aidandj

iTrader: (5)

Also a diode across the fuel pump as jason stated. What would be suggested for heatsinking something like what jason posted. Thermal paste and a chunk of aluminum?

DSS60-0045B IXYS | Discrete Semiconductor Products | DigiKey

DaWaN

Whoops, being a bit late to this thread. The derating is most likely because of the slow switching of the SSR. Those things are most likely galvanically isolated through something like an optocoupler and these things are slow; they will limit the speed at which the MOSFET can turn on and off.
Because the MOSFET turns on and off slowly it will dissipate energy while it is switching, this is why they derate the thing when switching at 1kHz.
Normally I would never consider SSR as they are 'extremely slow' in my book, but when your PWM frequency is only 100Hz they can be used. You just cannot build DC/DC converters with them as those easily need >100kHz switching speed
As for the fuel pump there is no real need for galvanic isolation I think? So instead of using a SSR you could also pick a beefy protected MOSFET, that would have much less switching losses compared to a SSR at >500Hz switching frequency.

I am not sure about how much power that diode has to absorb, but I guess that diode looks suitable. I think the diode only sees the peak winding current for a short period of time.
That TO-247 package has a thermal resistance (junction-air) of 30*C/W, so even if the diode has to dissipate 3-4 watts you are still fine without a heatsink.
Just slap it on a piece of aluminium and check temperature when you are running a 90%-ish duty cycle: if it does not instantly burn your finger it will be fine.

aidandj

iTrader: (5)

I'm pretty sure the Hella SSR is just a MOSFET in a fancy package. I might scope it and see how fast it can switch.

Joe Perez

iTrader: (8)

Pretty much all DC-rated SSRs are based upon a MOSFET (AC-only SSRs typically use a TRIAC or SCR instead), though as Dawn noted, they usually hang some additional buffering hardware on it as well, such as an opto.

I'm sure it'll work fine. Kinda cool, actually. I had no idea Hella was packaging these in automotive-relay cases.

The one spec I'd like to see on it, which I haven't found, is RDSon.

aidandj

iTrader: (5)

They aren't pin compatible. But they are physically compatible.

I have a DC power supply and an oscilloscope. Tell me how to measure it and I will.

aidandj

iTrader: (5)

@Ben can you confirm the operation of the fuel pump output on an MS3 when in open loop mode?

Will it only run when the engine is running? I know thats why we use the ECU to trigger the fuel pump (so that it doesn't run when the engine is off) but does it do the same thing for PWM control?

That would make it a little different than the generic PWMs. A generic PWM might have issues priming.

Ben

iTrader: (33)

You did look at the fuel priming settings that are literally underneath the open loop control mode drop down, right?

aidandj

iTrader: (5)

Yes. Hence my comment about a generic PWM having issues with priming.

Nothing about when the pump is on/off