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  #1  
Old 12-09-2003, 07:00 PM
Wayne2970
 
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Location: Grand Prairie, Texas
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what is an overload protection relay

1992 300 D


I am told that I need to replace the overload protection relay!

What is it?
What does it do ?
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  #2  
Old 12-09-2003, 08:34 PM
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Actually, its the overvoltage protection relay, and it keeps voltage spikes or a runaway alternator from frying the electronics. Cuts the voltage to all sensitive circuits when the voltage gets too high.

It also tends to get "tired" and cut the current when it's not supposed to as well, probably the reason you need to replace it. Usually just cracked solder joints, but can also be burned contacts.

Peter
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  #3  
Old 12-09-2003, 08:54 PM
Wayne2970
 
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is there a way to test the relay?
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  #4  
Old 12-10-2003, 12:00 PM
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Where are the W123 experts? I'm 90% certain your car doesn't have an OVP relay.
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  #5  
Old 12-10-2003, 12:47 PM
Wayne2970
 
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1992 300D is a 124 body...
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Old 12-10-2003, 01:07 PM
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Oops. I read 82, not 92. Sorry about that. The OVP should be between the two firewalls on the passenger's side, and should have a fuse on the top of it. I've never seen a procedure for testing, most people just replace them.
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  #7  
Old 12-10-2003, 01:16 PM
Wayne2970
 
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thanks for the reply...the dealer wants 135.00 I ckd fastlane there price was more reasonable
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  #8  
Old 12-10-2003, 05:00 PM
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Testing procedure is thump it with the handle of a screwdriver and see if it starts working again! When it fails the ABS light will always come on and the engine may run rough, stall when D is selected or become hard to start when hot.

But seriously, you can open them up and re-solder all the pcb joints - it worked for me and the car ran fine for another 2 years before I sold it.
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  #9  
Old 12-10-2003, 05:22 PM
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what is an overload protection relay hmmmmmm

its a belt with a buzzer in the buckle.

If you eat too much it goes off BUZZZZZZZZZZZZZz
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  #10  
Old 12-10-2003, 05:58 PM
Wayne2970
 
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69.00 from the dealer with my MB club card....yahoo

The fuse is good...and now I broke the plastic shield between the battery and the firewall....
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  #11  
Old 12-11-2003, 09:09 AM
Wayne2970
 
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New Overload protection relay from Parkplace Midcities 69.00
self install saved 108.00
a happy wife...PRICELESS


power restored, I am assuming the relay does a alot mor than originally suspected.


Thanks for everyones input!
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  #12  
Old 11-12-2005, 08:54 PM
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Thumbs up Yes

Our friend the OVP keeps expensive electronics from turning into toast.
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  #13  
Old 11-12-2005, 09:30 PM
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Ovr

I just replaced mine awhile back...but before replaced my tach would fall down to nothing and it appeared that the turbocharger wasnt working. Darn lights on the cluster acted like a pinball machine. So I took the forums advice and replaced it with an OEM relay and sha...zam it worked...no more odd stuff has happened since... I cracked my plastic shield upon reinstallation also..oh well
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  #14  
Old 11-12-2005, 10:05 PM
Geezer
 
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Quote:
Originally Posted by wayne2970
What is it?
It is a voltage-sensitive relay that 'protects' voltage-sensitive electronics from voltage that is too high for them.
Quote:
Originally Posted by wayne2970
What does it do ?
It reacts to high voltage by energizing and shorting its positive lead to ground, thus melting a fuse and cutting off power to the protected electronics. The theory is that no voltage is better than too much voltage.

It is sometimes known as a 'crowbar' circuit, from the idea that you protect the circuit by throwing a crowbar across the incoming line, causing a short circuit that guarantees that the fuse melts and protects the circuit. After all, OFF is safe...

That is a method of preventing electronics developed before electonics coud withstand any voltage that the alternator can reasonably produce. For many cars the OVP is no longer needed.
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  #15  
Old 04-09-2008, 11:40 PM
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Is this my Overvoltage Protection Relay, I am working on my wifes 1993 190e 2.6? She is having cold start problems.






I thought it was suppose to look like this with 2 fuses instead of one, this is why I am asking.



Thank you.
Attached Thumbnails
what is an overload protection relay-2015403745aq5.jpg   what is an overload protection relay-mercedes016ci6.jpg   what is an overload protection relay-mercedes018nh6.jpg  
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Last edited by whunter; 12-29-2008 at 10:14 PM. Reason: attached pictures
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Old 04-09-2008, 11:40 PM
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