Due to other topics here about starting Voltage issues,
has anyone fixed separate/direct 12V to the ECU w a fuse inbetween?
I do know my el system on my late 80`s Italian bike is not so well built.....

Would it be a good idea or not?
What fuse would be sufficient, 10A?

greenmonster wrote on 11/23/09 at 09:11:04:

Due to other topics here about starting Voltage issues, has anyone fixed separate/direct 12V to the ECU w a fuse inbetween? I do know my el system on my late 80`s Italian bike is not so well built..... Would it be a good idea or not? What fuse would be sufficient, 10A?

what do you meen with separate supply?
Two batteries? I have been thinking about tvo batteries just for a test to learn some thing more. Maybe connect a small lipo to supply the ECU during engine start

Jocke......

The coils and stuff are not powered through the ECU, just grounded through it. I think a 1 amp fuse would do but I use a 3 amp.

At least on my bike, the starter has a sepearate heavy 12V feed and depending on how you look at it, that means the ECU already has a "separate" feed... at least separate from the starter.

I think a separate ground strap from battery to ECU and another one from battery to near the starter will do more good. But I have no idea how your flavour of Italian electrics are laid out.

Having some cabin fever already, I just played a little with numbers. I found out that at high(ish) rpm and load, both injectors and both ignition coils are at times powered simultaneously. That means the ECU needs to dissipate 14-15 amps to ground. That's quite a bit more than the couple of hundreds of milliamps that are needed at the 12V feed.

I meant to make a direct connection battery-ECU lead to avoid the Voltage dip that eventually makes the ECU malfunction and therefore the bike does not start.
Just to b sure it has as steady 12V as possible.
I know the wiring on my bike takes the long route to feed various functions, the V drop at front light is a classic example.
I guess the ECU itself does not need much current to work.

But I f sure could be wrong, I do suck at electrics.  ::)

The ECU only requires current in the 100ma range if you allow for Optimiser or serial adapter.

I was thinking of using a 9V rechargable battery at one stage. The voltage booster added to the MkIII was the final solution. The starter relay will fail before the ECU.

I think Raz raised a good point, the ground to the unit needs to be really good, much better than the supply needs to be or you run the risk of interference. I'm sure some of the instantaneous currents would be much higher than 15 Amps, by simple Ohms law one coil by itself can draw over 15
Actually pin 17 of the multipin cable is +12 Volts direct from Fuse No1 bypassing the ECU relay but Cliff doesn't use it on the circuit board. It might be a bit tricky as you would be by-passing "The engine Stop Switch". (I was told not to call it a Kill Switch ) ::)

I don't see how to attach a drawing but if you look on V11lemans.com forum you will find a drawing "Test Point Layout" that shows the wiring and expected resistance readings from the plug.
Roy