Two battery/altenator questions - PeachParts Mercedes-Benz Forum

TWeatherford · #1 11-01-2006, 11:12 PM

First off, a friend and I were jump starting another friends car, and he was wondering if the altenator was always running. I said that it does, but then he said he thought it wasn't, and was switched on and off by something, depending on if the battery needed charging or not. I have never heard of an "altenator controller" needing repacing, so my guess is it doesn't exist. Is an altenator running any time the engine is (of course it is turning, since it is on a belt)?

Secondly, how should my MB do as the power provider for a jumpstart? I tried, and couldn't get the other car to start. The other car wouldn't turn over fast enough, even when I let it charge for a few minutes and revved the engine. Then the friend in question #1 hooked up his oldsmobile, and it worked. Does a gasser have a bigger electrical system than a diesel MB?

t walgamuth · #2 11-01-2006, 11:16 PM

the alternator always spins but doesnt always generate. if the battery is full it just freewheels. i thnk the controler is generally called a regulator.

your benz has just as strong a system as a gasser. the lack of success must have been due to a poor connection on your jumper cables.

tom w

Nate · #3 11-01-2006, 11:32 PM

ok, for jump starting a vehicle, never put the negitive battery clamp on the dead battery terminal, it could blow up that battery. Hook it up to a ground (i've used strut mounting bolts, and engine blocks... whatevers handy)

make sure it sparks when u jiggle the connections, else u have no connection

I bet you had either ****ty cables, or a bad connection

voltage regulator is what regulates the voltage

~Nate

#4 11-01-2006, 11:43 PM

The alternator is always working. She battery starts the engine and the alternator supplies power for all the electrical devices. With the engine running, the battery only supplies energy if the alternator can't keep up with demand.

Hook up an inductive ammeter to the alternator output wire, there will always be some amperage coming out of it when the engine is running.

TWeatherford · #5 11-02-2006, 12:26 AM

Ok cool.

Some nutjob I worked for a while ago used to say to never hook to the negative battery on the jumpee car. But we jumped a lot of stuff on his place (he was dumb, always leaving lights on and generally breaking stuff, sent himself to the hospital once trying to light a fire with gasoline), and it would never work no matter what we hooked to. So I've always hooked to the negative anyway, because everything else he said was wrong. Maybe I'll stop. Oh yeah, the cables were pretty pathetic too, like 6 feet long and pretty small gauge. Someone borrowed mine a while ago...

Regulator! Thats the word I was looking for.

whunter · #6 11-02-2006, 12:33 AM

Quote:

Originally Posted by ForcedInduction

The alternator is always working. She battery starts the engine and the alternator supplies power for all the electrical devices. With the engine running, the battery only supplies energy if the alternator can't keep up with demand.

Hook up an inductive ammeter to the alternator output wire, there will always be some amperage coming out of it when the engine is running.

The newer vehicle charging systems draw so much power that it is very possible to drain the battery (running OE accessories) below ECU/PCM operating voltage while at idle = vehicle dies = jump start = massive fault codes = possible limp mode, depending upon which vehicle, and if the jump was done correctly.

While cruising at higher speed, the ECU/PCM commands alternator charging, only when required, to reduce alternator parasitic MPG losses.

I can not think of a 2006 model car or truck where the alternator function is not totally controlled by the ECU/PCM.

On the older models, they are correct, it charges all the time.

Have a great day.