I’m looking to retrofit a car, and I’d like to keep the keyed ignition switch (off - acc - on - start). What would be the best way to wire it to the ecumaster battery isolator and PMUs so that everything shuts down and turns on properly, and so that I can use the state of the switch to control the startup sequence?
Wiring the switch directly to the components (such as PMU inputs) is fair game. Wiring the switch to a canbus switchboard and using canbus is also fair game. Hybrid strategies are also fair game.
I typically wire the Isolator out to the PMU’s 12V turn on and the ignition, start and accessory positions to the PMU’s analog inputs.
There have been a few cars where the need for the PMU is on ignition only so the key’s 12V gets wired to the ignition position from the key.
No wrong answers really, comes down to how you want the car to function. My bench power supply puts the PMU’s idle amp draw under 20mA, very low compared to most other PDM’s i’ve measured, so it’s pretty ok to be left permanently on until you park the car long enough to warrant using the isolator’s power save switch.
Hey man! Fair enough! This is exactly the kind of relatively technical answer I wanted. Specially regarding the PMU power draw at idle.
I just wanted to know if there were better strategies out there that could shut off the PMU completely, leaving maybe only the isolator in ready state, and how far could I take it into an elegant solution.
I’ll give a few more days to see if we get other suggestions.
So, a 6 pin ignition switch receives power at B1, which connects to Acc (accessories) and IG1 (everything that is essential to be on, even during engine start). So, ignoring the B2 side of the switch, which drives non-essentials (IG2) and Start, when you turn the key it goes Off → B1-Acc → B1-(Acc, IG1) → B1-IG1.
What does everyone think of the strategy where the battery isolator engine kill line connects to B1, and then Acc and IG1 connect together to the ignition input on the PMU? (I believe Acc and IG1 connection to the PMU needs diodes for this to work)
They also connect individually to analog inputs to determine the state. IG2 and Start also connecting to individual inputs. B2 can probably be bridged to B1 as well, simplifying the wiring.
Does this seem like an elegant strategy that shuts off the PMUs? If yes, can anyone one-up this strategy? If it doesn’t work, can anyone the fault in the logic?
How about a strategy similar to above, but while Acc and IG1 simultaneously connect to the PMU, the individual wires connect to something like a CAN switchboard? This board gets energized as soon as the PMU turns on (so with the key in any position that is not Off), because it is connected to a PMU output that drive “always on electronics”, such as this board and maybe some others. The CAN switchboard then sends each ignition output through CAN bus. This strategy saves PMU inputs and can send the ignition state to multiple PMUs through CAN.
Again, if this sounds good, can anyone one-up it? Maybe something simpler than a CAN switchboard for example? Or if this doesn’t work, can anyone point the fault?
I’m just trying to give some options to spark a discussion on the strategy, get some feedback. I’m also trying to actually offer something, instead of coming here asking for everyone’s advice with nothing to offer.
I’d be very careful doing anything load wise beyond the PMU turn on or analog inputs. the isolator’s 12V out isn’t capable of much more then a relay coil or the PMU’s switch 12V input.
I don’t think you’ve suggested otherwise, but just in case that was an idea.
By chance is this a Toyota or Mazda?
Only issue I can see with this is if you have stuff you want on ACC then the PMU needs to be on.
Simpler imo to have the isolator go to the PMU turn on, B1 to ground, IGN and ACC into pmu analog inputs with a pullup enabled, program away.
You could probably dream up a way to MUX the key positions to save on inputs.
2nd plan sounds like it would work too. My only caveat is that for mission critical stuff I try and keep that hardwired into the PMU just for reliability.
Yes, I believe it’s capable of something like 1.5 A max, so I wasn’t really suggesting hanging anything on it. It’s just a 24 awg wire.
In my case, I’m retrofitting the wiring of a Mazda RX7 FC, which is my car (and daily drive).
Good point about reliability. I have a PMU in the cabin and one in the engine bay, and the one in the bay also needs to know the state of the switch to power other goodies. The idea with the CAN board is that the switches on the cluster are also being transferred to the CANbus (so that they can talk with the engine bay PMU to pop up the headlights and things like this), and the gauge cluster is being retrofitted, so there is generally a place nearby to receive the ignition switch state and forward it to the CANbus.