A word on fuses when installing

[FridgeFreezer]

Following the repair of a MS for another forumer, I thought it worth mentioning this:

The ECU itself draws very little current - less than an amp flows into the +12v pin on the D37 (hence why you can run it from a PP3 battery on the stim!)

All of the higher current stuff (injectors, coils, relays) is fed externally from +12v and grounded by / through the Megasquirt, so there may well be plenty of amps flowing into the various other pins of the MS and the EDIS and out through the ground wires, hence why decent grounding is important.

However, as the MS (and EDIS too) do not use much current in themselves, it's a good idea to fuse them separately with a low-value fuse (3A being the smallest automotive fuse, and being plenty for an MS*) as this will ensure the fuse blows rather than any (major) damage occuring to the ECU. The MS has various internal protections against over-voltage/reverse-voltage/over-current but nothing is 100% idiot-proof.

The protection relies on there being a fuse which will blow and remove power quickly under fault conditions and hence force you to stop and investigate the fault - if the fuse is too big (or worse, not there) the protection circuits can't hold out forever and something's going to give.

In the case I have just repaired, the copper trace on the circuit board was the weak link, and heated up and vaporised. Luckily this was repairable, but it's not always the case. It also takes a shedload of current to do this to a circuit board.

* = I haven't measured the supply requirements of an EDIS yet.

[zim]

Thanks for the tip !

I'm away at the moment, but having a think - mine is wired like this :

http://forums.lr4x4.com/index.php?showtopic=15317&st=460#entry376853

So on the one relay i've got it supplying the injectors and ecu. I need to route the wire to the ecu through a smaller fuse.

G