Questions about PWM fuel pump control & relays

[turbo bob]

Starting to put together everything I need to upgrade my MS2 to MS3 while I'm upgrading my fuel system and wanting to set up my new fuel pump for PWM control.

I'm still reading through the manuals on everything, but wanted to ask if anyone had a good suggestion for a solid state relay because I noticed that DIY doesn't sell any and wanted some input from you folks

[matthunter1448]

i did same research awhile back but didn't find too much other than to use a solid state relay

[kjones6039]

Using the search function on this forum should be very helpful. I have seen this topic discussed several times in the past.

Ken

[matthunter1448]

With no real answer

[kjones6039]

?

[Speedy_G]

yes this topic has been discussed a few times. I startet also a thread.
But they all did not come with a satisfying answer or solution.

For example:

1) Which Flyback-Diode? to limit the cutoff voltage
2) Which Zener-Diode? to reduce the release time
3) Is it okay to use the INJ Outputs from the Mainboard instead of a SSR, when max. current is less than 14 A; Is there any safety circuit for the voltage peaks, or do i still need the two diodes?
4) Is the FP-37 Output still activ, when i use a different port to pwm control the Fuel Pump

After some very long research in electronic forums, maybe i found some informations how to select the diodes properly. But as far as i have not testet it yet, i can not say if its right / working.

As the MS3 offers this function, there should be a at least a little help in the manual.

[dontz125]

I'm not sure anything much past a 1N4001 is needed for a flyback diode, simply because the voltage is clamped so low. Unless someone snuck something in on me, you don't use a Zener on PWM - you WANT the voltage to fall off fast. You use Zeners etc on injectors because the high flyback voltage helps slam them shut fast.

Using the V3.0 mainboard injectors for a max of 14A is certainly an option, and yes there is significant protection. I would suggest taking a look at the V3.0 schematic in the manual. I might suggest that running signal jumpers (with 1N4148 diodes or similar) from U4-2 to R32 (fb_inj1) (and U4-4 to R36, fb_inj2) should take care of your flyback concerns nicely.

DB37-37 remains on; that's your fuel pump relay pin, and - depending on how you have your system wired - is very likely what's keeping your injectors and coils powered. It stays fully on, and you modulate via a separate port.

[Speedy_G]

okay thanks for the informations dontz125 !


i'm a bit unsure.
But when i use the mainboard INJ transistor to drive my fuel pump (for example maximum 6A) directly, i guess i will have to use a other diode than the 1N4001 ? Because my forward current needs to be as high as the maximum current in the coil before shutting it off. So i would need a diode with 6A (in this example). So the 1N4001 only when i use a SSR?
Same voltage as 1N4001 (50V) should work as far it is more than the maximum voltage at the fuel pumpe relais .. or maybe 2x safety factor.


According to some research i should use a zener diode in series to the fly-back diode, to reduce to shut-off time.
The cut-off voltage should also be on the same level as on the flyback diode.

[dontz125]

i guess i will have to use a other diode than the 1N4001 ? Because my forward current needs to be as high as the maximum current in the coil before shutting it off. So i would need a diode with 6A (in this example).

Whoops! Good catch on the current rating - try this UD1006FR instead.

According to some research i should use a zener diode in series to the fly-back diode, to reduce to shut-off time.
The cut-off voltage should also be on the same level as on the flyback diode.

you don't use a Zener on PWM - you WANT the voltage to fall off fast. You use Zeners etc on injectors because the high flyback voltage helps slam them shut fast.

If you're suggesting the use of a 12v Zener in reverse-series with the flyback diode going to 12v, I really don't see the point - nothing will flow until the flyback voltage exceeds the 12v upstream of the FB diode.

[hardline]

Only way I have been able to PWM control my pump without destroying the pump or relay is by using a ford fpdm.

[dontz125]

The fact that the Ford module can do it says it's possible on your vehicle. The only thing I can think of is that your flyback strategy isn't up to the job.

What's your maximum current draw?

[hardline]

It's been a while since I looked at it, New fuel pump is around 30 amps. Once I got the fpdm working, I haven't had to mess with it since, so I am content to just leave it the way it is.

[matthunter1448]

What's the ford fpdm off of?

[hardline]

Mine is off of a ford escort, but if you are wanting to feed a larger 2 pump system, the newer mustangs, f150s, and other v8 powered vehicles can drive 2 returnless pumps from 1 control signal.

[matthunter1448]

Mine is off of a ford escort, but if you are wanting to feed a larger 2 pump system, the newer mustangs, f150s, and other v8 powered vehicles can drive 2 returnless pumps from 1 control signal.

I just need one that will support around 20 amp at most

[hardline]

Then just about any FPDM will work

[jb007]

DB37-37 remains on; that's your fuel pump relay pin, and - depending on how you have your system wired - is very likely what's keeping your injectors and coils powered. It stays fully on, and you modulate via a separate port.

Hi Don and possibly James. I've been playing with my MS3 with a JimStim and JimStimX plugged in. If I select the Fuel Pump as the Fuel Pump Output pin under "Fuel Pump and Pressure Control" then it lights the FP LED on the JimStim. Swapping the output to say "Inj A" then the Inj A LED lights on the JimStimX. So far so good, except the FP LED is now not lit, therefore can not be used for powering an Fuel Pump relay that powers the +12V side of a SSR controlling the PWM'ed Fuel Pump, as well as injectors, coils etc.

Am I missing something? The way I see this is the way it currently works is you cannot have the FP O/P functioning in the original sense and a separate PWM O/P. Help!

Edit. PS You have to power cycle when changing O/P pins. Could someone else confirm this problem?

[matthunter1448]

DB37-37 remains on; that's your fuel pump relay pin, and - depending on how you have your system wired - is very likely what's keeping your injectors and coils powered. It stays fully on, and you modulate via a separate port.

Hi Don and possibly James. I've been playing with my MS3 with a JimStim and JimStimX plugged in. If I select the Fuel Pump as the Fuel Pump Output pin under "Fuel Pump and Pressure Control" then it lights the FP LED on the JimStim. Swapping the output to say "Inj A" then the Inj A LED lights on the JimStimX. So far so good, except the FP LED is now not lit, therefore can not be used for powering an Fuel Pump relay that powers the +12V side of a SSR controlling the PWM'ed Fuel Pump, as well as injectors, coils etc.

Am I missing something? The way I see this is the way it currently works is you cannot have the FP O/P functioning in the original sense and a separate PWM O/P. Help!

Edit. PS You have to power cycle when changing O/P pins. Could someone else confirm this problem?

Im going to confirm mine does the sam e on the stim tomorrow and will also verify with multimeter to be sure

[jb007]

Hi all, Iv'e created some text and diagrams on my blog, on how you can connect the SSR's up. I'm not an expert, but I have tested the first connection (see diagram one) on my bench. You have to have the input connected up as per both of the examples if you want to use the Generic PWM settings as I'm using to control my radiator fan based upon coolant temp, otherwise since there is no polarity inversion, the coolant/PWM duty curve will work in reverse.

As per usual, please leave feedback on my blog.Hopefully I've not made any mistakes!

[racingmini_mtl]

About your diagrams, why are you taking 12V for the pump from the main relay and not the fuel pump relay? Also if you do use that 12V source for your pump, you can also use it for the input side of your SSR which may make it easier for your wiring (or not).

Jean