Comp Power Supply - Rosewill 1200W - Blown Component - Need help Identifying

Hello everyone. I am stumped and need help identifying a component inside this power supply. This is the 2nd psu I have gone through with this company and now this one has failed. The first one I originally purchased lasted less than 24 hours. This one made it almost 3 1/2 weeks before blowing the same exact component. I am hoping someone can point me in the right direction so that I'm able to purchase a new component (possibly maybe recommend one that is better than the one it's designed with) Luckily I have been keeping an eye on it for the past week so I was able to shut it down before it blew up. Once it started showing signs of visible exterior cracking and discolor in the center so I knew it was just a matter of time. Below is the specs, operating conditions, and devices that It's powering. Simply put I don't have the money to go out and buy a better one so any help to repair this one would be much appreciated. If you have a bitcoin address I would be more than happy to donate for some good leads. I know this power supply is still good as I caught it before it blew up.. The component basically turned to dust as I tried to wipe the surface to show some of the lettering leaving what u now see in the image.







ROSEWILL 1200 PSU 80 PLUS GOLD
CAPSTONE G1200
115-240V 12-6A 60/50HZ

3.3 +5 +12 -12 +5VSB
25A 25A 100A 0.3A 3.5A

--150W-- 1200W 3.6W 17.5W

TOTAL 1200 -------------------------

line voltage 120.
2 WIRE NO GROUND (old structure) apt

using only the pci-e connectors on supply. 4x4 from psu to 2 6 pin per run. total 8 pci-e connectors (using only 6 out of 8).

each run is going to an ASIC miner. using 130w per blade x 6 at the wall and i switched out the stock fan for one that has higher airflow rate operating in 30F at night and 52 during daytime.


Any help would be much appreciated.. and thank you for your time =) and please direct me to where I can purchase another component if possible to upgrade the one It had in it to better quality, etc...

Shawn G
Las Vegas NV

Is the component about 3/4 inch diameter? It looks like a varistor (MOV), not a capacitor.

Failure was pretty much explosive. This suggests sudden overvoltage and/or overcurrent. You'd have to be very lucky if it's the only thing that failed.

It's a good idea to replace it with a higher rating. However that will not necessarily save it, if other components are failed. You'll need to do detective work to find other failed components.

Or there is a chance its volt rating is slightly low. Therefore when spikes came along, it was easily overtaxed. A varistor's life is reduced by repeated overvoltage.

I could be wrong.

It didn't have a chance to take out anything else. I powered it off before it had a chance to explode, brought it inside, and dis-assembled the casing. It looks like that cause i moved it back and forth a few times trying to see what visible markings it had on it.. It then turned to dust. The last psu I had was in the process of melting.. I smelled something funny on my balcony (I have thisequipment outside this time of year as it keeps everything cool under an enclosed balcony 8x8). When I went outside to see who was bbqing it looked like what a piccole pete firework looks like as its whining away before it goes out... and the equipment was still running... thats the funny thing... I sent it back RMA but they said that they weren't going to honor future RMAs from me even though the packaging states 5yr warranty right on the box. I'll never again buy a psu from this company... I have a corasier 750w psu powering the same amnt of equipment without fail for almost a year straight. Even my seasonic is outlasting this junker and it';s been in use for almost 2 years....

I figured it was a MOV but how do you find the one u need what specs do you need to go off of in order to replace? Do you go under a few volts for min (ie. 115-250) for 120-240 and there was typical i think I Saw a classification for that.. I know it's a hole mount just not sure the fine line specs to get the right one. Why would they state its 1200w and its doing what a 750W does all day?

Thanks again for your help... Yes it was about 3/4 diam 10mm I think maybe

Shawn

Almost All mains-connected (offline) SMPS will eventually be killed by mains overvoltage transient which eventually takes out the MOV.....(ie it takes out the fuse and the mov)
Because yours blew so quick, it sounds to me that there is too much undamped ringing at startup etc, in the smps, due to poor design, and this is making the mov quench this, which is blowing it up...replacing the mov = no good, you've gotta solve the underdamped ringing...


….Mains Transients:
As you know, this is potentially a threat to the longevity of a power supply. Especially in areas where there is much load switching or lightning etc.

As you know, power lines unfortunately have a multitude of high voltage transients on them. Lightning strikes produce transients as high as 6kv with a duration of about 100ns. Power network failures, (eg fuse breakage, switch flashover, etc) also cause many high voltage transients up to 1.2KV, duration up to 60us. Eighty percent of all power line transients are up to 1.2kv, duration 1-10us.

The following confirms that such mains transients are one of the reasons that small LED light bulbs fail early…
**broken link removed**
…please see the first “Frequently Asked Question”.

Here is a surge protection module, intended to augment the surge protection that already exists inside every offline switch mode power supply.
Surge protection module: (Using thermal disconnect varistor technology)
https://www.littelfuse.com/~/media/...ghting_surge_protection_modules_flyer.pdf.pdf

If an offline SMPS experiences a particularly strong mains transient, then the MOV will conduct and do its job of suppressing the transient, but of course, in so doing, it may well blow the fuse (all offline smps’s are required to have a fuse). The fuse is supposed to blow in such a situation , else otherwise the strong mains transient may cause a fire by blowing electronic components up. However, it might be the case that the offline SMPS is actually un-damaged. –However, this is no consolation, because the SMPS will not work with a blown fuse, and will have to be replaced. (nobody is likely to bother to try and diagnose that the fuse has blown).

4….Input filter overvoltage ringing at switch-ON and MOV activation:
[A MOV is a metal oxide varistor, and is fitted close to the input connector of an offline switch mode power supply in order to ‘suppress’ mains transients & stop them from damaging the SMPS or causing fire.]

All offline SMPS’s have an input EMI filter, comprising inductors and capacitors. Unfortunately, if the power switch to the offline SMPS happens to get switched ON at the instant of the peak of the mains voltage (ie the peak of the mains sine wave), then if the MOV is positioned downstream of some of the filter inductors and capacitors (which it often is), then the MOV may unfortunately end up “quenching” the overvoltage due to the ringing of the power supply’s EMI filter at switch-ON. This is bad news, because every time a MOV quenches a transient, its lifetime is reduced. –And when the MOV eventually “dies”, the power supply may well die with it. At least it will if the MOV fails short. If the MOV fails open, then the power supply will not be immediately dead, but it will have no MOV to prevent damage due to mains transients, so its lifetime may well be much reduced.

This problem of “overvoltage ringing at switch-ON-at-mains-peak” can be remedied in many ways..eg…
a)…Use a MOV with a high voltage, and spec all the components (capacitors etc) with high voltages, such that they don’t get overvoltaged by EMI filter ringing at switch-ON-at-mains-peak.
b)….Add series resistance to the power supply at its input..this will act so as to damp the ringing in the input EMI filter that occurs at ‘switch-ON-at-mains-peak’. (the resistance should be big enough to damp the ringing, but not so big that its huge and dissipates lots of power in normal operation.
c)…..Use an NTC (negative temperature coefficient) resistor at the power supply input. This will act so as to damp the ringing at power supply switch-ON, but when the power supply is in normal operation, the NTC resistor heats up and reduces its own resistance. (in fact, a great many offline SMPS’s have an NTC). The problem with NTC resistors used as such, is that if somebody switches the power supply ON……OFF..ON, then the NTC will already be warm for the second ‘on-coming’ and so will not offer enough resistance to damp the ringing.
d)…Use an “Active inrush limiter”. –This can damp out any overvoltage ringing that would occur at ‘switch-ON-at mains-peak’.
The “Active inrush limiter” comprises a power resistor, as in part (b) above, but has a mosFET in parallel with it, and once the power supply has started up, the resistor is shorted out by the mosFET, and so the resistor does not dissipate lots of power whilst the power supply is running normally.
e)…..Use a “zero crossing detector” so that the power supply only ever switches ON at the lowest point of the mains voltage waveform.
If this is done, then the voltage on the EMI filter at the input of the power supply rises up slowly and smoothly, and so there is reduced ringing in the power supply’s input EMI filter.
Often, very high power offline SMPS’s use a zero crossing detector in conjunction with an “active inrush limiter”.


In the problem of “overvoltage-ringing-at-switch-ON-at-mains-peak”, the problem is obviously worse at high mains, ie 265VAC.

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hang on a minute, if that component is connected series, then it could be an NTC resistor.
Is it connected series or shunt?...MOV is shunt...NTC is series connected

You just cut off the legs and then power on the PSU. If the unit turns on happily, then it was a MOV and it will run in that condition. It is expected to be the first in line to fail.

Now if you remove the damaged device and the PSU does not turn on after power on, then IT WAS not a MOV and you need to dig deeper.

MOV failings are not uncommon. You can run the PSU without it.

yes, mov failing often also mean fuse blown ...."crowbar" protection

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also, maybe its an inrush NTC that never got switched out.

treez said:

yes, mov failing often also mean fuse blown ...."crowbar" protection.

Click to expand...

The thing I hate most about these beasts is that they fail with a short-circuit mode. They force you to open the box.

lvshawnlv said:

I figured it was a MOV but how do you find the one u need what specs do you need to go off of in order to replace?

Click to expand...

I had to replace an MOV in my 2500W sinewave inverter, after a freak short-circuit. (It caused the inverter to shut off immediately.) I looked at a list of replacement MOV's. There are several volt ranges and other specs to choose from. It is difficult to know how to pick the right one.

I looked for the closest matching numbers and went with that. The inverter worked fine afterward. I forget if the MOV was the only thing wrong, or if a fuse blew too.

Do you go under a few volts for min (ie. 115-250) for 120-24

Click to expand...

There is every possibility it is an inrush limiting switch, or temperature related switch (per post #4).

However if it is an MOV then I would go with the next higher volt range. Overly high mains AC would deteriorate the lesser-rated MOV.

But looking at the appearance of your broken component, it appears as though a lot of current went through it, busting the coating but not necessarily the electrical part. Are you certain it doesn't conduct electricity? Perhaps a different component failed invisibly, conducting heavy current through several components?

I'm not worried about opening the box =) unless something is going to jump out and bite me :drevil:

Copy -- Thanks. I'm going to try now and see if it works. If it doesn't turn on do you need to join the 2 legs with some silver soldier?

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I'm not sure. Maybe you can tell me by these images i just took...




I would like to use this equipment still because it's new.. don't understand why all my other psus work without fail.. if there was so much over voltage here wouldn't a majority of the people have issues similiar? The power lines and transformers in the area look pretty old though (overhead) maybe that can be a cause ?

It was broken due to the fact that when I pulled open the case I wanted to get a better look at it... it turned to dust. It will still intact when i opened the case. From previous experience when the 1st unit caught fire i wanted to make sure i kept an eye on it. That MOV is located on the exhaust part of the PSU So you can easily see it from the outside of the case when it's closed up... funny thing to mention my girlfriend caught me sniffing the power supply all the time and she thought I was crazy... but I do remember when it was running it had a very odd smell coming out right where that MOV was.. not a burnt smell of electronics burning up... I don't know how to explain the smell but it smelled like it was under load..

The item is clearly a surge protector because I have similar looking things in my power supply too! Please do not try to short it because it may produce some fireworks.

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But the orange disk near the fuse is ALSO a varistor?

Something is drastically wrong here. If that power supply is rated up to a 240 vac input then the MOV would easily shrug off a high 120 vac line. I wish you would have looked at the markings of the component before it burned up.

Without taking measurements you can only guess what the problem is. The case size determines how much power the device can handle so i bumped up the 10mm to 16 to 20 mm. Here is a digikey search for my best guess of what the OEM should have used.

https://www.digikey.com/product-sea...&rohs=0&k=&quantity=&ptm=0&fid=0&pageSize=500

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have you got a DMM?...if so, you can use it to see if its connected series or parallel.....put the (good) fuse back in and see if one side is connected to live and the other to neutral..of so then its a mov.....

DO NOT do this with the power supply plugged in......and wait a bit after its unplugged as capacitors can hold charge and give you a zap even when psu no longer plugged in.

To see if its an NTC, put a resi.......uuuuhh....oh , its blown up, so you wont be able to test the device itself....but you can use the dmm to test to see how this thing is connected.

c_mitra said:

The item is clearly a surge protector because I have similar looking things in my power supply too! Please do not try to short it because it may produce some fireworks.

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But the orange disk near the fuse is ALSO a varistor?

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Im not sure... I have no idea what the components are.. that is why I was trying to figure out what I need to order so that I can replace it...

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Okay I went there and ordered 4 different kinds.. Lets see if that works... It will be here next week. I never really thought to look at the blown mov because it was sealed in the case now that it obviously had issues i just decided to hell with it and broke the seal on one of the case screws.. There isn't a way to find out what it is by the mfgr blueprint or whatever ??

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That's a Cantherm NTC Thermistor that's blown (Negative temperature coefficient thermistor, where resistance decreases as temperature increases. The resistance increase is non-linear, which makes it perfect for OTP use to shut down the PSU after a specific temperature is reached).

Apparently though it's bypassed with a jumper wire, making it next to useless:





JohnnyGuru is extremely helpful for PSU reviews, seeing as he disassembles the PSU as well to rate what's inside.

**broken link removed**...

The model number is MF72 5D20. It'll run you $3.33:

http://www.digikey.com/product-detail/en/MF72-005D20/317-1225-ND/1191000


Does this sound right?

Appears it was NTC

You did pick out the OEM NTC, but it burned out in two power supplies. So you probably need a different one. NTC's are a little harder to pick out them MOV's are. With MOV's you can go higher in power rating. With an NTC this usually not a good idea. If you oversize them they may not heat up enough and will keep to high of a resistance long term and burn out. You need to know how much current you are really using. Do you have an AC amp meter, or a kill-A-watt meter.

https://www.newegg.com/Product/Prod...dbfRmI7J5Ubu-6bEIcuKsxoC2uHw_wcB&gclsrc=aw.ds

I just have a DVM .. I can give you what my equipment pulls by the specs off their machine

1288 Total Watts consumed if running full machine. But I'm running minus one hashboard so 1288 Minus 161 is the total wattage draw off that power supply.

At 110V, the current will be larger and the NTC will be stressed more than usual. If you are sure that this is a NTC, perhaps you can simply short it off and run it as usual. In the review version (see the jonnyguru review) the NTC is shorted.

also, you can just short the ntc out, and make your own external inrush current limiter...eg, shove a resistor in series with the power cord, and switch it out after you've plugged it in...that way youll stop any inrush happening and wont need the NTC.....but whatever you do don't forget and accidentally plug the psu in with the resistor already shorted out.

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if you want to be real sure you can add another damping resistor in series with the inrush one and leave that in circuit.....just in case you need it to dampen any emc filter ringing that the psu may have.
To size this resistor , we must know your maximum rms input current, then we can use I^2.r.

Yes it is an NTC inrush limiter, a few ohms at cold start and then they run hot (80-100C) and their resistance drops to a fraction of an ohm, they cheap ones do die quite often,

Go to element-14 or similar and buy one rated for the current at 110Vac, say 15 amps min, clean up the board and fit the new ntc and you're away...!