Ecu 101

[260DET]

My brain has turned to shit, thought I knew this stuff :sad: Not enough practice, anyway correct whats wrong with the following, talking about a MoTec ECU but I guess they are all the same.

Equipment such as thermo fans are operated by the ECU's AUX out facility which sends current to activate the fan's relay. Or in the case of a low draw item such as a LED the current sent operates the LED directly, no relay necessary.

I have some idea in the back of my mind that the ECU does not send current, when appropriate it grounds the current which is already wired in to the piece of equipment. For a thermo fan the relay would be wired so that the ECU grounds the relay circuit, so making it send current to the fan. This idea does not gel with the basic MoTec wiring diagram but for some reason I can't dismiss it.

Please put me out of my misery:)

[jezza323]

depends on the ECU, but usually they ground the relay circuit.

[Glenno]

Different circuits do different thing in regard to which way they switch. Higher current devices tend to earth as the semiconductors can "sink" more current than they can "source".

What model ECU and which ouput?

[260DET]

This is the MoTec wiring diagram referred to, see particularly the right side.
http://www.motec.com.au/drawings/ecu-m600.pdf

[Glenno]

They are all linked to the positive through the loads therfore they all sink current (go to ground when on) so you connect positive to one side of the relay coil and the ecu to the other.

[260DET]

Thanks Glenno but no understand. Should the AUX out relays ground through the ECU or not?

PS Think that is the right question (XXXX) I should be able to understand this shit.

[Glenno]

Yes the relay coil should ground through the ecu

[RB30-POWER]

dunno really what your asking, but this might help?

relay pin 30 (high current contacts) +12v fused battery supply (heavy guage wire)
relay pin 87 (high current contacts) +12v supply to thermofan (heavy guage wire)
relay pin 86 (low current coil) +12v fused ignition supply (small guage wire)
relay pin 85 (low current coil) -12v ground from ecu (small guage wire)

most if not all ecu's use npn transistors so they usually always ground aux devices.

[Supashake]

Delco is one ECU i can think of that switch pos but the rest neg.

[260DET]

Sorted, yay for MoTec info http://www.motec.com.au/drawings/L07.pdf