Automotive Circuit Protection - Part 1

Tom Sharpe twsharpe at mtco.com
Wed Jul 26 01:47:10 GMT 2000



Garfield Willis wrote:

> On Fri, 14 Jul 2000 20:27:23 -0500, Tom Sharpe <twsharpe at mtco.com>
> wrote:
>
> ><snip> isn't it enough to just make sure the battery does not become
> >disconnected?? Get your power from the battery + and - ,,, then the alternator
> >can't get to the ECU when disconnected.
> >
> >One more thought about jumping, the alternator sees (any) two batteries as one
> >discharged battery and promptly attempts to charge it (max). Tom
>
> Uhh, lemme get this right, Sharpie. You're replying to a message posted
> 3 weeks ago, and asking "isn't it enough to keep the battery connected"?
>
> Wow, I can't possibly match your attention span! :)  But I'll try to
> catch up some.  Lemme see, your first suggestion seems to be, "get power
> from the battery, then if you disconnect the battery, the "alternator
> can't get to the ECU when disconnected". Uh huh.
>
> OKAY, yes well (in my best Montie Python/John Cleese voice), if you "get
> power from the battery", then if you disconnected the battery, would you
> imagine the ECU follows on like some dangling bit of kelp? No? Alright,
> so you disconnect the battery, but the ECU stays connected to the main
> bus? Probably. Rightee hoo then, but what THEN is it still connected
> toooooo? Ahha, just possibly the ALT!

You are right - I've been travelling an was 2500 messages behind..  I run the
battery in the trunk with a disconnect switch between it and the starter. The efi
is hooked up before the disconnect with a relay. The alternator and rest of the
vehicle are hooked to the starter hot lead (solenoid). Ground is the same way,
separate grounds for vehicle and ECU. As long as the battery to cables connection
is good, it's a pretty big capacitor.

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