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BenandAmber
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Joined: 16/02/2019
Location: United StatesPosts: 961 |
| Posted: 06:41am 02 Mar 2019 |
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Hey warpspeed or anyone else what kind of wattage could a person expect to get out of the mosfets pictured above 320 amp 100 volt just 4 in a h Bridge 48volt battery would this make for a more dependable inverter how much D rating should something like this have
Thanks for your time
be warned i am good parrot but Dumber than a box of rocks |
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Warpspeed
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Joined: 09/08/2007
Location: AustraliaPosts: 4406 |
| Posted: 07:45am 02 Mar 2019 |
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well lets assume that at a junction temperature of 160C the device has a zero power rating, because it has its toes right on the edge of the abyss, and even one microwatt more will send it to silicon heaven.
And lets assume that the advertised device at a 25C junction temperature can handle a thousand amps. To actually keep the junction at that temperature may require a heat sink temperature below freezing.
So you decide that a thousand amps is just about right for your new inverter, and the mosfet is cheap and it will do very nicely.
The only problem is the size and cost of the refrigeration plant needed to keep the junction temperature at the rated 25C.
So you draw a straight line on a graph between 25C and 160C knowing that at 25C you can probably get the published maximum power rating, and at 160C the power rating falls to absolutely zero, because there is absolutely nothing between that 160C and total meltdown..
So you think about this a fair bit, and figure that on a 40C day your heatsink is probably going to run at maybe 65C, and your junction temperature at perhaps 92C.
And that is half way between 25C and 160C and the power rating of the device is actually only HALF what the advertised power rating is at 25C junction temperature.
Then you begin to realize that that thousand amp rated device might just burn to a crisp at a lot less than a thousand amps. But the novice pushes it to the max and wonders why it blew up.
How far can you push it ?
Well some fairly basic thermal calculations can tell you, but you first need to know the maximum ambient temperature, and the thermal resistance of both the heat sink and the mosfet package thermal resistance.
No way is it going to handle the full advertised power or current unless you can keep the junction at the specified 25C which is almost always a practical impossibility.
You have to find the "infinte heatsink" that can only cool down to ambient, which may be a lot higher than 25C anyway. Or you need to apply some very serious de-rating.
That is how it is, and how brave you are at pushing the limits.
The real heroes blow stuff up all the time.
Me, I am a super cautious coward that reads specifications and takes measurements and prays a lot.
Edited by Warpspeed 2019-03-03
Cheers, Tony. |
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BenandAmber
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Joined: 16/02/2019
Location: United StatesPosts: 961 |
| Posted: 08:45pm 02 Mar 2019 |
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Bravo bravo
Amber said you could be a writer
you make anything sound very interesting s I knew the four mosfets wouldn't give a Giant output wattage
I learned this from reading everything you've already wrote
I was just curious to know what kind of wattage you thought they might put out safely and reliable
I'm trying to get my head wrapped around how much I should d rate mosfets
without blowing a lot of them up. if I read what you said right it's going to take me blowing a lot of them up just to get the learning experience
I to pray Lots everyday
they are very expensive so I would be very cautious
Is there a general rule of thumb us newbies could go bye so we don't have to blow a lot of expensive mosfets up
I can get these 320 amp 100 volt mosfets just as cheap as I can get a Hy 4008
I'm trying to figure out which one I should buy
the guy selling these bought out a small inverter manufacturer that went under so I'm pretty sure all these components are the real deal and not fakes
When I go to buy a hy4008 I just don't know if it's fake or real
I'm not experienced enough to know the difference
I was hoping that someone on here could tell me if 320 amp 100 volt mosfet is as good or better than Hy 4008
by the way my soldering rework station came in today makes me feel like a little kid again
Thanks again to everyone for sharing your knowledge and wisdom thank you for your timeEdited by BenandAmber 2019-03-04
be warned i am good parrot but Dumber than a box of rocks |
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mackoffgrid
Guru
Joined: 13/03/2017
Location: AustraliaPosts: 460 |
| Posted: 10:19pm 02 Mar 2019 |
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Hi Ben,
They're in the same camp. As with everything, the data sheet can't tell us everything.
Rds is important, its a bit higher than the hy4008 but similar.
What caught my eye was Ciss, its way bigger than the hy4008, which is not desirable.
But get some anyway and play with them. You likely to blow some up anyway 
cheers
Andrew |
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Grogster
Admin Group
Joined: 31/12/2012
Location: New ZealandPosts: 9308 |
| Posted: 10:24pm 02 Mar 2019 |
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@ Warpspeed - then you probably remember the "Matched-pair" arrangement they used to use in high-power class-A or class-B audio amplifiers. If the output transistors blew up, it was an absolute must to replace them with matched-pairs. You could not just go out an get some generic transistors with the same part number from Jaycar or Dick Smith etc - the amplifier would usually blow them up again rather quickly, as one of the pair would not be matched to the other, so would conduct more or less then the other in the pair, and....magic smoke again. 
.....but I digress.
Smoke makes things work. When the smoke gets out, it stops! |
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Warpspeed
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Joined: 09/08/2007
Location: AustraliaPosts: 4406 |
| Posted: 10:55pm 02 Mar 2019 |
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Oh yes, I am ancient enough to come from the "valve era" and well remember the first germanium transistors, and finally silicon transistors.
Transistor matching became a fine art back then, but the introduction of integrated circuits and op amplifiers eliminated all of that. Its still a problem for the IC designers but not our problem anymore.
Getting back to mosfets and dv/dt switching problems at turn off.
Back in the days before mosfets, but for completely different reasons, turning off bipolar transistors could also be problematic, especially with inductive loads.
One solution to that was the turn off "snubber" which reduced the rate of voltage rise to make it as slow as you wished to make it.
Something similar should work equally well on the lower pair of our mosfet bridge.
Once you have made the gate drivers as good as you realistically can, it about the only thing left to do if the induced shoot through problem still remains.
Cheers, Tony. |
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