Need advice for DIY surge supression

[Eric]

I'm working on a DIY "power center" for my basement theater system that will be hard-wired to the 120v breaker box in the house. It will feature balanced power (60-0-60vac) for the front end (preamp, cd, dvd), have EMI/RFI power filtering, and time-delayed AC outlets that are controlled by heavy-duty relays that are controlled by the DC Triggers on my preamp.

The only thing missing is over-voltage protection. I've been searching the web trying to learn more and it seems that many designs feature multiple MOVs and Gas Discharge Tubes (a series of 2-4 MOVs followed by a similar number of GDTs).

I have a few questions about these devices and how they are used. If I use multiple MOVs, what rating is appropriate? Are all MOVs rated at the same specs, or are the ratings staggered as you move through the "chain" ? The same set of questions applies to Gas Discharge Tubes: How many is ideal to use? What ratings are appropriate? Are they all the same or somehow staggered?

I also came across some discussion of TransZorb Diodes and Crowbar Circuits, but these seem to apply to DC power supplies....

Can someone help me fill in the gaps here?

Thanks,
Eric

 

[geraldfryjr]

MOV's are just paralleled across the line.
When I lived in Fla. I used to work in a T.V. repair shop and we made are money in the summer during lightening season.
I very very rarely ever seen a MOV not do It's job.
I believe there are a few different voltage ranges to choose from around 200v and above as it has been a while since I have looked up any specs on them.
But usualy lightening will just blowup the MOV and/or fuse and maybe a diode and thats it.
However, you can't stop lightening and I have seen it do a whole lot more than just blow up the MOV.
But they are a very cheap form of protection and a wise investment. jer

 

[Speedskater]

Or then you could get a store bought unit that mounts inside your breaker box (like a dual breaker) for under $100 US and installs in 5 minutes.

 

[geraldfryjr]

MOV's on are only a few dollars.
I used to install them in all of my power strips and I have had them for more than 15 years. jer

 

[Eric]

Thanks for the input, guys. I do have one that I installed on the main breaker box for the house, I think it cost me $50. When overloaded, it shorts and pops the main breaker to the entire house.

I was just thinking of adding something to my power box for the theater system that would provide an additional level of protection. As I read more, it looks like MOVs are the typical device used in this area. I came across a neat little MOV from Littlefuse that has an integrated thermal fuse and third leg that can be used as an indicator that the MOV has not gone bad. Its from their iTMOV product line.

My original thought was to try to duplicate what Panamax and other do: shut down the system when the voltage rises above 135v or drops below 85v. I haven't found any schematics that represent this circuit, though.

Eric

 

[geraldfryjr]

I used to have 1000 watt ups from UPC that kept the compter,mixer,amps and tape machine running just In case of such a situation accurd while we were recording and it did many times.

It was funny listening to the playback of when the power went out as we were still recoring!

There are ones in that power range and bigger that have outputs that are a continuosly regulated line voltage with battery backup as well as there one that don't have backup protection
This also insures no noise from the power source. jer

 

[Eric]

Ha- I was thinking about this as well. I have two UPS devices, both have dead batteries and I've been too lazy to pull them apart and replace the batteries. I didn't spend the time to "exercise" the batteries on a regular basis, so they don't work anymore. Perhaps its time to dust them off...

 

[geraldfryjr]

They are usualy 12v lead acid type or two 6v's in series.
I have always wondered if A car battery would work?
This would be a much cheaper replacement and it would give a very long backup down time. jer

 

[Eric]

Yes, the ones in my UPS are twin 6v sealed lead acid batteries that weigh a ton. A car battery would not work the same way. Car batteries are intended for short bursts of high current draw and cannot sustain a prolonged draw at any kind of "real" current. If you are thinking of going this route (which you certainly can) you should look for a "deep cycle" battery that has a very different physical construction than a car battery. The downside is that the price of deep cycle batteries is accordingly higher...

 

[Speedskater]

Thanks for the input, guys. I do have one that I installed on the main breaker box for the house, I think it cost me $50. When overloaded, it shorts and pops the main breaker to the entire house.
Eric

That just doesn't sound correct.
Well, maybe in a thunder storm.
What does overloaded mean?

 

[Eric]

Its called a whole house surge protector or something similar that is produced by Square-D. Its a 2" cuber that has 2 wires, and indicator light, and a nipple that fits into a knockout for the main breaker box. When more than the rated voltage (I think its a 240v model) is present, it is designed to short and pop the main breaker. I haven't opened it up to see whats inside, though.

 

[geraldfryjr]

Oh yes I know about deep cycle batteries,but,I'm sure that a standard car battery would last longer than the little batteries that are in your average UPS.
It would certainly be interesting to find out but mine burned up from some kind moisture that shorted out the main board so I scrapped it for parts instead of trying to fix it. jer

 

[Speedskater]

Its called a whole house surge protector or something similar that is produced by Square-D. Its a 2" cuber that has 2 wires, and indicator light, and a nipple that fits into a knockout for the main breaker box. When more than the rated voltage (I think its a 240v model) is present, it is designed to short and pop the main breaker. I haven't opened it up to see whats inside, though.

That's what it supposed to do!
More like 270 Volts than 240 Volts.
The question is:
What is causing this very high voltage that last long enough to trip the breaker?
Even most thunderstorms don't last long enough to trip the breaker.

 

[Speedskater]

Not a whole lot of difference between a deep-cycle battery and a car battery for our audio UPS proposes. Unless you want to listen to your hi-fi during long power outages.

We have been using motorcycle and lawn tractor batteries on our sailboats for years. The batteries power the navigation lights, radios, digital compass and interior lights, they work great. No engine is involved.

 

[Speedskater]

After further thought, the breaker tripping could be caused by a "Lost Neutral" problem. If you have a high resistance connection or wire from your breaker box back to the power companies transformer, your Neutral voltage may drift a long, long way from 0 Volts under some load conditions. One 120V line could drop to 90V and the other rise to 150V. The surge protector would short this high line and trip the dual breaker.

 

[Eric]

What is causing this very high voltage that last long enough to trip the breaker?
Even most thunderstorms don't last long enough to trip the breaker.

Dunno - hasn't yet happened. It just there for some protection...

I've seen a great many pieces of electronics fried over the years (none of mine, thankfully), so I'm interested in adding protection where I can.