If id wanted to rig a voltage regulator in the car that would be able to keep the 14V that go to the ECU steady or at least steadier than what it is now when electrics are used in the car simultaneously, what would i be looking for?
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The regulator is supposed to provide steady voltage.
I soldered two diodes onto my regulator, so it makes a little over 15v at the alternator, and approx 14.7v at the battery.
Along with fat wire and relays, this gives me 14.6v at the fuel pump and approx 15v at the headlights.1995 RS2 on Alcohol (6.8sec 100-200km/h)
1994 80E Avant
1986 2L Golf 2 on Alcohol -
Agreed - I wouldn't worry - ECU monitors battery voltage... Has its own internal regulators and stuff.
Agree with Espen that big fat solid 14V onto the fuel pump is the way forward though... Thats on my job list.
If running halogen lights then the relayed 14V feed is also a great recommendation from our esteemed Norwegian friend with a fetish for Ethanol
Paul Nugent
Webmaster http://S2central.net
Administrator http://S2forum.com
1994 S2 Coupe ABY - aka Project Lazarus
2001 A6 allroad 2.5TDi - family tank
2003 S4 Avant 4.2 V8 - daily burble
Purveyor of HomeFries and Exclusive agent for Samco hose kits (S2/RS2)
There are only 10 kinds of people that understand binary - those that do, and those that don't
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Well im not worried about motronic. Im talking about VEMS.
reason for it is that since i can manage to get an absolute acceptable and non oscillating idle on slight load situations, it becomes quite difficult to manage to have that same thing on load (AC/lights/blinkers/heaters on etc). SO i figured that if there was a way to maintain OR reduce the fluctuations that VEMS sees, then less work would have to be done with manipulating the ISV valve through VEMS.
Would a system of relays on the cable tree that powers the ECU would be able to do the job? Those voltage regulators that plug to the battery are of no use i think. VEMS reads 14v of battery voltage on normal conditions.(same as shown on the gauge of the rs2). Gauge goes down to 12 when all electrics are on. I believe though that battery voltage,is still not much affected.So my aim would be to reduce the drop that VEMS sees.
Is that possible?Comment
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With all electrical consumers on, gauge will drop some, but not down to 12v. This means that your alternator is not able to charge the battery properly.
I seem to remember from your VAGCOM log that battery voltage dropped quite a bit under load?1995 RS2 on Alcohol (6.8sec 100-200km/h)
1994 80E Avant
1986 2L Golf 2 on AlcoholComment
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Stupid question time, how does the Motronic or VEMS compensate for engine load at idle? i.e. when you load up the alternator does it know about the load, or does it just watch the RPM's and try to regulate it. ...i guess the same question applies for AC.91CQ20v - Gone to a new home
93UR-S4 - The Magic Carpet
94S2Bus - The Emerald ExpressComment
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i had a look at the log, it seems that voltage does not seem to alter a lot on the ecu....Comment
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Motronic "knows" you're at idle from the throttle switch. At that point it tries to maintain idle RPM whatever the engine load by altering the air bypass valve that connects bypassing the throttle butterfly. So, no it doesn't know about alternator load directly, it just tries to maintain idle RPM. The same is true for manual A/C but on climate controlled versions the option exists for an A/C "on" signal to be sent to Motronic which ups the idle RPM to around 1100 I think, so you still get effective cooling when stuck in traffic.
JohnComment
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on my climate controlled rs2, that does not happen. When the AC comes on idle does not rise.it stays there but it does not drop at least not that much,as the ISV valve is working properly and everything is done nicely.
VEMS unfortunatelly does get up to 2V fluctuation when electrical systems are on all together,but most of the times,if it is just the fan kicking in, it is able to maintain things.So i believe that if i can reduce that fluctuation to the ECU voltage maybe the idle settings may be easier to set for all circomstancesComment
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The best way to do this would be to use a relay and take power directly from the battery.Comment
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I'd go with a 15V voltage regulator on the alternator and use a 12V zener clamp for the rails into VEMS if it doesn't protect itself from supply fluctuations... Then again - check with VEMS first !!!Paul Nugent
Webmaster http://S2central.net
Administrator http://S2forum.com
1994 S2 Coupe ABY - aka Project Lazarus
2001 A6 allroad 2.5TDi - family tank
2003 S4 Avant 4.2 V8 - daily burble
Purveyor of HomeFries and Exclusive agent for Samco hose kits (S2/RS2)
There are only 10 kinds of people that understand binary - those that do, and those that don'tComment
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Paul, You can't do it that way. You'd need some zener clamp to do that since in theory it would have to dump 3 volts (15-12) at 120 amps - that's some load and would give smoking wiring!
If you fed the ECU via a series resistor, you're back to poor regulation again.
You could feed the Vems via a 12 volt regulator but then you're back to the question of why bother.
JohnComment
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yes some more info on that would be nice,
but i must say since then, my idle configuration has altered and i dont get any problems with idle anymore regardless of the voltage drop. In practice i have never used all electrics on the car at the same time, and so with a good PID control on idle changes things are handled well.
i would always be interested to find a way to get steadier voltage to the ECU thoughComment
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