Solid-State DME Relay- Beta Testers Wanted
 

I have been developing a new DME SSR (Solid State Relay) for the Porsche 944/968/924S/964/968/993, and now have prototypes ready for beta testing. Only four of these are in existence and I am looking for Porsche enthusiasts in the Phoenix area who drive one of these cars as their daily driver to test one. If you’re interested, please sent me a PM. Keep in mind, these are not production units, there are a few of changes that will be made on the final version. All of these changes are very minor, the most significant being the small green wire (look closely in the picture). Once production units are ready, I am going to need these prototypes back, but I will give you a shiny new one out of the first batch for helping me test.

Here is a picture on the new Solid-State DME relay next to a factory DME relay:

http://forums.pelicanparts.com/uploa...1435957511.jpg

Some Information about the new Solid-State DME Relay

I think everyone is aware the OE relay suffers from various issues that cause no-starts and other erratic and shall we say “interesting” behavior. Lots of guys, including me, keep a spare relay in their glove box just in case. And I suppose I could have just bought a new OE relay form Porsche or one of the OEM or aftermarket options. But I am basically a 944 junkie with an engineering degree, so enviably I was going do a full redesign and make it better. The main issue with the OE relay, in my view, is cracked solder joints. The reason this happens is because the mechanical relays are made of metal which is heavy. Combine that with several amps of heat, constant engine vibration and one to three decades of driving… Yep, cracked solder joints. Even if the joints are re-soldered they will eventually crack again at some point in the future. But that’s assuming the relay armature and contact points don’t wear out first. In comparison, this new Solid-State DME relay is less than half the weight, which will preserve the solder joints indefinitely. Plus, it has no mechanical parts or contacts and therefore cannot “wear out”. And because I have way too much time on my hands, I went ahead and put in a timing circuit in it that primes the fuel pump for two to three seconds when the key it turned on. This is a standard feature on most modern cars because it helps bring the fuel pressure up before the DME/ECU starts firing injectors. It's a handy feature if you have opened you fuel system and want to bleed out the air without cranking the engine. And a nice no-start troubleshooting aid because you can faintly hear the fuel pump cycle on KOEO.

I welcome everyones input, so please don’t hold back with the question and/or comments.

Thank you so much for doing the work on this! We need this product and I'd like to purchase two of them when they are in production.

I'm not sure if you're aware, but many of us 964/993 guys pull the relay before starting the car after a period of hybernation. Then crank several times to build oil pressure. Then re-insert the relay and start the car. It might be a cool thing if there is a way to incorporate a "kill" switch in the relay. It could also work as a theft deterrent ;)

Count me in! I do not daily drive mine so I am not a good beta tester. I'll take one of the production units though.

I am in as well,; if/when production comes about.

EDIT: Never mind.

This is awesome! I'll be buying one when they come out. :)

Fantastic!



Andreas

Wow!! Great idea. I'm too far away to be a beta tester, but I'm definitely interested.

Heinz

PM'ed

I drive mine daily and would be interested in beta testing.

this is great.

Update
 

The Solid-State DME relay project is alive and well, all of the Beta Testers are reporting back with no issues. The design has been finalized and we are moving into the production phase. I will reserve a relay from the first batch for everyone who requested one prior to this posting. I estimate the first production units will be available in one to two months.

sub'd for the final production run

Better late than never, I'm in

http://forums.pelicanparts.com/uploa...1435957511.jpg

1. The issue of less reliability with the high component count verses the original relay
hasn't been discussed, i.e. the reliability decreases as the component count of any
system increases.

2. A solid state fuel pump relay is less reliable and prone to failure when the fuel
pump stalls or may generate excessive start-up currents than a mechanical relay.

3. Most all automotive OEMs still use mechanical (contact type) fuel pump relays.

4. The inductive discharge voltage when the fuel pump turns off can over-stress
solid state switching devices.

5. Solid state relays are more prone to failure during an intermittent over-charging
alternator.

All good points! Let me know if this addresses all the concerns or if I need to include more details. I welcome all the input I can get. Keep in mind this SSR is installed in my Porsche too, if there is an issue you can be sure I will want to fix it!

1. As a rule of thumb reliability does decrease with complexity. Device failures are the summation of the probability of failures for all individual components plus assembly defects. Mechanical relays use largely stamped metal parts in their construction along with complex assembly processes such as winding the coil, stamp welding, and riveting. Each of these processes inherently will have radically higher defect rates than equivalent electronic manufacturing processes used to create the SSR. Only high-quality name-brand electronic parts are used. The odds of any of these parts being defective from the manufacturer is similar to winning the lottery. In terms of assembly the SSR just needs parts placed somewhat accurately on solder paste which is then heated in an oven. The surface tension of melted solder will pull the part into the correct position on its own. There will also be version without the Pump-Prime feature which reduces the part count by more than half. Officially, I will warrantee it for double the period of highest warrantee of any replacement DME relay.

2. The transistors inside the SSR are rated radically above the 15 amp fuse that protects the fuel pump. The fuel pump could be in full stall until the battery runs dry and the transistors that drive it would never feel more than warm to the touch. I am not sure what the issue would be with startup current. The windings in the fuel pump (an inductor) will dampen the current flow (flywheel effect) when power is applied far more efficiently than switching it on slow. Dave, could you clarify the concern? I just want to make sure I’m not missing anything.

3. OEMs use mechanical (contact type) relays because they are cheaper, and not because of reliability factors. Car makers don’t hesitate to save a buck event if that means some people will get hurt or worse because of it. It has only been in the last several years that the semiconductor industry has come out with transistors that can handle very high current without huge heat sinks. At some point in the near future the cost of a mechanical relay is going to be the same as an equivalent transistor. When that happens OEMs will start switching over.

4. The “kick back” voltage generated by inductive devices when the electric field collapses is easily handled any number of ways. In the SSRs case, the transistor is a high-power P-Channel MOSFET configured as a high-side switch (switching Battery Positive Voltage). All MOSFETS have a “Body-Diode” that connects the input and output of the transistor (i.e. Drain and Source). In this configuration, when the fuel pump generates a high voltage spike it forward biases this body diode and is simply absorbed into the vehicles power system. Operating the power windows ,let alone the starter, generates far bigger voltage spikes.

5. All electronic devices attached to a vehicles power system must be protected against voltage spikes and high alternator output. The SSR has the same power protection circuit found in your Porsche’s DME (actually it’s a good measure better). If the SSR fails due to alternator issues, you will likely need to replace the DME too. At least the SSR will be covered under warrantee for like 4 or 5 years.

1. Failure Rate - You answered it yourself. The SSR is inherently more
complex and thus less reliable:

"As a rule of thumb reliability does decrease with complexity. Device failures
are the summation of the probability of failures for all individual components
plus assembly defects."

2. You did not mention that fuses don't protect for transient currents that exceed their
rating but can destroy a semiconductor.

3. OEMs make component decisions based both on cost and reliability. There are many
applications where high-side semiconductor ICs switches are used but mechanical relays
are also still used.

4. Few if any automotive applications use discrete PMOS switching devices because of cost,
current handling capabilities, and driver circuitry versus NMOS. That's why the use of
a relay is more appropriate when switching a battery voltage and not ground.

5. The DME ECM does not 'see' the same type of voltage and current spikes as does
a fuel pump relay.

Bottom line: Once an original DME relay is properly re-soldered, the likelihood of its
future failure is significantly reduced. The key problem results from the heat sink effect of
the large relays in the DME relay and the wave-soldering assembly process used in
manufacturing, resulting cold solder joints. If each relay pin is heated and soldered
individually, the long term reliability is significantly increased of the OEM DME relay.

Additional Note: The cantilever mounting of the OEM relay contributes to its poor
reliability by allowing it to vibrate vertically weakening its solder connections.

I understand completely what you are saying, but all of you concerns have been addressed through proper engineering practices. I have over 5 year of professional industry experience designing automotive electronics plus another 2 years designing medical x-ray equipment. In addition I designed most of the circuitry in the Rogue Tuning DME. If you feel the mechanical relay is more reliable then definitely stay with it.

Interested to hear on a price as well!

would like one when they are ready