Jim bailey - 928 International

Often this ..."I've charged up the battery a number of times," is enough to kill most batteries which on average only last about 2 1/2 years anyway ! The alternator should put out about 13.8 volts when charging drop back to 12 volts when not , much over 13.8 will cook the battery boil off the fluid.

BrianG

Ok.... here's a new twist on a battery problem.

Battery is about 2 months old... didn't have a problem with it until last week.

Went to start the car after it had sat for a week without running..... one half hearted turn and then clickety-clikitey....

Jump started the car off a good battery jumpered to chassis gnd and the engine compartment jumper terminal. Started fine / ran fine all day. Re-started as required all day.

Failed to start the next morning....... same symptoms.

Attached battery charger........ saw 20 amps charging flow immediately. Charge current dropped to 12 amps within 4 hours but did not fall further over night.

In the morning the charger was hot (no surprize) but the battery was not. Battery water level not substantially different after overnite charge session.

Usually, I have noted that charge current can be high at charge outset but usually falls rapidly ( in a couple of hours - tops) to less than 2 amps and then drops to essentially 0 overnight.

Took car to service facility...... tester reads "battery good - needs charging".

I have never seen this kind of issue with a battery.

I fear what the alternator is doing to itself if the battery charger is seeing this charge current.

MGW-Fla

I just replaced the battery in my '85 yesterday with the Autozone Duralast 850cca/1000ca battery for $70 with core trade in. Cranked right up. The 20-22 month old Interstate battery that the po installed only had a brief blip the other week but still started up just fine. Before that, no other hints of it failing. Over the years it seems rare that I've gotten a battery to last more than a few years, no matter what the vehicle or the battery.

Also interesting reading the post from back in April about batteries for our sharks. The Interstate 850/1000 costs $115; the Autozone/Duralast cost me $70; Walmart has one for $50(but I couldnt locate a store that carried one). All three are apparently made by Johnson(sp?) & are pretty much the same battery other than the label & the price tag! Even the salesman at Autozone said as much. One other interesting thing was that the Autozone I got mine from had four on the shelf!! Must fit some other german car other than a 928 for them to carry that many in stock!

heinrich

Wellllll..... mmmayyyyyybe ...... My FS Bronco runs a very consistent 15.1/2V when charging.

Alan

Dont worry too much about the alternator - it doesn't really care what the charging current is...

The alternator just sees a total load current - part of that goes to charging. It could easily sustain 40 A of charging under normal run conditions - and when it can't you see this by its output voltage dropping - which reduces the current directly (even more so with charging current).

However on a regular charger (if its well regulated) you should never see
as much as 20A sustained for long periods - thats odd.

BTW - if your battery seems totally dead - don't use a battery charger as you described with the battery connected - pull the ground strap and charge the battery disconnected... whan batteries go bad - you don't know what the battery charger voltage may end up being - they aren't designed to be used open loop and who knows with a dead battery (risk to ECU's etc).

Seems your battery has been damaged - quite possibly by repeated deep discharge cycles... even in 2 months apparently (!) you should test your parasitic leakage current - it may just be too high. Also after charging have the battery load tested at a good store (take your warranty!)

Alan

Alan

Jim - I dont know where you get this...? the alternator has no idea if its charging the battery or not... it just tries to put out its regulated voltage at all times. It will struggle to do this at idle and its voltage may fall (just because it cant generate enough power). Otherwise there are some temperature related effects - but the voltage should be at the set point of the regulator +/- some tolerance (allowing for min/max loading effects).

On our cars this should be at about 13.8v (+/-) permanently.

As H points out some other cars use a different set point - some as high as 14.5v deliberately (15.1 is a bit high but...) - using the same generic batteries means they are far higher stressed on these cars and will recharge at faster rates.

What boils the fluid is a very high charging current - certainly related to voltage - but also at least equally to battery health and the degree of routine dscharge that is happening between charging cycles. Deep discharge & rapid recharging (on or off the car) kills batties fast!

Alan

BrianG

Thanks for that.... I don't really want to replace that little unit!



Yes... I don't get it either. It is particularly odd in that the battery liquid was not even bubbling notably (electrolysis or boiling), and the battery did not get warm as one might expect with a shorted cell.

Indeed... I pulled the gnd strap prior to charging

I left the charger on another night, and this morning the charge rate was down to essentially 0 and the "battery charged" idiot light was on. It had still been charging at over 15 amps after the first 4 hours of last evening.

I will check for stand-by power consumption. I know that the alarm and clock use some power, but I have no idea about what stand-by current draw is appropriate for our cars. Has anyone seen any service manual reference to this value?

Alan

There isn't much documentation on it. Ideally it should be about 15mA, (and that is doable) but anything less than about 50mA won't give you any real issues for a car thats driven regularly (say weekly). The battery is ~75Ah so 50mA would give you 375 hours to a 75% remaining charge level - that's still well over 2 weeks.

Alan

BrianG

Thanks, Alan.... I'll look for numbers in this range.

Bill Ball

Brian: Wiggle the posts on the battery while you measure the voltage. I had a new battery in one of my other cars that worked erratically but tested fine. I put some torque on the battery posts, and it failed the test.

Also, I'm a fan of the Autozone battery. Mine is getting on 5 years.

Alan

Brian - also when they test the battery - don't let them use the little handheld tester - that is only a rudimentary check - you need the big load tester.

I once took in a battery under warranty that I knew was bad - one cell totally dead - they guy at the store with the handheld tester told me it was fine and just needed charging.. The voltage was an obvious give away anyway - but the unit still said "OK- needs charging" I told him he was nuts and demanded the full test - it crapped out almost immediately under load also..

Alan

sharkmeister85

I hate posting dumb questions, but since they're usually the only ones I have...How exactly do you test for "parasitic leakage" current?
Glenn

Bill Ball

Put a mutlimetter set for amperage across the battery ground then pull the ground cable so the mutimeter now serves as the current path. Set the mutlimeter on the hatch floor so you can read it with the hatch closed. Close all the doors. Leave the pasenger window down - alternatively, you can jam something to depress the door pin on that side and leave the door open. In later models you need to wait for the fan temp monitoring circuit to time out, and that can take 45 minutes after the car was last run. Anyway, once you think the lights and other activity should be gone, look at the multimeter. It should read about 30ma. Anything more is parasitic, although I don't get excited unless it's more than 50ma.

Expose the CE panel and start pulling fuses. You might get lucky and find the responsible circuit(s) right there. Then it's just a matter of identifying devices in the circuit(s) that could be drawing current. However, it may be a circuit still in the CE panel that is not fused there. You can identify that by pulling the mutliwire plugs that are on the bottom of the CE panel. If you find a plug that is drawing, then you construct a jumper and jump the connections from the plug to the panel connector until you find the guilty party. Dave A found a power window circuit that way that fed a relay under the driver seat of a 91 S4. The relay would not release like it is supposed to once the ignition was off and the door was open and pulled 150ma all the time.

There are a few other circuits outside the CE, such as the direct feeds from the positive battery post to the alternator. You will see a bunch of smaller wires on the battery post that you can remove one at a time to isolate them as well.

There are some circuits fused outside the CE panel. The rear hatch motor, for example.

**************************
BTW, my first question after I bought my 928 was "where is the lug wrench supposed to be stored?" I had taken it out earlier that day and couldn't remember where from. I average a couple of questions like that per month.

Kevin in Atlanta

My 87 S4's voltage dropped to less than 10 out of the blue Thursday with no red warning light. Ran fine except the voltmeter registered as low as it could but will twitch when I use the turn signals. Drove home parked it.

It barely started Friday afternoon and the battery was unable to start the car late Friday night.

Put a charger on it for ten minutes or so and it started right up. Turn the car off and disconnect the charger and car won't start to the sound of the starter solenoid clicking.

Took some measurements:
Jump post at rest : 11.66 At idle: 11.57
Battery at rest: 11.68 At idle: 11.47
Cigar lighter at idle: 10.94

Battery is less than 2 years old. Bought from Advance Auto.

I think the battery is in need of replacement. I am charging the battery and will run past Advance Auto this morning.

Alan

I think you will find its the alternator that needs the most checking here - seems like you need at least a new regulator (poss. belt...?). The battery may be OK but you severly depleted it by not recharging it - so charge it up well and then take it in for a test.

When the car is running - the battery has very little to do with the voltage you see - that is all down to the alternator - unless its not playing at all... Now not getting any charge light warning here may mean you have just lost the exciter connection to the alternator somewhere OR just as likely that the regulator is totally dead...

Alan