Solid State Relay Board Options

[Steve_R]

Well, it’s been about a year since I finished my 914 restoration, you can read all about it

HERE.

Everything works perfect except for the electrical problems I’ve been having with the relay board. I spent lots of hours trouble shooting electrical issues with the fuel pump. It turs out that my relay board had some bad connections for the fuel pump relay. After searching this site I discovered that the relay board is truly the weakest link in the 914. I tried to remove the epoxy bedding underneath the board and resolder the connections. This worked for a while but the fuel pump would sometimes stop and kill the engine. I finally figured out that the contacts for the fuel pump relay to the board were causing the problem. This seems like a never ending problem. I could buy another 40 year old used board and have the same problems.
So, to make a long story short, I decided to design a new relay board from scratch. I replaced the original electromechanical relays with industrial solid state relays. They have the same connection labels as the stock relays: 85 & 86 for the coil and 30 & 87 for the switch. The relays are available at most electrical parts dealers like Mouser or Digi-Key if one ever needs to be replace. They also use a lot less power than the original 914 relays. Also, since they are solid state and don’t have any moving parts they will last a lot longer and are more reliable. I also replaced the old ceramic fuse with a modern ATC style fuse and added an LED that illuminates when the fuel pump has power. This is great for trouble shooting fuel pump issues. It comes on for a few seconds after the key is turned on and stays on when the engine is running. Also, I removed the connections and plug for the rear window defroster. I used wires soldered to the connectors eliminating all of the riveted connections. All connections are soldered. To make the board I CNC machined the board out of high density polyethylene plastic.
I built a few extra boards to offset some of the development costs. They are quite labor extensive to build so I don’t plan to mass produce them. PM me if you want one. I would like to get $500.00 each. That includes the board with the solid stare relays. It does not include the voltage regulator. I used a solid state one from Pelican Parts. Both the stock and solid state voltage regulators will work.

[Mikey914]

We've been spending some time putting together a redesigned board with solid state relays. I have to finish the 19mm master cylinders before I jump full bore into this, but these would look OEM until you pop the cover.

[peteyd]

We've been spending some time putting together a redesigned board with solid state relays. I have to finish the 19mm master cylinders before I jump full bore into this, but these would look OEM until you pop the cover.

@Mikey914 have you made any progress on this project?

I am interested for a build here.

Pete

[Mikey914]

We've been spending some time putting together a redesigned board with solid state relays. I have to finish the 19mm master cylinders before I jump full bore into this, but these would look OEM until you pop the cover.

@Mikey914 have you made any progress on this project?

I am interested for a build here.

Pete

Actually we are working on the board. We decided that with the reliability of the relays we are making now going through 500,000 cycles the solid state thing built into the board, is really an added expense for no real extra value. The new boards are underway now.
Mark

[Spoke]

Actually we are working on the board. We decided that with the reliability of the relays we are making now going through 500,000 cycles the solid state thing built into the board, is really an added expense for no real extra value. The new boards are underway now.
Mark

Solid State relays are quite sexy but not really needed here. High speed and extra cost are not advantages in the 914. Good call to stay with mechanical relays.

A little side story about SS relays. I'm a consultant for a major rail manufacturer and I was brought in a couple of years ago to analyze failures of a certain board with a high number of returns. It was a very complicated board with several power supplies, CPUs, FPGAs, and a lot of analog circuits on the board. I narrowed down a majority of failures to a particular SS relay on the board. There were six of these SS relays. They would not turn on. They had an LED input and LED receptors on the output side. Over time the current transfer ratio (CTR) would decay to the point where the relays would not turn on and the board would fail.

On one board someone thought a large FPGA had failed and it was replaced. The board worked fine for about 4 months then failed again. The FPGA was the driver for the SS relays. In my investigation I found that the SS relay could be annealed with heat and its CTR improved which is what happened on this board. The heat of removing and replacing the FPGA annealed one of the relays but it failed a short time later.

Here's the kicker: The relay was originally designed and manufactured by Bell Labs in the 1980's. I was in that group which designed the SS relays and I knew the part number. I did not design that SS relay. I did receive my one and only US patent with a SS relay. If you're interested, it's patent # US5360979A.

Spoke's SS Relay Patent