Wilton, I think your voltages are OK. It's normal for a NEW battery to
be
somewhat discharged. It likely sat on the shelf for weeks between the
time
the electrolyte was added and the time you bought it. All lead-acid
batteries self-discharge. The fact you saw 14.2+ volts with a relatively
"topped up" battery (from the 300D) indicates descent alternator
function.
Lead-acid batteries die for a variety of reasons but chronic
undercharging
(or sitting without recharge) is the most common cause.
You generally cannot draw a conclusion from just the battery charging
voltage unless you also know the charge current or the battery state of
charge.
I don't have tech data all Bosch regulators. But here's what you should
see:
Phase 1: The alternator will put out the maximum charge current until
the
voltage reaches 14.2-14.4 volts. The RPM limits the maximimn current the
alternator can produce. With the engine idling, this may not be a lot of
current so the voltage could be anything between 12.5 volts and 14.4
volts.
If you rev the engine the alternator should produce more current and you
should see a higher voltage in this phase.
Phase 2: The battery is mostly charged and the alternator can produce
more
than enough current to get the voltage to 14.2-14.4 volts. Now the
regulator reduces the charge current so the voltage does not exceed the
preset 14.2-14.4 volts. If you drew a graph of current vs time you would
see the current tapering off asymptotically as the battery approaches
full
charge.
Plug-in battery maintainers and some AC chargers have a third phase where
the voltage drops down to about 13.8 volts (trickle charge) after the
battery is fully charged (defined as charged to the point the charge
current
below threshold at 14.x volts). I don't know if Bosch regulators do this
or
not. Because you don't drive 24 hours a day for days at a time, this
trickle mode isn't as important in an alternator.
-----Original Message-----
From: Mercedes [mailto:mercedes-boun...@okiebenz.com] On Behalf Of WILTON
Sent: Wednesday, May 29, 2013 5:02 PM
To: Mercedes Discussion List
Subject: Re: [MBZ] '91 350SDL not charging? - starter?
My thoughts, too, 'bout "charging" voltage. Shoulda called it "voltage
across bat terminals with engines at idle and no load on systems."
Didn't
chk bat V before starting and after running few minutes, but I suspect
both
bats are fully charged; SDL bat is new/never driven. I'll check V's
again
tomorrow before starting, running, run bat's down a bit with headlights
on
with engines off, then chk V for re-charge, etc. Not gonna mess with 'em
any more today.
SDL charging V was 14.27 yesterday with 300D battery in it after having
"tortured" that battery the day before trying to "jump" start SDL.
BTW, both start in the usual manner with just a touch of starter.
Wilt
----- Original Message -----
From: "Craig" <diese...@pisquared.net>
To: "Mercedes Discussion List" <mercedes@okiebenz.com>
Sent: Wednesday, May 29, 2013 4:15 PM
Subject: Re: [MBZ] '91 350SDL not charging? - starter?
On Wed, 29 May 2013 15:59:43 -0400 "WILTON" <wilt...@nc.rr.com> wrote:
Engines at idle.
The 300D voltage is very low.
The SDL voltage is a little low.
Craig
> On Wed, 29 May 2013 15:40:27 -0400 "WILTON" <wilt...@nc.rr.com>
> wrote:
>
>> 300D charging V now, with its "old" battery and after driving it on
>> 2
>> trips "around" town today = 13.10.
>> SDL charging V now (not driven since new battery yesterday) = 13.77.
>
> Are those voltages measured with the engine running (and preferably
> above idle)?
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