Help fix surge protector

[erwin1978]

I have an APC Pro8T2 surge protector. Can anyone tell me what the section of the circuit I circled is for? There are three 2K Ohm resistors in that section that are overheating and the ceramic coating have cracked and chipped off. The resistors appear to still be working except that they are hot and have turned the PCB and casing brown.

 

[SOFTengCOMPelec]

Burnt PCB, overheated electronics, somewhat high voltage mains equipment.
I don't think that it can be SAFELY repaired, except by replacing the burnt PCB etc (unlikely to be available and/or economically viable), and still would probably be risky, as the case may have been damaged as well.

The electrical insulation properties of the materials (e.g. PCB and/or components) are put at severe risk, by the burning/over heating and probably should not be used.
I would be much more worried about it setting fire to your premises, rather than trying to repair a relatively inexpensive item.

If it was me I would play safe, and my rubbish/trash bin would be fuller this week.

EDIT: Anyway, sorry if I am giving you news, that you don't want to hear. But I don't want anyone to get electrocuted or hurt, needlessly.

 

[Jeff7]

It's also very possible that the burned electronics aren't the only ones that were damaged.

I'd also throw it out.

 

[bryanl]

I can't make out the circuit traces very well, but I believe the three 2K resistors are in series and limit the current from the 120V AC to 10-20mA to power an indicator LED on the smaller circuit board connected by the black and white wires. Judging by their size, the resistors appear to be rated 1/2 watt, and substituting 1 watt resistors will prevent overheating in the future but may not be possible due to their larger physical size. 1/2 watt resistors are acceptable, but try to mount them 2 mm above the circuit board for better cooling. Discoloration of circuit boards from heat is common, and some TVs have run for over 10 years in that condition.

 

[uclabachelor]

Why would you risk safety to save a few bucks?

Toss it out and get a new one!

I design electronics and I wouldn't even want to take apart a surge protector, let alone repair one.

 

[SOFTengCOMPelec]

Why would you risk safety to save a few bucks?

Toss it out and get a new one!

I design electronics and I wouldn't even want to take apart a surge protector, let alone repair one.

I completely agree !!!

EDIT3: Removed, to avoid upsetting anyone.

 

[SOFTengCOMPelec]

Possible repair details....

In my opinion, it is just NOT worth it, and there may really be much more serious problems, causing the visible issue(s). So, it could be unsafe.

 

[PottedMeat]

It's also very possible that the burned electronics aren't the only ones that were damaged.

I'd also throw it out.

yup. and it's only $25 http://www.amazon.com/electronics/dp/B00000J3WQ

 

[westom]

Can anyone tell me what the section of the circuit I circled is for?

If they are R9, R10, and R11, then they power an LED entitled Protection Working. Each resistor should be dissipating maybe 0.4 watts. However if your voltage is high, then they may be dissipating closer to 0.5 watts.

 

[erwin1978]

Yah the resistors are in series. It was my guess that all that extra circuitry is just to power the LED. I removed the resistors and the LED is off but the outlets remain powered. When I unsoldered the LED I measured the voltage across the black and white wires and it's 66 volts if I remember correctly. Does that sound right? I might have forgotten to set the multimeter to DC so that may be in AC. LEDs run in DC, right? Are the other resistors, transistors and diodes part of a bridge rectifier?

I was gonna ask how many watts the resistors are. They are the same size as 1/2 watt resistors I had laying around so I guessed that much. How much larger are the 1 watt resistors? I'll probably get those.

I'm a cheapo that would rather troubleshoot this unit than spend $25 for a new one.

 

[Mushkins]

I'm a cheapo that would rather troubleshoot this unit than spend $25 for a new one.

I think every insurance underwriter in the entire world just felt a chill up their spine.

Seriously man, $20 is worth not potentially burning down your house.

 

[SOFTengCOMPelec]

I think every insurance underwriter in the entire world just felt a chill up their spine.

Seriously man, $20 is worth not potentially burning down your house.

I agree.

Why can't people understand the simple concept, that they may buy 10,000's of things during their life time, but you only get to die ONCE.

 

[westom]

I'm a cheapo that would rather troubleshoot this unit than spend $25 for a new one.

Understand what the circuit does. Protection is tiny. Hundreds of joules. So three tiny fuses connect MOVs to AC mains. During a potentially destructive surge, those MOVs must disconnect as fast as possible. To avert a house fire.

Those resistors are part of a circuit (that I believe also feature two transistors) to report on those fuses. IOW a surge and AC electric remain connected to appliances. But the fuses blow as fast as possible so that MOVs do not burn down the house. The LED only reports one type of failure. A failure that exists only when a protector is grossly undersized. LED does not report on the other and acceptable type failure.

And yes, those resistors remains constantly hot. Were not mounted with an air space for better cooling and to not burn a PC board. But should not cause a fire.

However those resistors probably need be a flame-retardant type. Replacing them with conventional resistors might create an additional fire threat.

Be more concerned about a fire risk due to that protector's near zero joules and fuses that might not blow fast enough.

 

[bud--]

Understand what the circuit does. Protection is tiny. Hundreds of joules.

The amount of energy that can reach a protector on a branch circuit is small. An investigation by the NIST surge expert found the worst probable case was 35 joules. Most of the very strong power line surges produced 1 joule or less at a protector. Protectors with far higher ratings are readily available.

So three tiny fuses connect MOVs to AC mains. During a potentially destructive surge, those MOVs must disconnect as fast as possible. To avert a house fire.

They disconnect as fast as possible in the junk westom buys. Don't buy protectors in the Dollar Store.

Be more concerned about a fire risk due to that protector's near zero joules and fuses that might not blow fast enough.

Since 1989 UL has required thermal disconnects for overheating MOVs. Where is the record of fires in UL listed protectors made since 1998?

I would replace the protector with overheating resistors.

 

[erwin1978]

I probably will get a replacement. But first I want to understand what went wrong. It's either the resistors are failing due to age or they are subjected to power far beyond what they can handle. This means a failure further up the stream.

So is the LED running in AC or DC?

 

[westom]

But first I want to understand what went wrong.

AC must be converted to DC for the LED. Numbers provided previously define resistors operating at their limits. Remember, these protectors are made as cheap as possible. Replacing the resistors with higher power ones and adding a 50 mA fuse would costs little. Even leaving it as is would not be a problem or threat. None of those solutions create the fire risk created by another part of that circuit - seriously undersized MOVs.

 

[bud--]

AC must be converted to DC for the LED. Numbers provided previously define resistors operating at their limits. Remember, these protectors are made as cheap as possible. Replacing the resistors with higher power ones and adding a 50 mA fuse would costs little. Even leaving it as is would not be a problem or threat. None of those solutions create the fire risk created by another part of that circuit - seriously undersized MOVs.

No manufacturer would fuse a circuit for LEDs.

Westom thinks plug-in protectors are "seriously undersized" because he can't figure out how they work. He googles for "surge" and compulsively posts his message that plug-in protectors do not work. Any protector in the US should be listed under UL1449. To pass the UL1449 test protectors must protect against a series of test surges and survive intact. Protectors with much higher ratings than are required for UL tests are readily available. Other UL tests are intended to cause MOV failure, and the protector has to fail safely - no fire.

 

[westom]

No manufacturer would fuse a circuit for LEDs.

bud's job is to promote undersized and extremely profitable protectors. UL1449 keeps being revised because grossly undersized protectors have still caused house fires.

Meanwhile, the OP is asking for a solution. Not for paperwork that says a fire 'should not' happen.

bud is my personal troll who has followed me for almost ten years posting naysayings. Because his job is to protect sales of 'point of connection' protectors that do not claim to protect from typically destructive surges. He also has no idea of the relevant circuit inside that protector. The engineer does. And provided watt numbers that even say why its PCB is slightly browned.

2K resistors probably should be flame retardant. A 50 ma fuse can be used for better safety with higher wattage resistors. But resistors left as is would not create a serious human safety threat. Eventually the LED will extinguish when one resistor fails.

Its MOVs, on the other hand, are a greater danger. As demonstrates by so many who had their UL1449 protectors catch fire.

 

[SOFTengCOMPelec]

The previous few posts on UL1449, got me very curious, so I googled it and found :-

UL1449:: Overvoltage (surges, interference) situations, particularly on mains supply systems, can cause resistors to overheat and flameout. This is known to cause flame wars between forum members, and, although not necessarily a safety risk to humans, can also lead to cat fighting between members.
Attempts to de-fuse the situation (even with 50ma ones), have LED (usually red, 10ma) to repeated disagreements.

Back on topic:
My policy is to bin burnt out electronics equipment, which is low cost (under $50 .. $100 value, and OLD higher value stuff), even if it appeared repairable. I don't want to take the risk.

Internet searches, seem to indicate that after about 5 years, a surge protector has usually lost most or all of its ability to absorb surges, so usually needs replacing anyway, when old. (I am NOT an expert on surge protectors).

Some models (probably your model, but I am not familiar with it), apparently have an led which extinguishes when the ability to absorb surges is FULLY exhausted.

 

[westom]

Some models (probably your model, but I am not familiar with it), apparently have an led which extinguishes when the ability to absorb surges is FULLY exhausted.

A degraded MOV cannot be reported by that light.
Degradation is a normal and acceptable failure mode even defined by MOV manufacturers.

LED will report another and catastrophic type failure. Failure due to a protector being undersized. And a reason for protector created house fires. This failure mode even violates Maximum Parameters defined by every MOV manufacturer datasheet. MOVs must not fail catastrophically.

His LED only reports a potentially catastrophic and completely unacceptable failure - an undersized protector. It cannot report when an MOV has absorbed too much energy; has only degraded.

A fire marshal discussed what in a protector causes fires: http://www.esdjournal.com/techpapr/Pharr/INVESTIGATING SURGE SUPPRESSOR FIRES.doc

... one such fire occurred in a fire station. Investigation of a fire that started behind a desk in an office revealed the ignition source was a surge suppressor. ...
When fire investigators examine fire scenes where surge suppressors are involved in the ignition few know what patterns indicate failed MOV's.

A grossly undersized protector must disconnect from a surge as fast as possible. While leaving that surge connected to attached appliances. If its fuse does not disconnect fast enough, then an MOV is a potential house fire. It is rare. But remains a problem with protectors that even meet UL1449.

LED, lit by three 2K resistors, reports on that fuse; if protector parts were disconnected to avert a fire.

Properly sized protectors remain functional for decades. But those devices are different devices that unfortunately share a same name.

 

[erwin1978]

I wish I had a personal troll. bud-- is very persistent to have followed you for 10 years.

The PRO8T2 has 2 LED green for protection status and a red one for house wiring fault. Looking at the trace it appears the green LED will turn off when any of the fuses blow and not necessarily when the MOVs fail. Based on other people's experience when a MOV fails it either shorts or remains open for all time. So, the fuse being in series with the MOV will only blow if the MOV shorts or the fuse is fast acting enough to detect the over current.

If you don't like these type of surge protectors then what are the ones you talk so highly of, westom?

 

[westom]

Based on other people's experience when a MOV fails it either shorts or remains open for all time.

Unacceptable MOV failure mode is an MOV shorting or opening. That is a potential fire condition as others have learned the hard way. A violation of Maximum Parameters defined in MOV manufacturer datasheets. And is why the fuse exists. Fuse is the last and emergency protection so that fire does not happen. That failure occurs only when MOVs are grossly undersized. Light is a warning that the protector was grossly undersized. Unfortunately, being grossly undersized and failing catastrophically gets naive consumers to recommend that protector. The naive believe protectors are one shot devices. Only grossly undersized ones are.

Normal failure mode for MOVs is to degrade. No fuse blows. No risk of fire exists. MOV has no visual indication that it degraded. No light reports an acceptable failure that occurs when the protector is properly sized.

One MOV manufacturer even defines how to test MOV life expectancy. Spike it with at least 10,000 surges. Its threshold voltage must not change more than 5%. IOW it must only degrade; not fail catastrophically.

Potentially destructive surges are maybe hundreds of thousands of joules. How many joules in that APC? A few hundred? So where are hundreds of thousands of joules absorbed? That question must always be answered to have effective protection. A completely different device, also called a protector, provides protection by answering that question.

Lightning is typically 20,000 amps. More responsible manufacturers provide a 'whole house' protector that is at least 50,000 amps. An effective protector does not stop, block, or absorb surges. Effective protectors connect to what does all (and so effective) protection. Single point earth ground. Then hundreds of thousands of joules harmlessly dissipate in earth. Nobody even knows a surge existed. Surge does not even enter the building. Everything is protected. And the protector does not fail.

Critical difference is a ground wire that makes a low impedance (ie 'less than 10 foot') connection to earth. Wire thickness is mostly irrelevant. Wire length to earth (as short as possible) is critical. Other critical factors are no sharp wire bends, ground wire routed separately from other non-grounding wires, and wire not inside metallic conduit. More conditions that say why APC will not even discuss earth ground.

Best protection for a TV cable and satellite dish is a wire from that cable to earth. Then destructive surges connect to earth without entering a building. Everything is protected. That wire must be low impedance ('less than 10 feet, no splices, etc). Other incoming utilities (AC electric, telephone) cannot be earthed directly. So a telco earths a 'whole house' protector for free (as also required by numerous codes and standards). Everyone has one.

Only incoming wire that has no protection is AC electric. Therefore a lightning strike far down the street enters the house hunting for earth ground destructively via appliances. Where does that energy dissipate? Will hundreds of joules inside the APC somehow absorb that energy? Of course not. Once permitted inside, that current will hunt for earth ground destructively via appliances. That surge is incoming to everything. May catastrophically destroy APC MOVs. Will damage appliances that make a better connection to earth.

Surge damage means that current has both an incoming path and an outgoing path. Protection means that current does not and need not enter the building.

Facilities that can never have damage earth BEFORE current enters. The 'whole house' protector connects current to what absorbs the energy - single point earth ground.

More responsible manufacturers provide these superior devices. Most are names that any 'guy' would know for their integrity. Including Siemens, Leviton, ABB, Polyphaser, General Electric, Ditek, Square D, and Intermatic. A Cutler-Hammer (Eaton) version was selling in Lowes and Home Depot for less than $50.

That protector is only simple science. It only does what a wire might do better. For AC electric, it should be 50,000 amps or larger So that MOVs and protective fuses do not blow. But earth ground (not any protector) defines the protection. A protector is only as effective as its earth ground. Questions about surge protection are mostly about how to install the single point earth ground. To both meet and exceed National Electrical code requirements.

Where does hundreds of thousand of joules dissipate? Destructively inside appliances. Or harmlessly outside in earth. The homeowner makes that decision. Because a protector is only as effective as its earth ground.

 

[SOFTengCOMPelec]

Unacceptable MOV failure mode

Why not seal the 'MOV' in a suitably sized, ceramic container, allowing the MOV to safely "burn itself up", if necessary, WITHOUT setting the surge protector casing on fire, and hence, potentially burning the premises down ?

This (fire safe) MOV, would be built like a standard fuse (protected by a sealed glass or ceramic envelope), where the fuse wire can temporarily reach a relatively huge, white hot temperature, and safely and reliably burn out (melt), disconnecting the fused circuit safely.

I.e. The ceramic (or suitable, very high temperature material(s)) would encase the MOV to make it fire safe. It may be necessary to have an outer metal casing, to strengthen it, so that it can hold even explosive forces (a bit like the metal safety anti-implosion, straps which went around the old fashioned crt tubes, to stop them imploding and throwing out tiny fragments of glass at high speed, when the tube was accidently smashed or something).

 

[westom]

Why not seal the 'MOV' in a suitably sized, ceramic container, allowing the MOV to safely "burn itself up", if necessary, WITHOUT setting the surge protector casing on fire, and hence, potentially burning the premises down ?

More responsible companies do things similar to what you have suggested. But understand the purpose of some protectors.

Take a $3 power strip. Add some ten cent protector parts. Sell it for $40 or even $120 (ie Monster, Furman). It is not an effective protector. It is a profit center. Does not claim to protect from the other and potentially destructive transient. It sells to the many who see it fail, assume that is good, and then recommend it to friends.

Effective protectors are properly sized. Do not fail. So nobody knows it even exists. More of your money goes into protection; not into a profit center.

Solution is to earth a 'whole house' protector provided by companies with integrity. Because even that APC needs to be protected.

 

[SOFTengCOMPelec]

More responsible companies do things similar to what you have suggested. But understand the purpose of some protectors.

Take a $3 power strip. Add some ten cent protector parts. Sell it for $40 or even $120 (ie Monster, Furman). It is not an effective protector. It is a profit center. Does not claim to protect from the other and potentially destructive transient. It sells to the many who see it fail, assume that is good, and then recommend it to friends.

Effective protectors are properly sized. Do not fail. So nobody knows it even exists. More of your money goes into protection; not into a profit center.

Solution is to earth a 'whole house' protector provided by companies with integrity. Because even that APC needs to be protected.

What a horrible market situation.

From my (somewhat brief) internet googling about this, earlier, it seems to say that the user is expected to regularly check on the status of the led(s), on their surge protector, so that when they (at least one) fail to light, they can disconnect it and/or repair/replace it.
I'm sure a huge number of owners know nothing about the need for a regular safety check, and probably NEVER check the lights, let alone regularly.
I bet most surge protector owners, ASSUME that there is no particular fire risk associated with surge protectors (without going into a, DOES UL1449 completely remove all fire risks, or NOT, thread war).