topic as I´m starting to plan my build.

I´m working on my Audi A4 B5 1.8T. I´m installing a Power Distribution Module and I want to plan the power outputs. My doubt is, could I run same output for injectors and coils with a mid current output rated at 15 A? By the moment, I have VAG Coils (usually 2-3ms dwell time) and High impedance injectors with 12 Ohm resistance. I know injectors in normal conditions will consume 1 A, but, what about coils. I know for wire gauge can be subestimated because duty charge is really small and heat produced is different to a continuous current, but I supose my PDM won´t be able to manage current peaks higher than the output rating, right??

Sorry for my English, I´m not native, I´m from Spain.

Thank you everybody.

If the coils are fired in direct spark mode the single 15A output will be fine for coils and injectors combined. Those VAG coils do pull high current if you use high dwell, but only for the last bit of the dwell, so average current is quite low generally. In direct spark with a common road car engine you will only ever have one coil charging at a time. If running them wasted spark you could potentially exceed 15A.

I agree with you. However you talk about a higher current at the end of a long dwell. My cuestion is, ¿Can PDM power more current than 15A momentary? I know ECU and wiring could support it because it is a very low fraction of time, but will PDM be able to provide that current?


The 15A rating on your PDM is generally max continuous, usually you have some other "inrush" or other similar over current allowance for a short time and the load is also heavily filtered so for instance a short spike of current above the max wont trip it.

VAG R8 coil current below in blue (pic from google, not mine but my test gave a similar result). Reaches 16A after 3ms dwell. I have never needed more than 2.5ms dwell with these coils on reasonably powerful boosted ethanol engines.

I was taking a look to the datasheet and talks about 80A inrush current when running a 15A output. Is that information enough to trust using injectors and coils on same output? I think so.

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