volts too high/regulator mod success

scott thomas scott at dreamtheater.zzn.com
Sat Dec 14 14:34:32 EST 2002

Yeah, I don't think 15 volts is too bad, but I didn't want to chance
it. I was seeing 15.2 towards the end of last night. What I did was I
got the stock Bosch regulator...a supposed 14v model that's more like
13.6. That later number is essential to the reason why I used the
bosch, as opposed to the no name smooth back style that WILL put out
14.4 volts. Anyhow, I didn't have one of those, nor did I want to
spring for one, or the adjustable Volvo regulator because there is
a .69 cent mod that one could make to bring it up to 14.7-ish. You
need a 1n5402 diode. Cut the ground lug off the regulator and solder
this in its place. The anode(striped) goes to the ground rivet (it's
brass), the other to where the lug origianlly connected. Anyway, I
installed it this morning and VOILA! My regulator puts out a STABLE
14.81 volts, down to a stable 14.55 after warm. With all the
accessories (headlights, full a/c with compressor on, rear defog,
driving lights, brake lights, and stereo), I'm not seeing lower than
about 13.9-14.1 volts at idle. The noticeable thing is how stable the
output is, along with little sagging when the second stage fan comes
on. I don't have alot of the whine through am radio, either.

I posted the site yesterday, but if anyone wants to see it again, the
yahoo search is "Bosch voltage regulator mod". The site is a Detomaso
one. Apparently, the Panteras used our VW alternators.

Oh, the "essential" thing I spoke of is the fact that the diode adds
a voltage drop to the sensing circuit of the regulator. The site
says .49 volts, but I saw .895. So, using the no name may bring it up
too high at 14.3-14.4 +0.9, where the Bosch, at 13.6-13.8 + 0.9 will
get it to where I want it. Some other sites have mentioned how the
regulator can even add a higher amperage output to the Bosch
alternators because it seems that they were designed for the higher
output, but the regulators keep them too low.

I've seen the 200's voltmeter isn't too inaccurate, unless you go
outside the 14.4 volt range :)

As far as too high, I'm not sure. When I installed the alternator
with a "22 volt" reg on my previous 5000, the light came on after
15.5, but not sure where.

Huw, with your 15 volt regulator, how has battery life been? Do you
know where to source brushes from? I might use the 15 volt reg down
the road, if I install more electronics. Right now, I have the
110/115 amp alternator and two batteries, a setup I've been using for
years with no problem. According to some sites, the alternator, with
a higher output regulator can put out 10-20 more amperage. I can't
confirm this, though because I really wasn't in the mood to remove
the alternator again and then test it at the nonFLAPS.
---- Begin Original Message ----

From: Huw Powell <human747 at attbi.com>
Sent: Fri, 13 Dec 2002 21:06:35 -0500
To: scott thomas <scott at dreamtheater.zzn.com>
CC: quattro at audifans.com
Subject: Re: system volts too high?

> Yesterday, I replaced my 200's tired alternator with a known freshly
> rebuilt unit from a junkyard. The standard Bosch regulator puts out
> ~13.8 volts wheras the rebuilt unit on the car (200q) had a no name
> regulator and consistantly put out 14.5 volts, as confirmed by a
> separate voltmeter. Anyway, I decided to replace the brush assembly
> ... I had a new one in the package. I put it on
> and now voltage is going up to 14.9 at speed. Idle is about 14.7.
> Sometimes I do see 15v. I keep the headlights on to control the
> output. How high is too high?

14.7/15 volts sounds nice.  Anyone really know when these older cars
into over voltage trouble?

So long as you don't hear your battery boiling, I wouldn't worry too
much.  You might also want to "calibrate" your cars volt gauge by
checking with a decent multimeter - I suspect the pretty vanity gauges
we get are not exactly benchmarked at NASA - although having a volt
gauge read a volt or two high would not be very useful.

> Should I just stick with the 14 volt Bosch that was on it? I'm used
> to having the car with the higher output voltage regulator, so I
> don't know if the 13.6 volts is what I should be getting.

14 sounds good, too - and I suppose less worrisome than 15.  That
13-point-whatever level bugs me.

Remember, I'm sure you have seen that the 200 is much more known for
being able to decent job of recharging its battery than for having too
much alternator juice!

Huw Powell



---- End Original Message ----

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