MOV voltage

And expensive to replace the PCB mounted fuse. That's why i want to by-pass it (short it or increase it to 1.5A) and put in line protection.

At least the fuse, could be other components as well.

I think you'd need to know more than that, to apply a suitable cure. If only nuisance fuse tripping, demonstrated through resurrection by simple fuse replacement in subject units, then that is the weakness that needs addressing.

If it's nuisance fuse tripping, due to repeated line brown-out or dropped cycles, a voltage surge limiter won't stop the nuisance behaviour. This is something that would also be characteristic of non-SF area operation.

If there is no control over the specific equipments' package internals, the external protection would need to include series limiters that were effective under those circumstances. I find it hard to understand how there could be no influence over the specific equipments' supply source, sufficient to rectify the apparently faulty behavior.

For coordinated and effective voltage surge limiting, as you seem to be directed to apply, a series impedance would also be required in an external protection network.

RL

Has this unit passed UL?

If so, there are few line-side internal modifications that would not require re-submission. This includes any fusible links.

Placed after the bulk caps, this fuse wouldn't be subject to inrush surges, unless the load side also had a capacitive characteristic or uncontrolled loading behaviour.

You need more board-level failure analysis. Small-signal line-connected circuitry is not as prone to safety regulation document control and could feasibly be altered to control loading behavior.

RL

st acting fuse? Thermal fuse might not be accurate for current.

onds. Fastest fuses take milliseconds. That same defective design is why so many (maybe millions) of APC protectors had to be removed immediately - a serious human safety threat. Concern is to disconnect MOVs that fail cat astrophically - that become too hot and on the verge of creating a fire bef ore that fast acting fuse can respond.

fuse and MOVs protect it from over voltage.

em was replaired for $1000. The techician simply replaced a pair of boards . It failed again. Preliminary analysis of the board showed on-board fuse deployed. The on-board fuse is behind the recifier and caps (2000uF), nam ely:

if we stock additional boards. So, we are thinking:

6 months

lace it outside the box. Should I short out the fuse with a relay during p ower up?

Most certainly did.

How about changing from PCB mounted fuse to removable glass fuse? Would th at require UL approval? What if someone "accidentally" increase it from 1A to 2A?

Yes, i am sure they had problem with in-rush current; so they placed the fu se after the big caps (4x 1000uF 200V).

We might build a power sequencer to bring up the voltage slowly via an AC i nverter. We can limit the current to 1A, so less of a safety issue.

You'd have to refer to the UL file to determine which parts are recorded and how.

Recertiying with variations to that list may not be a big deal, but just reopening the file has cost implications. These are probably not objectionable, considering the present situation. They'd have to repeat those test steps that involved the component in question. Again - sometimes this may have been limited to a notation of relevent component file numbers. If the part reacted during abnormals in original testing, then they'd expect a repeat of those specific tests.

This fuse location issue is one of the reasons I asked whether the product had been examined for UL certs. Unless there's some other limiter in the AC line circuitry, it could have presented a serious problem in assessing line input integrity, requiring notes about xsectional area of any harnessing or printed wiring involved, in order to safely clear a (specified) external breaker.

On the load side of the fuse, there may be some operating characteristic responsible for overstressing the fuse under less than optimal input supply.

You can do whatever you want outside the box. If you can identify the root cause for the fuse blowing in a normally functioning unit, and can reproduce the behavior in a repeatable manner, then your external solution will have more likelihood of success in demonstrating its effectiveness, wherever employed.

RL

fuse after the big caps (4x 1000uF 200V).

You are confusing the purpose of a fuse with your suspected anomaly. A fus e is for disconnecting equipment AFTER damage has occurred. For human safe ty. BTW, UL is only about human safety. UL says nothing about the equipme nt working properly.

A fuse after the rectifier and capacitors makes no sense. Those would then feed a regulator that already includes protection features such as current fold back limiting. What you are suggesting a fuse might do should alread y have been solved in that regulator design.

Again, a fuse is to disconnect power after damage has happened. So the fus e should be on the incoming AC line - before rectifiers and capacitor.

All this is completely unrelated to the original request for a recommendati on. Long before changing anything, first an anomaly must be defined. Curr ently, an anomaly is only defined by speculation. If a fuse blows, then kn own is how many amps for how long existed to trip that fuse. A chart of num bers. Now test equipment and a good tech finds the source of that excessiv e current draw.

The anomaly will exist constantly. Therefore a fuse will trip intermittent ly. Finding the anomaly should be easy. Long before seeking any solution, first define an anomaly. A fuse is never used to reduce or cure an inrush current. A fuse is to protect from furthe r damage - ie fire. A good tech with proper equipment defines the anomaly with specific numbers before discussing any solution.

fuse after the big caps (4x 1000uF 200V).

You are confusing the purpose of a fuse with your suspected anomaly. A fus e is for disconnecting equipment AFTER damage has occurred. For human safe ty. BTW, UL is only about human safety. UL says nothing about whether equ ipment does its job - only addresses human safety issues.

A fuse after a rectifier and capacitors makes no sense. Those would then f eed a regulator that already includes protection features such as current f old back limiting. You are suggesting a fuse to do what should already hav e been solved in that regulator design.

Again, a fuse is to disconnect power after damage has happened. So a fuse should be on the incoming AC line - before rectifiers and capacitor.

All this is completely unrelated to the original request for a recommendati on. Long before changing anything, first an anomaly must be defined. Curr ently, an anomaly is only defined by speculation.

If a fuse blows, then known is how many amps for how long existed to trip t hat fuse. A chart of numbers. Now test equipment and a good tech finds the source of that excessive current draw.

The anomaly will exist constantly. Therefore a fuse will trip intermittent ly. Finding the anomaly should be easy. Long before seeking a solution, first define an anomaly. A fuse is never us ed to reduce or cure an inrush current. A fuse is to protect from further damage - ie fire. A good tech with proper equipment defines the anomaly wi th specific numbers before discussing any solution.

e:

e fuse after the big caps (4x 1000uF 200V).

use is for disconnecting equipment AFTER damage has occurred. For human sa fety. BTW, UL is only about human safety. UL says nothing about whether e quipment does its job - only addresses human safety issues.

feed a regulator that already includes protection features such as current fold back limiting. You are suggesting a fuse to do what should already h ave been solved in that regulator design.

The 1A fuse protects the 4A MOSFET (IRFPG40) from excessive current.

e should be on the incoming AC line - before rectifiers and capacitor.

If the fuse is placed before the capacitors, it would need to be more than

1A to avoid the in-rush current.

On Wednesday, March 16, 2016 at 1:11:29 PM UTC-4, snipped-for-privacy@gmail.com wrot e:

Will never happen. Fuses take tens of milliseconds or sometimes up to an h our to trip. MOSFET is damaged in microseconds.

That damage would not happen due to standard practices found in regulators; even long before PCs existed. Even found in single chip power supplies.

Short together all power supply outputs. That creates a demand for the mos t current. Even that will not damage power supply parts. An Intel specifi cation for power supplies even defined how thick or thicker that shorting w ire must be.

That fuse would disconnect power AFTER a MOSFET failed. If a MOSFET failed due to something incoming on AC mains, a rectifier likely would fail first followed by a catastrophic capacitor failure. So again, that fuse is need ed on the input between AC mains and rectifiers.

Sounds more like a regulator design mistake or maybe something else such as counterfeit parts. Either way, curing symptoms with varistors or fuses is not a valid or recommended solution.

** Mosfets that are being switched hard on or off can pass high rms currents for long enough to blow a 1A fuse.

The 1A fuse also stops excessive current after a circuit failure and the ensuing PCB fire.

** Spike voltages are well supressed by filter electros which also protect the diodes in the rectifier. ** A supply side fuse needs to pass a large inrush surge, so cannot be fast acting or of only 1A rating.

A varistor on the incoming AC line protects EMI suppression caps from voltage spikes.

.... Phil

Gee, so everthin's workin swell. All he's gotta do is keep his bizniz outa San Mateo!

RL

Traditionally the reverse is true :}

In that case, we will just short out the fuse and let the MOSFET protect itself. To fire marshall, someone told me to do it.

Or do what is repeatedly recommended. Stop trying to cure a symptom. Instead fix a defective design. Start with what may be a defective regulator design. Rather than fix a defect, apparently someone tried to ignore it with a fuse.

Maximum current demand is when supply outputs are shorted. Even that short circuit (maximum current demand) should not damage a MOSFET or blow a fuse - if a supply is designed according to standards that existed even long before PCs existed.

On 3/14/2016 8:31 AM, snipped-for-privacy@gmail.com wrote: (snip)

!! What happens if the bridge rectifier fails shorted?

(snip)

It will be forced open or until the 15A main break. This fuse is more for the protection of down stream equipment.

We can add a slow blow fuse or ramp-up the voltage via an inverter. The in-rush current could be hundreds of Amp.