Alternator killing battery? 240d, strange issue - PeachParts Mercedes-Benz Forum

Schmanman · #1 04-23-2015, 11:21 AM

I have a 1983 240d and I did the Bosch Saab 9000 AL129x alternator swap for higher output. I also have brand new terminals, and a brand new 900 CCA battery in the car. For some reason, my battery still dies overnight. I ordered a new belt since this one is squeaking, but I'm wondering if it could be the alternator being wired in backwards. I had to cut the connector off that plugged into the old alternator and crimp on new connectors so I could attach to the terminals. there were two red wires and one blue wire. the small blue one I figured was to tell the alternator when and when not to charge the battery, but the two red wires are up in the air and I think I may have an issue there. I have heard that an alternator hooked up in reverse will kill a battery very quickly. Any help would be greatly appreciated.

Thanks!
Alex

vstech · #2 04-23-2015, 11:59 AM

the two red wires can be crimped together, and tied to the new alt output, but they should be replaced with a larger conductor to handle the increased output capabilities of the new alternator.

the small blue wire is the charge sense circuit, and it goes to the small terminal on the alt.

if your battery is dying... there could be a circuit drawing power with the ignition off and it will kill the battery.

hook an amp meter between Neg and chassis, with the battery cable off the battery, and start pulling fuses until the draw drops below 25milliamps...

Schmanman · #3 04-23-2015, 12:28 PM

Thank you! That was exactly the info I was hoping to hear. There is a small blade connector on the back of the alt as well. If the voltage regulator on the back is at 12:00, the bladed connector is underneath the hub in the center at about 6:00. what is its purpose?

http://www.autopartsapi.com/eEuroparts.com/images/parts/lg_1120d664-6338-4233-a514-9c5b21032cc2.jpg

barry12345 · #4 04-23-2015, 03:26 PM

Or disconnect the alternator overnight to establish if it is the culprit or not. Might be a leaky diode in there. Especially if problem only originated when you changed alternators.

barry12345 · #5 04-23-2015, 03:28 PM

Or disconnect the alternator overnight to establish if it is the culprit or not. Might be a leaky diode in there. Especially if problem only originated when you changed alternators.

I cannot think of any way you could hook up an alternator backwards basically.

Schmanman · #6 04-23-2015, 03:35 PM

I will try pulling the ground cable to test for draw when the car is off, if that doesn't give me any ideas, I will try removing the alternator cables overnight. I re-crimped the connectors, and I'm going to add a 4 gauge wire from the alt to the battery later today.

Alec300SD · #7 04-23-2015, 03:58 PM

Quote:

Originally Posted by Schmanman

Thank you! That was exactly the info I was hoping to hear. There is a small blade connector on the back of the alt as well. If the voltage regulator on the back is at 12:00, the bladed connector is underneath the hub in the center at about 6:00. what is its purpose?

Hi Schmanman,

I did the same upgrade to my 1978 W116 300SD on my DIY thread here: http://www.peachparts.com/shopforum/diesel-discussion/364297-diy-al129x-alternator-1978-w116-300sd.html

The spade connector built into the alternator housing is for the condenser (location "4" on the old style alternator and location "C" on the AL129X alternator) as shown on the thumbnail photo from my Post #5 on the jpeg link below:

http://www.peachparts.com/shopforum/attachments/diesel-discussion/128106d1426524009-diy-al129x-alternator-1978-w116-300sd-alternator-wiring.jpg

97 SL320 · #8 04-23-2015, 06:21 PM

Quote:

Originally Posted by Schmanman

For some reason, my battery still dies overnight.

Did you verify that the old alt was causing the battery to discharge?

SD Blue · #9 04-23-2015, 07:43 PM

If you connected the alternator backwards, the first thing you would notice is a lot of heat. And in some scenarios, a melted battery case. It doesn't take long.

My guess is either a bad grounding situation or a leaking diode.

It is easy enough to check with a multimeter across the battery. What are you getting DC volts? should be ~13 Vdc while running
AC volts? should be <100mVac while running

Schmanman · #10 04-24-2015, 12:30 PM

I put a belt about an inch shorter on my 240d last night, which was a terrible job since I had to unbolt the bottom of the alt so I could get enough slack to slip it over the pulley. it was a lot of work but it was worth it since I have a ton of adjustability left in the bracket now, whereas before it was maxxed out and still slipping before. I replaced both terminals, I also reconnected the wiring as was suggested and ran a 4 gauge wire from the alternator to the battery. the car starts nicer, all my lights are brighter, my aftermarket sound system is much sharper and has less distortion, and most importantly it doesn't die every time I drive it now! Thank you everyone for the help.

Also, I never took the condenser off the old alternator before I exchanged the core. it may sound dumb but how essential is it?

vstech · #11 04-24-2015, 01:25 PM

Quote:

Originally Posted by SD Blue

If you connected the alternator backwards, the first thing you would notice is a lot of heat. And in some scenarios, a melted battery case. It doesn't take long.

My guess is either a bad grounding situation or a leaking diode.

I was thinking this at first also... but I don't think it's the case.

Reversing the connections on the alternator would result in... nothing I think.
Reversing the BATTERY would result in lots of smoke, but I don't think anything would work if the alternator leads were switched. ..

barry12345 · #12 04-24-2015, 01:39 PM

I would expect if there is no static type of noise in your audio system present. It may be okay without a condenser. I doubt but do not know if the condenser is part of a buffer system for the voltage regulator but strongly suspect it is not.

Your last test is to read the voltage across the battery terminals with the engine running. Voltage between thirteen point two five volts and fourteen point two five is what I personally would like to have. This verifies the charging system and battery are probably okay. Higher voltage is overcharging the battery and lower is inadaquate output in general. Or the battery has issues.

I too have found that a few times you have to improvise to get a shorter belt on to allow the adjustment range to have adaquate adjustment scope left on belt driven accessories .

You pretty much want some range left as many new belts will require another adjustment not too long after they are installed. To avoid too much stress generally I set alternator belts up just so I cannot turn the cooling fins on the alternator by hand. If I can I feel the belt is too loose and needs further adjustment.

My method in my mind reduces the loading on the main engine pulley I hope. There have been many of these old diesels developing harmonic loose balancer problems over the years. Besides perhaps a design of not really being all that strong. Past experience has indicated to me it is perhaps engine impulse shock loadings that eventually may be doing the damage.

Many of my thoughts are unproven but I would never want to run these engines at more than two degrees of timing advance. The pulley to crankshaft failure if it occurs can do signifigent damage.

The addition power requirement of a larger alternator is not an issue at least in my mind for loading that pulley as I really feel it is not the causitive factor of the loose harmonic balancers particualrily. Really over tight belts I do avoid though. Your not setting guitar strings.

I still think it is almost impossible to hook up an alternator electrically backwards. Although some people have managed the same effect by installing there battery reversed. This could instantly burn up the diode pack in the alternator.

Old fashioned car electricals are not that complex. The newer the cars get the more cautions should be excercised.

For example if I have any car with a lot of electronic management systems on board. I never actuallly put a pair of jumper cables from another car on them and crank. You will pull it off usually but there will come the time you did not. Then you will never do it again.

Instead I just let the other cars electrical system sit and run until my battery is charged up enough. Then with those jumper cables removed the car will self start. Technically if the car was really advanced I might even take further precautions. For some reason a direct boosting and cranking has also resulted in damage to the boosting vehicles electronics.

I added the part on boosting as just general information from my own personal experiences. Plus the hope at least some may give it some consideration. It has of course nothing to do with the alternator in general unless you perhaps hook up the booster cables backwards. That is another thing you can live to have serious regrets about doing.

Also give consideration to the presence of very explosive gasses present when a battery is charging. One misteak on your part can be one too many. Lead acid batteries can go off like a small bomb. Fore warned is far better than experiencing a learning situation. Good fortune has enabled me to examine only the aftermath of some of the things I mention. Other than electronic failures I have personally been involved in with boosting the old fashioned way.

I even suspect I know why these electronic damages occur sometimes. It is better just to not allow them to happen. The boosting cars alternator goes into its highest charge rate so fast the voltage regulator does not regulate fast enough before a large voltage spike gets out. This is just a suspicion by me as well but is possible technically.

biopete · #13 04-24-2015, 01:56 PM

FYI Autozone seems to commonly stock belts that are too big. It happened to me twice. I checked on the parts store here and the dimensions were off by 5 mm. Always a good idea to check a reputable source for the correct size and verify.

Schmanman · #14 04-24-2015, 02:25 PM

Thank you! I may buy a new condenser to be on the safe side.
I got my original belt from an O'Rileys and it was slightly too long and much too wide. It became badly glazed within a week. I should try to return it since I was told it was correct and it was far from it. I wish these cars were built with a belt tensioner pulley instead of the original adjustments. There isn't much room for error.

vstech · #15 04-24-2015, 05:02 PM

Proper 19mm width is important also... Mc parts stores all carry 11.5mm... it makes a difference!