Hi
I need to protect the load from voltages above about 13V whit out complex circuit. but in the market i can not find under 60V MOVs or TVS diods. What can i do? If i place a simple 12V zener diode it can burn the 10A glass fuse?
Thanks

 

So called TVS diodes can be applied for protection. For instance , 1.5KE15

 

So called TVS diodes can be applied for protection. For instance , 1.5KE15

TVS not exist too!

 

You can put two series-connected 30V MOVs and get almost the same performance as a single 60 volt MOV except the total resistance will be about twice what you would get with a single MOV.

 

You can put two series-connected 30V MOVs and get almost the same performance as a single 60 volt MOV except the total resistance will be about twice what you would get with a single MOV.

I need 14V mov!

 

I need 14V mov!

digikey search This link is for low voltage 5A to 60A. Most parts are surface mount because that is the way now days.
Digikey through hole 13-14V small parts.
I searched again for 14-15V at all currents, through hole. Larger parts.

 

A TVS will have a sharper and tighter tolerance breakdown voltage than MOV.
And they are available in low voltages, low enough to protect logic circuits.

 

What exactly is the load? Is it damaged by short-term high voltages (in microseconds) or small overvoltages that last long periods of time?

 

What exactly is the load? Is it damaged by short-term high voltages (in microseconds) or small overvoltages that last long periods of time?

it is a FTTH modem. 12V 1.5A

 

it is a FTTH modem. 12V 1.5A

Is it really bothered by voltages >13V? I'd be surprised if some 12V power supplies are that accurate.
If it is designed to be powered by a small switched-mode supply, then it will have enough protection to deal with the transients from a small switched-mode supply.

 

The first question is about the load, sort of answered, the second question is about the power source and what is anticipated to be protected against. If it is a "wall wart"power supply provided by the FTTH modem supplier then it will not need additional protection. If you are powering it from a battery with a mains connected charger, maybe, if the charger is one intended for an automotive starter battery.
Also, consider that most of those cable modems, including the fiber input ones, already have internal regulation and protection.

 

And, if you do install a fuse, a 10 amp device will only be tickled from the current available from a 1.5 amp supply.
The fuse capacity requires to be sized according to the circuit, they are not arbitrarily chosen.