Maker Pro
Maker Pro

what is the joule rating on surge protectors?

J

John Fields

Jan 1, 1970
0

---
He did.
---
"Electricity follows the shortest path" is qualitative folklore.

---
But, given that it follows the path of least resistance, and that's
the shortest electrical path, the folklore isn't wrong.
---
I wonder what the inductance of a cow is.

---
I dunno, and that leaves me in udder confusion, but maybe you could
figure it out by measuring the milk content of an O'Henry candy bar.

Geez, John, why have you suddenly turned into an asshole?

Maybe it's _not_ just a newsgroup any more...?
---
So any MOV can absorb a megajoule?

---
I don't think so, and I don't think that's what can be inferred from
what I said.

John Popelish posted something interesting relating to your query.
Did you read it?
 
J

John Popelish

Jan 1, 1970
0
John said:
Yeah, but the big one clamps at about 7 kilovolts!

Some of the curves sort of imply a lifetime of 1 to 1e6 shots,
depending on the energy per shot, with a fuzzy disclaimer.

Oh, you have a clamping voltage requirement, also? ;-)

I would expect any MOV that absorbed its rated joules in a single
pulse to have fulfilled its purpose and be ready for replacement.
Derate that peak energy to half and it is an entirely different
situation. Derate it to 1/10th, and it can be expected to last a long
time, as long as it cools off between pulses. I don't think
integrated energy is a very good way to calculate life. It wears out
by hitting peak temperature.
 
S

Sjouke Burry

Jan 1, 1970
0
John said:
Oh, you have a clamping voltage requirement, also? ;-)

I would expect any MOV that absorbed its rated joules in a single pulse
to have fulfilled its purpose and be ready for replacement. Derate that
peak energy to half and it is an entirely different situation. Derate
it to 1/10th, and it can be expected to last a long time, as long as it
cools off between pulses. I don't think integrated energy is a very
good way to calculate life. It wears out by hitting peak temperature.
You want to replace the MOV anytime your
air conditioner switches? Its no 1shot device,
it acts like a zener diode, one voltage for any
current you apply.
It reduces any line transient to its rated voltage,
whatever the current.
Lightning by the way causes most damage by
secondary induction, up to 1000+ volts/meter
(or yard), and this happens much more than
direct hits, those are almost always fatal.
Those induction spikes can be found in a wide
range of voltage and current, for which the MOV
can be a nice protection, dont forget that a Megawatt
pulse of one microsecond duration is only 1 joule,
so that a 40 joule MOV can dissipate 40 MW for 1 usec,
and thats much more than your electronics can stand.
The rated joules is just the amount of energy/heat,
that will cause a tolerable temperature jump,and some damage,
because the MOV is overheated in some spots,with local failure.
When to much local damage is done, the MOv voltage will
go below the mains voltage,and it will burn out/blow the
fuse.
 
W

w_tom

Jan 1, 1970
0
John said:
Nobody has yet answered my question: what are typical one-shot versus
lifetime joule ratings for MOVs?

Your question was answered last month even with numbers. MOVs are
not 'one-shot' devices. A one-shot device is grossly undersized;
ineffective protection. Some plug-in protectors are grossly undersized
so as to be damaged by a first surge. Being grossly undersized sells
more ineffective protectors. Answer to John Larkin's question
reposted:
MOVs that vaporize or disintegrate were used beyond what the
manufacturer intended. An unacceptable and catastrophic MOV
failure is not what joules are measuring. MOVs fail by degrading.
A degraded MOV has no physical burning, but has a voltage
change of typically 10%. ...

To determine how long an MOV may last, consult charts provided
by manufacturers. For example, a 180 joule MOV may shunt 1
million 20 amps transients, 1,000 300 amp transients, 10 600 amp
transients, or 1 4000 amp transient. In each case, the MOV has
no observable damage. ...

As MOV joules increase, joules that it may shunt to earth
increases exponentially; increased life expectancy. Those joules
shunted to earth are vastly more than the MOV joule rating
because the function of an MOV is not to absorb energy. Its
function is to shunt as much energy as possible to earth.

As MOV degrades, its varistor voltage changes. MOVs degrade;
must not blow out or open circuit. Some mistake that open circuit
MOV as normal operation.

One shot operation means an MOV was grossly undersized for that
design. Again, as MOV joules increase, joules that it may shunt to
earth increases exponentially. Answer starts with manufacturer
datasheets such as John Popelish provided:
http://www.littelfuse.com/data/en/Data_Sheets/CA.pdf
.. John Larkin would not be making his claims and not be asking this
question had he first read manufacturer datasheets and application
notes. He would then understand why an MOV shunts energy to earth; why
it does not absorb the surge.

A 20,000 amp lightning surge will only contain 200 joules? Of course
not. First MOV in that datasheet will shunt (divert, earth) a 20,000
amp transient - and in the process that entire 20,000 amp transient is
only 200 joules? Of course not. That 20,000 amp transient may
dissipate hundred of thousands of joules into earth while only
dissipating 200 joules in the MOV.
 
J

John Popelish

Jan 1, 1970
0
Sjouke said:
John Popelish wrote:

You want to replace the MOV anytime your
air conditioner switches? Its no 1shot device,
it acts like a zener diode, one voltage for any
current you apply.

My air conditioner switching off does not dump rated peak joules into
any MOV I have installed across my power lines. (and I have many)
It reduces any line transient to its rated voltage,
whatever the current.
Lightning by the way causes most damage by
secondary induction, up to 1000+ volts/meter
(or yard), and this happens much more than
direct hits, those are almost always fatal.

I agree with all of this, to some degree.
Those induction spikes can be found in a wide
range of voltage and current, for which the MOV
can be a nice protection, dont forget that a Megawatt
pulse of one microsecond duration is only 1 joule,
so that a 40 joule MOV can dissipate 40 MW for 1 usec,
and thats much more than your electronics can stand.
Yep.

The rated joules is just the amount of energy/heat,
that will cause a tolerable temperature jump,and some damage,
because the MOV is overheated in some spots,with local failure.
When to much local damage is done, the MOv voltage will
go below the mains voltage,and it will burn out/blow the
fuse.

Yep. Maybe you should read what I said, again. I did not mean to
imply (and certainly didn't say) that most line spikes come any where
near to dumping rated joules into any MOV. For instance, I have has a
very small one across my furnace burner motor starting winding, to
keep the starting switch contacts from flashing as they open. It
absorbs essentially all the stored inductive energy from that winding
each start, and has been doing so for twenty something years. But
each pulse is a small fraction of its peak energy rating.
 
J

John Larkin

Jan 1, 1970
0
figure it out by measuring the milk content of an O'Henry candy bar.

Geez, John, why have you suddenly turned into an asshole?

Been drinking again? You always get mean when you drink.
Maybe it's _not_ just a newsgroup any more...?

It is until the pie is done. Blackberry and pluot.

John
 
B

bud--

Jan 1, 1970
0
John said:
---
I don't think so, and I don't think that's what can be inferred from
what I said.

John Popelish posted something interesting relating to your query.
Did you read it?

One of the parameters of a MOV is the Maximum Continuous Operating
Voltage which is the voltage at which a MOV starts to conduct,
specifically the voltage (on average - lot of individual variation) at
which the current is 1ma. The MOV Joule rating is the single shot
energy absorption that shifts the MCOV by 10% (lower) which can be
considered a performance limit. At lower (but still relatively high)
energy hits, the MOV can progressively degrade.

With lower (but still relatively high) energy hits the MOV can have a
much longer life. See w_'s post:
http://www.littelfuse.com/data/en/Data_Sheets/CA.pdf
Fig 7-11 which gives the number of pulses that can be absorbed (1 to 1
million) at different surge current vs duration combinations - from
which surge energy can be calculated..

bud--
 
J

John Fields

Jan 1, 1970
0
One of the parameters of a MOV is the Maximum Continuous Operating
Voltage which is the voltage at which a MOV starts to conduct,
specifically the voltage (on average - lot of individual variation) at
which the current is 1ma. The MOV Joule rating is the single shot
energy absorption that shifts the MCOV by 10% (lower) which can be
considered a performance limit. At lower (but still relatively high)
energy hits, the MOV can progressively degrade.

With lower (but still relatively high) energy hits the MOV can have a
much longer life. See w_'s post:
http://www.littelfuse.com/data/en/Data_Sheets/CA.pdf
Fig 7-11 which gives the number of pulses that can be absorbed (1 to 1
million) at different surge current vs duration combinations - from
which surge energy can be calculated..
 
J

John Larkin

Jan 1, 1970
0
One shot operation means an MOV was grossly undersized for that
design. Again, as MOV joules increase, joules that it may shunt to
earth increases exponentially. Answer starts with manufacturer
datasheets such as John Popelish provided:
http://www.littelfuse.com/data/en/Data_Sheets/CA.pdf


Figures 7-11 imply permanent change in the voltage-current curve with
as little as a single zot, but culmulative effects over megazots at
lower energies. They say that the device "continues to function" but I
can't imagine many applications that wouldn't eventually notice a
series of 10% changes. Looks to me that MOVs do accumulate damage. I'd
have to analyze the curves to understand whether it's total lifetime
joules that damage an MOV, or some other relationship. Maybe later.
. John Larkin would not be making his claims and not be asking this
question had he first read manufacturer datasheets and application
notes. He would then understand why an MOV shunts energy to earth; why
it does not absorb the surge.

It absorbs what it absorbs. The math is simple.
A 20,000 amp lightning surge will only contain 200 joules? Of course
not. First MOV in that datasheet will shunt (divert, earth) a 20,000
amp transient - and in the process that entire 20,000 amp transient is
only 200 joules? Of course not. That 20,000 amp transient may
dissipate hundred of thousands of joules into earth while only
dissipating 200 joules in the MOV.


A lightning strike has typical numbers like 200 megavolts
cloud-to-ground and 1e9 joules of energy, sometimes a lot more. Most
of that energy is dissipated in the bolt itself, and very little in
the earth. The dissipation in the earth doesn't really matter, except
to note that it represents a minute fraction of the energy involved.

I don't like MOVs because of their leakage, their very soft conduction
curve, and their tendency to accumulate damage.

John
 
W

w_tom

Jan 1, 1970
0
John said:
I don't like MOVs because of their leakage, their very soft conduction
curve, and their tendency to accumulate damage.

MOVs have other problems such as too much capacitance (see
datasheets). But MOVs have superior life expectancy compared to gas
discharge tubes (GDT). A rather unique 'MOV like' solution that
replaced GDTs was once standard in telephone protection. That solution
has since been obsoleted by a semiconductor solution. Some examples of
semiconductor solutions include Sidactors and products from Sematech:
http://www.semtech.com/pc/downloadDocument.do?id=532

Above solutions are when protector's capacitance could impact signal
integrity. AC electric does not have same restrictions. MOV
technology is a best AC electric protection when considering other
parameters such as life expectancy and costs.

MOVs are typically selected so that only serious and destructive
transients cause an MOV response. Lesser transients should be made
irrelevant by protection inside appliances. A typical transient
frequency would be maybe one transient every eight years. A number
that changes significantly even within a same town due to variations
such as geology.

If frequency of transients is significantly higher (ie central FL or
some parts of WV), then joules are increased so as to improve MOV life
expectancy exponentially. Joules are a ballpark number to estimate MOV
life expectancy.
 
R

Rich Grise

Jan 1, 1970
0
100 of the largest of these in parallel might.
http://www.littelfuse.com/data/en/Data_Sheets/CA.pdf (10 kj each)

Yeah, but the big one clamps at about 7 kilovolts!

Some of the curves sort of imply a lifetime of 1 to 1e6 shots, depending
on the energy per shot, with a fuzzy disclaimer.
[/QUOTE]

In the 1970's, I worked at an outfit that used a lot of high-voltage stuff,
and they used MOVs, which caused more problems than they solved. One day,
one of the engineers saw a press release for Transzorbs, and we tried one,
and within days had issued ECO's to replace every MOV in the product line
with a Transzorb.

Hope This Helps!
Rich
 
R

Rich Grise

Jan 1, 1970
0
But, given that it follows the path of least resistance, and that's the
shortest electrical path, the folklore isn't wrong. ---

Both of these are technically inaccurate. The current follows _ALL_
possible paths, which share the current in proportion to their
conductance. (i.e., the reciprocal of resistance.)

Cheers!
Rich
 
Top