Alternator Test Quick Question
 

Hey everyone,

I have a quick question, I know on gasoline powered cars that if you disconnect the battery and the engine/electrics die then the alternator is bad.

I dont see why this test wouldnt carry over to the diesel powered cars as well..minus the engine dieing (for obvious reasons)..but you never know.. I am just wondering.

I have my dad's SD here and I checked voltage at the battery, it was 13.6 when the car was running. We put on the headlamps, blower and a few other things and I disconnected the battery...everything turned off (minus the engine). I checked voltage across the disconnected battery terminal and ground..got nothing. I also tested the dist. block on the rail..got nothing.

Safe to say dead alt? correct?

Just thought I'd double check this with everyone...


Also: how is changing the alternator on a 126 617 compared to a 201 103? I've done the 201 a few times. Its a pain in the ass. I'd think the 617 is easier due to the belts and what not

Thanks,

Kris

NEVER disconnect the battery with the motor running, it can damage the alternator diesel or gas.

Leave the battery connected and check voltage with no load(lights off) should be almost 14V, then with a load will probably be about 13V. The voltage should also go up when you rev the motor to about 1500-2000 RPM.

You cant get 13.6 V at the battery with a dead alt. Bosch alts dont like having the battery removed when they are running. Its a good way to toast the regulator. I can speak with experience on that. Dont do it on any car. What is the real problem? If you have a problem with the voltage dropping back to say 12 V when you turn the head lights etc on with the engine revving over 1000rpm. The first thing I would look at is the lead from the alt to the battery, If you can take the back off the plug on the alt, you could test the alt output voltage, should be approx 13.6v. If a lot less, check the alt brushes. If they are good, then the alt needs looking at further.

Noted. I am curious though is there a reasoning behind this? I understand that the sudden change in voltage could damage some electronics such as computers and what not however there does not exist any in the SD.. I'm not questioning your advice just wishing to understand more.

I did test it at idle it was 13.6 roughly.

Further:

The problem originated when my dad tried to leave work today, he said that the glow plug light on the dash did not come on when he first put the key in. He turned it off and then it came on. Tried to start, and nothing happened. She cranked but wouldnt turn over.

So I dove into the gp system. GP's are all near 1.3 to 1.4 ohms. I swapped out the relay box with one from my other SD (stored for the winter) as I believed that the 80amp fuse might have a fracture in the metal. I couldnt find my spares and rather than risk breaking the fuse when swapping fuses with the other SD. I opted to just swap relays.

With the GP system back together, I had him turn the key on and I verified that the GP's were firing up.

So we were going to take it down to the Advance Auto to have them check the charging system but they changed their hours to 8pm instead of the usual 9pm.

I'll go run a few other load tests as suggested. I'll return with the results.

My apologies for the disconnect the battery when running test. I was unaware.

Will return shortly.

You may have damaged a perfectly good alternator by disconnecting it with the engine running! That so called test goes back to the 1940s when cars had generators, generators had no sensitive electronics in them and that was a semi reliable test, it only showed that the gen had SOME output,not that it was up to spec. With an alternator there are diodes in the alternator and more diodes and IC chips in the built in regulator,when you remove a battery cable with the engine running you can and most likely will get voltage spikes high enough to damage those components if at a slow idle you might get away with it, if you revved the engine up with the cable off its very likely you did some damage. I dont know how this so called test has hung on for so many years and couldnt even guess how many alternators and regulators have been ruined by it. Don

Alternator Check
 

here's my method, some will agree, some won't.
With car off, check battery voltage. Should be 13.4 to 13.6 <> on most good 12 volt batteries.
Start car. Check voltage at battery, should be about the same as car not running ( at idle ).
Run engine up to about 1800/2000 rpm's. Voltage at battery should go to around 14.2/14.4 . Shows that alternator is charging . Keep rpm's up, turn on lights and other high amperage items. Check voltage , should be able to maintain at least a 13.4 or so. Alternators do wear out, brushes can go but main problem is a diode that fails and will drain battery .
Hope you don't have to work on this in the cold we are having at present time.......

Thank you for the explanation. I appreciate it. I will pass it on.

Results from the various tests:

Battery - Car Off - 12.43v
Key On - Car Off - 11.65v - No GP Light On
Cranking Voltage - 10.4v
Started Idling - 13.3v -
Started Revving - 13.6v peak
Only Blower High @ Idle - 12.63v
Only Blower High @ Rev - 13.6v
Blower High + Lights @ Idle - 12.2v
Blower High + Lights @ Rev - 13.4v
Blower High + Lights + Rear Defrost @ Idle - 12.0v
Blower High + Lights + Rear Defrost @ Rev - 12.5v

So I am leaning towards maybe alternator is OK, maybe voltage regulator?

Also, the GP light would not come on, it did come back on after I turned the key on and off 3x..then it came on as per usual. I've not been able to repeat the situation where the light does not come on..However based on the voltages I suspect the GP's are running despite the light being on..

oldiesel,
You are correct. The regulator uses the voltage as a reference, when it gets a spike on it. it usually pops a transistor in the reg, you cant replace it as they are not discrete components, Part of an IC.

Approximatly twelve point seven five volts is a fully charged battery without the alternator running I believe. This is with letting the battery sit awhile probably.

There is a change I guess if the battery was read instantly after the engine was shut down it may still reflect what the actual chargeing voltage was. Be careful here.

My normal sequence was always to pop the hood with the car cold. Read the voltage at the terminals. Then start the car and check for the increased voltage to indicate the alternator was indeed charging. Check it out for youself.

James,
Can you get the cover off the plug into the back of the alt? need to check the output voltage of the alt (thick wires). The voltage at the battery is a bit low under load.
The fact that you had to turn on x3 to get the glow plugs to work suggests a connection problem.
With the load & revving, given the low battery voltage, I would expect the charge light to be glowing dimly.
I once had this type of problem, ended up I ran a new heavy wire from the plug to the battery, it fixed several other elec probs that sometimes occurred.

I believe the cover to the alt is off. I can see the regulator. Can I conduct this test at the dist block on the frame rail? That would be easier.

It did take x3 key turns to get the light to kick on for the glow plugs however I believe they were working prior to that, as the one time I had my dad turn the key on and he reported the light off I heard the relay click and verified voltage at the #1 GP..

Which tests would you like me to rerun measuring from the dist/alternator?

I also found this interesting read about how to test a battery:

Results of tests round #2 measured from alternator output:


Battery - Car Off - 12.28v
Key On - Car Off - 11.50v - No GP Light On
Glow Plugs verified to be running, voltage @ GP #1 ~11.05
Cranking Voltage - 10.4v
Started Idling - 13.14v -
Started Revving - 13.70v peak
Only Blower High @ Idle - 12.55v
Only Blower High @ Rev - 13.42v
Blower High + Lights @ Idle - 12.13v
Blower High + Lights @ Rev - 13.33v
Blower High + Lights + Rear Defrost @ Idle - 11.87v
Blower High + Lights + Rear Defrost @ Rev - 12.68v
Blower High + High Beams + Rear Defrost @ Idle - 11.69v
Blower High + High Beams + Rear Defrost @ Rev - 12.36v

It does not seem to cope well with loads. Not sure if thats an indicator of the battery or the alternator.

I have another SD, its battery is currently on trickle charge, it has not been driven since snow hit. (not a winter car)

Not coping with loads is a sign of the charge circuit not being up to spec. Until you have the output voltage at the back of the alt, you cant tell what is the cause.

Those measurement were conducted at the back of the alternator.

Sorry James, didnt see that.
looks like alt or reg has a problem. I would first take the reg out, 2 screws (Battery disconnected when doing this) & check the brushes, if they are good, not wonky or warn down to nearly nothing, then its the reg or the alt. You could try the reg out of your other car. If it still gives readings like these, then the alt should be replaced, you will probably get a new reg with the replacement alt.

When the Key is On and No Glow Plug light is on I would be curious to know if you are getting Voltage to the Glow Plugs? In the Glow positoin there should be no other current drawn but the Glow Plugs and the Clock.


Since the Battery voltage drops to 11.50 Volts it appeas that something; if not the Glow Plugs is drawing the current.


And, you said that the Glow Plug Light works sometimes and sometimes not. This makes me think that the Ignition Switch might be haveing a problem. However, I know of know way to test the switch.

Diesel911 see the line right below the one you highlighted in blue. I verified that the plugs were running, I also heard the relay click.

I've never taken the regulator out of one of these before, is it difficult? I assume it can be done on the car.

Should look something like this:

http://imgur.com/pZYdJ.jpg

maybe not as filed down as those are...

James, If you end up having to get another alt, chances are you can get a higher amp one. If you just need a reg, you may be able to get a higher amp one as well, as long as it fits. There is no difference with the alt's the higher amps come from different internal setting in the reg.

I'll go pull the one SD's regulator and snap a picture for you guys to see...

cant look at that link.
There are 2 screws holding the reg in. When you remove them, careful you dont drop them! PITA !!!
When you come to putting it back in, it can be a little fiddly, you need to put the reg in the space & then move it towards the middle of the alt to line the holes up for the screws, again its a PITA and screws can fall out. Or maybe my fingers are not as nimble as they used to be!
I will be away for the next 45 min.

Photos:

http://i98.photobucket.com/albums/l250/MafiaNicky/IMG_9423.jpg

http://i98.photobucket.com/albums/l250/MafiaNicky/IMG_9425.jpg

from a 1982 300SD (Green)

Removal was trivial.

I can only hope re-install is as decent.

I'll leave it out until I hear back from you. The car isnt going anywhere anytime soon.

havent gone out yet!
That reg's brushes look ok, the ones in my cars are a lot more warn. I think you may need to try the reg from your other car, if it doesnt improve things, another alt is required.

Alright so I should pull the regulator from my other SD and install it in the broken down one?

I'll try to repeat the tests and post back.

Higher amps are not a function of the voltage regulator exactly. The regulator adjusts the output voltage of the alternator in comparison with the variable output currrent. . I think I have this right.

The ability or lack of ability to deliver the current is more a function of the other components of the alternator.

One thing I did notice was an underpreforming alternator is suspected. I would first bring the cars battery up to a sitting static voltage of at least 12.5 volts by charging it first. Twelve point two eight volts is too low.

Otherwise the indicated voltage drop you see may be the alternator voltage sagging a little to bring up that semi depleted or defective battery. As the alternator is trying to deliver its maximum output it just may sag voltage wise a little in the process.

Remember you are now asking it to increase the charge substantially into the battery and at the same time deal with a fairly heavy drain. You may be demanding too much output as some of these alternators are just 55 amps.

Now if the battery cannot be charged up to at least 12.5 volts under static test after an external battery charge the battery is shot. That will drag the alternator down and can destroy it over time.

uhm...

well I kinda locked myself out of my house. Its cold outside. I went out to get a drink and check the battery charger on my SD in the garage. Then I went back in to get the light to do the work...and the door was locked..as well as every window and other door around my house.

Furthermore, the doorbell is useless, as is holding down the van's horn. I had an ingenious plan though: I was able to start up the one SD that I am working on...I was going to drive to my grandma's (about 1 mile away) and phone home..(my cell was in the basement) and tell my parents to unlock the door. However this plan was a failure as I couldn't figure out how to bypass the steering lock out. I was proud that I got the engine to run though.

What fun. Also, there is about a pound of oranges and grapefruit on my roof.

Needless to say I'll resume work on the SD tomorrow. I have a few other things to reconnect up (switch off vac line namely)

I ended up banging on the ceiling (my parents room is above the garage) with a 4 foot lead pipe. Impressively enough, I manage to break a wire for the garage door opener clean in half with the blunt end of the pipe (i had a coupler on it)....

This was one of my original thoughts. I was thinking about putting it on a 2-amp charge overnight... Would that be permissible? Or is that too long?

Must repair broken wire on garage door.

Barry,
The voltage regulator monitors the output voltage of the alt and attempts to keep it at a preset voltage. It does this by adjusting the voltage across the rotor coils. The difference with high amp regs is they are just able to give a higher voltage across the rotor coil. The low amp ones just reach a certain voltage and then flat line. The higher the primary voltage ( rotor coil) the higher the output of the alt.

James,
It wont hurt to put the battery on the charger over night. That wont fix your alt though.

No eight hours at two amps will not boil the battery. Almost just a heavy trickle charge. If after charging you do not see about 12.75 volts there may be an issue with that battery. Or you are still low on charge.

In fact if the transportation is available it might be nice to have a free test done on it with a good computorized battery checker tomorrow morning. At this point you have to be certain it is good or you may spend money and effort not needed.

The car not starting may have been as a result of low voltage earlier. The starter turns slower and the glow plugs do not get as hot as usual.

Or drive the whole car down to a place with a decent reputation for a charging circuit check. They will put a load on the alternator to force and read it's maximum output. Plus check the battery. Usually can be had free at many places in the states I am told. You may even get the printout and post the results on site.

Agreed. I dont believe it will fix it either. Atleast I'll be able to check if the batter holds charge and once its fully charged I'll retest to see Barry's comments apply. It never hurts to test and I've got time.

I'm debating on bringing the battery in to charge it. I dont really feel like leaving the hood open, especially if it snows. That way I can check it periodically.

Whats the worst that could happen? I get locked out...oh wait that did happen. haha. brb.

Yeah, thats the plan for tomorrow. I'll pull the battery and charge it up over night. Then tomorrow I'll pop the voltage regulator back in and take it down. Last time I got my 190E checked they gave me a nice printout.

I'll scan it in and post up.

Who knows, it could just be this battery is really low and my dad's driving habits could use a lot of power and not really give the battery much chance of recharging.

I have a 143amp alt in my 190, all the other cars are stock.

Just for fun reach down to the alternator pulley tomorrow morning. Grab on to the cooling fins just behind the pulley itself. Can you turn the pulley by hand? I assume you may have already checked this.

On occasion if loose the belt will not squeel. But alternator output will be substandard. You should never be able to turn that pully by hand. Remember
the transfer of several horsepower to the alternator are required at full alternator output.

Also try not to lock yourself out again this evening. If my wife and myself were your parents we might be then discussing how safe it was to let you out. Or I would be asking the wife if you were really one of mine.:D

All kidding aside it is nice to see you helping out your dad. I think you will get to the bottom of this pretty fast.

I checked the belts yesterday they seemed ok but I will look more into them and check again.

When I went to get the battery out, I grabbed a set of keys and my phone and made sure both the garage and side door were unlocked.

Always fun stuff.

Plans for tomorrow:
1) batt should be charged fully (according to research: roughly 12.66 volts see post #13)
2) reinstall voltage regulator
3) conduct full battery of tests as laid out in previous posts.
4) charging system test from the parts store

As always, I appreciate everyone's quick responses and helpful tips.

-Kris

Good luck James! Let us know what you find.

Well your still awake and in the house. :) I never trusted the deflection test. I found that a notorious subjective test that does not allow for glazing and wear etc over time. In otherwords it can fool anyone. A vee belt riding on it's bottom could be extremely tight by deflection and the pulley will still turn by hand for instance.

So I switched over to the pulley test. I do not think that can decieve anybody. Plus I was never able to describe the deflection methology properly to another person. The distance or span alone between pulleys has to be taken into the calculation. For example a half inch deflection with no applied
force vector standard is pointless. No two belt tensions would be identical.

The only time I use the deflection test is to try to acertain if the belt or belts are too tight and perhaps stressing the bearings.

I have also locked myself out on occassion. The wife preffered hatchback cars for awhile there. She was leaving the keys inside when locking the car. By leaving the hatchback unlocked she did not have to phone me to bring other keys.

You also might remember that famous one. The guys girlfriend was scratching at the locked bedroom door. He felt so bad he got up and let her out.:D Well time for bed I suppose.

Charged up battery overnight.
I turned off the charger at around 7am and let the battery sit until about 1040.
voltage read about 12.62volts

Results of Test Run:

Battery - Car Off - 12.62v
No GP Light On
Glow Plugs verified to be running, voltage @ GP #1
Started Idling - 13.3v -
Started Revving - 13.70v peak
Only Blower High @ Idle - 12.76v
Only Blower High @ Rev - 13.46v
Blower High + Lights @ Idle - 12.26v
Blower High + Lights @ Rev - 13.46v
Blower High + Lights + Rear Defrost @ Idle - 12.01v
Blower High + Lights + Rear Defrost @ Rev - 12.60v

To be done:
1) check belt using non-deflection methodology
2) drive down to parts store and test.

Observations:
1) its cold outside
2) the stupid timer I have didnt run the block heater
3) diesels do not enjoy starting at 14F,

Will scan the results from the test soon as I get one

It sounds to me like your charging system is working. If the battery doesn't hold a charge, I would suspect the battery is the problem.

just got back from Advance Auto...

slightly less detail than I had wished for but they said that the alternator was outputting fine and that the battery was low

Results:
http://imgur.com/ALD1P.jpg
sorry for the crap angle on the scan

alt cant be putting out full amps as it is not keeping up with lights /blower /defrost.
if it was me, I would try another regulator.

I agree with you...

I left the car sit outside w/ heater plugged in and I checked the batter voltage and it has dropped to 12.42v.

I will swap the regulators real quick and run my usual battery of tests.

Another thing the guy at Advance mention was that when I started the car the alternator wasn't putting anything out. Once the engine was revved a little bit the alternator started outputting normal voltage levels.

Is that normal operation? I've seen this in the past on my other SD as well. I've not been able to explain/repair. The other SD (the Gold SD) has a new alternator too.

Observation:
Different part number on the Gold SD's regulator: 1 197 311 022
Green SD's regulator: 1 197 311 023

Not sure what is different.

Test results were much more encouraging:

Battery - Car Off - 12.42v
No GP Light On
Key On - Car Off - 11.42
Glow Plugs verified to be running, voltage @ GP #1 - 11.07v
Started Idling - 13.9v -
Started Revving - 14.02v peak
Only Blower High @ Idle - 12.90v
Only Blower High @ Rev - 13.80v
Blower High + Lights @ Idle - 12.12v
Blower High + Lights @ Rev - 13.60v
Blower High + Lights + Rear Defrost @ Idle - 11.74v
Blower High + Lights + Rear Defrost @ Rev - 13.00v
Blower High + Brights + Rear Defrost @ Idle - 11.66v
Blower High + Brights + Rear Defrost @ Rev - 13.04v (this number climbed gradually the longer I held the engine at higher rpm)

It looks like a new voltage regulator is in order. This seemed to have been the problem.

If you guys agree, I'll most likely keep this 022 regulator in the Green SD and buy a new one for the Gold SD.

If at all possible one that will put out more. If not I'll find a 022 regulator.

Let me know what you think.

A brief search on some parts websites turned up 1197311028 when I entered either part number the 022 and the 023

one of those regs may be a 55amp , the other a 65amp. I would ask the place you are getting your reg from what are the details on each part number.
Given that you are not in a hurry, you could always pose the question to Phil on here at Fastlane. I cant buy from Fastlane as the wont ship outside of the USA.

It looks like the other reg has done the job. The climbing amps while revving indicates the battery is charging. only having to replace the reg is cheaper than an alt.
Good luck!!

I sent phil off an email.

I always believed that alternator power output was largely a function of stator/rotor coil.

My search across many websites leds me to the "updated" regulator: 1 197 311 028. Looks like between $20-$35 or so. Not bad at all.

One issue still remains: the fact that the GP light on the dash doesn't come on 100% of the time. Every time I've tested the GP system its passed without issue. Every time the key is turned, the box clicks and voltage appears at the plugs. I know its not the relay box because I've swapped the two SD's relay boxes.

You may note that initially, I had you running around testing to see if you had bad leads/connections. The light problem was one of the reasons for that. I do think you may still have a few gremlins in the electrics, we learn to live with them. You could spend days trying to find a bad connection, I sometimes do !!

Well I'd like to thank you for all your help on this project. I've never did much work with the voltage regulator unit now.

I'll make some notes in my records book and order up the replacement regulator for my Gold SD. I have quite a bit of updating to do on my records. Last entries were mid October. I keep pretty meticulous records. I have nearly every insurance and registration card for my Gold SD since it was purchased in 82.

Thanks Again!

Good luck to you James !!
I can skite at a Rotary meeting some time about how I helped a guy on the other side of the world fault find his electrics on a car that didnt even come to Australia ( we dont have turbos here).
Make sure you get the reg that gives you the highest output (amps) that you can fit to that alt.
You have just done a job that an auto elec would charge $$ to do & he would probably have just sold you a change over alt that you didnt need.

For experimenters:

http://www.peachparts.com/shopforum/forumdisplay.php?f=15