Is your alternator connected to the ECU - ie, is it a DP type or similar? If it is, be aware that I haven't detailed how to UIBI that - merely the traditional chargeLight types.
If you have the L type, the it won't screw up the ECU.
I'm not sure what you mean by the relay hysteresis though - that has nothing to do with the UIBI. (I know off voltage is much lower than on...)
i guess youd be right about the hysterisis. its not needed since the light is already controlled.
i have a 99 ranger, and i would have to imagine the alt light is based off the ecu- since everything else is. i guess one way to tell would be to bring up my scanXL software and see if i can see charging status on it. but either way, a mosfet on the charge light like you said should work for anything.
I don't think it is that common for the ecu to control the alternator - especially not in the '90s.
I know it has become popular (Mazda etc) even though I think it is a stupid idea (worse fuel economy etc) - though I am open to factuals.
Essentially though the alternator still regulates its voltage (hence output) - it is simply that at times the ECU will signal it to cut out (for better acceleration). At least that is my understanding of it....
I do recall looking at the DP and "the other" ECU controlled alternator systems and thinking that the UIBI could still be rigged.
That's not to say that traditional D+ and L-type alternators instead signal the ECU or other uPC system so that charge status can be monitored and displayed, though traditionally D+/L types need a trickle (or tickle) current to ensure the rotor magnetises, but that current can be much smaller than that provided from traditional charge lamps (eg, 2-3W => ~100mA upwards), and ECUs etc can provide all that.
But as far as the UIBI is concerned, functionality wise, any dash charge lamp is a charge lamp - whether LED or whatever.
[ FYI: The charge lamp is actually a "NOT charging" lamp, hence the UIBI is off (isolated) when the lamp is on. It is when the charge lamp's ground from the alternator goes high (+12V) that the UIBI relay switches on.
The polarity is easily be changed, but traditional vehicles use ground switching - ie, dash lights are hot on one side (+12V) and things like oil pressure, parking brakes and brake-fault etc switches - as well as alternators - connect to ground to light their respective lamps.
That's where a MOSFET front end would be handy - the UIBI would then be universal without concern for the relay's coil current (especially for relays that switch several hundred Amps), and signal inversion would simply require an extra inverting FET. (A production model would have both +12V & ground triggering input options.) Likewise filters (time delays) or extra triggers would be a breeze - extra inputs (like please connect my batteries together for cranking) merely being diode-connected etc in the UIBI's circuit.
Alas I haven't bothered yet with that, nor has the Master of Invention that comes up with these DIY & income prevention ideas. ]
Sorry for the reawakening, but a googling of "UIBI isolator" located this thread.
The past few days has seen interesting allegations about relays to connect batteries on mp3car. Call that my "due diligence" to you for what it's worth...
Not that I have responded to the last 2 replies, but the system discussed cannot be compared to the UIBI or even smart of voltage controlled battery isolators. As I suspected, the complainer used an IGN and manually switched relay, hence in all likelihood their problems - their "current surges" do not occur with UIBIs & smarts.
Ah - the same ol' same old. It simply enforces what I wrote on page 1 of this thread. Plus the person involved now has battery voltage problems. Der! What else is new? That's an old problem with well known solutions - though it's a pity I wasn't here back in 2005. (Gawd - imagine the extra GBytes and boredom of my replies with an extra 4 years!!)