SS Relay to replace RED FP relay

[7783911]

To all the electrical gurus, has anyone tried to adapt the F9 solid state relay to replace the round red fp relay and if so, how did you wire or how would you wire the pins



versus




I like the 3 second prime feature

any guidance appreciated!

bob

[BoxsterGT]

Anyone?

I too want a 40a "RELIABLE" relay for a Fuel Pump.

Len

[wazzz]

Your original fuel pump relay for CIS is a standard automotive relay. It contains one SPDT relay switch.
The F9 relay is a replacement for the 3.2 Carrera DME relay. It contains two SPDT relays that are wired in cascade. The two units are totally different and I doubt you can use the F9 relay to drive and prime a CIS fuel pump.

[76FJ55]

You could look into using one of these Hella sold state relays. It is rated at 20A continuous with an 80A inrush current capacity. You could then use a standard relay socket with leads to remotely mount the SS Relay and then add round pins to plug into the factory socket.

[wazzz]

Originally Posted by 76FJ55

You could look into using one of these Hella sold state relays. It is rated at 20A continuous with an 80A inrush current capacity. You could then use a standard relay socket with leads to remotely mount the SS Relay and then add round pins to plug into the factory socket.

This SS relay wouldn't fit. If you look at the details, it is a SPST, that is just a simple switch, while the fuel pump relay needs a SPDT, which is a crossover switch between two lines. Look at the schematic posted above.

[pmax]

Originally Posted by BoxsterGT

Anyone?

I too want a 40a "RELIABLE" relay for a Fuel Pump.

Len

The red relays are "RELIABLE".

It's the darn socket which loosens up.

[BoxsterGT]

Looks like a whole replacement Fuse panel in in store with Square relays, IF such a thing is available.

Len

[pmax]

That would be like getting a set of implants instead of patching just that tooth.

[BoxsterGT]

Yes, IF IT WAS THE ONLY PROBLEM.

However we all know the issues with the stock fuse panels.

I plan to keep this one forever.

Ha, "Famous Last Words".

Len

[PeteKz]

I'm with Gilles. I don't think the F9 relay can be directly adapted to replace the OE FP relay. It would require some additional creative wiring. The Hella solid state doesn't look like it will work either.

The CIS does not need the pump to run to prime it. Lots of SC's start on the first turn of the key.

As for reliability, I'm pretty sure the CIS relay in my 1973 car is original, and it's 50 years old. Hard to beat that.

[spuggy]

Originally Posted by BoxsterGT

Anyone?

I too want a 40a "RELIABLE" relay for a Fuel Pump.

Len

40A? Seems a tad, uh, overkill...

Fuel pump current draw is proportional to the regulated pressure; Bosch 044 motorsport pump typically draws ~11 Amps w/ CIS - and half that with EFI (~45PSI instead of 100PSI). Bosch cite absolute maximum current for that pump (which requires upgrading the electrical connectors from the factory M4/M5 to M5/M6) as 15.5 Amps - at which point it would be close to overloading "regular" 14 gauge wiring...

Even a 930 - which, stock, runs two fuel pumps, front and rear, through a single fuse position and a shared single relay (a common cause of unreliability readily addressed by a rewire to split each pump out to its own fuse and relay), wouldn't need 40A.

Fortunately, my (as far as I know) original relays in a 275,000 mile tub seem to working just fine - touch wood.

Nevertheless, I've thought about it a bit. Random thoughts.

Firstly, modern relays supplied as replacements are reported to be no better than the no-name garbage. Because they're likely the exact same garbage with a markup. Many have shared horrific pictures of the internals when their replacements died - and reverted to/still getting good service from used 40, 50 year old originals...

Secondly, part of the problem with the original relay bases is that the "round pin" configuration can cause overheating with too much current, especially when they get old/loose/dirty. Also, the relays seem to tend to work out over time as well, probably from expansion/contraction with heat cycles - which can't help. Cleaning/spreading the pins etc can help a lot - but it's like the old-design fuses; no substitute for clean, new contacts with as much contact area as possible. Hey-ho for ATO fuses.

Thirdly, apparently if you buy a new relay base these days, even if you specifically order the fuel pump one, you'll get the one with the thinner wires in the pigtail used everywhere else. Timmy2 builds these - and can supply replacements with the original thicker wire spec for the fuel pump(s).


There's more than one way to address these issues. I haven't done either of these - and flip-flop between the two approaches every time. Sigh.

PP member flightlead404 was printing relay bases (with 16 gauge milspec/tefzel wiring pigtails) that allowed you to use an ISO automotive relay instead. Which you can source at your favorite FLAPS... The industrial Panasonic ones have a good reputation, sealed, contacts rated for 10^6 operations, readily available/cheap as chips, and rated to 40A.

Alternatively, Restoration Design make a solid-state relay rated at 30A (suitable to replace the red fuel pump relay), part #RD-911.615.109.02. It plugs into the factory 5 pin relay base and accepts your original plastic relay cover. So no-one would ever know it's fitted unless they pull the relay and pop the cover - a plus for the concours types...

I don't know why our host doesn't offer it - maybe someone should ask them to?

[76FJ55]

Originally Posted by wazzz

This SS relay wouldn't fit. If you look at the details, it is a SPST, that is just a simple switch, while the fuel pump relay needs a SPDT, which is a crossover switch between two lines. Look at the schematic posted above.

Ok, I see that now. My mistake. I didn't look at the diagram initially as I thought you'd posted a diagram of how the F9 works.

the 87a terminal and associated yellow wire are part of the starting circuit. the yellow (bus 50) wire receives power during cranking and ensures the fuel pump runs during the cranking phase before the airflow sensor contact closes and grounds the trigger coil in the relay.

the easiest solution would be to use a diode to supply power to the fuel pump during cranking and the Hella SS relay to supply power during running.


below is a quick sketch of the circuit with the Hella relay and diode wired to the original relay socket.

[Tonger]

I'm running the Restoration Design relay -works well. You can reuse the red cap of your old relay or buy an aluminum can from them - plug and play.

https://www.restoration-design.com/store/product/RD-911.615.109.02

This is on an '86 930 running dual 044 fuel pumps.

[wazzz]

Originally Posted by spuggy

40A? Seems a tad, uh, overkill...

Fuel pump current draw is proportional to the regulated pressure; Bosch 044 motorsport pump typically draws ~11 Amps w/ CIS - and half that with EFI (~45PSI instead of 100PSI). Bosch cite absolute maximum current for that pump (which requires upgrading the electrical connectors from the factory M4/M5 to M5/M6) as 15.5 Amps - at which point it would be close to overloading "regular" 14 gauge wiring...

Even a 930 - which, stock, runs two fuel pumps, front and rear, through a single fuse position and a shared single relay (a common cause of unreliability readily addressed by a rewire to split each pump out to its own fuse and relay), wouldn't need 40A.

Fortunately, my (as far as I know) original relays in a 275,000 mile tub seem to working just fine - touch wood.

Nevertheless, I've thought about it a bit. Random thoughts.

Firstly, modern relays supplied as replacements are reported to be no better than the no-name garbage. Because they're likely the exact same garbage with a markup. Many have shared horrific pictures of the internals when their replacements died - and reverted to/still getting good service from used 40, 50 year old originals...

Secondly, part of the problem with the original relay bases is that the "round pin" configuration can cause overheating with too much current, especially when they get old/loose/dirty. Also, the relays seem to tend to work out over time as well, probably from expansion/contraction with heat cycles - which can't help. Cleaning/spreading the pins etc can help a lot - but it's like the old-design fuses; no substitute for clean, new contacts with as much contact area as possible. Hey-ho for ATO fuses.

Thirdly, apparently if you buy a new relay base these days, even if you specifically order the fuel pump one, you'll get the one with the thinner wires in the pigtail used everywhere else. Timmy2 builds these - and can supply replacements with the original thicker wire spec for the fuel pump(s).


There's more than one way to address these issues. I haven't done either of these - and flip-flop between the two approaches every time. Sigh.

PP member flightlead404 was printing relay bases (with 16 gauge milspec/tefzel wiring pigtails) that allowed you to use an ISO automotive relay instead. Which you can source at your favorite FLAPS... The industrial Panasonic ones have a good reputation, sealed, contacts rated for 10^6 operations, readily available/cheap as chips, and rated to 40A.

Alternatively, Restoration Design make a solid-state relay rated at 30A (suitable to replace the red fuel pump relay), part #RD-911.615.109.02. It plugs into the factory 5 pin relay base and accepts your original plastic relay cover. So no-one would ever know it's fitted unless they pull the relay and pop the cover - a plus for the concours types...

I don't know why our host doesn't offer it - maybe someone should ask them to?

Doesn't appear to be SSR. No mention of solid state relay on their product page. It seems to be a standard PCB relay mounted on a round circuit board with an external diode and 5 pins. Looks neat though, and if it uses high end relay like Panasonic, it should probably be as good as the original round relay. But this is no SSR and because of this it is probably more reliable.

[wazzz]

Originally Posted by 76FJ55

Ok, I see that now. My mistake. I didn't look at the diagram initially as I thought you'd posted a diagram of how the F9 works.

the 87a terminal and associated yellow wire are part of the starting circuit. the yellow (bus 50) wire receives power during cranking and ensures the fuel pump runs during the cranking phase before the airflow sensor contact closes and grounds the trigger coil in the relay.

the easiest solution would be to use a diode to supply power to the fuel pump during cranking and the Hella SS relay to supply power during running.


below is a quick sketch of the circuit with the Hella relay and diode wired to the original relay socket.

It is actually the other way around. When ignition is on, but before cranking, relay coil is energized as it receives power (+12V) on 86 from Ignition On (bus 15) and ground on 85 through the sensor plate switch, which is closed because engine is not running yet. Since coil is energized, SPDT relay switch has toggled and closes circuit between 87 (bus 50) and 30 (fuel pump positive side, not to be confused with permanent power bus 30).
So when cranking, power is applied on bus 50 (yellow wire) and goes to FP through 87-30. FP is then powered and running. As soon as engine begins to turn, airflow lifts the plate and sensor switch opens, hence the relay coil no longer receives a ground and is no longer energized. Relay switch toggles back to rest position 87a-30, which takes on to provide power to FP from bus 15.

Safety feature: in case of accident, if ignition is still on (driver unconscious), provided the engine has stalled, sensor plate switch closes again, so ground is provided to relay coil, which is therefore energized again, and relay switch toggles to 87-30, but since there is no power on 87 from yellow wire, terminal 30 has no power. Therefore FP is no longer powered and running.

I'm not sure you diagram with the diode can emulate this behavior.

[spuggy]

Originally Posted by wazzz

Doesn't appear to be SSR. No mention of solid state relay on their product page.

My bad - you're right of course, I missed that. Although it'd probably take all of 10-15 minutes to desolder that guy with a hot air reflow station and fit an PCB-mount SSR - if you really, really wanted that.

I have a box of Pansonic ISO relays that I paid like $4 each for; any industrial relay from a reputable manufacturer really couldn't fail to be a massive improvement over this horror-show:



(From The infamous Chinese red relay [pics inside])

Which is what we're trying to avoid getting at all, right? - much less paying $40 a pop for, only to discover something like 40% of them don't work out of the box...

Turns out the 914rubber guys developed their own relays too. In 2019. They built a test bed, picked one at random, put a "real" load on it (cycling a 914 headlight motor every 7 seconds) and tested for 600,000 cycles before failure. From BIG announcement form 914Rubber NEW REALYS Improved design, w/ 1 yr warranty

I bet if you popped the cap on theirs, you'd just see actual good quality mass-produced industrial components under there...

Interestingly, thread on the teener board says they initially tried SSRs - but had early failures in testing/got better reliability with actual relays...

[76FJ55]

Originally Posted by wazzz

It is actually the other way around. When ignition is on, but before cranking, relay coil is energized as it receives power (+12V) on 86 from Ignition On (bus 15) and ground on 85 through the sensor plate switch, which is closed because engine is not running yet. Since coil is energized, SPDT relay switch has toggled and closes circuit between 87 (bus 50) and 30 (fuel pump positive side, not to be confused with permanent power bus 30).
So when cranking, power is applied on bus 50 (yellow wire) and goes to FP through 87-30. FP is then powered and running. As soon as engine begins to turn, airflow lifts the plate and sensor switch opens, hence the relay coil no longer receives a ground and is no longer energized. Relay switch toggles back to rest position 87a-30, which takes on to provide power to FP from bus 15.

Safety feature: in case of accident, if ignition is still on (driver unconscious), provided the engine has stalled, sensor plate switch closes again, so ground is provided to relay coil, which is therefore energized again, and relay switch toggles to 87-30, but since there is no power on 87 from yellow wire, terminal 30 has no power. Therefore FP is no longer powered and running.

I'm not sure you diagram with the diode can emulate this behavior.

Thanks for the clarification. I was thinking along the lines of L-Jet not K-Jet, and misinterpreted the airflow contact sensor contact. I should have know since 87a is the normally closed contact and 87 is the switched contact. You're probably right that the initial proposed diode I proposed. I'll have to think about it and see if I can come up with a viable solution with this new information.

[Locker537]

914Rubber relays work well.

[AndrewCologne]

You can modify every round standard Relay to make it behaving like a red one, just solder a flyback diode between terminal 85 and 86 in a direction shown in the graph



It just avoids voltage spikes when closing which can harm i.E. the rev limiter module.

[AndrewCologne]

Example: