Did I charge the battery enough? - PeachParts Mercedes-Benz Forum

muleears · #1 12-22-2009, 06:49 AM

Had a no start situation after filling up at the fuel station the other day. That morn. I started the car (the 87 124) and drove 3 mi. to the fuel station. Left the lights on while I dispensed 10 gal. of D2. Climbed back in and no start, battery too low. After a jump, I drove to Advance Auto to buy a battery, but had them check the charging system first. They told me the batt. was OK, alternator not charging properly, "low voltage" and "battery needs charging" was the diagnosis. Without lights and accessories on the car seems OK. Took the car home and installed a voltage reg. I had on the parts shelf for just such an occasion. There was no noticable change in voltage across the batt. terminals (car running) after the reg. was installed. My cheap analog multimeter still showed around 12 volts, same as before the reg. install. I then drove the car 6 miles with everything on (lights, accessories) to test. Afterwards I turned the car off and left the lights on high beam for 5 min. I then attempted to start and the battery didn't have the juice to do it.

Did I not drive it far enough? I now realize I probably should have left the electric stuff off so the batt. could charge. Do the brushes on the VR need to be broken in before they operate at full capacity? Where do I go from here? I have the batt. on a 2 amp. charger and it will have been on about 21 hrs. before I get home from work to try again.

layback40 · #2 12-22-2009, 07:09 AM

20 hrs on a 2 amp charger should start it. Battery should be at least 1/2 charged.
I would be more worried about the lack of charging by the alternator.
Is the ignition light on the dash working? If its not, maybe thats the problem (blown globe).
If you disconnect the 3 alternator wires, the 2 thick ones should have 12 v
above earth on them. When the ignition is turned on there should be a voltage (maybe not as much as 12) on the thin wire. If not then maybe thats the problem. I assume you cleaned the brushes on the replacement regulator and you knew it to be good.

muleears · #3 12-22-2009, 07:18 AM

The replacement reg. was new. Alternator light on the dash works at startup but is not illuminated any other time. Shouldn't I get about 13.5 v. across the batt. terminals when the alt. is charging?

layback40 · #4 12-22-2009, 07:26 AM

If the alt is charging 13.5 could be expected. I would be concerned about connections first. When the engine is on a fast idle, is the voltage any different?
You need to make sure you have voltage at the alt end of the small wire with the ignition on. If you dont, the alt will not start charging.
when you put the new reg in did you make sure you sort of wiggled it in and didnt break the brushes?

layback40 · #5 12-22-2009, 07:30 AM

you may need to clean the connections for the 2 thick wires on the alt and inside the plug.

muleears · #6 12-22-2009, 07:51 AM

[QUOTE=
when you put the new reg in did you make sure you sort of wiggled it in and didnt break the brushes?[/QUOTE]

I was careful putting it in, I kinda stuck the brushes in first and wiggled it around until the mounting holes lined up.

This is all great advice. I won't be able to check anyting until after work, around 330 EST.

When I do get home should I drive it or just check the voltage after it starts?

junqueyardjim · #7 12-22-2009, 09:16 AM

Most of these hard start problems begin with the battery. How old is it? Also, a 2 amp charger is hardly worth the effort. For $15.00/$18.00, if not new then at a garage sale pick up a 10 or 15 amp charger with a 50 amp booster for starting. Then you will have a low cost tool worthy of the effort to plug it in and hook it up. Every diesel owner should have one.

muleears · #8 12-22-2009, 09:27 AM

Jim,
I beleive Santa is bringing me one!

Should I just drive and see if it charges? Battery age is unknown, it doesen't look terribly old, but I know that means nothing.

Graplr · #9 12-22-2009, 09:52 AM

Quote:

Originally Posted by muleears

Should I just drive and see if it charges? Battery age is unknown, it doesen't look terribly old, but I know that means nothing.

It wouldn't hurt to drive it for awhile but I don't think that will solve the problem as you are only getting 12ish volts you have a charging not a battery issue. If you do drive it make sure it is during the day and not rainy/snowy/cloudy where you will need the headlights. I drove my SD when the alternator went out for an hour and a half with no electricity. Then park it and turn it off at a place where you feel comfortable letting it sit for a bit (like your driveway).

Have you checked the belt tightness yet? Make sure you can't spin the alternator pulley by hand when the car is off.

Have you checked the connection at the back of the alternator? Craig had a charging problem with a bad plug as did I.

If you are only getting 12V from the alternator it seems the charging system not the battery is at fault. This could be any combination of the belt, the alternator itself, the voltage regulator, or the wiring connections. Since you replaced the voltage regulator I would check the belts and the wirings. If it doesn't improve the situation it seems you are in line for a new alternator. Buy a quality Bosch rebuild...you will only have to do the job once rather than a few times for a slightly cheaper version...ask me how I know.

Crazy_Nate · #10 12-22-2009, 10:20 AM

The voltage spec in the FSM (15-5010) says 13V-14.5V @ 3000RPM.

If it's above 14.5V
1. Replace regulator
2. Replace alternator if regulator is in order.

Below 13V
1. Rectify contact resistance at electrical connections of charging system
2. Perform diode test (in a section below).

I'm not sure you can do the diode tests with a multimeter (some tests for harmonics - determines whether to replace the regulator or alternator - if the harmonics are fine, you replace the regulator, if not, replace the alternator). There are scope pictures detailing what each case is in the FSM.

http://www.ps2cho.net/downloads/MB%20CD/W124/Index/602_603/15EngineElec.htm

Junkman · #11 12-22-2009, 11:16 AM

You really need to get a full charge. It is preferable to charge with a charger and not expect your alt to bring a drained battery up to full charge. You can either use your own charger or take the battery to a chain store. While at the store, have them load test the battery. My alternator output varies and was previously "rebuilt" locally. Diodes intermittently tested bad on the chain store machine. I'm going to have the guy that rebuilt it replace the diodes when I have a chance to pull the alternator.

Have any replacement alternator bench tested before leaving the store if you end up with any of the reman replacement alternators currently on the market. Only the alternator, regulator, battery & wiring are involves making repair relatively straight forward.

JHZR2 · #12 12-22-2009, 02:07 PM

All good ideas. Make sure everything is very clean.

most car batteries are 40-80Ah, so you are likely 50-100% charged after 21 hours.

The best way to tell is to apply a small load for a while (chargers are over 12.7V, and thus a "surface charge will form - indicating that your battery is >13V when it is not). Either install the battery to the car and turn on the dome light for a bit or try to run something 12V off the battery for 30 seconds.

At steady state, OCV for a fully charged battery is 12.72V or so. 12V is roughly "dead" if the battery has no load on it.

Id take a battery that shows full charge, and put it someplace where the temperature is consistent. Let it sit for a day or two, and check the voltage. It should not drop - if it is, you may have a slight internal short.

Id also put a multimeter inline with your positive cable (negative hooked to the battery) and check current. This will indicate if there is some sort of small short in the car. The reading shouldnt likely be more than 40mA, but verify that number as I may be incorrect.

Older MB alternators (good ones) are pretty low. With little load, it is easy to be far below 14V. Some battery chemistries want a charge at 14+V. Everything may be "fine" but mismatched enough that with time, degradation and now cold weather, it just does not work right...

turbobenz · #13 12-22-2009, 06:33 PM

I have a similar problem. My alt. is either getting weak or my load is too high. If I go for a 10 mile drive and blast highbeams, run the radio, have the blower on high and have my aux headlights on I usually wont have enough power to start. However, If i run the blower on medium and dont use highbeams when unneccessary I have plenty of power.

I myself carry a fully charged full size diesel battery in the trunk and set of heavy welding cables (i had normal cables and they melted after 15 seconds of cranking. I can usually get stranded and have my car started in about 2 minutes. Everyone with an amp hungry diesel should do this

layback40 · #14 12-22-2009, 07:48 PM

muleears,
You now have a ton of advice!! If you have had the chance to test the voltages on the wires that I suggested, let me know what you found.

Junkman · #15 12-22-2009, 08:16 PM

Quote:

Originally Posted by turbobenz

I myself carry a fully charged full size diesel battery in the trunk and set of heavy welding cables (i had normal cables and they melted after 15 seconds of cranking. I can usually get stranded and have my car started in about 2 minutes. Everyone with an amp hungry diesel should do this

Suit yourself. I'm just going to fix my charging system and make sure that I have a good battery. Wealthy people originally owned these cars AND would not put up with having to pop the hood for a jump from a battery stored where the golf clubs are supposed to be. Frequent non-start because of battery or charger = pp maintenance.