Diagnosing charging problem

[mark schofield]

Gil Bourcier wrote:


> Taka,
> It sounds like you have a draw issue rather than a charging problem.
Quick
> way to test is to run your multimeter between the negative battery cable
(red
> probe from meter) and the negative pole of the battery (black probe from
> meter).  get a reading as to what is the norm, the pull fuses one by one
> until you see the reading jump some and stay.  The circuit you pulled the
> fuse from is the culprit.

I've only just re-joined the list so I haven't seen the earlier postings on
this subject but it may be similar to an ongoing  flat battery problem I
have been having with a 1987 200. Leave the car a day or three and the
battery is flat. Putting a meter in the circuit indicated an intermittent
draw of either 0.9A or 1.6A (it varies) for a few seconds before settling
back to negligible (ignition off).

Pulling the fuses didn't do the trick or identify the cause because it only
happens sometimes.....

The air-con has never worked properly on this vehicle in the 3 years I've
had it (yeah, I know that's a bit slack) but last summer it developed a
tick-tick from what I guess is a relay or ratchet mechanism in the flap
control box at the left-hand corner of the dash (RHD) and I could no longer
adjust the heat output. Kind of annoying so I disconnected it. I understand
the climate-control box is not the most reliable unit that was ever designed
so on the off chance that the fault was down to a dry-joint and might have
gone away I re-connected the flap control-box and went back to the
tick-tick...... And then the flat battery problem started. I've since
disconnected the flap control-box once more and have not had any more
problems with flat batteries since.

I can't say for certain if the problems are related but I do know that there
are a lot of different electronic units on these vehicles which have to draw
a small current at all times (e.g. clock, computer) because they contain
electronic memories. There may then be a possibility that a malfunctioning
unit may be trying to drive something that consumes enough power to drain
the battery but not enough to be detected (no heat or smoke) even when the
ignition is off. For example, if the electric seats are out of position on
my vehicle (with reference to the last 'saved' position) then each time the
battery is re-connected the draw goes up to about 6A as they 'hunt' for the
correct position. (My meter's only good to 10A and unfused on this range so
I don't make a permanent connection less I turn the ignition switch too
far).
I suggest if pulling fuses doesn't isolate an unwanted current draw then if
you should have any electronic systems for which you know the control units
are not 100% reliable, then try disconnecting them as well.

Mark Schofield
1987 200 Avant