[T3] Keith's T4 Charging Dilemma

[Keith Park]

Well, another observation.
Drove it home from camp on Sunday, but before dark this time.
Startup it kept 14v even at idle, wandered down to 13.9 at times but held
right around 14V for a half hour or so on the secondary roads till I got on
the interstate, then after 8 minutes it went down to 13.6 where it stayed
for the rest of the hour home.  No headlight use.

Hmmmm....

Keith


Topnotch Restorations
topnotch at nycap.rr.com
http://www.topnotchresto.com
71 Squareback  "Hothe"
65 Notchback  "El Baja Rojo"
93 RX7  "Redstur"
13 Subaru Outback "Blendin"
 
-----Original Message-----
From: type3-vwtype3.org [mailto:type3-vwtype3.org-bounces at lists.vwtype3.org]
On Behalf Of Jim Adney
Sent: Friday, May 29, 2020 10:44 AM
To: type3 at vwtype3.org
Subject: [T3] Keith's T4 Charging Dilemma

I've relabeled this thread, since this topic seems to have hijacked the
original 
thread.

Keith,

And yet, we both know that there's still an undiagnosed problem. I have 3 
suggestions:

1) I have a nice little Hall Effect "amp clamp" that will drive any DVM and 
does DC. If you have access to something like this, you could use it to
clamp 
around some of the possible "alternate" ground paths, to see if there 
happens to be current where there should not be. I'm thinking about the 
clutch and accelerator cables. If you do this, clamp around the cable AND 
housing together, so you get to see the sum of the currents in them. Of 
course there should not be any current in these cables, so if you find
current 
there, you are pointed toward the problem, and a possible solution.

For the most sensitivity, do this test with your headlights and wipers on.

If you want to borrow my clamp, that can be arranged, but I'll bet you have 
something like that available at GE.

2) Make a 3" test wire with male push-on connectors at each end. Pull the 
connector off the VR and connect one end of your test wire to the DF lead in

the connector. Connect your DVM across the battery so you can watch the 
voltage there while doing this test. Then, with the engine running, touch
the 
other end to each of the other terminals in turn. One of them will have no 
effect, the other will turn the alternator on full blast. This is called
"full 
fielding." Do this ONLY BRIEFLY! Don't overvoltage the FI brain! You only 
want to see if the alternator is capable of pushing the battery up above 14
V. 
If it can't, the alternator or the VR wiring harness is at fault.

Note that if the system has been running at low voltage for a long time, it 
may take some time to push the battery up above 14 V. You may also have 
to give the engine a little more rpm to get more output from the alternator.

3) There are 3 wires going from the VR to the alternator VR: D-, DF, and D+.

As a test, remove the existing D- and D+ wires from the VR connector, tape 
them off, and replace them with temporary wires that you've run directly to 
the battery + and - terminals. Since the D+ and D- wires are essentially 
voltage sense wires, I'll bet you will find that your system voltage now 
regulates above 14 V. (Assuming you got above 14 V in Test 2, above.)

This test may be confusing, because the return path for the field current
now 
depends on the ground path in the car, which is in question. This may or 
may not work, but I expect that it will, since the field current is only
about 
1/20 of the alternator output current.

Jim

On 28 May 2020 at 21:31, Keith Park wrote:

> Its possible that its a diode in the alternator, that was a new alternator
> when I built the engine because I never wanted to have to change it again,
> yea, its not coming out of there any time soon, with this setup you have
> to drop the heater box. its not the regulator and all the grounds are in
> place and fresh, this car has a beefed up harness for the additional
> electronics with a second fuse box, so grounds were beefed up too many
> years ago.


-- 
*******************************
Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
*******************************

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