Do the S8 IGBT Outputs have Protection Diodes

[M_Gargantua]

Good afternoon, I'm chasing down some intermittent issues on a nearly decade old S8

Do the IGN1-8 and/or Fuel1-16 outputs have any protection diodes?

For visual reference:

[stevieturbo]

Can't answer the question, but what are the issues ?

[M_Gargantua]

Going through checks and trying to rule out things I hadn't noticed before. Figured it was just because I had never had cause to look previously: The outputs are floating at around 7.5V when off, and I got a relay that doesn't seem to like that. I'm an EE, and my thought was that it could making a voltage divider between the Vbatt, IGBT outputs, and the ground connection through the leakage current of the internal protection diodes. But better to ask the community rather than make assumption you know?

[stevieturbo]

Don't know the details inside

But even the most recent S8 I did, I've a few IGN outputs operating relays and they all work fine. Although I've never measured voltage with no relay attached.

I've other relays and also the Hella SSR on some of the FUEL outputs, again, no problems

But in an off state, I'd have expected them to be closer to 12v ?

Is it IGN or FUEL outputs, or both ?

I assume the correct IGN outputs are specified only for the ones triggering coils ?

[M_Gargantua]

Its any of them. Only when the kill switch relay is open though though, elsewise they toggle normally between Batt and 0. Its only when they're floating that they have that intermediate voltage. I know its nothing in the Setup that's off. These S8's have been in constant use for years without issue. This is just a modernized installation.

[stevieturbo]

kill switch relay ?

Surely if kill switch, however you have it configured is open, nothing should have power ?

What sort of kill are you using and how is it wired ?

[M_Gargantua]

There is a Battery Disconnect before anything, seperate from the kill switch. The ECU gets 12V from its own fuse, so its still on and logging even when you hit the kill switch. Kill switch opens an independent relay that breaks the power supply to all of the fuel and ignition systems, which has always worked flawlessly since 2014 using mechanical relays. I think the downstream solid state electronics just have a high enough input impedance that that floating ~7.5 doesn't get pulled to ground, but I hadn't expected that voltage to be there in the first place which comes back to the original question.

[stevieturbo]

Unusual way to wire things.

Could this be back feeding somewhere in the system and doing strange things ?

Although you seem to say about the outputs pulling to ground, they would only do this when the ecu is powered and the output is active. In their off state, ecu on, they would float around 12v. At least that is what I'd think.

I can probably test one of mine easily enough tomorrow to see what voltage they're at when ecu is on, but outputs are off.

[stevieturbo]

Not quite what I expected.

Fuel outputs, referenced to battery ground. In their off state, the couple of outputs I measured were sitting at a few millivolts.

IGN output ( not used for ignition coils ), this one with no relay plugged in was sitting around 6v, but with relay plugged in, changed to 12.x, nominal battery voltage ( presume voltage reading through windings of the coil )

I didn't trigger the outputs, as no point as I know they pull to ground and work.

Both a combination of regular solenoid relays and Hella SSR's in use on the Fuel outputs with no issue, and regular solenoid relays on the IGN outputs with no issue.

Only kill I have on this car is a proper modern solid state battery disconnect, with line to the ecu to shut down the engine prior to full disconnect.