Alternator Test Quick Question - Page 4 - PeachParts Mercedes-Benz Forum

JamesDean · #46 01-08-2010, 09:50 PM

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.

layback40 · #47 01-08-2010, 10:47 PM

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 !!

JamesDean · #48 01-08-2010, 10:57 PM

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!

layback40 · #49 01-08-2010, 11:08 PM

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.

Diesel911 · #50 01-09-2010, 12:46 AM

For experimenters:

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

pixelsblack009 · #51 01-09-2010, 09:16 AM

Hello,
I remember when I removed my dad's alternator when I had no idea what I was doing, anywhooo here's what I think,
is this alternator a stock 35 amp with 6 diodes and has a regulator at the back of the alternator thats slightly bigger (fater) that the slimier transistorized ones that require 3 additional diodes ?
I have heard that its bad and can cause dammage to the alternator to disconect the battery from it while its spinning,
having said that when I too was un aware here's what I noticed,
if you have the fatter regulator which does not come with a diode plate of 3 additional diodes, if you remove the ground from the battery while its spinning the electronics will die, (this alternator was working at the time of the test) and it was a 35 amp stock,
after we upgraded to a 50 amp alternator with a upgraded new diode plate with the 3 additional diodes, and the slimmer transistorized regulator, if you remove the ground or the whole battery for that matter while the alternator is spinning the electronics will NOT die the stator coil winding is in a different style on the transistorized one, so depending on what type of configuration you have pulling out the ground of the battery and seeing the electronics die does not mean that the alternator is broken,
someone correct me is this a safety feature perhaps if the terminal comes off when you are driving in the night the lights wont go off

so its a safety feature or perhaps they used it for petrol cars ????
its easy to check if your alternator is working and make sure your terminals are tight clean and conduct well and the warning light go off after you have started,
place a voltmeter or multimeter on the battery check the readings with the lights on high beam record them,
now start the car and check the current with the lights on high beam, the current should be higher that earlier 14 volts to 13.6 or so
and rew the engine and the readings should not go higher that 14.6 the should not climb with speed.

PS: both alternators are bosch the ones that come for benz originaly, this is not a modified alternator they probably used this transistorized style on newer cars or somthin but both transistorized slim ones and the normal fat ones both come stock on these cars
hope this helps jeremy brett

JamesDean · #52 01-12-2010, 05:14 PM

Well...

Apparently the glow plugs were all bad. I tested all of them and got 1.3-1.5Ohms at the start of all of this but the car was towed to the shop last night and they said the plugs were all bad..

Strange.

barry123400 · #53 01-12-2010, 05:30 PM

Not strange actually. Instead an indication the glow plugs may have been intermittently coming on causing all your apparent other problems. The dash glow plug light would not reflect that event.

I would run a wire from one glow plug to a light in the cabin for the next while to indicate when they are on. Otherwise you might start chasing your tail again or burn out the latest plugs as well.

Or perhaps the many cycles back to back when testing earlier might have done it. Either way I would run the wire and light just in case. This would either indicate the problem or clear the possibility of it.

Get your old plugs from the shop and test them for continuity if you can.

layback40 · #54 01-12-2010, 08:43 PM

Sounds like you have had a series of problems james. I never use ohms as a test for glow plugs. Best to take them out & connect them to the battery. That way you can make sure they glow red properly.

JamesDean · #55 01-12-2010, 08:56 PM

True. eh well at least the charging system is up to snuff and my other 126 get a new regulator which might fix a long standing issue I had with it.

My dad opted to leave the SD at the shop for them to change out the glow plugs. I told him I'd to do it but it was already up there...

At least the shop gets a good laugh at the temporary headlamp switch.

my123ca · #56 01-16-2010, 09:46 PM

Quote:

Originally Posted by oldiesel

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

Could your statement be true also if you have a known bad battery, jump start the car and run the lights with the alternator only? Will that destroy the regulator?

layback40 · #57 01-17-2010, 12:17 AM

If you have the battery in place even if it is low on charge, jump starting and then running the lights should not damage the alt/reg.
If you have no battery in the car when you jump start it, the alt should not start to generate power, the only way it could would be if there was any residual magnetism in the alt.
I have disconnected the alt on a stationary engine, used jumper leads to start it & run for days without a battery, no electrics.

JamesDean · #58 01-17-2010, 01:02 AM

So, the new regulator arrived, installed pretty easy.

Part number was 1 197 311 028

Had to clean up the glow plug relay, car wasnt starting otherwise.

Once i did she fired up and was putting out near 14 volts at idle.