Suitable high current mosfet for switch/disconnect?

Thread Starter

bigjoncoop

Joined Feb 1, 2019
154
What electrical characteristics of a N-Channel Power MOSFET do I need to check in order to verify that is capable of acting as a high current disconnect / Switch?

I understand the basic ones. (Vgs, Rds-On, Vds, Id, PD, max temp, etc...)

I found this N-Channel High current logic level mosfet that seems to suitable my application. "PSMN2R0-30PL,127"

Datasheet - (screen shots below) https://www.mouser.com/datasheet/2/916/PSMN2R0-30PL-1600491.pdf

It's capable of 30v, 100amps, and Logic Level

If I use 10/15 of them in parallel they should be more than capable of handling a 28volt 300amp(Max) load continuously with a adequate cooling solution and be controlled by a 5 volt relay connected to their gate, correct?

They don't need to be fast switching etc... I just need them to handle 28 volts and up to a 300 amp load(Max) (normally much lower) for a continuous amount of time(few hours etc..) and be controlled by a 5 volt relay connected to there gate...
* with a adequate sized heat sink and fan

I just want to make sure these mosfets will work for my situation and if not maybe you could suggest one that would , before I whip up a schematic

Thx
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Papabravo

Joined Feb 24, 2006
15,431
I think your problem is more complex than you imagine. With such high power levels I think you need to consider the multiple stress factors that each device will encounter and build your system to be fault tolerant in the extreme. I would be thinking about managing the maximum junction temperature of each and every device and have spare devices that you could switch in an out if required. You cannot be too careful with this kind of thing. IMHO you have stars in your eyes. For a 28 volt system @300 Amps, I think you need more than a 30V part in a TO-220 package. Maybe you should look at some brick type industrial strength switches. Maybe something liquid cooled. The words "under estimation" keep coming to mind.
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
154
I think your problem is more complex than you imagine. With such high power levels I think you need to consider the multiple stress factors that each device will encounter and build your system to be fault tolerant in the extreme. I would be thinking about managing the maximum junction temperature of each and every device and have spare devices that you could switch in an out if required. You cannot be too careful with this kind of thing. IMHO you have stars in your eyes. For a 28 volt system @300 Amps, I think you need more than a 30V part in a TO-220 package. Maybe you should look at some brick type industrial strength switches. Maybe something liquid cooled. The words "under estimation" keep coming to mind.
Thx @Papabravo
First, thank you for your concern and your recommendations. But...

I don't think we're quite on the same page.... I'm going to write a detailed explanation of exactly what this is for and some detailed information / explanation. You or alot of people may know this stuff already but just in case...

Let me explain a little bit more of what this is for:
This is basically just a small part of a Entire Very Smart and Advanced Battery Management System (BMS) Which has been created by the DIY community surrounding DIY power walls and large lithium-ion battery packs.

Some Background Info:
Basically every lithium-ion battery that consists of more than one cell in series almost always has a BMS. 90% of them are very simple with no integrated circuits for the most part and just deal with cell balancing as well as over and under voltage disconnect.

So from the very simple ones to some of the more complex ones they basically all use a bunch of mosfets in parallel to act as a disconnect. Everything else on the PCB is basically just for cell balancing...

(this is the average type of BMS found in 90% of commercially made lithium battery packs & in diy battery packs)
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They usually consists of two different parallel sets of mosfets controlling the input and output disconnecting.

Even the more sophisticated or expensive ones are basically the exact same thing they just have a more extensive heatsink and cooling solutions.

But regardless they all use a bunch of paralleled mosfets in order to disconnect the battery from either being charged or from the load.

More on my question / usage case:
As I mentioned above, I'm using and much more advanced battery management system. Which basically monitors all aspects of the battery including individual cells, the load that is attached to the battery, the environment, and much more.

The BMS is running off a ESP32 microcontroller. That microcontroller monitors everything and then controls a 5volt relay which can be used to trigger whichever type of battery disconnect you would like to use. Most people using this type of system choose to use a large contactor, SSR solid state relay, etc....

I've been an electrician for over 25yrs and have seen my share of failed contactors and relays:oops:

So currently I am using a large continuous duty 500amp contactor as means of disconnect but would like to create a solid state circuit using a bunch of parallel mosfets connected to a big beefy circuit board / busbars or my battery disconnect...

So that's where my initial question comes in:
I'm trying to figure out which Mosfets I should use for this application? (using 10 or more in parallel)

My Use Case:
30v Max
300a Max
5v Signal


@Papabravo
So from what I gathered from your original response is, those mosfets I originally listed would work but I should find some with a higher maximum voltage? And if so the rest of the characteristics of that mosfet are fine for this application?

Or could you / anyone recommend a better suited mosfet for my application?

Thanks a lot every everybody for your help and input.
 

Orson_Cart

Joined Jan 1, 2020
43
the biggest issue is protection against over-volts at turn off - which depends on the inductance of the line - slower turn off helps - but the delta T of the mosfet die needs to be calculated.
 
Ive had lots of experience in the Power Electronics Industry and also know contactors well.
The most robust switch you can get is a correctly sized contactor. Its easy to protect a contactor from destruction. Any silicon is less robust than a contactor, particularly in the event of faults. Its hard to protect them adequately.
A contactor will provide perfect isolation but slow operation, whilst a Mosfet, for example can switch quite quickly but is subject to failure due to heat and overcurrents and overvoltages.
As you have discovered, paralleling up many Mosfets is the common way to made an adequately robust switch but it still has its faults
And remember that in a battery switch you need a P and an N channel device back to back as the body diode provides a reverse current path which is not desirable where currents can flow into and out of the battery.
 
Just some points to consider:
  • If feasible, consider to interrupt the GND return line, not the plus line. This eases the overall design. (Otherwise you'll need a floating power supply to drive the gates.)
  • I'm reading a lot about a "5 V relay", but nothing about the Ugs to be applied. Do yourself a favor and plan for Ugs = 12 V to get Rds as low as possible!
  • "Logic level" sounds nice, but I'd suggest to use as few MOSFETs as possible (with a lower Rds each). "Logic level" does not qualify for this and Ugs = 5 V does not drive the MOSFET(s) to the lowest Rds,on.
 
Correct for Standard FETs.
PROFETs, also likely available from other automotive parts suppliers, have a logic interface integrated and do not need any additional drive parts. These chips also contain extensive protection functions. Some offer current measure possibility and a failure output.
These devices are available for line and ground switching as well, in a large power range for various applications.
Quite simple to use and reliable, but of course more expensive than standard FETs. Depends on your application ..
 
Correct for Standard FETs.
PROFETs, also likely available from other automotive parts suppliers, have a logic interface integrated and do not need any additional drive parts. These chips also contain extensive protection functions. Some offer current measure possibility and a failure output.
These devices are available for line and ground switching as well, in a large power range for various applications.
Quite simple to use and reliable, but of course more expensive than standard FETs. Depends on your application ..
The PROFETs seem a smart choice - at the first glance.
Looking closer, you either get a 2-digit mOhm Rds or a maximum operating voltage of less than 30 V. None of these serves the requirements specification with a reasonable number of FETs.
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
154
Thank you everyone for your help/input/recommendations. It's greatly appreciated.

Currently at work and will thoroughly go over everything when I get home.

Just wanted to follow up and let you know this is still a ongoing question and I'm here.
 
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