Standalone and tacho question

[Woo]

I'm wondering how people with full standalone ECUs drive their indash tacho and alternator warning light?

The only way I can think of doing the tacho it is to retain the stock ECU and send a ref/synch signal (piggy backed from the standalone) to the stock ECU.
Then the alternator can be controlled by the stock ECU (NB8A) but I've found the charge light is on all the time although the alternator is still producing the correct current and voltage. Is a single wire alternator the only option? If so does the charge light output go high or low when out of range? The warning light needs an earth to activate.

Any ideas especially on the tacho?

[ampz]

Hi Woo,

You're running this on an NB right? (or NB engine) As per this thread the mazda ecu regulates (of sorts) the alternator output, once you put an external regulator and remove the ecu, you may have to put a sense voltage to the dash light (to warn you if the system isn't charging). See if you can get some pointers out of it.

As for the tacho, when i switched to cops and megasquirt, i needed a +1V pullup on the tacho signal as the mazda tacho doesn't apply voltage for the ecu to ground (and give it's signal) therefore it needs to see a difffering voltage. Sabretooth explains it in his write up at ozmx5, check out his explanation pic, a 1Kohm on +12V should give you the +1V you ned to drive the tacho, otherwise you may need to build a tacho driver circuit like the older megasquirts needed (I'll dig that one up after work)



Thanks Sabretooth for taking the time out to document your findings making it easier to explain this.
Cheers
Nuno

[mx52nv]

Just on the (actual) alternator - if you can't be stuffed with getting the alternator to work with whatever ECU you have, then you can just swap it for a NA8 alternator.

[Woo]

Sorry for the delay getting back to you, I've been doing the blue-arsed fly thing.

Firstly, thanks ampz, a lot of good info there, unfortunately the info I sought wasn't there (kind of). I'll explain.

I was aware the alternator was controlled by the ECU, cool just leave it in place I thought. But alas no, the charge light stays on because the injector/coil outputs from the stock ECU are now just floating (both now controlled by the standalone). Mx52nv's advise is how I'm doing it as I am running short of Auxillary outputs from the standalone (it's fully capable, but I'd prefer other things on the Aux), cheers.

Here is the news on the tacho.
As the tacho, when connected to the stock ecu, requires a synch and ref signal to trick the stock ecu into thinking the motor is running (which it is), I piggy backed the ref and sync signals from the standalone. This works except the cam gears I have (Fidanza specials for the NB8A) only has one pickup, not two (three actually, but the tacho only uses pulses from two). this was causing the tacho to read erratically. So I disconnected the piggy back ref/sync from the standalone and the tacho dies. But thats not all, disconnecting the ref/sync also kills the alternator outpu as the ecu senses that the motor isnt running (which it is).

So the outcome is that I will use an Aux output from the standalone to drive the tacho, easy to do just run the standalone output through a contactless relay into the dash wire. Then I've just sourced an 80Amp alternator from an MX6 that fits and has a single wire for the warning light which I'll run directly to the dash display.

Again, thanks ampz and mx52nv, I'm now just that bit wiser and the the car is that much closer to being reliable.

Cheers,
Bazz

[mx52nv]

Woo,
You are most welcome.
We are all so courteous on this forum