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My secret go-to relay is this one... They are commonly found on 1993 to 2003 Jaguars and probably other makes as well. For the Frugal among us... NO-ONE takes electrical parts from Jaguars you can often find them used at you local pick-and-pull by the hand full, often still in-situ in out of the way places shielded from the elements. The back Story is my 928 came to me not running with many electrical problems and failed relays. I have boxes of these Hella relays from a few Jaguars and one Aston Martin that I parted. So in they went to the 928. Years later still no problems with these relays on the 928 and multiple Jaguars I have.
Ford owned Jaguar then and starting in about starting in 1992 they improved the quality greatly. These relays were part of the changes Ford Made and they are high end and seldom fail. I value these relays so much that when I'm tinkering / prototyping with an engine swap harness or some other project I use Tyco's and dont put the Hella's in until the end. They also make a very distinct and quality sounding click on activation that I've come to know and appreciate.
For me no reason to consider using any SSR. I see no cost / benefit and only see risk to expensive hard to find components and additional difficulty in diagnosing. I've come to know and love the normal click sound you get when turning the key on a 928. When I dont hear those sounds I know something is arwy.
By doing away with those clicks you are also eliminating a specific part of the mechanical charm of a classic car.
Last edited by icsamerica; 12-10-2021 at 11:41 AM.
It won't work for the window winders, HVAC fan, rear window defroster and maybe the starter relay and ignition relay. For those of us with a separate fuel pump relay, it won't gain us much in that case either.
Fuse #15 is for the "Window Winders" and is supposed to be 30 amps. I'm making the assumption that if you were to operate both windows simultaneously, it may exceed 20 amps. Without having actually traced the wiring to confirm the path for the load, I made an assumption.
The Hella solid state relay does say that it can sustain higher than 20 amp loads for short periods, so it's entirely possible that you could get away with it on the windows.
Oh ya, thats what I thought. Windows wont be a sustained current.
But IMHO, only 3 relays are going to leave me stranded somewhere and I would focus on those.
Solid state relays, in general, are more heat sensitive than electromagnetically switched relays. The hotter that they get, the less current that they can support. And they generate heat while in operation. Which is why it has a built in heat sink and heat dissipating fins. The Hella relay is rated for 20 amps at 23C (73F). With the almost zero air flow across the CE, I would expect the solid state relay to get hotter than 73F in that location. The Hella relay has an overload cut off of 80 amps, but no temperature rating given for that specification. So, the maximum continuous amps and maximum inrush current (and over what timeframe) are variable. With no specifications provided on those aspects, it would be hard to predict what current it will actually support in any particular scenario..
I did some temperature testing on the CE panel recently for some troubleshooting. I found the existing relays to run at about 70-75-degrees when not in use and to run at 90-100 degrees when running. That was with the panel off and outdoor temps in the 40's. I would imagine the temps go up with the panel and in summer time.
I did some temperature testing on the CE panel recently for some troubleshooting. I found the existing relays to run at about 70-75-degrees when not in use and to run at 90-100 degrees when running. That was with the panel off and outdoor temps in the 40's. I would imagine the temps go up with the panel and in summer time.
+1 I also did this and got...same temps...I found a couple at 105-106....oddly though, this readings depended on where I had the beam aimed....seemed consistent the top edge was where I recorded hottest temps.
+1 I also did this and got...same temps...I found a couple at 105-106....oddly though, this readings depended on where I had the beam aimed....seemed consistent the top edge was where I recorded hottest temps.
Makes me wonder if this is heat from older/carboned up, poor contacts.
I replaced my regular ice cube ones a few years ago...I didn't think they'd be energized at all unless they were in use...figured the trigger turned the whole thing on but seems they sit there idling like an engine.
In diagnosing and tracing some problems, I end up replacing various relays...especially the fuel injection relays.
Sometimes, I replace these relays because I know that they do fail....and they are dirt cheap....especially compared to my labor rates to trace intermittent problems.
And if a new relay "fixes" the intermittent problem.....that's a fantastic bargain for the client!
Interestingly enough, a large percentage of the relays, which I replace, are the original units that came with the vehicle.
30+ years old!
Remarkably reliable parts, in my mind.
While perhaps not good comparisons (but all I really have):
I can't seem to get a laptop to last more than three or four years.
And I'm not sure that I've ever had a cell phone that long.
I'm pretty sure I don't have a television much older than that,
they seem to last as long as the extended warranty is good for and then magically quit soon after.
I don't even want to think about a modern toaster....if one is more than two years old, you better have a spare on the shelf.
A modern refrigerator? I think our last one made it four or five years. (Needed three icemakers in that period of time.)
Makes me wonder if this is heat from older/carboned up, poor contacts.
So would SS be a wash, energy wise in the CE
Relays dissipate heat in the coil when operating - of the order of 1W - 1.5W so in an enclosed space - with no airflow - they get warm and generally warm the enclosed environment.
While operating there may also be some minimal contact resistance heating - but this should be lower than the coil power - if it isn't the contacts will degrade quickly because this dissipation is very localized in the contacts - leading to rapidly higher contact temperatures.
The ambient temperature in the CE area (covered) will rise due to external ambient temps, internal cabin (HVAC) ambient temps, engine heating though the bulkhead/firewall and the general effects of collective active relay heating. On a 928 - when the relay is inactive there is no dissipation at all since 87a NC connections are not used. SS relays dissipate essentially no power for the "coil" control - but dissipate power proportional to the power they are controlling through the FET switching element. These FETs have a finite on resistance that is much higher than relay contacts in good condition - so their 'on' dissipation is much higher - and this on resistance can affect the voltage supplied to the switched device (much like happens with deteriorating relay contacts - however this rarely causes any problems - until the relay fails functionally). SS relays also essentially dissipate no power when they are inactive. Given the many different configurations of relay use - I think the standard relays work very well for long term usage and replacing critical ones preemptively is both cheap and easy.
12-10-2021, 11:10 AM
