Rebuilt alternator now charging intermittently
 

About five weeks ago I had my wrench install a rebuilt alternator that I had sitting on the shelf for about four years. I got it from a place called Eagle Auto Electric, which sells rebuilt and upgraded OE alternators on eBay. This one is 70 or 80A, I forget which.

Anyway, when we installed it and started the car, we noticed it did not want to charge until the motor was revved pretty high. I am aware that these voltage regulators don't 'excite' until 1200 rpms, but this took well over 2000 rpm to come to life. Anyway, it was charging fine so I put the hesitation down to the unit having been sitting a long time.

Shortly afterward I replaced the battery with a Maxx H8 unit from Wallymart.

All has been well until yesterday, when I did the glowplugs and left the trunk and driver's door open all day. When I went to crank it over to get the last of the air out of the lines, the battery died in about 5 seconds.

I boosted it, drove it, seemed okay. This morning it had very little grunt. Later I drove for half an hour doing errands and when I tried to restart it after the last stop, wouldn't even crank the motor over. By the weirdest of luck that stop had been to buy a booster pack, so I got it going with that.

Sat for a while revving it with just the parking lights on (was dark by now). Noticed the dash lights were very dim, I don't think any charging was happening. Suddenly they brightened up.

Drove for a while and noticed the lights had dimmed. Also they are dimming and brightening a bit with engine revs when parked, which is not something that should be happening with a new alt and regulator.

Looks to me like it's taking very high rpms to excite the regulator, so on short drives it isn't charging at all.

Measures 11.58v at the battery at idle and 11.8 when revved right now. Was not able to get it any higher even with revving it high.

Voltage regulator bad here, or....?

Many things could be causing this problem but I would first check the regulator and its brushes to see if the rebuilder forgot to put in a regulator with new brushes or if there was corrosion of some kind while the alternator sat on the shelf.

Jeremy

Well, buyer beware! Unless it's a reputable rebuilt from Bosch, I've become very leery.
My '82 240D came with a recently-installed, but dead, rebuilt alternator.
Then the replacement Mexican-rebuilt 240D Pep-Boys alternator started working intermittently after six months. Took it back, which of course when they tested it, worked just fine, so no refund or exchange. When I pulled the regulator, I found the armature slip-rings were badly mis-aligned and one of the brushes had worn into the gap between the two rings.
Meanwhile, a friend had given me a couple used Bosch Mercedes alternators. The one I installed on my 240D has been working perfectly for 5 years now.
The other, after a new regulator, has been working fine in my 300TD for 3 years!

Happy Motoring, Mark

Check for corrosion between the regulator and alternator housing. Ran into this on mine. A little clean up, and a dab of conductive grease have eliminated the problem.

what is the voltage at the battery with the car off?
you could have a stuck GP relay keeping the alt from charging the battery...

12.9

... 12.9! wow that's high. it should not be over 12.75... but when you turn on the key, the GP relay kicks on, dropping your voltage to around 10.6 then once you start the car, the relay should shut off, letting your alternator bring battery voltage back up. if the relay stays on, it'd take a big alternator to keep from discharging the battery.

Actually I rounded that off... it was 12.92. It had been on the charger for a few hours earlier in the evening. However, the charger indicated it wasn't done when I turned it off, said the battery was only at 90 percent (and was still pumping in 2.4A on a 12A charge setting).

If I take that car to work tomorrow, I will wait and listen for the relay to click off before I fire it up.

A fully charged new battery will float at ~13 Volts disconnected from the car but system voltage will gradually drop due to "phantom loads" (clock, radio memory, etc.) and, over the years, aging of the battery.

The preglow relay should click off after ~30 seconds. If it does not, it will not only eat the glow plugs but drain the battery, since the glow plugs draw more than the typical alternator can supply in typical driving.

Jeremy

Later you said battery voltage was 12.9v. Presumably after charging? (BTW, batteries do have high voltage for a short while immediately after charging). If voltage is 11.8v, regulator should allow battery to be charged and you should see something like 14.5V until regulator cuts out.

It does sound like the alternator is not charging, but why would this not happen until you ran battery dead? Also, why would the charge light not come on? If it doesn't come on when you first turn key on, that could be the problem. Burned bulb can cause charging problems. If regulator is bad, light should be on but very dim - probably only see it in dark.

I would first fully charge the battery, then do a load test on the battery. If you don't have a load tester, take the battery back to Walmart and have them check it. If the battery is good, then clean all terminals and ground and try again.

After that - back to regulator or alternator.

Last time I had an alternator problem, I just took original in and had it refurbished. We have a couple of places that do that in Kingston. I used a small shop Starter, Alternator,Generator,Rebuilt Starter, Rebuilt Alternator, Rebuilt Generator, Rebuilder,Auto Electric, Auto Electric Rebuilders. Worked out fine.

Good Luck with it.

Actually a few Members have bought higher amp Alternators from EagleElectric on this forum and others and this is the fist issue I have read where there was a problem with one they rebuilt.

If you just remove the Battery from the Charger and take the Voltage the Voltage will be higher then if you let it sit 30 minutes and take the Voltage.

If the Car Doors were open all day and the light were on you could have damaged you new Battery and that could cause the Alternator issues.

On the other End is the Alternator Electrical Connector nice and Clean and what conditions are the grounds and cables in.

Is the Alternator Pulley and Belts in order. Just because a Mechanic installed them does not mean there could not be a issue with that.

I appreciate all the input. I had hoped to look at it today but we have 40 mph wind gusts and intermittent rain so I'm not too keen on even opening the hood.

I don't think that having two courtesy lights on for ~6 hours should have drained a fresh battery to that extent. During the summer with the old battery installed I would be surprised if I didn't do exactly the same thing on several occasions.

The alternator was put in five weeks ago and there was no hint of any issue until now. I mention this as we have had some pretty lousy weather for the time of year, during that time, and there have been many days when I was driving relatively short trips with all the accessories on: headlights, wipers, blower working hard, rear defroster operating.

Had the alternator not been charging properly, I think it would have showed up then, even if only the starter turning more slowly -- and we have had very cold mornings as well.

I am going to follow up on all the suggestions, though it may now be a few days before I can do anything. For the moment I will be driving with the booster pack in the trunk.

Thanks

I use a simple voltmeter that plugs in the cigarette lighter in all my 84+ cars. Most are the $4 (on sale) LED lights one from Harbor Freight, but also have a $15 Eqquis w/ digital display from Amazon. The HF one has lights for engine off and engine on. Ideally 12.6 V off and 13.4 V on (alternator working). My 60's Mopars have an in-dash ammeter to monitor battery charge/discharge.

I also have a Black & Decker "smart" battery charger with a alternator function test. It doesn't measure output current, but simply looks for a sinusoidal voltage that indicates your alternator is active.

I also bought an H8 battery for my 85 300D (Duralast Gold). It fits fine and was cheaper than the factory "74 frame" (or such, forgot).

FYI
 

The RPM issue = it should be charging as low as 550 - 600 RPM if the correct SMALL pulley is on the alternator...

I find many older MB have had the alternators replaced with WRONG (Large) V-belt pulley's = causes low RPM and idle charge issues.

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