lightning protection circuit for set top box

[borg]

nel

your idea is good , compared to a telephone line in case of stb the signal level is very low and frequency very high so my only concern will be if the series impedance and shunt capacitance of the protecting elements causing any interference during normal operation(PQ/SQ),if you dont see any such problems when using this then great, best of luck

 

[nel]

nel

your idea is good , compared to a telephone line in case of stb the signal level is very low and frequency very high so my only concern will be if the series impedance and shunt capacitance of the protecting elements causing any interference during normal operation(PQ/SQ),if you dont see any such problems when using this then great, best of luck

i have use the 0.010/k 250v/PPC to filter any interference during the operation (PQ/SQ) should this be not ok?
pl. reply.
thanks

 

[borg]

i meant the elements like ptc, mov, gd tube will have some resistance and capacitance,so this will be a filter and any filter will have insertion loss and could interact with its input and output
so any effects in the signal from lnb due to these,
that is what i meant not any "interference" that a capacitor will solve

above all are theoretical, just connect the protection ckt and check for yourself , if you dont see any problem in pq/sq then go ahead and use it

 

[nel]

The fuse or MOW won't protect you. Lighting will jump across a blown fuse. Do you know how many KV lighting is? The fuse is designed for 250V, and many MOV are designed for 1KV. That is well below the lighting voltage ability.

i also agree with you as at my work place we have a 11kv substation and i have seen if the 11kv fuse blow off and if the gap between the 2 fuse point are close by there is a sparking as you said and so i can imagine how much spark will be there in the case of lightning as it is a very high voltage. so pl. sugest what to do?

 

[nel]

i meant the elements like ptc, mov, gd tube will have some resistance and capacitance,so this will be a filter and any filter will have insertion loss and could interact with its input and output
so any effects in the signal from lnb due to these,
that is what i meant not any "interference" that a capacitor will solve

above all are theoretical, just connect the protection ckt and check for yourself , if you dont see any problem in pq/sq then go ahead and use it

ok i got you. i have connected this circuit on 19/11/10 and i did not find any signal drop after connecting it as i have purchased a new LG 26LE5300 led lcd tv and the PQ is very good before and after connecting the circuit.
thanks.

 

[cmsajith]

The fuse or MOW won't protect you. Lighting will jump across a blown fuse. Do you know how many KV lighting is? The fuse is designed for 250V, and many MOV are designed for 1KV. That is well below the lighting voltage ability.

Yes, for a high voltage air will also act as a medium if the contact points are near. In effect any circuit or a switch will be fried before it detects a surge.

 

[captrajesh]

i also agree with you as at my work place we have a 11kv substation and i have seen if the 11kv fuse blow off and if the gap between the 2 fuse point are close by there is a sparking as you said and so i can imagine how much spark will be there in the case of lightning as it is a very high voltage. so pl. sugest what to do?

From various informative posts by the members, it may be fairly accurate to deduce that you cannot have protection circuit using currently available components.

Traditional wisdom says 'If you can't face the trouble, divert the trouble'

So IMO, it may be better to install a well designed lightning arrester at a sufficiently higher level than the dish near the dish with its cables well away from the one carrying the signal from the dish.

 

[nel]

From various informative posts by the members, it may be fairly accurate to deduce that you cannot have protection circuit using currently available components.

Traditional wisdom says 'If you can't face the trouble, divert the trouble'

So IMO, it may be better to install a well designed lightning arrester at a sufficiently higher level than the dish near the dish with its cables well away from the one carrying the signal from the dish.

Yes that i will be doing before the next rains, but this circuit is not for the protection of direct lightning strike but only to ground the excess voltage and current from the cable if there is any lightning strike in a radius of say 1 km.

As the lightning is a very high voltage it creates a magnetic field which gets induce in all metal so it will not leave the RG6 cable also.

Now comming to the gap of the fuse i think it does not matter as even if it jumps the voltage it will get grounded through the GDT and if that should burn then atleast if not a good state MOV then atleast a burnt MOV will continuously ground the Voltage and current since the two points of the MOV will be close to ground the excess.

Thus it will not let through the excess further through the STB/TV. As we all know that the current takes the shortest way to ground.

Comming to the frying of the circuit it cost just less then Rs.100 so it will be worth losing the Rs.100 then calling the Tv tech. for repair and pay say Rs.500 for his service and also replace the full PCB of the Tv as we know that the PCB's of LCD tv's can't be repaired so you'll have to spend atleast Rs.10,000 to install a new PCB.

So my opinion is better waste Rs. 100 then to spend Rs. 10,000.
i would be happy to know the opinion of the other members. Also i am not saying the earlier opinion of the members are false. like the one say better disconnect the STB/Tv then risk it.

But then a lightning will strike first and then you will see and rush to remove the cable but it could be late by then so i think better to have one connected for additional protection.

What you'll say?