Author Topic: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?  (Read 11319 times)

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Offline iamdarkyoshi

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Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« on: September 17, 2017, 01:29:37 am »
So I bought a cheap 150w electronic load from ebay. The listing said 150w (yeah not with the stock heatsink), though with the massive CPU cooler I stuck on it, I had no issues dissipating 200W from a 19V laptop adapter. Or so I thought. After a couple hours of this, the mosfet just shorted.

Its a single IRFP250N, which is rated for about 200W disspation at 25C in the datasheet IIRC. However, mine was running at about 65C package temp.

I wouldn't be surprised if they put a knockoff mosfet in here, but I bought some replacements from a reputable source, but before I put one back in, I'd like to know what went wrong.

Any ideas? I used high quality thermal paste and everything when I put the CPU cooler on it, so its not that I had inadequate cooling.
 

Offline nidlaX

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #1 on: September 17, 2017, 01:41:11 am »
This type of "150W" electronic load has been discussed before on the forum. There is variability in circuit design, component selection, and quality control. You should post a few pictures of your particular variant.
 

Offline iamdarkyoshi

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #2 on: September 17, 2017, 01:45:46 am »
This type of "150W" electronic load has been discussed before on the forum. There is variability in circuit design, component selection, and quality control. You should post a few pictures of your particular variant.

This is what my unit looks like after a cooler upgrade.
 

Offline nidlaX

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #3 on: September 17, 2017, 01:46:57 am »
This type of "150W" electronic load has been discussed before on the forum. There is variability in circuit design, component selection, and quality control. You should post a few pictures of your particular variant.

This is what my unit looks like after a cooler upgrade.

Pictures of the PCB and circuit so we can actually see which variant you're using...
 

Offline iamdarkyoshi

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #4 on: September 17, 2017, 01:52:35 am »
This type of "150W" electronic load has been discussed before on the forum. There is variability in circuit design, component selection, and quality control. You should post a few pictures of your particular variant.

This is what my unit looks like after a cooler upgrade.
-snip-
Pictures of the PCB and circuit so we can actually see which variant you're using...

I've made some small modifiations to mine.

 

Offline najrao

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #5 on: September 17, 2017, 02:20:57 am »
You must be confused with the method of rating power mosfets: "200W@25C case temperature", the rating assigned, is just an extrapolated value, and applies if the user somehow managed to hold the metal base temperature at 25C. At 65C cooler temperature, the centre of the mosfet's base will be even hotter, may be 85C. It needs a correctly attached thermocouple  to check this. And at this 85C base, the chip inside will reach 150C for a power dissipation of just 100W!, not 200.That it survived for a time at 200W demonstrates a margin of performance not meant to be exploited by the user.
Though you might get a 400W@25C mosfet in the same case, it is best not to push temperatures so far. I would use THREE IRF250's in parallel, and hold their bases at 65C by the heat sink. Obviously,  the mosfet's should attach to the heat sink directly i.e., without any shims or spacers.
 
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Offline Armadillo

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #6 on: September 17, 2017, 03:27:50 am »
The cooler looks huge but
It is definitely necessary to know the reliable published thermal resistance performance rating of the cooler and not just the huge looking size.
By the look of it, the plates look very thin, and the region where the tube connects to the plates [compression flare] looks ..... ehm... not too promising.
Then you wonder whether it is a genuine Heat Pipe technology, and the preferred orientation of the installation for the migration and return of the flow of the refrigerant inside the tube.
So, I would say you firstly need to calculate the required thermal resistance performance of the heat-sink before you buy one.

Edit: Rated in the market as useless stuff, do not buy it. Further info on fake can be found here

https://www.eevblog.com/forum/repair/part-identification-150w-constant-current-electronic-load-60v-10a/
« Last Edit: September 17, 2017, 03:51:30 am by Armadillo »
 

Offline IanMacdonald

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #7 on: September 17, 2017, 06:16:17 am »
Thermal resistance and heat dissipation calculations might be a good subject for a video. It's not that difficult a subject, but I've met plenty graduates who didn't understand it. Basically just Ohm's law applied to heat.

If the device's rating is quoted at 25C and it's running maxed-out with  the case at 65C then it's running well outside of its rating, because if the chip has a max temp of 175C, then it will actually be at 215C.

https://www.infineon.com/dgdl/irfp250n.pdf

Though, the 214W claim seems to be a bit of an exaggeration since the thermal resistance is quoted at 0.7C/W, with an additional 0.24C/W for mounting. Thus the actual max power is 159W, even with the mounting at 25C.

If you were to allow a max heatsink temp of 65C, and assuming a direct mount with no washer, then the rating is 117W.

So, this is partly a case of not understanding ratings, but also partly a case of manufacturers making bullshit claims, there being no way that a 214W rating could be achieved in practice, short of refrigeration.   
« Last Edit: September 17, 2017, 07:12:16 am by IanMacdonald »
 
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Offline najrao

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #8 on: September 17, 2017, 09:03:28 am »
NidlaX's comment on the manufacturer's claim being b-s,- is misplaced to the extent that the 214W rating assigned applies at 25C BASE temperature (actually specified and measured at an exact location directly under the mosfet die inside the package); the manufacturer has no control over the extra thermal resistance between the base and the heatsink, as much depends on the quality of the surfaces and their coupling through air/thermal grease and  the clamping pressure. Thus, the 214W results from 175-25=150÷0.7=214. It only needs elementary application of mind to understand this well standardized rating method, and to apply all the 'deratings' needed in a practical application.
The finned heatpipe cooler is, again, a highly optimized design; there is nothing wrong with the fins being "too thin" or "too closely spaced", as the heatpipe carries the heat with little temperature gradient right to the centre of each fin, and as a powerful draft is set up by the fan.
 

Offline Armadillo

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #9 on: September 17, 2017, 09:17:07 am »
The finned heatpipe cooler is, again, a highly optimized design; there is nothing wrong with the fins being "too thin" or "too closely spaced", as the heatpipe carries the heat with little temperature gradient right to the centre of each fin, and as a powerful draft is set up by the fan.

Your statement implies All finned heatpipe coolers are constructed same regardless from china, usa, or from reputable manufacturer or from street side manufacturer?
Be real, ask for the certificate.
Tell us the exact liquid and the material inside the tube and of this particular cooler in question, since you know all finned heatpipe cooler.
« Last Edit: September 17, 2017, 09:22:20 am by Armadillo »
 

Offline Gyro

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #10 on: September 17, 2017, 09:56:28 am »
You're also using what looks like a switching specified mosfet in its linear region (I assume the gate drive is linear rather than PWM- I don't see any inductors).

Most switching mosfets get unhappy if used in their linear region and can fail due to localised hot-spots on the die. It's normal to significantly de-rate them for linear operation, regardless of heatsinking.

200W is an awful lot of dissipation for one package anyway. I would look at parallel operation across a couple of FETs. Such a massive heatsink on a single package just looks 'wrong'.
« Last Edit: September 17, 2017, 09:58:52 am by Gyro »
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Offline mikeselectricstuff

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #11 on: September 17, 2017, 10:00:47 am »
Thermal resistance and heat dissipation calculations might be a good subject for a video.
Youtube channel:Taking wierd stuff apart. Very apart.
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Offline Armadillo

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #12 on: September 17, 2017, 10:11:08 am »

 there is nothing wrong with the fins being "too thin" or "too closely spaced",

Elementary question;?
 

Offline najrao

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #13 on: September 19, 2017, 05:01:50 am »
Armadillo, I do not claim to be the sole depository of all knowledge on this subject. Nor that there are no differences between 'reputable- read American' manufacturers and 'street side vendors'.
Other things being equal, thick fins conduct heat to their extremities with less temp drop, so should cool better. By how much? In engineering practice, it is not uncommon to compromise when the returns start dropping off. It is called optimisation, just in case.
The most common liquid - and the most appropriate at that - in low temp heat pipes is demin water. There is no way of telling what it is in a specific model.
Thank you for your comment.
 

Offline Assafl

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #14 on: September 19, 2017, 06:02:30 am »

 there is nothing wrong with the fins being "too thin" or "too closely spaced",

Elementary question;?

Interesting quote. I wonder why A/C manufacturers bent on getting an A energy rating use a large amount of pipe, and lots and lots of thin fins.

My ongoing assumption is that indeed it is the amount of pipe + square section of fins that affect cooling performance. However, you'd also add to that the fins access to convective cooling "air" (which would want a larger surface area).

Maybe in Aerospace, the fins only radiate energy (IR) and that requires less fins?
 

Offline Armadillo

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #15 on: September 19, 2017, 07:28:10 am »
I wonder why A/C manufacturers bent on getting an A energy rating use a large amount of pipe, and lots and lots of thin fins.

Number of fins per inch?

How many FPI does the cooler in question has?
 

Offline Simon

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #16 on: September 19, 2017, 11:54:06 am »
Please can you calm down Armadillo!

AC heat exchangers are likely different from CPU coolers as gas is pumped through them. I don't see any circulation in CPU coolers, just conduction.
 

Offline Armadillo

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #17 on: September 19, 2017, 12:21:23 pm »
Please can you calm down Armadillo!

AC heat exchangers are likely different from CPU coolers as gas is pumped through them. I don't see any circulation in CPU coolers, just conduction.

I did say HeatPipe Technology, and you are referring to gaseous phase, but heat exchanging should be the same as m, c, delta T.
The pertinent matter would be the actual published Thermal Heat Resistance of the said cooler other than contorting into abyss.
Cool!
 

Offline Armadillo

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #18 on: September 19, 2017, 12:50:52 pm »
Armadillo, I do not claim to be the sole depository of all knowledge on this subject. Nor that there are no differences between 'reputable- read American' manufacturers and 'street side vendors'.
Other things being equal, thick fins conduct heat to their extremities with less temp drop, so should cool better. By how much? In engineering practice, it is not uncommon to compromise when the returns start dropping off. It is called optimisation, just in case.
The most common liquid - and the most appropriate at that - in low temp heat pipes is demin water. There is no way of telling what it is in a specific model.
Thank you for your comment.

How can you assert that the specific model cooler had been "Optimised" when there are so many unknown to you particularly the heat pipes running on "demin water" is kind of a joke, don't you think so? If you truly do not claim to be the sole depository of all the knowledge, would you not faults others comment like you had own the knowledge of the subject?


NidlaX's comment on the manufacturer's claim being b-s,- is misplaced to the extent that the 214W rating assigned applies at 25C BASE temperature (actually specified and measured at an exact location directly under the mosfet die inside the package); the manufacturer has no control over the extra thermal resistance between the base and the heatsink, as much depends on the quality of the surfaces and their coupling through air/thermal grease and  the clamping pressure. Thus, the 214W results from 175-25=150÷0.7=214. It only needs elementary application of mind to understand this well standardized rating method, and to apply all the 'deratings' needed in a practical application.
The finned heatpipe cooler is, again, a highly optimized design; there is nothing wrong with the fins being "too thin" or "too closely spaced", as the heatpipe carries the heat with little temperature gradient right to the centre of each fin, and as a powerful draft is set up by the fan.

« Last Edit: September 19, 2017, 01:00:05 pm by Armadillo »
 
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Offline Karlo_Moharic

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #19 on: September 19, 2017, 04:13:14 pm »
Quick question , why the hell don't just buy a decent DC load , instead of cheap crap off of ebay?
 
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Offline Armadillo

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #20 on: September 19, 2017, 04:25:01 pm »
Can the heatsink sit flush to the mosfet.

And also the current sense wire, is it the original wire material? What material wire is used if not.

Just curious.

Thanks.

 

Offline Simon

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #21 on: September 19, 2017, 05:07:40 pm »
Please can you calm down Armadillo!

AC heat exchangers are likely different from CPU coolers as gas is pumped through them. I don't see any circulation in CPU coolers, just conduction.

I did say HeatPipe Technology, and you are referring to gaseous phase, but heat exchanging should be the same as m, c, delta T.
The pertinent matter would be the actual published Thermal Heat Resistance of the said cooler other than contorting into abyss.
Cool!

Believe it or not your not the only one talking on this forum! a comparison was made to AC heat exchangers.
 

Offline Armadillo

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #22 on: September 19, 2017, 05:30:29 pm »
Please can you calm down Armadillo!

AC heat exchangers are likely different from CPU coolers as gas is pumped through them. I don't see any circulation in CPU coolers, just conduction.

I did say HeatPipe Technology, and you are referring to gaseous phase, but heat exchanging should be the same as m, c, delta T.
The pertinent matter would be the actual published Thermal Heat Resistance of the said cooler other than contorting into abyss.
Cool!

Believe it or not your not the only one talking on this forum! a comparison was made to AC heat exchangers.

Now, you weigh on something irrelevant and you ought to substantiate the difference.

Well, can you show or demonstrate that the mathematical formulae are much different between the cooler and the AC heat exchangers regardless whether it is mentioned or not mentioned. By the way, in the HVAC industry, they are also using the heatpipe system as part of energy conservation particularly in Fresh Air treatment in industry like wafer fabrication foundries, cleanroom, data center or what have you not.

So my question is WHAT IS YOUR POINT?
 

Offline Simon

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #23 on: September 19, 2017, 05:33:00 pm »
I suggest you read the whole topic.
 

Offline Armadillo

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Re: Blew a MOSFET dissipating 200W.... Fake mosfet or bad circuit?
« Reply #24 on: September 19, 2017, 05:49:28 pm »
I suggest you read the whole topic.

I suggest you do too.
 


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