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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:
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 l 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 everyone input, so please don’t hold back with the question and/or comments.
Same here. That's a really neat idea and I would buy one in a heartbeat if for nothing else than the fuel pump priming (if I hadn't just deleted my DME relay entirely).
Excellent! If you find yourself with even more time on your hands how about a solid state circuit for the heater fan resistor module and also I would love to get rid of those pucks that control the radiator fans. Good work
That looks very interesting, but it doesn’t look like it has the current handling capability of the relay. Have they been able to miniaturize components that much and increased the current handling capacity also?
That looks very interesting, but it doesn’t look like it has the current handling capability of the relay. Have they been able to miniaturize components that much and increased the current handling capacity also?
Good point! And yes the switching components are absolutely rated properly. The DME relay is actually two relays. One relay powers up the fuel injection while the other runs the fuel pump. The factory relay has a 15 amp rating and there is a single 15 amp fuse protecting the whole thing. I have to assume that each internal relay is rated for the full 15 amps because it is entirely possible that a short can happen on ether side. The switching components in this SSR have only 0.0011 ohms (1.1m ohms) of resistance. That means under normal operating conditions the switches stay cool to the touch. And even if each channel sustained 15 amps indefenetly you could still touch it with your fingers comfortably. It could even handel short bursts of more than 50 amps per channel, but the fuse would blow long before then.
Dear Fetch 9: don't be daunted by the 15$$ Amazon specials...your looks superior in every way..hope the tests work out OK for you and many others, myself included!
07-03-2015, 06:48 PM
Solid-State DME Relay- Beta Testers Wanted
