Drive with alternator cable unhooked? OK? - PeachParts Mercedes-Benz Forum

NoCalMer · #1 03-26-2006, 01:15 PM

I need to get a voltage regulator since mine went bad. It is overcharging my battery and already took out one headlight. I could smell it too driving. Don't want to drive it again with it charging battery since it could explode the battery and is dangerous.

Can I just unhook the terminal where it plugs into the voltage regulator on the alternator or is there a fuse or easier way? I realize my battery might not have enough charge to start again. I am sure I can get a few more starts out of it before I have to charge it. I just want to protect my electronics while I drive to get a voltage regulator.

Thanks

81Wagon · #2 03-26-2006, 01:46 PM

Unplug it at the alternator, there shouldn't be any problems.

pawoSD · #3 03-26-2006, 05:04 PM

You could probably go for quite a while with the alternator unplugged so long as its not real cold out or your driving at night....and leave the climate control and radio off too....I bet it'd run for a week of regular use (maybe less in the city because of brake lights/signals etc...but you could always put it in park at lights and get off the brakes to save power

For those of us with the afterglow relays from Bosch (like me) I'd probably be doomed after 4-5 starts...as it glows for a good 3-4 mins after its running, that'd eat the battery in no time.....

NoCalMer · #4 03-26-2006, 07:53 PM

I unhooked the alternator right above the voltage regulator and drove to get a voltage regulator with no problem. Got home and pulled the old voltage regulator one and it was worn out. Replaced it with a new one and it went in fine and was easiler to get at from underneath the car. I pulled the battery and cleaned the battery tray with a mix of warm water and baking soda to get rid of any battery acid that had came out. Check the battery water level and found it dry. Refilled the battery with distilled water and checked it with my battery charger and it tested fine with full charge.Installed the battery and car started this time without the battery lights illuminating after starting.

The battery was measuring 13.1V before I turned on the car and with it idling dropped to about 12.9V. When I reved the engine the voltage went up to about 13.7V and stayed there no at around 3K rpm. This was with radio and all lights on.

Looks like the voltage regulator was the problem. I will keep an eye on the battery to make sure it holds the charge.

Strife · #5 03-26-2006, 08:04 PM

I'm glad you recovered everything, but you really need to be aware that the battery will have a shortened lifetime after this experience. If you can spend the money and/or can't afford to be "surprised", I'd replace it.

imdavid28 · #6 04-05-2006, 09:47 PM

Dumb question time: Where is the regulator? Is it separate from the alternator? How much was the regulator? Was it easy to replace?

My alternator isn't producing a charge, but I checked the wires going to it and seen that two have battery voltage, one appears to be a grounded. Is this right?

Trying to avoid replacing the alternator. Would be nice to get away with this w/o spending $140...

Hit Man X · #7 04-05-2006, 10:39 PM

Quote:

Originally Posted by imdavid28

Dumb question time: Where is the regulator? Is it separate from the alternator? How much was the regulator? Was it easy to replace?

My alternator isn't producing a charge, but I checked the wires going to it and seen that two have battery voltage, one appears to be a grounded. Is this right?

Trying to avoid replacing the alternator. Would be nice to get away with this w/o spending $140...

Bolts to the back of the alt. I think mine was $22? Maybe 10min of your time to replace.

imdavid28 · #8 04-05-2006, 10:48 PM

Mmm... tasty. I will have to try it. Is it something you can buy off the shelf at Autozone, or do you have to order it?

pawoSD · #9 04-05-2006, 11:07 PM

Quote:

Originally Posted by NoCalMer

I pulled the battery and cleaned the battery tray with a mix of warm water and baking soda to get rid of any battery acid that had came out. Check the battery water level and found it dry. Refilled the battery with distilled water and checked it with my battery charger and it tested fine with full charge.

Looks like the voltage regulator was the problem. I will keep an eye on the battery to make sure it holds the charge.

Your using a battery that requires the adding of distilled water??

Its How Old??? I thought that era ended a long time ago....at least for car batteries!

Hit Man X · #10 04-05-2006, 11:42 PM

Quote:

Originally Posted by imdavid28

Mmm... tasty. I will have to try it. Is it something you can buy off the shelf at Autozone, or do you have to order it?

I picked mine up at O'Reilly, BorgWarner brand I think. Lifetime warranty.

Matt L · #11 04-06-2006, 08:44 AM

I know that this is an old thread, but note that running the alternator without a load (as with the output terminal disconnected) can burn out the diodes due to overvoltage (in reverse bias). The same is true of running the car with the battery disconnected, but in that case you risk the rest of the electronics in the car as well. The alternator can put out a lot of voltage if there's nothing to absorb the spikes.

vstech · #12 04-06-2006, 10:08 AM

if the voltage reg was bad, and overcharging the system, removing the power lead should kill the field in the alt, and any damage done would be repaired by replacing the regulator right?

and imdavid28 , if your alt. is not charging, take it with you to autozone or wherever and have them free test it. you may have bad brushes and a fine regulator.
good luck!
John

SD Blue · #13 04-06-2006, 10:56 AM

If power is disconnected at the terminals, there is no way the alternator can overvoltage or even produce voltage due to no field excitation.

The large rectifying diodes are in the alternator. When/If you take the alternator apart you will see a matrix with the diodes. Actually, an alternator is unbelievably easy to rebuild. It just takes time to round up all of the parts. Rebuild kit: 2 bearings, 4 diodes, voltage regulator Clean everything up, conformal coating on the diodes after replacement, put it back together and wala.

The only time you would run into a problem is if the alternator became too hot and caused windings to short.

imdavid28 · #14 04-06-2006, 01:39 PM

[QUOTE=SD Blue]If power is disconnected at the terminals, there is no way the alternator can overvoltage or even produce voltage due to no field excitation.[QUOTE]

So I had an EE explain this to me today. The battery acts like a capacitor (smoothing out the signal) when its running as well as providing a reference voltage for the regulator. You can run the car without the battery and it will still produce a voltage, but it is possible for it to wander off since there is no reference (from my understanding of what he said anyway...)

I been to the part store twice in the past 24 hours and keep forgeting to bring it in and let them test it. Third time is the charm.

imdavid28 · #15 04-06-2006, 09:46 PM

Ok, I ordered the regulator today from mercedesshop, and was messing around with my alternator, thinking of tearing it down, pokeing around, sand blast it, etc. when i realized that the capacitor mounted to the back was not pluged in. Would this cause it not to work?