Homemade surge protector

[pavithra_uk]

in here Sri Lanka, most commercially available surge protectors are cheap but it doesn't provide adaquate protection. Good quality protectors are very expensive. So I plan to build my own AC surge protector. I need some advices from experienced persons.

I can easily get 12mm MOVs for cheap (Model: 12D471)

AC Voltage in here 230V Single phase. Neutral is grounded at main branch transformer (11,000V -> 230V) So it necessory to protect all modes. LN, LE, NE

Here an idea:

3 MOVs per power rail & then two series line inductors & then 2 MOVs per rail again.

My questions here:

1. To protect computer & its other devices, how many 12mm MOVs per each mode needs ??

2. Can cable diameter affects the protection ability ?? (Between Input Power socket & MOV
)

[westom]

Re: Homemade surge protector

in here Sri Lanka, most commercially available surge protectors are cheap but it doesn't provide adaquate protection. Good quality protectors are very expensive. So I plan to build my own AC surge protector. I need some advices from experienced persons.

Best protectors cost many times less money. But first you must unlearn some very popular myths that promoted ineffective protectors.

First, no protector does protection. Not one. Either the protector connects hundreds of thousands of joules harmlessly to the protection (and completely different system component). Or your protector may even make appliance damage easier.

Second, see that number? Hundred of thousands of joules. Any protector that would stop, block, or absorb a surge will somehow claim to make hundreds of thousands of joules magically disappear in MOVs that are only hundreds of joules. And yes, an overwhelming majority believe that myth because advertising promoted it.

Third, the NIST (US government research agency) defines what effective protectors have done for over 100 years. That (and not the scam power strip) is what to learn:

You cannot really suppress a surge altogether, nor "arrest" it. What these protective devices do is neither suppress nor arrest a surge, but simply divert it to ground, where it can do no harm.

Demonstrated are two important facts. First is where hundreds of thousands of joules must dissipate. And second, the only honest answers also include numbers.

Once you let a surge inside the house, then it does hunting for earth destructively via appliances. Nothing (especially not a 2 centimeter MOV) will stop what three kilometers of sky cannot (again, more numbers). The MOV is effective when it absorbs less energy. And connects that energy as short as possible (ie 'less than 3 meters) to single point earth ground (again more important numbers).

Short because the connection to earth must be low impedance. That connection also must have no sharp wire bends, no splices, be separated from other non-ground wires, not be inside metallic conduit, etc. All factors to main a low impedance (not low resistance) connection to where hundreds of thousands of joules must dissipate.

Every single wire in every incoming cable must connect to single point earth ground. Not just any earth ground. Single point. AC electric and telephone wires must be earthed by a 'whole house' type protector. Cable TV and satellite dish need no protectors. Each is earthed short by a dedicated wire. That wire does what an MOV must do - just better.

Appreciate this is not what urban myth and retail advertising has taught an overwhelming majority. And yet that is the science well understood for over 100 years.

This is only an introductory explanation of the concepts. Far more is waiting to be learned. Only introduced is the concept. No protector does protection. Protection is only done by the 'system' component that absorbs hundreds of thousands of joules - harmlessly. Single point earth ground. Protectors are simple science. The art of protection is what does protection. Earth ground.

Welcome to why useful answers provide numbers. And why so many, instead, believe popular myths. Sound bytes easy to read. Involve junk science reasoning which means no numbers. Reality involves many paragraphs, over 100 years of well proven experience, and what makes most eyes glaze over - numbers.

What is the least expensive protector? The most effective. The soundbyte most never learned. Protection is always about where energy dissipates. A protector is only as effective as its single point earth ground.

[Per Hansson]

Re: Homemade surge protector

I was going to post something here.
But I forgot what it was?

Oh right, 100 years knowledge in this thread right here:
https://www.badcaps.net/forum/showthread.php?t=10893

Why the long time lurking westom?
Did someone say something to make you silent since you posted last?

[pavithra_uk]

Re: Homemade surge protector

I have an idea to build whole house protector from 20mm MOVs. 10 mov per each line..

There is a home made Spark gap that I was built two years ago.. working like charm.. I made it from 3 brass bars bolted very closed each others (2 mm).

this DIY spark gap can divert high surge current into Ground without harming power line wires. but it can't protect sensitive electronics... even bulbs..

[westom]

Re: Homemade surge protector

this DIY spark gap can divert high surge current into Ground without harming power line wires. but it can't protect sensitive electronics... even bulbs..

That was how surge protectors worked even 100 years ago. Today we do same with Gas Discharge Tubes (GDTs). But MOVs are some of the best components for a least amount of money.

Critical is how each MOV connects an incoming wire to earth. Noted was the term 'low impedance'. Sharp wire bends or wires inside metallic conduit increase that impedance unacceptably. Wire distance (not wire thickness) is more important. The MOVs (or spark gap) will only be as effective as the impedance (not resistance) of that connection to single point earth ground. The spark gap may have been compromised with how it connected a surge to earth.

For same impedance reasons, distance (increased impedance) between a protector and appliances means better protection.

Single point ground is another critically important parameter. If any wire inside any cable enters without first making that short connection to earth, then the entire protection is compromised. Telephone has two wires. Both must connect to earth. But if either connects directly, then phone service does not work. Do not use MOVs here due to excessive capacitance. GDTs or better semiconductor devices (ie Sidactor, low capacitance avalanche diodes, thyristors) are best used for connecting each telephone wire to that single point ground.

Protectors are only simple science. The art is earthing. Earthing is optimized for equipotential and conductivity. Important characteristics provided by superior solutions such as Ufer grounds or by encircling the building in a buried ground loop. One accomplished this superior earthing atop a hard rock terrain:
http://scott-inc.com/html/ufer.htm

In every case, a protector is only a connecting device. The art of protection is earthing.

And finally, care must be taken so that protector parts will not cause a house fire. Some solutions include thermal fuses so that catastrophic failure does not occur. Littelfuse makes an MOV with internal fusing. And (of course) encasing those circuits inside a fire protected case. Locating it where a catastrophic failure does not create a hazard.