charging woes part IV 'The Wrath of Tim'

[tim eh?]

#$%@


I'm just about ready to torch this car.

Thanks to you who have made it this far, I feel like I have an army of help.

main symptoms: (part III covers the details if you have the time)
battery loses some charge (+/- 0.5V) overnight
I don't get enough charge with all the electricals (lights,heat,defrost) running and the system drops below 12.0V measured across terminals.

-battery is nearly new, has passed a load test (not sure what ca), and doesn't seem to lose charge by itself. (see below)
-alternator is third rebuilt in a row from a good parts store and all 3 have given the exact same results.

I am assuming the two problems are related. Upcoming third problem of winter.

Suspects I just ruled out:
It's not the foglight fix, at least not the foglight circuit which I suspected. I pulled the fuse and get the same poor charge.
Same with the rear defrost, I thought maybe something got bumped during a rear shock mount install. Pulled that fuse, same drop in charge.
I haven't looked behind the C pillars yet though.


What I'm focusing on now:

The Instrument Cluster
It is the early grey-back design so it could be whacky. The fuel guage is nutty and it has done the odd weird thing now and then like a full reset on the RPM guage while idling. I happen to have another one I'll swap in. (then I can maybe sell the car with only 200,000km on the odo... heh...) I wonder where there are other capacitors and such I can examine... maybe the stereo amp in the trunk?

The Battery

Maybe still a short in it?

Monday 10pm.... 12.60V.... dammit....


Maybe this alarm system?

we go way back... you've seen this pic already, and this one and this pic where you can just see the fix on the left. (i admit i used i slightly higher guage wire there i think... pretty sure the fix is good tho) That's the only place where any of that 5lb. pile of wire was spliced.

Where else can I check that you might wire an alarm?

Weird thing, just happened, maybe related... I mentioned already the running lights flicker ever so slightly when I reconnect the cable at the neg battery terminal. Well today when I first reconnected the battery the factory horn went off... first time this has ever happened on just connecting the battery. I say factory b/c there are aftermarket horns installed... the factory horn only goes off when the factory alarm (code on obc) is tripped... if I use the steering wheel pads I get some kind of pissy euro horn pair that hangs around the power steering reservoir.

Anyway, I'd rate this BS alarm as suspect #1 at the moment ... wtf?
Two alarms on this bitch? wonder what they were haulin'?


As I'm sure you can imagine any ideas, no matter how whacky, will be gratefully received, but I'd say it looks like I've had the same problem for a while now.
I am going to get some beer.

[russiankid]

Try unplugging both of the alarm modules and see what that does. I doubt your alarms are drawing so much current.

[bmwrp8]

hmm.. i remember in a thread waayy back that one of the causes of the discharge is the system that automatically increased spring pressure on the windshield wipers, to keep them firmly pressed on the glass. Sorry don't know what it's called. But some e34's does not have that, but if you do and that is the cause all you have to do is disconnect it.

[Ferret]

Okay, I'm no longer sure you've got a charging or battery problem.

What are your average temperatures over there at the moment?

12.6 volts is approximately 60-70% charge at 10-15 celcius, much higher percentage charge at lower temps.

I think you may have a ground or starter fault - I think we may be looking in the wrong place here. Your hard starting may be down to the start circuit. Let me work out the maths for the battery discharge rate @16mA

[Ferret]

Hmm,

Just been thinking about this...

Lets assume your battery is a 110A/hr battery (Please correct me here)

Your car is drawing ~20mA, which is 0.02A

110A/hr is the batteries rated capacity at cranking amps. Due to the internal resistance of the battery, and we err on the side of caution, assume 25% capacity at low currents. (~27A/hr)

This means that the battery should last 100%-~0% 27A/hr/0.02A=56 Days Meaning it should take two weeks for the car to chew through 25% of the batteries capacity.

Even if you've got an 85A/hr battery it'd take 11 days to eat 25% of the batteries power.

Your battery drain is good, you've got an electrical fault elsewhere that's causing the starter to turn slowly.

You will get a 2A surge as you reconnect the battery terminals - that's natural as all the capacitors in the vehicle charge up, they're in almost every electrical system in the car so they're going to surge at start up.

The way to get an accurate current reading is as follows.

Set your meter to the low current reading (the one that keeps blowing fuses) attach the battery +ve lead to the battery +ve terminal. While still attached, clip your meter to the bottom of the battery post and the lead, then disconnect the battery lead from the battery.

This means the initial surge is going through the battery lead and your meter then picks up the continuity as you disconnect the battery lead from the battery.

[Ross]

Ferret says

"Lets assume your battery is a 110A/hr battery (Please correct me here)

Your car is drawing ~20mA, which is 0.02A

110A/hr is the batteries rated capacity at cranking amps. Due to the internal resistance of the battery, and we err on the side of caution, assume 25% capacity at low currents. (~27A/hr)

This means that the battery should last 100%-~0% 27A/hr/0.02A=56 Days Meaning it should take two weeks for the car to chew through 25% of the batteries capacity.

Even if you've got an 85A/hr battery it'd take 11 days to eat 25% of the batteries power.

Your battery drain is good, you've got an electrical fault elsewhere that's causing the starter to turn slowly.

You will get a 2A surge as you reconnect the battery terminals - that's natural as all the capacitors in the vehicle charge up, they're in almost every electrical system in the car so they're going to surge at start up."

I'm calling you from now on.

[Ferret]

I'm calling you from now on.

Hrm, I may have got the internal resistance thing the wrong way around, but it's still erring on the side of caution that way around...

[Ross]

Tim,
I have taken pitty on you and you plight so am offering a grey back cluster for your use.
It had the caps replaced I was told.
Send me a PM. If your mounties don't have an issue at the border it's yours for shipping cost.

[tim eh?]

(blush) the battery is 65A/hr Moll .... model 91 here.
That is listed as stock size in my owners manual, and judging by the size of the battery tray I could upgrade to the 93R but not bigger.
I know it's not big but it ought to be adequate.

This morning 9am it reads 12.53V, it went down to around 0'C last night, high of 6'C today, that's pretty average this time of year (on the balmy side, actually).
It was working very well last winter, i was keeping a good eye on it for the first couple of months and it charged very well and was always full o' juice.

Hmmm... my starter motor is ugly, very ugly. But when the battery has a good charge it cranks like it is new.
Never had a reason to check it, not so much as a 'clik clik'. Is there a way I can test it for shorts or stuff?
I'm absolutely certain when it turns slowly it is due to low battery voltage.

I'm pretty sure my draw test is good - I did exactly what Ferret described for a while and was getting 16mA.
I just assumed my 0.02A readings were good after a while, because it's a pita to do.

However, a voltage drop is there when the battery is connected. If I leave it in there overnight there is always a loss but not a consistent one.
Must be an intermittent draw or a short somewhere with the 20mA draw readings being so consistent.

Ross, this is very generous, and pity to boot! awww - I think the cluster would be a direct swap no matter what it comes from as these clusters don't have a coding plug, it is located in the plugs that attach... will pm you. Even if it doesn't solve this problem I will put it to good use and experiment on it regarding my upcoming 299,960km problem (here under 'electronics'). I am suspecting connector D to it also (153-EWD)- connects to obc (inc. fuel reading...nutty and speed sensor - i think that whacky self test it did actually was on the speedo not the RPM meter, and the speedo is quirky once in a while)

Will check the wiper thing but I don't think I have it, i did replace the ds arm but there were no wires involved.

As far as the alarms... Bentley only has diagrams for Anti-theft systems from '91 models up, but my obc 'code' alarm functions.
Am I missing something? How can I disable mine?

couple other things...

-ground202, pretty much all the wiring and grounds I can find look as good as new.
My fuseboxes and all the relays look the same... not just good, everything looks new!
Some fuses have been replaced at some point... I will check what circuits they are on and have a look.

-the fps door sensor doesn't work. I get no error messages and no lights, it is as if the car sees it closed all the time.

-what does the 'unloader' relay do? I keep seeing it in wiring diagrams.



so... prime suspects today...

-starter motor
-instrument cluster

I will try not to set off the alarm horn at armistice.

[Tiger]

The common battery for E34 is group 49... the biggest battery. On 6 cylinders... they have group 92. However, Group 49 battery is cheaper.

Tim, go swap out that battery. If it is under warranty, you should be able to swap it out no charge or prorated.