Why Fuse is not breaking but MCB is braking.

[Shivam Maury]

Hi,

As per attached circuit, trying to protect the circuit with zener diode(P6KE20A). But in that case when I connected 5A fuse in first circuit, it's blowing off but when I connected 2A or 6A MCB to it's tripping immediately. Also I am attaching DSO spike we captured.

Note:

1. We used multimeter as a ammeter but it's not reading because while blowing off the fuse spike only for 10 Micro second.
2. This kind of circuit is causing the to damage costly camera.

please give the suggestions how to prevent it.

 

[LittleInch]

Don't understand the question?

The diode appears to be doing what is supposed to be doing and sorting the supply so bit fuss and mcb will disconnect/blow.

Fuses can take a small amount of time to melt.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[che12345]

Mr. Shivam Maury (Electrical)(OP)7 Aug 23 06:57
".....As per attached circuit, trying to protect the circuit with zener diode(P6KE20A). But in that case when I connected 5A fuse in first circuit, it's blowing off but when I connected 2A or 6A MCB to it's tripping immediately...".
1. I also Don't understand the question? as Mr. LittleInch asked. Both of your test circuit are "incorrect?" to test the characteristics of the zener diode.
2. What is your problem? Are you facing problem that the circuit goes above a) 48Vdc or you want to limit the voltage to NOT exceeding 21Vdc ?
3. In general,
a) if the source is 48Vdc, but you to wish to prevent it exceeding 21Vdc, it is better to reduce the source voltage. It is incorrect to use the zener diode to clamp it down.
b) If the source is 48Vdc OK but you want to prevent it from exceeding 48Vdc, select a higher rated clamping voltage zener diode.
3.1 zener diodes are connected in parallel (NOT in series) with the - end connected to the + potential of the supply. In this way, there is NO current flow through it unless the voltage of the source > the min break down voltage.
Che Kuan Yau (Singapore)

 

[waross]

Try a ballast resistor.
Better yet, use a voltage regulator chip, followed by a Zener at a slightly higher rating, for safety, in the event that the voltage regulator chip fails.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[RRaghunath]

Dear Shivam,
The circuit creates a short across battery terminals, the moment you switch on.
This is because the zener diode rating is well below he voltage available across it.
It is good the fuse / MCB are operating, if not, you would end up with a battery blast.
The purpose of the circuit is not clear.