Internal Surge Protection On PSU's

[james1701]

Why have no PSU suppliers implemented internal surge protection in their power supplies? As small as electronics are getting, there is plenty of room, and it would save them a ton of money on RMA's and dead units. It would also save consumers money because it could be implemented cheaper than buying a sand alone unit.

 

[Modelworks]

Just about all of them have it as well as a lot of other consumer gear like tv, audio, dvd.
Look near the power cord connector. Usually you will see some parts that are blue in color. Those are MOV that are there for surges. The same thing used in power strips that say surge protection. The number on the bottom , 385 is the voltage when the MOV will short the surge.

It doesn't prevent surges from other sources though. If your speakers are connected to the pc and they do not have surge protection a surge can come through them into the system. When I worked in warranty repair we had a lot of tv destroyed by surge damage. Almost all of them originated through the RF or video connectors. Very few through the power line.

 

[james1701]

Then why is the first thing an insurance agency asks you when you file a claim about a power surge, they want to know if it was hooked up to a surge strip?

Thanks for the pic, I will check and see what mine look like.

 

[Stefan Payne]

What das that MOV do?

As I understand it's resistance gets lower, the higher the voltage is, so it burns itself or am I mistaken?

 

[Mark R]

Surges are very short burst of high voltage.

When a MOV is exposed to voltage higher than their trigger level, they instantly reduce resistance, almost to zero. The result is that the surge current goes through the MOV, instead of the electronic circuits.

When a MOV diverts a surge in this way, a small proportion of the surge energy will be absorbed by the MOV, heating it up. A big surge can release so much heat that it can burn out or explode a MOV.

By and large most surge strips and internal surge protection in PSUs only provides protection against small-medium surges. They are rarely adequate against damaging surges, such as nearby lightning.

The only real benefit of buying surge strips is that they come with insurance. The strip itself may not do much, but the insurance is reasonably easy to claim off. And, this is the reason why your insurance co wants to know if you use a suge strip - if you do, they'll simply pass your claim to their insurance - and they won't need to pay up.

 

[Zap]

The only real benefit of buying surge strips is that they come with insurance. The strip itself may not do much, but the insurance is reasonably easy to claim off.

Are you sure about that? I've heard stories about surge strip insurance having a lot of fine print and being difficult to claim.

 

[Puffnstuff]

This is why I use an apc with avr and surge protection to feed my ps.

 

[anonemus]

Just about all of them have it as well as a lot of other consumer gear like tv, audio, dvd.
Look near the power cord connector. Usually you will see some parts that are blue in color. Those are MOV that are there for surges. The same thing used in power strips that say surge protection. The number on the bottom , 385 is the voltage when the MOV will short the surge.

It doesn't prevent surges from other sources though. If your speakers are connected to the pc and they do not have surge protection a surge can come through them into the system. When I worked in warranty repair we had a lot of tv destroyed by surge damage. Almost all of them originated through the RF or video connectors. Very few through the power line.

How will one know if one's PSU has this MOV without opening up one's PSU? Is it advisable then to do away with surge protectors?

Here's my setup at home:

 

[Stefan Payne]

Are there PSUs for the American market that don't have a MoV?

 

[Meghan54]

Are there PSUs for the American market that don't have a MoV?

I saw an OCZ reviewed by HardwareSecrets that didn't have one (StealthXStream 500W), a Huntkey Jumper 500W, and some HEC's, too, among other cheap pieces of junk.

How will one know if one's PSU has this MOV without opening up one's PSU? Is it advisable then to do away with surge protectors?

If it's a quality built power supply, it has an MOV. What ps are you using....brand, size, etc.

As far as doing away with your external surge protector, no, don't do it. But also remember, MOV's are subjected to small spikes all the time your surge protector is connected to power, so from what I've read, they slowly wear, leaving less and less ability to protect over time.

 

[Mark R]

There's no harm in keeping an external surge protector.

However, surge protection is not additive. Due to the characteristics of MOVs, what tends to happen is that a single MOV takes the whole surge. You've got no way of knowing in advance whether the PSU's internal MOV will try to take the whole surge, or the surge protector strip.

Similarly, if you've got 10 surge protectors - what tends to happen is that , 1 will end up taking 90-99% of the surge, the remainder will get the 1-10% shared amongst each other.

Professionally designed whole-building protection systems get around that by arranging so that the big whole-building surge protector at the electricity service inlet, is the most sensitive. Then specially selected medium-sensitivity MOVs are installed in the main electrical panel - then low-sensitivity MOVs are used on each receptacle. This way, the heavy-duty whole-building surge absorber takes the brunt of every surge that comes in. The smaller MOVs around the building only have to clean up the ripples and "shock-waves" that are generated as the bigger MOVs divert the surges.

 

[anonemus]

If it's a quality built power supply, it has an MOV. What ps are you using....brand, size, etc.

As far as doing away with your external surge protector, no, don't do it. But also remember, MOV's are subjected to small spikes all the time your surge protector is connected to power, so from what I've read, they slowly wear, leaving less and less ability to protect over time.

Currently using an OCZ ModXStream-Pro 500W. Not sure if this Sirtec-made PSU has MOV.

I'll leave the external protector then. Thanks, Meghan!

There's no harm in keeping an external surge protector.

However, surge protection is not additive. Due to the characteristics of MOVs, what tends to happen is that a single MOV takes the whole surge. You've got no way of knowing in advance whether the PSU's internal MOV will try to take the whole surge, or the surge protector strip.

Thanks, Mark! I'll try to digest your whole post.

If there's no harm in keeping my external surge protector, is there a benefit based on it providing first level of protection before the MOV takes a hit?

 

[Modelworks]

If you are really concerned about surges and want something that is not going to degrade with time then look for surge protectors that use a crowbar circuit. Called a crowbar because it has the effect of placing a metal crowbar across both wires.Crowbars use electronics to short the surge and get rid of the energy as heat. They are more expensive because it takes several parts and the design has to allow for some sort of heatsink to get rid of the energy.
http://www.brickwall.com/

 

[Mark R]

If you are really concerned about surges and want something that is not going to degrade with time then look for surge protectors that use a crowbar circuit. Called a crowbar because it has the effect of placing a metal crowbar across both wires.Crowbars use electronics to short the surge and get rid of the energy as heat. They are more expensive because it takes several parts and the design has to allow for some sort of heatsink to get rid of the energy.
http://www.brickwall.com/

A Crowbar circuit is used in voltage regulators as a final fail-safe for over-voltage. The crowbar circuit guarantees that the regulator will shutdown if it malfunctions and the voltage gets too high. A good quality PSU has a crowbar on each rail. E.g. the 12V rail will have a 15V crowbar.

If for some reason the voltage on the rail goes above the threshold (e.g. a PSU malfunction causes the 12V rail to reach 15V) - the crowbar will trigger and short out the 12V rail to ground. The key thing about a crowbar is that the rail remains shorted until all power-flow ceases. In other words, the crowbar will force the PSU to shutdown - by shorting it out, until the PSU circuits either trip out due to overload - or if the malfunction stops the PSU from shutting down, the crowbar will keep the PSU shorted out, until the PSU blows a fuse or burns out.

This is very different to surge protection - which diverts the surge energy, during the surge - but as soon as the surge is past, the diversion stops.

The brickwall surge protector is interesting. It works by providing a high resistance to surges, preventing them from getting into your equipment. However, series mode surge protectors have their own problems - which MOVs don't:
They add impedance to the power line, which means that sudden power fluctuations (as occur when you plug in a PSU and its capacitors charge from empty) cause much larger fluctuations in voltage than when connected direct to the power line. They also provide zero protection against 'common mode surges'. These are less common - and many electronic devices are immune to small common mode surges - but large common mode surges are still destructive. Additionally, MOVs act to dissipate the surge energy in the building wiring - but series type supressors have no way to dissipate the surge energy, and so the surge remains more destructive elsewhere in the building.

 

[Modelworks]

This is very different to surge protection - which diverts the surge energy, during the surge - but as soon as the surge is past, the diversion stops.

That is why you implement a circuit breaker into the design should it latch into a constant on condition, most often it doesn't . I have several surge protectors I built about 5 years ago and they all implement crowbar circuits as well as tvs diodes and inductors but no MOV. MOV are really bad for dumping voltage onto the neutral and ground wires. I want to know when a surge occurs so I like the circuit breaker approach vs just having surges occur and not knowing they are taking place.

The circuit I use trips at 154 volts in under 5 picoseconds which is much lower than most surge protection on the market.