upgraded FETs - Page 21

charliebrown · #**301** 07-13-2004, 12:17 PM

Hey Jshwaa, I couldn't contact you via email, but what I'm trying to say is that I didn't mean to get under your skin with all those questions, it's just that all those principles you mentioned were new to me, I hadn't really been taught that stuff, so learning it here was a bit difficult. I didn't mean to insult you or anything, if I did then I'm sorry.

So, anyways, I hear that there's already a regulator in the Xmod board stock to keep sensitive components safe, but the FETs for the motor and steering system are grounded....so, I'm thinking, perhaps we can just upgrade the stock reggie or something?

Also, I was talking to dirtjump9 yesterday, and an idea he had was to install, say, a 220uf or a 4700uf capacitor onto the batteries. This way, when the car is turned on, the capacitor will charge up from the batteries, and when the throttle is punched, the capacitor would dump all of the stored voltage into the ESC at once, and then it would fade out, but the car would already have started going in motion....it's more of an idea for acceleration purposes...after it's done boosting the speed, though, it could put a strain on the ESC and slow the system down or something....but since the car would already have gained momentum, there wouldn't be much of a noticeable difference anyway. It's just a theory...oh, and you can get this capacitor at www.pnracing.com

Just a theory....

Chuckster...

Jshwaa · #**302** 07-13-2004, 07:32 PM

Really, there was no harm done. I was agravated and starting to gather a hunch that you might have just been mocking me. Who cares?

About your theory. Yes, there is a phenomenon of applying caps for a punch off the line. I tried it myself and I'm not sure if there's a noticeable difference or not. You are relieving your cells of having to provide that punch, that's for sure. Also, there's no voltage regulator on the xmod board. What you might be referring to is the zener diode. That helps maintain voltage, yes, but it works much different than a voltage regulator. Also, that zener has a max voltage too, and I'm not sure if it's greater than 8.4V.

The zener acts like a dam in a way. If you have it in a circuit(cathode to positive, anode to ground), the cathode will be at 5V (or whatever the designed breakdown voltage happens to be) any excess voltage is shorted to ground, through its anode. So the more voltage you apply, over the zener breakdown, is just being wasted.

THAT's why the regulator is novel in that it SWITCHES on and off in just the right frequency to allow 5V at its output, no matter what voltage variance happens to occur at its input(within design contraints found on data sheet). The excess voltage is not shorted to ground. So, for example, if you have 10V at the regulators input, the regulator is going to be on half the time and off the other half, emulating 5V at its output. Very little wasted power.

meteoraclown · #**303** 07-20-2004, 11:05 AM

Quote:

Originally posted by neurokinetik

N channel 2x IRL3705N $2.60 each in single quantities
P channel 2x IRF4905N $3.21 each in single quantitiies

[/b]

ok i just searched digikey for the fets and here's what i got
for the IRL3705N http://www.digikey.com/scripts/DkSea...272945&Site=US
i hope thats the one but there out of stock with those.
and the IRF4905N they can't find it. anyhelp on that.

jon.jon · #**304** 07-20-2004, 11:35 AM

Try irf4905 its in stock

meteoraclown · #**305** 07-20-2004, 11:50 AM

is it the same?

jon.jon · #**306** 07-20-2004, 11:56 AM

Quote:

Originally posted by jon.jon
Try irf4905 its in stock

IRF4905N

IRF4905

try it without the N

LINK

meteoraclown · #**307** 07-20-2004, 01:32 PM

ok thanks. now where can i get a circuit board? i have to check my rat shack.

jon.jon · #**308** 07-20-2004, 01:48 PM

yeah the shack got a few small varieties.

But my questions is what would you gain or benefit from stacking these large mosfets?

Or can you?

meteoraclown · #**309** 07-20-2004, 01:56 PM

you could read all 16 pages and find out. all it does is you can run larger faster motors with out have the risk of frying you esc.

jon.jon · #**310** 07-20-2004, 02:11 PM

I should know this topic word for word by now

but thats how I was able to install my fets but I believe no one ever spoke of it and I dont think anyone has tried it Im thinking less resistance and more power but I dont know nothing about this stuff I just try to follow the insrtructions

Jshwaa · #**311** 07-20-2004, 04:16 PM

Quote:

But my questions is what would you gain or benefit from stacking these large mosfets?

What you have to gain with the larger FET's is the same as what you have to gain with the smaller ones. You gain power dissipation, which really means that you gain a higher level of current flow before your FET's fry. With the larger FET's, stacking might not be needed. To stack the larger ones, you just do the same as what you do with the small ones. Just attach the legs of the stacked one to the legs of the one being stacked on and solder.

jon.jon · #**312** 07-20-2004, 11:32 PM

Quote:

Originally posted by Jshwaa
What you have to gain with the larger FET's is the same as what you have to gain with the smaller ones. You gain power dissipation, which really means that you gain a higher level of current flow before your FET's fry. With the larger FET's, stacking might not be needed. To stack the larger ones, you just do the same as what you do with the small ones. Just attach the legs of the stacked one to the legs of the one being stacked on and solder.

thanks
I might give it a try to see what will happen if I do it Ill post results

Kevmiester · #**313** 07-29-2004, 06:21 PM

i have know idea what the science of fets are so ihave this to say: I like cheese

charliebrown · #**314** 08-19-2004, 07:33 PM

Jshwaa, I have a few questions about how you went about unleashing the full power of the batts on the FET/motor system....

One would think that you would just connect a wire from the ground pin on the regulator to the source pin on the P channel FETs (since the P channels handle the postive current and the N's handle negative), but for a P channel FET to be on, the gate voltage has to be lower than the source voltage...am I correct? Now, my question is how did you go about unleashing 100% of the voltage on the FETs/motor.

Also, the regulator data says that you can only let 1 amp go through it, so how did you take care of that?

Asking all these questions would be so much easier if I could talk to you in chat or by email....

Chuckster...

Jshwaa · #**315** 08-19-2004, 08:56 PM

Quote:

One would think that you would just connect a wire from the ground pin on the regulator to the source pin on the P channel FETs (since the P channels handle the postive current and the N's handle negative), but for a P channel FET to be on, the gate voltage has to be lower than the source voltage...am I correct? Now, my question is how did you go about unleashing 100% of the voltage on the FETs/motor.

First of all, regardless of how an FET works, the ground pin of the regulator is connected to 0V. A cell has a positive terminal(+) and a negative terminal(-). The 0V is at the negative-most terminal of the series combination of cells. So if you have 4 cells in series......
connect input of regulator here--------------->(+)(-)(+)(-)(+)(-)(+)(-) <----------- connect ground pin of regulator here