Over Voltage Protection Relay Setting?
 

Does anyone know at what voltage the OVP relay is supposed to protect at? The relay contains a zener diode that caps the voltage level to a certain specification. How would a person know if the zener was working? I know the setting is not adjustable. Is that voltage 12.5V, 13v, 14V?

1986 500SL
MAGV5

That's an Arthur Dalton question
 

AND here's his "Test" procedure for a Nine Pin OVP relay:
http://www.peachparts.com/shopforum/showthread.php?t=258907&highlight=OVP+voltage

(I assumed you wanted to know if the OVP was good or not?)

All the ADV. Search answers related to AD and OVP:
http://www.peachparts.com/shopforum/search.php?searchid=4292442

a zener relay doesn't cap, it works both ways...

and the OVP is VERY OVERRATED and typically not required but very often replaced for no reason at all, other than to garnish profit for the agency repairing your machine.....

In the wiring diagrams it seems more like a load-reduction relay than over-voltage however, it also serves to disconnect sensitive electronics from the alternator when the key is turned off, preventing them from exposure to a "load dump" which can be up to 60VDC reverse-polarity caused by an electric field collapsing in an alternator when switched off etc.

In electronic design for automotive, most electronics are protected from this load dump by MOVs, relays, zener diodes, etc. Basic spike supression or isolation.

Test it like a normal relay-array, the procedure has been outlined by Arthur fairly recently.

Thanks for weighing in cliff, and wrong as always.

Always required, without it several items such as the tachometer, ABS, ASR, and even the engine module will malfunction or not function.

Fortunately those of us who actually know Mercedes cars know enough to suspect the OVP relay when there are related malfunctions.

OK, here we go again. It's function is to blow the fuse if the voltage exceeds 22 or 23 volts. This happens when battery cables are reversed. The fuse protects the ECU and the ABC computer.

How does reverse polarity cause high voltage?