In a recent video Wil made the comment that FET BMS fail often. This is why:
A common problem I see in circuits on YouTube and other sites is that someone's circuit failed, and went up in smoke.
People in the more esoteric realm's blame this on things like "Subtle Energy" overload and other such minutiae.
Here is the far more realistic explanation:
The very old GE SCR Manual Including Triacs and Other Thyristors goes into all of the gory details of what is happening inside the part, when the "Magick smoke comes out", as it is unlikely you have the Manual at hand, in a nutshell:
What lets the Magick Smoke out of IGBTS, FETS and SCRs in most cases is turn them on too slowly, causing 'Spot Heating' of the die.
Think of a FET, or SCR, as hundreds of thousands, possibly millions, of very small resistors all in parallel (Resistors in Parallel give a lower total resistance), where each one can be turned on and off individually. The 'resistors' closest to the gate turn on first, and as the gate potential spreads across the die the rest turn on. The ones farthest from the gate pin turn on last.
With a slow gate turn on, a few of the small 'resistors' nearest the gate are trying to carry all of the load, which they can't do, so they burn up, but the device does not fail quite yet. The next time the device is turned on, which may be only milliseconds away depending on your switching frequency, or days away depending on the application, some more of the resistors further in burn up. When the point is reached that there is simply not enough of the 'resistors' left to carry the load is when the Magick Smoke escapes, and the part dies a catastrophic death.
This is why the parts generally run "for a while" before failing. If it fails as soon as you fire it up the first time, you either have a catastrophic short in the load, possibly shorted caps that take a bit of time to 'wake up' before they hold a charge, generally fixed with 'Soft Start', or the gate drive really sucked big time.
There needs to be a few *Amps* of current pumped in the gate of the larger parts, in very short periods of time, to get the gate potential to spread across the entire die as fast as possible.
You also want to get the thing turned off as fast as possible.
If you are not familiar with the concept of Magick Smoke, this is where all electronic parts run on Magick Smoke, because once the smoke comes out of the part, it no longer runs...
The bottom line is that the designers need to stop cheeping out on Gate Drive and do it correctly with a lot of current in a very short time.
Then there other considerations about too much too fast that need dealt with but that is beyond what I wanted to cover here.
A common problem I see in circuits on YouTube and other sites is that someone's circuit failed, and went up in smoke.
People in the more esoteric realm's blame this on things like "Subtle Energy" overload and other such minutiae.
Here is the far more realistic explanation:
The very old GE SCR Manual Including Triacs and Other Thyristors goes into all of the gory details of what is happening inside the part, when the "Magick smoke comes out", as it is unlikely you have the Manual at hand, in a nutshell:
What lets the Magick Smoke out of IGBTS, FETS and SCRs in most cases is turn them on too slowly, causing 'Spot Heating' of the die.
Think of a FET, or SCR, as hundreds of thousands, possibly millions, of very small resistors all in parallel (Resistors in Parallel give a lower total resistance), where each one can be turned on and off individually. The 'resistors' closest to the gate turn on first, and as the gate potential spreads across the die the rest turn on. The ones farthest from the gate pin turn on last.
With a slow gate turn on, a few of the small 'resistors' nearest the gate are trying to carry all of the load, which they can't do, so they burn up, but the device does not fail quite yet. The next time the device is turned on, which may be only milliseconds away depending on your switching frequency, or days away depending on the application, some more of the resistors further in burn up. When the point is reached that there is simply not enough of the 'resistors' left to carry the load is when the Magick Smoke escapes, and the part dies a catastrophic death.
This is why the parts generally run "for a while" before failing. If it fails as soon as you fire it up the first time, you either have a catastrophic short in the load, possibly shorted caps that take a bit of time to 'wake up' before they hold a charge, generally fixed with 'Soft Start', or the gate drive really sucked big time.
There needs to be a few *Amps* of current pumped in the gate of the larger parts, in very short periods of time, to get the gate potential to spread across the entire die as fast as possible.
You also want to get the thing turned off as fast as possible.
If you are not familiar with the concept of Magick Smoke, this is where all electronic parts run on Magick Smoke, because once the smoke comes out of the part, it no longer runs...
The bottom line is that the designers need to stop cheeping out on Gate Drive and do it correctly with a lot of current in a very short time.
Then there other considerations about too much too fast that need dealt with but that is beyond what I wanted to cover here.
...or at least to change your broken smart electricity meter and ask you to stop whatever you were doing to it.
