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Old 11-28-2007, 08:00 PM
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Alternator Volts - 300SEL

How many volts does an alternator put out. My 300SEL, 1988 alternator outputs between 1 - 2 volts, the car starts very well with 13plus volts, but when voltage is 12 and below the car won't start. You crank and wipers come on. How does the iginition coil factor in this case? If this coil is bad will the car fail to start or start randomly.
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Old 11-28-2007, 09:50 PM
aam aam is offline
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Quote:
Originally Posted by jb300sel View Post
How many volts does an alternator put out. My 300SEL, 1988 alternator outputs between 1 - 2 volts, the car starts very well with 13plus volts, but when voltage is 12 and below the car won't start. You crank and wipers come on. How does the iginition coil factor in this case? If this coil is bad will the car fail to start or start randomly.

Need more info. to help you.
Check for louse connections on battery.
2) Age of it.
3) Do a volt drop test.
4) 12.6 v, normal. 13.5v, charging normal.
5) Connect a multimeter on battery have someone start the car while
you are looking at the meter under 10.5 car will not start.
6) Crank, wipers come on, there is a short somewhere.
Or volts are to low driving the modules crazy.
Regards,
aam.
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Old 11-28-2007, 09:52 PM
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Join Date: Dec 2006
Location: tacoma washington
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Quote:
Originally Posted by jb300sel View Post
How many volts does an alternator put out. My 300SEL, 1988 alternator outputs between 1 - 2 volts, the car starts very well with 13plus volts, but when voltage is 12 and below the car won't start. You crank and wipers come on. How does the iginition coil factor in this case? If this coil is bad will the car fail to start or start randomly.
Hey not an Mercedes mechanic but....Everything I know about a 12 volt alternator out put should be between 14.5 and 15.5 volts. Could be the alternator (some "REPUTABLE" auto parts stores can bench test them if you take it into them ) or could be the voltage regulator. Best test i know of........put your volt meter on the battery (read voltage) start the car and start reving the engine............the volt meter should read 14.5 to 15.5. That shows the charging system is working. Also a good test for alternators is ....start the engine....Disconnect the "positive battey cable.....if the car keeps running the alternator "should" be good. Why your wipers come on when cranking............Is it raining outside ? HA HA ! Good luck Dave Keep us posted.
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Old 11-28-2007, 10:28 PM
aam aam is offline
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Originally Posted by smallblock450sl View Post
Hey not an Mercedes mechanic but....Everything I know about a 12 volt alternator out put should be between 14.5 and 15.5 volts. Could be the alternator (some "REPUTABLE" auto parts stores can bench test them if you take it into them ) or could be the voltage regulator. Best test i know of........put your volt meter on the battery (read voltage) start the car and start reving the engine............the volt meter should read 14.5 to 15.5. That shows the charging system is working. Also a good test for alternators is ....start the engine....Disconnect the "positive battey cable.....if the car keeps running the alternator "should" be good. Why your wipers come on when cranking............Is it raining outside ? HA HA ! Good luck Dave Keep us posted.
Do not disconnect the Battery with engine on............................
You are going to be a very sorry man or woman.
You will fry expensive modules and the icing on the cake is, you are going to fry your gauge cluster.
Go a head make my day.
  #5  
Old 11-29-2007, 09:06 PM
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Location: tacoma washington
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alternater testing

Quote:
Originally Posted by aam View Post
Do not disconnect the Battery with engine on............................
You are going to be a very sorry man or woman.
You will fry expensive modules and the icing on the cake is, you are going to fry your gauge cluster.
Go a head make my day.
To all that read my post........Take AMM's advise and "DO not disconnect the battery while running"!!!!! I usually use a volt meter for electrical and charging diagnostics but I have used the positive battery cable disconect on both older and newer computer cars without damaging things. But I repeat!!!! If AMM says it will damage your car, PLEASE DONT DO IT !!!!!! I would never want you "To make my day" by damaging your car with info I gave you! Sorry for bad advise.
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