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A bit of context, I have a BEAMS-powered endurance racecar. It's done a few 15-hour races, and mostly survived. The main target for it is the NASA 25 hours of Thunderhill, maybe in 2023. On a good day, it looks something like this:
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For the last year or so, it's had intermittent electrical problems. Annoying electrical problems that led to the ECU and fuel pump occasionally losing power for a split second while on track (it's especially scary once you're side-by-side with another car mid-corner, fighting for position). We did lots of relay swapping / bypassing / chasing bad wires in the harness / etc. Eventually, all the shady last-minute fixes in the pits caught up to us, one of our bypasses ended up shorting main ECU power mid-race, and we ended up losing another engine. Not great.
So, I decided to take the car offline for a few months and do a full from-the-ground-up rewire. And "while I'm there", make it easier to observe / debug / and generally mess around with. I was mostly excited about swapping all the relays with a PDM (modern technology from the 1950s! transistors!), but going that far, it made little sense to keep the stock ECU -- it's a giant black box after all. All in all, that means, standalone ECU, PDM, a solid-state battery isolator (instead of a mechanical kill switch), and a CAN keyboard to control everything (just two wires for all switches!). And of course, shiny new custom harnesses to connect all that -- hopefully in a reliable way. I had an ECUMaster Black from some previous plans -- the rest of the stuff is also from their line of products (PMU16, etc).
I've gotten to a point with the design where I think I have most of the basics figured out, and I'm comfortable sharing. The attached files have a basic functional diagram of the wiring, a tally of rough total power consumption for the PDM, and some notes for the first section of the harness I'll start to build now (firewall to engine bay). Notes / comments / critique more than welcome. There's still a couple of things I need to figure out -- how to drive the wipers motor, how much power the cooling fans actually draw, but these should be pretty simple.
Depending on the answers of these, there might be 1-2 PDM output ports left for switching future things, like night lights. But generally, even in a basic stripped down racecar like mine, 16 PDM outputs run out pretty fast, and I had to make some compromises (like, would've been nice to put the data logger on a separate line to restart mid-race -- AiM stuff is notoriously prone to freezing).
I went back and forth quite a few times on the physical placement of things. For a while, I was set on putting everything in the trunk (battery, PDM, ECU) to minimize the really thick wiring between the alternator / starter / battery / PDM. But then I remembered how much of a pain it is to run wires between the trunk and the cabin -- and the cabin accessories (cameras, dataloggers, night lights, etc) are the thing most likely to change over time. So, the final placement plan is much closer to stock -- the battery stays in the frunk, along with the solid state isolator and the power distribution module. This way, wiring between the PDM and all the cabin stuff is pretty easy to change. The main difference is the ECU is also in the cabin -- in the back, on the firewall. There's a single bulkhead connector in the firewall that leads to the engine bay, for all the wiring that needs to go there (minus the big alternator and starter wires). There's only a couple of things left the trunk (stoplights, taillights, accusump) and their wiring can be set in stone. All fuseboxes and relays are gone.
I'm excited -- this is definitely a big project (not to mention, still need to rebuild an engine, and tune it with the standalone), but should be pretty good (and hopefully bulletproof) once it's done.
For the last year or so, it's had intermittent electrical problems. Annoying electrical problems that led to the ECU and fuel pump occasionally losing power for a split second while on track (it's especially scary once you're side-by-side with another car mid-corner, fighting for position). We did lots of relay swapping / bypassing / chasing bad wires in the harness / etc. Eventually, all the shady last-minute fixes in the pits caught up to us, one of our bypasses ended up shorting main ECU power mid-race, and we ended up losing another engine. Not great.
So, I decided to take the car offline for a few months and do a full from-the-ground-up rewire. And "while I'm there", make it easier to observe / debug / and generally mess around with. I was mostly excited about swapping all the relays with a PDM (modern technology from the 1950s! transistors!), but going that far, it made little sense to keep the stock ECU -- it's a giant black box after all. All in all, that means, standalone ECU, PDM, a solid-state battery isolator (instead of a mechanical kill switch), and a CAN keyboard to control everything (just two wires for all switches!). And of course, shiny new custom harnesses to connect all that -- hopefully in a reliable way. I had an ECUMaster Black from some previous plans -- the rest of the stuff is also from their line of products (PMU16, etc).
I've gotten to a point with the design where I think I have most of the basics figured out, and I'm comfortable sharing. The attached files have a basic functional diagram of the wiring, a tally of rough total power consumption for the PDM, and some notes for the first section of the harness I'll start to build now (firewall to engine bay). Notes / comments / critique more than welcome. There's still a couple of things I need to figure out -- how to drive the wipers motor, how much power the cooling fans actually draw, but these should be pretty simple.
Depending on the answers of these, there might be 1-2 PDM output ports left for switching future things, like night lights. But generally, even in a basic stripped down racecar like mine, 16 PDM outputs run out pretty fast, and I had to make some compromises (like, would've been nice to put the data logger on a separate line to restart mid-race -- AiM stuff is notoriously prone to freezing).
I went back and forth quite a few times on the physical placement of things. For a while, I was set on putting everything in the trunk (battery, PDM, ECU) to minimize the really thick wiring between the alternator / starter / battery / PDM. But then I remembered how much of a pain it is to run wires between the trunk and the cabin -- and the cabin accessories (cameras, dataloggers, night lights, etc) are the thing most likely to change over time. So, the final placement plan is much closer to stock -- the battery stays in the frunk, along with the solid state isolator and the power distribution module. This way, wiring between the PDM and all the cabin stuff is pretty easy to change. The main difference is the ECU is also in the cabin -- in the back, on the firewall. There's a single bulkhead connector in the firewall that leads to the engine bay, for all the wiring that needs to go there (minus the big alternator and starter wires). There's only a couple of things left the trunk (stoplights, taillights, accusump) and their wiring can be set in stone. All fuseboxes and relays are gone.
I'm excited -- this is definitely a big project (not to mention, still need to rebuild an engine, and tune it with the standalone), but should be pretty good (and hopefully bulletproof) once it's done.
