Good to know, thank you. I found the FQP47P06 which can handle 47A.The maximum current rating of that MOSFET is 27A which is too close to 25A for decent reliability. And it has a maximum on resistance of .07 ohms which would drop 1.8V when conducting 25A and dissipate 45W which would require a large heat sink for the transistor.
You should derate at least 75%, so find a MOSFET that has at max current rating of 33A or more. The larger the transistor the lower the ON resistance which means lower ON voltage and power dissipation, which also reduces the heat sink requirements.
Yes.So, in conclusion, you're saying that ALL fets have this Rds(on) resistance and that there will ALWAYS be a voltage drop from source to drain ....?
Yeah, it doesn't get much better than this for that voltage/current rating.
MOSFETS aren't like mechanical relays which may have only a few milliohms of contact resistance. Even with that low MOSFET resistance of 12 milliohms you will still be dissipating 7.5 watts at 25A so be sure to mount the MOSFET on a decent heat-sink.
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