Acer Predator Helios 300 Laptop Bad MOSFET?

[silver60618]

Hi Guys I have a laptop Acer Predator Helios 300, it had liquid spill, the laptop works, but does not charge battery.

Ive identified DC IN MOSFET has a short between Drain/Source. The Mosfet is BA8Y12 6406 (30v, Id=170 amps).

Can i replace this with a similar mosfet 6414A (30v Id=30amps)?

is that amp rating important in terms of variations?

thanks

[Stevedb]

Re: Laptop Bad MOSFET?

You need to change the mosfet with the exact values s0 30v 170A mosfet not one with less amps

[reformatt]

Re: Laptop Bad MOSFET?

A little common sense here would tell you the answer that this simply won't cut it.

This is a gaming laptop with a 12th gen CPU. The adaptor for it is rated at 200W (nearly 10 amp peak). This thing is going to pull a LOT of amps at peak CPU load and charging the battery. All of that going through that one MOSFET. So the designers have looked at the worst case scenario (100% CPU/GPU, battery dead flat) and chosen that device. If you are going to substitute, you need at least the same specs if not more. Underrate the replacement, you'll likely end up with it failing catastrophically and potentially burning the board.

If you want a more technical response. No FET has zero on resistance. The more current that flows through it, the more power (heat) the device produces. This is dictated by the Rds value when the device is on. P=IR remember. More current, the higher the heat generated within the FET. A lower spec FET pulling this much current will fail pretty quickly via thermal runaway etc. Resulting in potential damage to the PCB in the process.

[mon2]

Re: Laptop Bad MOSFET?

Err..typo,

P=I^2R

[silver60618]

Re: Laptop Bad MOSFET?

Thanks for the explanation. that makes sense. I wasnt able to find any online , digikey states its no longer manufactured, and the substitutes are lowerer amps 140ish

Is there any place else you can recommend I look? thanks a bunch!

https://www.digikey.com/en/products/...N6406/10244078

[reformatt]

Re: Laptop Bad MOSFET?

Lack of coffee. P=VA or I2R.

[reformatt]

Re: Laptop Bad MOSFET?

You can still get them on Aliexpress. If you can't wait, then Alpha and Omega's recommended replacement is a AONS32304 but this is rated at 140A. Parametric search shows AON6500 (Id=370A) or AON6560 (Id=200A) would be appropriate replacements.

[ktmmotocross]

Re: Laptop Bad MOSFET?

how do u explain rating of this mosfet?

170A*19V=3200W but charger is only 200W = 10.5A

[silver60618]

Re: Laptop Bad MOSFET?

Thanks again reformatt! I ordered the AON6500 Appreciate all your help! have a great holiday!

[reformatt]

Re: Laptop Bad MOSFET?

how do u explain rating of this mosfet?

170A*19V=3200W but charger is only 200W = 10.5A

You aren't dropping 19V across this FET when it's on. When acting as a switch, power dissipation is function of the current and the resistance (Rds) when the FET is saturated (from Vgs values in the datasheet).

Rds (on) @ Vgs=10V is <2.3 milliohms
Id=170a @ Vgs=10V

Therefore, using P=I2R, this equates to 66.47W (using 2.3 mohms@170amps). This is generated as heat in the MOSFET itself. You would never run it this way though, as Id=170amps is with Tc=25 degrees C. Without heatsinking, this MOSFET will get rather hot, and the Id will begin to drop off. Sustained power dissipation, at high ambient temperatures could result in thermal runaway and failure. BTW, 66W in this case is power lost as heat within the FET itself, and would subtract that from the adaptor itself. So the selection of MOSFET in this case is often based on the Rds value rather than the Id value. You want to minimise the power loss across this device when the FET is on after all.

It's up to the designer to consider worst case scenarios, and they will often overrate a device to cover the bases. MOSFET failure often occurs during state transition between on/off so this is also a consideration in a high current environment with such a small package.

[ktmmotocross]

Re: Laptop Bad MOSFET?

You aren't dropping 19V across this FET when it's on. When acting as a switch, power dissipation is function of the current and the resistance (Rds) when the FET is saturated (from Vgs values in the datasheet).

Rds (on) @ Vgs=10V is <2.3 milliohms
Id=170a @ Vgs=10V

Therefore, using P=I2R, this equates to 66.47W (using 2.3 mohms@170amps). This is generated as heat in the MOSFET itself. You would never run it this way though, as Id=170amps is with Tc=25 degrees C. Without heatsinking, this MOSFET will get rather hot, and the Id will begin to drop off. Sustained power dissipation, at high ambient temperatures could result in thermal runaway and failure. BTW, 66W in this case is power lost as heat within the FET itself, and would subtract that from the adaptor itself. So the selection of MOSFET in this case is often based on the Rds value rather than the Id value. You want to minimise the power loss across this device when the FET is on after all.

It's up to the designer to consider worst case scenarios, and they will often overrate a device to cover the bases. MOSFET failure often occurs during state transition between on/off so this is also a consideration in a high current environment with such a small package.

didnt u overcalculate it?. as charger gives max 10.5A u cannot calculate 170A as heat dissipation value. max dissipation with this charger is 2.5W. i was thinking about some spikes in charging, but 17times more is way overvalued

[reformatt]

Re: Laptop Bad MOSFET?

You posed a question about 3200W being the potential rating of the FET. My calculation was just demonstrating why that assumption was incorrect, not what it is being used for in this application.

This FET is passing all of the adaptor current, which is max 10amps. There could be many reasons why the designer selected this device. Primarily, it could have been it's low Rds value (which at 10A equates to 0.23W lost across the device while on). Cost and availability of the FET can also be a factor too. AOSMD may have been selling them cheap as they are now discontinued.

But if a design uses this specification, it's risky to underrate a device unless you know all the reasons it was selected in the first place. Rule of thumb in electronics is to equal or overrate the device as a replacement based on how the device is used and comparing specs in the datasheets. In this application, Rds, Id and Pd are probably the most important.