Date: Mon, 26 Jun 2000 12:23:10 -0400
Reply-To: David Beierl <dbeierl@ibm.net>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ibm.net>
Subject: Re: How does one get a battery to charge up to where it is
supposed to??
In-Reply-To: <001901bfdf5c$18cc7120$7c0924cf@default>
Content-Type: text/plain; charset="us-ascii"; format=flowed
Huh -- we should have looked harder at the grounds.
Get ye to an electronics place and if you're not feeling stingy, get a
Fluke multimeter (or Hickock, or any of the high-priced spread). If you
*are* feeling stingy, get Radio Shack or whatever's handy. Look for these
specs:
Must have:
Measures DC volts down to single millivolts, ohms at least 2 megohms but
preferably 10 or more, amps down to single milliamps. (practically
universal -- all but cheapest should have 10Mohm range)
Has diode-check range (practically universal)
Accuracy -- +/-2% of *reading* +/-1 digit on DC is enough -- better is nice
but you pay for it. Not worth paying for better than 0.5%/1 digit. We
don't care about AC.
Input Impedance -- >/= 10 Megohms on DC (all but cheapest)
3 1/2 digit or better resolution (i.e. the display has 4 numbers but the
first only goes up to 1 or 2 or 3, depending on the meter. More is better,
but extra full digits are pointless for this use).
Autoranging is nice, but must be able to select manually as well.
Detachable probes with banana plugs, both for wear and to allow accessory
probe sets.
Choice: Common probes for volts/ohms/amps ranges, or separate. Depends on
your taste. Either way you will sooner or later hook the ammeter across a
voltage source and pop an internal fuse or worst case fry the meter (Ohms
ranges are usually protected against overvoltages).
Very Nice Things:
AC ranges will not respond to DC voltages (common, and you'll probably only
know by trying it).
Diode test function uses at least 3 volts, so you can check LEDs. (in
specs, or check an LED...)
"analog" faster-responding bar-graph display along with numbers -- the more
segments the better.
10-amp (DC) or greater range (probably not fused, be careful).
Even higher amp ranges (buy external shunt, or build your own. Or get
cheap "automotive" analog meter with 100-amp or higher range.)
Drop-resistant, with or without protective holster. ?Fluke? industrial
meters used to be rated for *one* 4-foot drop onto concrete.
Salt-water-resistant (for...er...*auxiliary* purposes -- good luck, you
won't find it).
Half-second or less cycle time (these meters average over a certain time,
the shorter the better).
Fast-responding continuity beeper that responds only to </= ten ohms. One
or two ohms would be even better. Some meters call 1000 ohms "continuity"
but it isn't in automotive work.
Peak reading/display hold
"Vari-Pitch" variable-frequency beeper that corresponds to reading on
display (wonderful, but only Hickock has it -- $$$)
Nice Things:
Slower-responding continuity beeper with whatever threshold you can get...
(practically universal)
Min/Max readings.
Delta readings
2-ohm range (rare and expensive).
20-ohm range (rare and somewhat expensive, not worth paying for).
Microamp range
Capacitor test (gives value, but not quality or breakdown under working
conditions)
Temperature readings and probe
Data logging output (if there's any chance of you using it).
Frequency counter -- not worth extra $$
Don't Care:
True RMS voltage -- AC applications only
Transistor checker
Decibel readings
High Frequency response (so-called AC voltmeter) -- $$$$ and you don't
care. Good for audio work, no need otherwise. Regular meters respond up
to several hundred Hz on AC, that's plenty.
Prolly lotsa other stuff... <g>
Ok, stop drooling and buy the thing. Get spare ammeter fuses (may be more
than one size) and look at accessory test lead sets. And get the
materials for a clip-lead about 20 feet long. Now, the van -- remember the
van?
Run the motor and make sure the regulator has kicked in. Measure voltage
from alternator B+ post to alternator case and note reading. Now measure
direct across battery *posts* and note that reading. I suspect you'll see
a volt or better difference. If very little difference, then alternator
problem -- bad regulator or bad diode. Drive to FLAPS and have them test
with handy rolling test machine.
Otherwise, set your meter on a range that reads millivolts, and go hunting
for the missing volt. Check from alternator case to negative battery post
for the total drop along the ground path -- if it's more than a tenth volt
or so, gotta find it. Alternator case to engine, engine to frame, frame to
battery ground lead, lead to terminal, terminal to battery post. All these
conductors are huge or short or both, so no need to worry about voltages
except at connections. Any time you see as much as ten millivolts, there's
at least a potential (potential, get it? I slay myself!!!)
problem. Bentley 97.6-97.9b will help a lot here.
Then B+ post to pos. battery post -- note the total and go looking. Here
you'll be getting noticeable drops along the length of wires, not much you
can do about that so measure them by sticking pins in the wire, add them up
and subtract from the total. The two wires from alternator to the post in
the wiring box on the firewall are in parallel and should have the same
drop across them (if not there's definitely a connection problem with one
or both) -- add this value in *once,* not twice. What's left is poor
connections -- post to terminal, terminal to wire. Find them and fix
them. Use the pin to test from terminal to wire... Wire path for the '85
is Alt B+ to pair of 12ga to wiring box, then 6ga to starter and 2-ga from
starter to battery. Watch out for hot terminals -- poor connections could
be dissipating several watts.
When you get done you should have practically no drops except along the wires.
If you want to get fancy, you'll improve charging by bringing an external
sense lead from the regulator to the battery plus terminal -- requires
bending an internal connection in the alternator so it doesn't touch the
regulator, then soldering a wire from regulator to battery. Let me know if
you want directions. But with clean connections you'll be as good as any
ordinary Vgon.
david
At 06:46 6/26/2000, Jonc wrote:
>In my 85 digijet Westy I have a new 90 amp alternator (10 months old) a
>new battery (41-4/810CA) 2 days old.. I just drove it 200 miles at 3500
>rpms... it never got above 12.9 volts and overnight it dropped to 12. with
>no load...
>
>I am under the impression, after reading the graduate course in batteries
>we have been generously given over the past week or so,... that a battery
>in good health should be charged to 13.something when all is right in the
>world... am I mistaken?? if not what should I do next... I am off on my
>annual long distance Westy cruise and would like to get everything in
>order before I get too far into the hinterlands...
>
>Please advise
David Beierl - Providence, RI
http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"
