Joules - surge protector question

Lucky thing they fail open circuit. And 300 joules into a 100 joule MOV means much of the transient continues on its merry way right into your wallet. Even at 10 joules bit by bit it consumes a MOV.

Personally I have never seen a shorted MOV. TVS and GDTs yes. MOVs no.

MOV's get "used up" when they get heat stressed. They get heat stressed because there's not enough of them. If you got a MOV rated at 100 joules and along comes a 300 joules transient, guess what, the part will get heat stressed.

Again, it all boils down to more is better.

MEXICOWANDERER wrote:
When a metal oxide varistor is "used up" the show is over.

When a metal oxide varistor is "used up" the show is over. Their weakness is relatively slow reaction time which limits usefulness with high frequency events. I did not spend extra money for 20mm devices for the heck of it. BTW the response time for a bi-directional TVS diode is four-billionths of a second. They compliment a MOV nicely. But the TVS need individual fuzing which makes them less attractive to gizmo manufacturers. A 180 volt rated TVS chops all transients off at 180-volts but they are fragile and that's where MOVs "should" take the load off.

You misunderstood wiki.

They state more is better. I concur.

SoundGuy wrote:

JoeH wrote:
I see surge protectors with differing values for joules.... but it doesn't say what is better ... is higher better than lower values ?

As with many things in life there's much more to the story of surge protector joule rating than simply saying "higher is better" ... because in fact it may not be necessarily so, particularly when we're talking about RV specific surge protectors which use MOVs (Metal Oxide Varistors) to direct excessive current surge & spikes to ground. From this wiki article ...

"The joule rating is a commonly quoted but very misleading parameter for comparing MOV-based surge protectors. A surge of any arbitrary ampere and voltage combination can occur in time, but surges commonly last only for nanoseconds to microseconds, and experimentally modeled surge energy has been far under 100 joules. Well-designed surge protectors should not rely on MOVs to absorb surge energy, but instead to survive the process of harmlessly redirecting it to ground. Generally, more joules means an MOV absorbs less energy while diverting even more into ground"

There is "apparent" then there is reality. The "official" printed number for CFE power and Mexican registered (NOM) power devices is 127 vac 60Hz.

127

254

508

No way on the face of the earth are Mexico-bound appliances any different than USA appliances other than language tags. NOM is a trade law gimmick used to sanction illegal importation of less expensive electrical merchandise.

In Mulege Baja California Sur 30-years ago living on Ice House Rd. I was measuring 560+ volt 12 millisecond transients when the 150 horsepower ammonia compressor motor started and stopped. On a 127 volt line. Fluorescent lamp ballasts failed almost immediately. When a phase goes offline to my place it causes a ringing of several seconds before a breaker trips and relay shunts to ground. The first harmonic is in excess of 800vac on the remaining pair of conductors. You would think the transmission to distribution transmission step down would isolate this. I have a fresh set of Panasonic caps for the Sola line tamer upon my return. My refrigerator in my kid's restaurant has a 700va Sola protecting it.

I am grumbling. Thinking how nice a bi-directional 100-amp avalanche rectifier would be. 155,000 1/4 wave amp capacity. Absurd. Six hundred dollars.

I've been thinking about making a modular TVS board strictly plug in components. TVS and MOVs on modules. Half dozen modules per unit. CFE has 890 Mw of generation capacity at Lazaro Cardenas. So this is like unzipping for a forest fire.

Are microwaves and other appliances sold in MX rated for the higher voltage in MX?
Just curious what the power label actually says.

MEXICOWANDERER wrote:
Some folks are slow to catch on why there are so many microwave oven failures in RVs.

I'd be one of them. :S The microwave oven in our previous KZ Spree worked just fine for a couple of years then suddenly out of the blue just quit entirely ... this was long before I began using any form of line protection and in looking back now I'm sure it was a surge of spike that did it in. :M

Ooooo why did I check the power strip? My little Daewoo 600-watt microwave played Permanent Possum last weekend and this thread jogged my suspicion. I picked up a brand-new scratch & dent Oster 900 watt Oster for 60 dollars eqvt Pesos.

At home I have ultra-quality power while on the road-in-the-toad the BORG will work fine 85-140 volts.

Some folks are slow to catch on why there are so many microwave oven failures in RVs.

Smkettner X2

Campground voltage and connections are a circus in the US. Down here connections are reliable and guaranteed (BAD) so there's no guesswork. But my opinion differs from senor Kettner's on the transients importance in snubbing them. Microwave oven boards last about a year down here before lights out. And voltage in many places is stable. And comparing the voltage quality in a dirty campground network to a clean dedicated transformer service drop in the US is a cruel joke.

Remember that pricey Belden power strip I laughed about here on the forum a few months ago? Well I took it apart last night and found all 5 MOVs deader than a doornail. Today I snip and hurl and solder in 5 20mm MOVS. I like the strip because it has an eight foot 14-gauge wire and eight taps.

Don't dwell on surge rating too much. Primary faults are voltage, polarity and ground connection.

If it has surge protection you should be covered for most events.

Also check length of warranty.