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  #1  
Old 11-06-2003, 06:51 PM
Wedginator Wedginator is offline
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upgraded FETs

o wow, its been a while since i posted... anyways, I replaced the Xmods' stock FETs with 4562's. I had some left over from stacking mini-z FETs.

At the moment, the FETs lie 2x1 cuz of the heatsink in the way (and of course, i'm too lazy to cut the heat sink). I don't notice too much of a difference cuz i'm using a stock motor but I do notice some torque increase. Before the modification, I couldn't tire spin, but after, i can spin the tires whenever i want when i bury the throttle.

I'm hoping to get a faster motor so I can feel more of this upgrade.

Sorry, I can't post pics cuz my digi-cam is horrible and can't make out the words on the FET. But however, I'll try to take pics of the stock FETs cuz they have this white goo visible on it.
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  #2  
Old 11-06-2003, 09:56 PM
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neurokinetik neurokinetik is offline
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Stock FETs are 2SA1792. Four of them are used, two on the top of the board, and two on the bottom. Not sure if this is how the Mini-Z does it or not, I only saw stacks of two in the pics.

I posted on Mini-ZRacer about an idea to use much larger FETs instead of stacking the small ones (though I didn't say it was for an XMod ) and I still think this is the way to do it. It avoids the heatsink problem (Heat sinks would be attached directly to TO220 packaged FETs) and allows you to pass as much as 70A through them. Of course at this point, thicker wires will be needed, and traces on the boards might need to be beefed up as well. But the reliability of such a setup should be far better, and more cost effective. Such a setup would cost about $10 for the FETs (two each of N channel and P channel would be required), and a couple of bucks more for the board and wires, and would be the equivalent of having more than 10 stacked FETs.

I just need to order my parts and test this setupto be certain it works.
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  #3  
Old 11-07-2003, 09:18 AM
mbartell mbartell is offline
so I re-wired it
 
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Do you think that by having fets on the top and bottom of the board, it already has a "stack" built in?
Now the othere thing I'd be wondering- do you put the new added ones on the top or the bottom? Or both?
One extra on each?
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  #4  
Old 11-07-2003, 09:59 AM
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neurokinetik neurokinetik is offline
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That's what I'm thinking. I need to examine the circuit board more closely to make a determination, but my initial look led me to believe that we are getting four FETs to run the motor, rather than just two. If that is indeed the case, then it really wouldn't matter which way you stack (up or down), as they are all connected the same anyway.
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  #5  
Old 11-07-2003, 10:15 AM
Wedginator Wedginator is offline
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The FETs on the bottom run the motor, and the FETs on the top run the steering servo. There's no point changing the servo FETs unless you want super high speed steering; which is kinda a waste of FETs....
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  #6  
Old 11-07-2003, 10:46 AM
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What we really need to know is what the specs are on the stock FETs. I have been unable to find them anywhere so far. If I knew who made them, it would help, but they only have part and lot numbers printed on them with no maunfacturer's logo. A1792 is what they say, I'm assuming they are 2SA1792 (Toshiba). They could actually be UPA1792 (NEC).
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  #7  
Old 11-07-2003, 02:56 PM
mbartell mbartell is offline
so I re-wired it
 
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Well, the only way I can figure it out would be to see what it can take, and compare it to what the known values are.... ummm I don't want to do that. I can wait.
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  #8  
Old 11-07-2003, 03:05 PM
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Quote:
Originally posted by mbartell
Well, the only way I can figure it out would be to see what it can take, and compare it to what the known values are.... ummm I don't want to do that. I can wait.
In theory, the manufacturer should have a data sheet out for the stock FETs. International Rectifier is really good about this, putting all of their data sheets online. Once we figure out who makes these things, then we can probably get this data.

Anyway, I ordered four of the big TO220 style FETs today from Digikey, and also a set of 10 IRF7389 FETs in case the other method doesn't work out.
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  #9  
Old 11-09-2003, 05:26 PM
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what's the diff of the P-channel and the N-channel power rating(Amp)..

which one is this one i should go by....i belive the p-channel is a negative amp rating and the n-channel is positive...
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  #10  
Old 11-09-2003, 11:49 PM
1fastRSX 1fastRSX is offline
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Newbie...

i just bought an rsx x-mod friday and im hooked...i already bought the handling upgrade and the stage 2 engine upgrade...could some one clue me in on all the abbreviations... fet, nml, and so on?? thanks
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  #11  
Old 11-10-2003, 11:47 AM
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neurokinetik neurokinetik is offline
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Re: Newbie...

Quote:
Originally posted by 1fastRSX
i just bought an rsx x-mod friday and im hooked...i already bought the handling upgrade and the stage 2 engine upgrade...could some one clue me in on all the abbreviations... fet, nml, and so on?? thanks
FET - Field effect transistor, used in the...
ESC - Electronic Speed Controller
NML - No Motor Limit, an individual that hand winds and assembles motors.
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  #12  
Old 11-10-2003, 11:56 PM
1fastRSX 1fastRSX is offline
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So what does all of this mean?
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  #13  
Old 11-10-2003, 11:59 PM
Wedginator Wedginator is offline
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read about FETs ESCs and NML at http://www.mini-zracer.com

do a search there and you'll find tons of topics that discuss this in extreme detail... in fact, so much detail, that you'll be able to teach a class....
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  #14  
Old 11-12-2003, 02:15 PM
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how do you get the old fets out 2 put new ones in i am new so just curious.
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  #15  
Old 11-12-2003, 02:53 PM
Wedginator Wedginator is offline
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You'll need to unsolder the old ones first.... then replace it with the new ones....
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