@JohnDeere630TOPIC MERGED.Could you take a few moments to Learn How To Use The Forum.Other general help and troubleshooting advice can be found here.It will help you get the best out of the forum.
The IXTX90N25L2 cannot handle anything like 70A, its got a whole 36 milliohms of on-resistance.For 70A you need either a big MOSFET or a parallel array.You will no doubt say but the IXTX90N25L2 datasheet says 90A.However that's entirely infeasible to use in practice except as a pulse rating, that package cannot sensibly dissipate the heat or anything like it at those currents. Unless you are planning to use liquid cooling don't believe a power MOSFET's nomimal current rating, other than as a pulse rating. Some manufacturers even quote currents that will fuse the bond-wires, together with a little footnote saying "current spec applies to bare die". International Rectifier hang your heads in shame I say!Lets assume you want at most 50W dissipated in your MOSFET at 70A. I-squared-R then says the maximumon-resistance you can afford to have is 10 milliohms.However that's almost impossible to find at high voltage, the best I found was https://docs.rs-online.com/f05f/0900766b814b7fa1.pdf which is 14.5 milliohm, so will dissipate about 75 watts requiring a massive heatsink.A good choice for high power is a screwterm style packaged MOSFET such as: https://docs.rs-online.com/365d/0900766b80a3b4bf.pdfThis will run cooler on a big heatsink and its leads really can handle 70A without stress, unlike the TO264 packaged devices. Its slightly higher at 18 milliohms though.
Anyway, I like the IXFN 140N20P part a lot. I didn't know that existed, as it didn't show up in my google searches, being 115 amps.
The way to find electronic parts is using parametric search at one of the electronics suppliers websites, places like Mouser, Farnell, Digikey, etc. You can search simultaneously on many different parameters including whether parts are going to be supported for the future, and most importantly price and availability.