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Date:         Sat, 2 Sep 2000 22:00:30 MDT
Reply-To:     d t <tinkerman@USA.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         d t <tinkerman@USA.NET>
Comments: cc: David Marshall <vanagon@VOLKSWAGEN.ORG>
Content-Type: text/plain; charset=US-ASCII

I started a thread about this same subject a little while back. I tghink I can add from my experience.

David Marshall <vanagon@VOLKSWAGEN.ORG> wrote: > I looked over this site - makes perfect electrical sence.

Only partly. See following comments.

> I have Bosch 90A > alternators in both my T3s - one produces about 12.5 to 12.8 when driving > (Syncro) and the other makes 14V when driving (Westie). Same alternator > same regulator (part number) swapping regulators makes the voltage change.

I have tackled this same problem quite a bit with no ideal solution yet. My alternator used to undercharge my battery to just 13.4V (instead of at

least 13.8V), resulting in a depleted battery on long drives with A/C and

headlightsd on. Finally, my battery bit the dust due to sulphurization (a

process resulting from excessive discharge). I had a long argument with my car electrician (who sold me both my battery as well as a rejuvinated alternator during my ownership of my car). I used to complain my charging was low but he said it was OK. FInally, when my battery bit the dust I took out my digital voltmeter and

proved to him that the alternator REGULATOR was low. So as an interim solution he installed a 15V aftermarket regulator instead of the 13.8V one I had previously. Charging improved dramatically - actually, I started fearing about overcharge. I now get up to 14.6V on the battery, which is a bit on the high side for long drives but good for short daily drives to compensate for the large starter consumption.

> My Bosch supplier sells users adjustable voltage regulators - they are > about $50 CAD They really caution me on installing this regulator and > adjusting the voltage too high - they used 14.5V as a top level as anything > more than that will cook (literally) the battery.

What it will do is cause loss of battery acid due to boiling. You must check and topup if necessary to prevent battery dry-out. And yes, 14.5V is a bit too high. It should be 13.8 (AT THE BATTERY, not the alternator output) for long drives and 14.4V for short ones. Actually, you actually need a double level (i.e. "smart") regualtor. There are some devices available to do just that but they are expensive and not easily adaptable to the vanagon.

> I haven't really looked into how a voltage regulator for an alternator > works, but if it is the same regulator designed used in DC circuits

I'm quite sure it ISN'T. The alternator regulator is more like a voltage sensitive current controller (controlling the alternator output current, not voltage. The battery regulates that), while a DC regulator simply regulates it's output voltage. An alternator regulator operation is different IMO and relies also on the alternator output characteristics.

>(like the Vanagon speedometer)

yes, AFAIK this is a conventional 10V voltage regulator.

>it should be fairly simple and very inexpensive to > adjust the voltage.

This is not enough! The problem is that the standard BOSCH regulator has no REMOTE SENSE (i.e. cannot measure the actual battery voltage but rather the alternator output voltage, which is typically 0.6 higher. This is because the battery is located quite far from the alternator and a voltage drop is induced due to the wiring resistance (voltage drop = current x resistance). Actually, this voltage drop is not constant but is also affected by current consumption (especialy by heavy loads such as headlights and more so the A/C circuitry). I get as much as 0.7V difference between light load and heavy load. 0.7V is A LOT in terms of battery charge voltage.

>Usually a regulator has an input, output and ground. > Adding a diodes inline with the ground will adjust the voltage. > Unfortunately in 0.7V steps if you use silicone diodes, germanium diodes > will adjust it in 0.3V steps - I'll be looking into this in the near future > I am sure!

This is not a good solution.

> Anyhow to answer the question of will it hurt the alternator - no, not > unless you connect it incorrectly.

but it might hurt the battery.

> At 09:37 PM 01/09/2000 -0700, Todd Last wrote: > >That is what I was hoping someone with some electronics background might tell > >us.

I am one...

> >I have not done this - I just saw it and it piqued my curiosity (not always a > >good thing)

Curiosity killed the cat...:-)

> >> >I found this web page that outlines replacing the BOSCH internal voltage > >> >regulator with an external Ford until. This is said to cure the > >> >low-voltage output of the BOSCH alternator.

I don't understand how this solves the problem without adding remote sense capability. Without it, voltage regulation is a moving target depending on heavy loads (A/C, headlights). I have an aftermarket regulator that does this exactly (increased voltage) with no need for modifications.

> >> > > >> >I've noticed a few posts on the low voltage of the BOSCH alternators, > >> >does anyone think that this could solve the problem?

Nope. I'm still looking for a resonable cost solution (yes, I've seen those $300 solutions and definitely didn't like them...:-) to add remote voltage sensing to my system.

> >> >The web page is here: http://www.turbobricks.org/alternator_ext-reg.html

Very nice and interesting page, but not a solution IMO yet. I'll be glad to get pointers for a real remote-sense solution (copies via

p-mail are welcome, since I don't read every post to this very active list...).

Cheers, T-man

(P.S.: appologies if this response came rather late, as I'm practically swamped with incoming mail...)

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