[T3] Battery

William Jahn willjahn975 at gmail.com
Mon Apr 15 18:29:09 PDT 2019

I used to get cars in when I was a tech that I could not find a draw and
took the battery out and let it sit over night and it was fully charged
then below 11 volts over night . On my 73 my voltage regulator would draw 5
mA not much so I got a new regulator . The old one offered 14.2 @2,000 RPM
the new on 13.97 @2,000 RPM if the battery is charged to 12,62 V then @
2,000 rpm I get 13.86 V . I find this odd , before it didn't seem to matter
the battery voltage it always charged 14.2 @2,000 . must be these new solid
state regulators. It does charge the battery fully it just seems odd to me
why it puts out a bit less.

On Fri, Apr 12, 2019 at 7:41 PM Jim Adney <jadney at vwtype3.org> wrote:

> On 12 Apr 2019 at 23:49, J. Jonik wrote:
> > Is there a way to check to find what, if anything, in a '71 Sqbk, might
> drain the battery in five or six days?    It was fully charged about a week
> ago...went for a nice drive with prospective buyer, but now, after sitting
> parked for most of a week, there's no cranking or anything.  Dashboard
> lights work.
> > Or is this just the battery's fault...easy to find out, I think, at
> local Auto Parts store?
> > But, just curious to know if something in the car could be draining the
> battery...and if there's a way to test to eliminate that question.
> There are 3 questions that you need to answer here. The first is,
> "Was the battery actually fully charged when I shut the car down?"
> The second is, "Was there something draining the battery while it was
> parked?" And the third is, "Is this battery any good?"
> It's easy to assume that the first answer must be yes, but that's not
> necessarily true. To answer that, you need to check your charging
> system, to make SURE that it's working correctly. The fact that the
> generator light went out when the engine started does not guarantee
> that the system is working.
> To check the charging system, you need a voltmeter and know how to
> use it. The system voltage needs to be up around 14 V whenever the
> engine is running at medium RPM or higher. At lower RPM the system
> voltage can sag as low as the mid 12s. If you never see the system
> voltage rise much above 13 V, something's wrong with the charging
> system. If it doesn't get above 14 V the battery won't ever get fully
> charged. The voltage must be above 13.5 V for the FI to operate
> correctly.
> To check for a drain while parked, you can leave the car parked with
> the battery ground strap disconnected. If the battery then stays
> charged, you may assume that disconnecting the ground strap
> eliminated some leakage current.
> Of course there's always the possibility that the battery is shot. If
> it seems to need a recharge after sitting unused for months, put it
> on a trickle charger for a week. In that time, it's voltage should
> slowly rise. Do NOT try to speed up this process by charging it at a
> higher current; that will damage the battery. If the battery voltage
> drops below 12 V after it's allowed to sit, disconnected, for a few
> days, it has a shorted cell and it's shot.
> Lots of FLAPS have the ability to test batteries to see if they are
> in decent condition, or at least if they are in a good charge state.
> I'm often skeptical about these tests, as they tend to be designed to
> sell batteries rather than actually tell you where the actual problem
> is.
> I have a charging system faq that I'll send you. If you're able to
> follow those more detailed instructions, that will allow you to check
> out your charging system and determine if it's working correctly.
> --
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
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