Help With a MOV (Varistor?)

[Tim]

Hi all, I know I could buy another power bar, but I'd like to fix up
this one. It had a surge hit it, and of course it took out the MOV,
although the bar's breaker did not pop. The makings are MDC Z131 09ul. I
believe this to be a 130 volt MOV. It is about 14mm in diameter, with
radial leads (like a ceramic cap).

My question is would the Littlefuse V130LA20A item be a good replacement
for it? It will fit into the power bar no problem.

Thanks,

- Tim -

p.s. here's the site I'm getting info from;
http://ca.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=302402&Row=
509003&Site=CA

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

Hi all, I know I could buy another power bar, but I'd like to fix up
this one. It had a surge hit it, and of course it took out the MOV,
although the bar's breaker did not pop. The makings are MDC Z131 09ul. I
believe this to be a 130 volt MOV. It is about 14mm in diameter, with
radial leads (like a ceramic cap).

My question is would the Littlefuse V130LA20A item be a good replacement
for it? It will fit into the power bar no problem.

The little penny sized MOVs are too small, the sub should be more like
the size of a quarter. Radio Smack used to sell the GE or whatever MOVs
that were the 'right' size, and the number was the same or similar to
yours, above.

However that being said, if you listen to "w_tom", you will _never_ever
trust a surge suppressor power strip to protect your equipment. I agree
with him on many points, but the guy's an opinionated hardcore fanatic,
IMHO. I say just cut out the MOVs and use the power strip without them.
If the power supplies in the equipment _really_ needed the MOVs, they
would have put them in the power supply. If you really want to protect
your equipment, use an isolation transformer between it and the AC line.

 

[Tim]

Well, I believe that the MOV are a good way to see is surges are
present. They will prove that the power line is at fault, and in my case
that is important, as I have been saying that to the site owners where I
connect the equipment. I realize that the MOV won't give great
protection for the equipment, but I like 'em to be in there anyways.

Thanks, for the nfo tho, I will check Radio Crap next time by, may be
cheaper than paying shipping from Digikey.

- Tim -

 

[w_tom]

First, to be properly sized, the power strip should contain
about 3000 joules. Notice how few joules were inside that
ineffective power strip.

Second, safety issues must be considered. Better is to
replace that MOV with TMOVs from littelfuse.com (or something
equivalent). This simplifies safety considerations.

Third, if the protector is intended to detect destructive
transients, then it should be plugged into a receptacle on
breaker box - with 6' power cord shortened as much as
possible. To have a grossly undersized protector detect
destructive transients, the protector attached to breaker box
receptacle makes short connection from AC wire to earth
ground. Furthermore, tranzorbs may perform detection better.
Use a smallest wattage tranzorb or transil or equivalent.

Fourth, protection from direct strike is performed routinely
in just about every town every year. That is what a protector
is for. To earth a direct lightning strike AND remain
functional. Ineffective protectors install too few joules.
It encourages myths and promotes more sales. Notice so few
joules inside ineffective protectors.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

Well, I believe that the MOV are a good way to see is surges are
present. They will prove that the power line is at fault, and in my case
that is important, as I have been saying that to the site owners where I
connect the equipment. I realize that the MOV won't give great
protection for the equipment, but I like 'em to be in there anyways.

Thanks, for the nfo tho, I will check Radio Crap next time by, may be
cheaper than paying shipping from Digikey.

- Tim -

They were RS cat no. 276-568 and were two bucks in their 2002 catalog.
But they've stopped selling so many parts at the stores that I seldom go
there anymore.

 

[Ross Herbert]

Hi all, I know I could buy another power bar, but I'd like to fix up
this one. It had a surge hit it, and of course it took out the MOV,
although the bar's breaker did not pop. The makings are MDC Z131 09ul. I
believe this to be a 130 volt MOV. It is about 14mm in diameter, with
radial leads (like a ceramic cap).

My question is would the Littlefuse V130LA20A item be a good replacement
for it? It will fit into the power bar no problem.

Thanks,

- Tim -

p.s. here's the site I'm getting info from;
http://ca.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=302402&Row=
509003&Site=CA

The V130LA20A would be suitable imo. As you suspected 130V is the
design breakover voltage. The "20" means that it has a nominal energy
dissipation of 20 Joules.

Full specs are;
Max input volts (RMS) = 130
Max recurrent peak volts = 212
Max DC input volts = 330
Max energy = 20Joules
Max average power dissipation = 0.85W
Max peak current for t < 6uS = 2000A
Varistor peak voltage @ 1mA AC (peak) = 184V (min) - 254V (max)
Typical capacitance = 1500pF
Max thermal resistance body to air = 37 degC/W
Calmp ratio @ 10A = 2.0

The VxxxLAxx nomenclature was originally used by GE back in the 1970's
for their GE-MOV VARISTORS and Harris continued with it when they took
over this product line.

 

[truegridtz]

Hi all, I know I could buy another power bar, but I'd like to fix up
this one. It had a surge hit it, and of course it took out the MOV,
although the bar's breaker did not pop. The makings are MDC Z131 09ul. I
believe this to be a 130 volt MOV. It is about 14mm in diameter, with
radial leads (like a ceramic cap).

My question is would the Littlefuse V130LA20A item be a good replacement
for it? It will fit into the power bar no problem.

Thanks,

- Tim -

Tim, This reply is from some research done a few years ago on surge
protection. I am recalling what I found.

The problem with MOVs is the reaction time. By the time they begin to
conduct the spike has already pentrated your equipment. A spike can be 10KV
with a duration of a small fraction of a second.

The more expensive spike filters use either a transient zener or a MOV in
conjunction with a large ceramic capacitor. The capacitor has the fastest
reaction time, but can't take a lot of juice. The cap will keep it under
control until the MOV turns on.

As far as I know they still don't put spike protection in televisions. I'm
sure this is great for the service industry. A cheap power strip is a
waste. As of a few years ago a good one was about 75-100 bucks. They write
the reaction time on the sockets.

Use an a.c. rated ceramic cap. An "across the line" ceramic will have an
a.c. rating of 130vac or better. About .02uf should do it. A standard
ceramic with d.c. rating has about 10% of that rating for a.c. There are
also many ATL plastic caps, but I don't know how fast they react. Hope this
helps you out. Mark

 

[mc]

Use an a.c. rated ceramic cap. An "across the line" ceramic will have an
a.c. rating of 130vac or better. About .02uf should do it. A standard
ceramic with d.c. rating has about 10% of that rating for a.c. There are
also many ATL plastic caps, but I don't know how fast they react. Hope
this
helps you out. Mark

Let me second the point that an ordinary capacitor should not be put across
the line unless it is rated for a VERY high voltage. "Across-the-AC-line"
capacitors exist and are appropriate here.

As I understand it, the difference is mainly failure modes. The
across-the-line capacitor is not likely to fail in a way that would cause it
to conduct heavily, and if it does, it will immediately burn itself out
without starting a fire.

Can anyone elucidate further?

 

[w_tom]

The reaction time even of slower protection devices such as
Gas Discharge Tubes (GDTs) has been more than fast enough.
However if discussing reaction time, then wire impedance even
in those two inch MOV leads must be considered. Also other
delays cause by sharp wire bends must be included. In short,
reaction time is irrelevant.

A transient is discussed as if it were a wave crashing on the
beach. It is electricity. That means the same current is
flowing through everything in that circuit as current
increases. IOW of course "the spike has already penetrated
your equipment". That is how electricity works. First
electricity flows through everything in a circuit. Then as
the current increases, something in that circuit fails.

MOVs don't stop, block, or absorb surges to keep them out of
equipment. MOVs shunt. All electronics contain effective
protection. Protection that may be overwhelmed if the
transient is not shunted - diverted - before it can enter the
building. Shunting the transient to earth is the function of
an MOV.

The problem with MOVs is not their reaction time. The
problem with MOVs is that many humans do not understand what
MOVs do. MOVs will only be as effective as the earth ground.
Quality of that earthing connection, distance to earthing, how
that connection is routed, and even that the earthing point is
the only earthing point. IOW if the spike is 10KV, then the
MOV is mislocated or not properly earthed.

Again you use the term 'spike filter' which has nothing to
do with what an MOV does. Filters would be series mode
protection. An MOV is part of a shunt mode protection
'system'. And yes, the MOV is only one part of a 'system'.
Some shunt mode protection 'systems' don't even need MOVs.
But all shunt mode protection 'systems' have one essential and
required component - the single point earth ground. SPG is
the one missing component that so often makes MOVs
ineffective. MOV will only be as effective as its earth
ground.

Meanwhile if spending $75-100 on a power strip protector,
then it is probably one of the most ineffective protectors
such as Monster Cable. For example, a minimally sized power
strip would be 3000 joules. How many joules in that $100
protector? Notice so much money and so few joules.

Money says nothing about the quality of a protector.
Quality is defined by the earthing connection. No earth
ground means no effective protection. And so we have myths
about reaction time - so that you will not learn about
earthing. Learn about earthing and you will never waste good
money on a power strip that costs tens of times more money per
protected appliance. Or in the case of that $100 protector -
100 times more money per protected appliance for a protector
that is not even effective.

Meanwhile, putting a capacitor across the line rated at only
130 volts is obviously wrong. First, anything a capacitor is
going to accomplish is already inside the TV. An informed
poster would have know that. Second, a 130 volt capacitor is
clearly undersized. Third, that post even tries to claim an
MOV is part of a spike filter. MOVs are not series mode
devices. They are shunt mode devices. Even the claims about
slow reaction time are completely wrong. That post contains
too many inaccurate claims and numbers.

The effective MOV protector is a 'whole house' protector
with a short connection to earth ground. A protector is only
as effective as its earth ground. Reaction time is quite
obviously irrelevant.

 

[truegridtz]

Tom: I'm short of time right now, but perhaps your concept of a spike
through the house wiring is incomplete. This is a very complex subject when
one gets deep into it.

An MOV doesn't have to be hooked to the house ground, it simply bypasses
voltages that excess its turn-on voltage.

They can be used on the secondary of a transformer to absorb the turn-off
overvoltage.

Across the line caps are rated at 130Vac.

The initial transient spike must be intercepted and the reaction time is
important.

This is what I recall to be the case.

If I get some time I will look in my MOV book and get some solid facts.
Mark

 

[w_tom]

You better have more than one MOV book. A book that is
better than the old GE MOV Application Book. You better have
sufficient EE training to comprehend the underlying concepts.
MOV databooks do not discuss the entire circuit and assume the
reader understands the many types of transients. To
understand protection, a circuit must include everything from
the cloud to earthborne charges. What an MOV does is both
trivial and little different from wire used by Ben Franklin in
1752. Does your MOV databook discuss any of that? If not,
then complex parts have yet to be learned.

Yes, concepts of house wiring during a transient get
complex. Many IEEE papers discuss this. Remember, even that
concrete floor is an electrical conductor. Did your MOV book
discuss the floor as part of a circuit? If a plug-in
protector attempts to earth a transient via the wall
receptacle, then a transient is induced on adjacent household
wires and other appliances. Did your MOV book discuss induced
transients? Just another way that plug-in protectors cause
problems for adjacent household appliances.

Demonstrated is why plug-in protectors typically are
undersized; have so few joules. Why spend more money for more
joules when the protector does not even claim to protect from
the typically destructive transient? Did your book discuss
the electrical characteristics various transients or what
joules define? Why not?

Household wiring is so complex that plug-in protector
becomes ineffective AND can even contribute to damage of the
adjacent electronics. Again, we simplify the complex circuit
inside a house by keeping the transient outside. That 'whole
house' protector is only as effective as its earth ground.
And not just any ground. A single point earth ground. Did
the MOV book discuss equipotential and other complexities of
earthing?

A protector is only as effective as its earth ground.
Rather than teach why, industry professionals are cited. One
full day worth of technical reading is hyperlinked in
alt.comp.periphs.mainboard.asus on 30 Mar 2005 entitled "UPS
unit needed for the P4C800E-Deluxe" at
http://makeashorterlink.com/?X61C23DCA

Again you claimed an MOV is:

... used on the secondary of a transformer to absorb the
turn-off overvoltage.

MOVs absorb energy as copper wire absorbs energy. MOVs do
not **"stop, block, filter, or absorb"** transients. If an
MOV protects by absorbing energy, then so does copper wire.
Numbers in those datasheets should make that blunt obvious.
If not true, then post those numbers. Show me.

The reaction time even for slower GDTs was more than
sufficient. Where are numbers provided by your source for
reaction time? No numbers means junk science reasoning.
Discover how that 'one days worth of reading' does provide
plenty of numbers. No numbers is a symptom of junk science
reasoning.

An MOV is only as effective as its earth ground. The MOV is
a temporary connection from the transient to earth ground.
Some 'systems' use only wire to accomplish same (ie protection
for CATV) - as even Ben Franklin demonstrated in 1752. No
earth ground means no effective protection.

 

[truegridtz]

I will post on top.

First, I was trying to help the original poster provide some cheap and
effective spike protection.

I was not trying to give you a reason and opportunity to grind your
egotistical axe.

The MOV turns on and has a constant voltage drop that generates heat. It
must absorb energy to survive, but it basically "clamps" the energy source
and diverts the spike to the system ground.

You are predicating your arguement on lightning strikes. Although this is a
valid concern, the real and erosive danger to equipment is the constant
bombardment by line noise. For example, when the neighbor's refrigerator
turns off and send a spike through the wiring.

MOV specs are from advertizing brochures that push the optimism to the
limit. I was simply stating that if he wants to be sure he is protected
then he should strap a line-rated cap (the plastic ones are probably as good
as the ceramics) across the MOV. MCM sells some 250Vac Siemens caps at a
good price, about 50 cents.

The initial spike is mostly voltage and has an erosive effect. Like ESD
into semiconductors, these line spikes continually erode semiconductor
junctions in solid state devices, thus leading to early failure.

An MOV is a package of series-parallel semiconductor junctions all of which
have a voltage drop and capacitance. The article that I read years ago
pointed out that the MOV is not all that it is supposed to be. Using the
conventional capacitor (which is always turned on) is the best way to be
sure that the initial spike is contained until the MOV responds.

There are also inductive filters like the CORCOM (spelling may be wrong)
that have been used for decades, but they cost a lot more.

Also, putting just one MOV on the house won't suffice. Turn-off transients
within the home react with wiring impedance on a localized basis. Having
the protective device as close to the equipment is best.

Time to go, too much to do, Mark

 

[w_tom]

Clearly, your intentions were never in doubt. Either was
the doctor who bled a patient to death to cure the fever. To
cure a patient, at minimum, understand basic electrical
principles such as the many types of transient.

Meanwhile, even a MOV manufacturer does not claim to absorb
energy of a surge. For same reason that a wire gets warm, so
does the MOV. It shunts .. and to earth ground.

Meanwhile, electronics already contain effective internal
protection as even demanded by industry standards of 30 years
ago. Items such as the Corcom or equivalent are already
inside appliances; even due to FCC requirements. Even that
capacitor is often inside the appliance - but with higher
voltage ratings for human safety reasons. IOW any protection
that might work on a power cord is already inside the
appliance. Plug-in protectors hope you never learn that; so
they publish brochures chock full of half truths.

Once Apple installed MOVs inside their products. Why does
Apple no longer install those $0.10 parts? Because MOVs
inside the computer or on a power cord are not effective.
Again (and to appreciate why, one must understand some first
year EE concepts), the effective MOV earths a typically
destructive transient. That means it must be located short
(less than 10 feet) to a single point earth ground.

Does a refrigerator generate transients seen by MOV? If so,
then the MOV will degrade to ineffective in but weeks or
months. A graph provided in MOV datasheets makes this
obvious. MOVs are installed for transients that occur
typically once every eight years. Any trivial transients such
as noise from the refrigerator - the appliance must already
have protection to make such transients irrelevant.

If a refrigerator generates such destructive transients,
then what protects your dimmer switches, GFCIs, smoke
detectors, and furnace controls? We don't visit the hardware
store weekly to replace these because, well, first learn the
numbers. Those transients are made irrelevant by protection
already inside appliances. Those hyping ineffective plug-in
protectors again hope you don't learn this.

You may wish to take a short break. Already posted are
significant technical facts that require grasp of basic EE
principles.

What does an MOV do when located on the appliance power
cord? It shunts a transient from one wire to all others.
Shunts - not stop, block, filter, or absorb. It does what Ben
Franklin demonstrated in 1752. The typically destructive
transient seeks earth ground. A transient on the black (hot)
wire has been shunted to white (neutral) and green (safety
ground) wire. IOW the transient now has three paths to find a
path to earth ground, destructively, via the appliance. Where
is the protection? As posted earlier, an adjacent protector
can even contribute to damage of the adjacent appliance.

No wonder plug-in protectors are so undersized (MOVs of too
few joules). But again - how many joules on that protector
you think is being protected? What are the numbers? Did that
brochure note why joules must be sufficient?

Again, I am only repeating what is provided in that 'days
worth of reading':
http://makeashorterlink.com/?X61C23DCA
Protectors adjacent to the appliance can even contribute to
damage of that adjacent appliance. Why? First, no short
connection to earth ground. What do destructive transients
seek when destroying transistors? Earth ground. What is the
most important component in a surge protection system? Single
point earth ground.

But again, what do all those industry professionals discuss
obnoxiously in that 'days worth of reading'? Earth ground.
What do you want? Something obnoxiously repeating what plug-in
manufacturer propaganda ignores? Or a sugar coated and
grossly overpriced solution sold in Staple, Circuit City,
Sears, and Kmart?

No earth ground means no effective protection. The MOV is
only as effective as its earth ground. What do ineffective
plug-in protector hope you never learn about? Earthing.

To truly help the OP, first read that 'days worth of
reading'. Appreciate how widespread the plug-in protector
propaganda is. Effective MOVs are installed, in greater
numbers, within well earthed 'whole house' protectors. The
protector being only as effective as the quality of and
connection to that earth ground. By tens of times, the
cheapest and most effective spike protection is properly
earthed 'whole house' protectors.

Meanwhile, I believe the OP wanted to detect surges - not
eliminate them. The tranzorb solution or something equivalent
would be a better solution. Since he has not asked, I have
not provided additional information.

 

[ehsjr]

The reaction time even of slower protection devices such as
Gas Discharge Tubes (GDTs) has been more than fast enough.
However if discussing reaction time, then wire impedance even
in those two inch MOV leads must be considered. Also other
delays cause by sharp wire bends must be included. In short,
reaction time is irrelevant.

A transient is discussed as if it were a wave crashing on the
beach. It is electricity. That means the same current is
flowing through everything in that circuit as current
increases.

Nonsense. You either presume that everything is a series circuit,
which is totally unrealistic, or you don't understand how
current flows in a parallel circuit.

Ed

 

[ehsjr]

w_tom wrote:

MOVs don't stop, block, or absorb surges to keep them out of
equipment.

MOVs absorb the surge energy they are exposed to at their terminals.
E=I*R applies. The MOV absorbs electrical energy and converts it
to heat energy, as long as it is working. They absorb whatever
amount of the total surge energy they are exposed to across
their terminals, again, only as long as they are working. Energy
arriving at their terminals beyond their specs will burn them
out, which, of course, demonstrates (sometimes dramatically) that
they absorb energy.

Ed

 

[Brian]

Hi all, I know I could buy another power bar, but I'd like to fix up
this one. It had a surge hit it, and of course it took out the MOV,
although the bar's breaker did not pop. The makings are MDC Z131 09ul. I
believe this to be a 130 volt MOV. It is about 14mm in diameter, with
radial leads (like a ceramic cap).

My question is would the Littlefuse V130LA20A item be a good replacement
for it? It will fit into the power bar no problem.

Thanks,

- Tim -

p.s. here's the site I'm getting info from;
http://ca.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=302402&Row=
509003&Site=CA

MDC = Maida - they're on the web... www.maida.com/

Cheers,
Brian

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

I will post on top.

First, I was trying to help the original poster provide some cheap and
effective spike protection.

Cheap and effective are mutually exclusive when it comes to lightning
storms.

I was not trying to give you a reason and opportunity to grind your
egotistical axe.

If you have a right to express your opinion, why are you trying to deny
others that same right?

The MOV turns on and has a constant voltage drop that generates heat. It
must absorb energy to survive, but it basically "clamps" the energy source
and diverts the spike to the system ground.

You are predicating your arguement on lightning strikes. Although this is a
valid concern, the real and erosive danger to equipment is the constant
bombardment by line noise. For example, when the neighbor's refrigerator
turns off and send a spike through the wiring.

Line noise doesn't reach a high enough voltage to cause a protector to
clamp it.

MOV specs are from advertizing brochures that push the optimism to the
limit. I was simply stating that if he wants to be sure he is protected
then he should strap a line-rated cap (the plastic ones are probably as good
as the ceramics) across the MOV. MCM sells some 250Vac Siemens caps at a
good price, about 50 cents.

PC switching power supplies already have both 'X2' and 'Y' rated
capacitors across the line and to ground. They also have a transformer,
usually toroid, with dual windings that filter the AC as it passes thru.

The initial spike is mostly voltage and has an erosive effect. Like ESD
into semiconductors, these line spikes continually erode semiconductor
junctions in solid state devices, thus leading to early failure.

The PC switching power supply makes its own noise - so much so that the
PS has to have good filtering on the AC power to keep it from disturbing
other appliances. But it still does - listen to your AM radio when you
turn on yout PC.

An MOV is a package of series-parallel semiconductor junctions all of which
have a voltage drop and capacitance. The article that I read years ago
pointed out that the MOV is not all that it is supposed to be. Using the
conventional capacitor (which is always turned on) is the best way to be
sure that the initial spike is contained until the MOV responds.

There are also inductive filters like the CORCOM (spelling may be wrong)
that have been used for decades, but they cost a lot more.

Some AT switching power supplies use a CORCOM filter built into the AC
power cord socket. Some have a toroid with both power leads passing
thru it several turns.

 

[R.Lewis]

Let me second the point that an ordinary capacitor should not be put across
the line unless it is rated for a VERY high voltage. "Across-the-AC-line"
capacitors exist and are appropriate here.

As I understand it, the difference is mainly failure modes. The
across-the-line capacitor is not likely to fail in a way that would cause it
to conduct heavily, and if it does, it will immediately burn itself out
without starting a fire.

Can anyone elucidate further?

See data for X and Y rated capacitors.
This is the job these caps are made for

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

Let me second the point that an ordinary capacitor should not be put across
the line unless it is rated for a VERY high voltage. "Across-the-AC-line"
capacitors exist and are appropriate here.

As I understand it, the difference is mainly failure modes. The
across-the-line capacitor is not likely to fail in a way that would cause it
to conduct heavily, and if it does, it will immediately burn itself out
without starting a fire.

Can anyone elucidate further?

They are X2 rated capacitors.
http://www.mcicorp.com/capacitor/intsupclssx2cap.htm
http://www.isc-distrel.com/pdf/faco_mktx2.pdf
http://cp.literature.agilent.com/litweb/pdf/5989-1242EN.pdf
And do further Google searching for more info on X2 and Y2 rated caps.