Difference MOSFET from v4.0 to v4.1


 
J

John Bostwick

TVWBB Wizard
Well, I finally soldered up a v4.1 board and I hook up my blower and it made my lcd brown out and I am only getting a max of 10volts(with or without blower connected). I tried a smaller blower and it was ok, I believe, although still maxing out at 10v

I have been using a Linksys wall wart (12vdc, 1000mA) without any issues with version 4 HM and the larger blower. But im going to order a 3amp wall wart

Blower BFB1012HH
Current Rating 1.1A

What would I need to do to run the larger blower? I know the mosfet changed from N-channel to a P-channel, so it makes it hard to compare the two so that I can find a P-channel that handle the load


Edit: Problem seemed to fix it self. Blower and servo both work fine
 
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I'm not sure why you'd get 10V at 100% output with no blower. I am almost certain that should read the full 12V that comes from the power supply.

The P-MOSFET is rated for 60V / 9.4A / 2.5W with an rds(on) of 185mOhm. The old N-MOSFET was 30V / 60A / 60W with an rds(on) of 9mOhm (though at our low gate voltage it was certainly much higher than that). You probably won't find a P-MOSFET with those stats just because they don't make them that high, but you're running at less than 1/10th max spec so I don't believe it will make a difference. At max current draw (1.1A) you should see 11.8V (or 0.2035V less than what your power suppy is putting out).

I'd check other things on your board because there's nothing that should exhibit the symptoms you're seeing. The PCB trace that feeds the blower adds almost as much resistance as the mosfet does!
 
on both legs of the mosfet I get 16.4 and 16.2 volts. my linksys wallwart is rated 12volts out so not sure why on two different wallwarts I have, they put out 16 to 17 volts
 
Measure the wall wart, you'll see it's also delivering 16 volts. The mosfet is simply acting as a gate, allowing the current to flow.
 
ok not sure what I did but I was able to get to work with a 75mm 12VDC 6.9CFM and im getting 15.5v to the blower and after testing with my bigger fan, it to works. Not sure what I did. I did not resolder anything. But it seems to be working fine.
 
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