upgraded FETs

[Corey]

Originally posted by Jshwaa
That is a 4 channel opto-isolator with NPN transistor outputs.

What does that do, and is it necssary?

[aaron]

There's a new option available now - I've been testing it in a few cars and it's a direct solder-on replacement for the stock FETs just like the IRF7389s are but with a much lower resistance.

Becuase they switch at voltages very simialr to those found ont he XMod and Mini-Z circuits they operate at their peak efficiency

w00t!

Check out www.ausmicro.com Mini-Z and Xmods forum for more details - Once it's all sorted 'there' I'll repost it here.

A.

[mod_o_matic]

OK..i got fets..2 N and 2 P channel...each handle 10 A..i want to use the circut that was posted IN THIS fourm..dose it matter how the FETs are arranged? Like i will have it 1 P and 1 N on each side, but in what order?...

With each FET able to take 10A..it is total of 10A? or total of 20A that my upgraded fet XMOD can handle?!
Thanks!

[Jshwaa]

What does that do, and is it necssary?

An opto isolator with NPN outputs works by utilizing light to bias on/off transistors. The 4 FET control signals are connected to the anodes of the LED's at the input of the opto-isolator. The LED's then turn on their respective NPN transistor at the output of the opto-isolator. The NPN's are then used to amplify the signal and provide an adequate amount of gate voltage to fully turn the FET's on/off.

Is it necessary? Well, if you don't have a method of stepping up the voltage from IC1, you only have 3.4V to drive a mosfet transistor that wants 10V(with some power MOSFET's). So with an H-bridge that's driven by mosfets that never get fully turned on/off, you have serious losses in power which shorts the MOSFET's and your cells. I'd say it's pretty necessary, but there are other ways to do what I'm doing with the device that I've chosen. There are mosfet transistor driver IC's which do about the same thing but with a CMOS/TTL type device. ph2t was telling me about it once, but I forgot the part number. Ask him, I think he's using it on his newer nelly turbo.

[mod_o_matic]

Aright..i got my setup done almost...I just have to solder the IC5/6 wires to the FETs...
My question:
Beacuse i am not sure which of my FETs are what channel, i might have to mess around on which IC5/6 pin goes to what pin on the fet...if i get it wrong, will it "burn up" or something?

Please reply to this ASAP!!

[Jshwaa]

Beacuse i am not sure which of my FETs are what channel, i might have to mess around on which IC5/6 pin goes to what pin on the fet...if i get it wrong, will it "burn up" or something?

YES!! If you don't have your logic set up right, you will directly short your cells through the FET's. You won't have any current channeled through the motor, just through the FET's, which will burn your FET's and/or your cells. Make sure you have that right. I don't know how you have your H-bridge set up, so I couldn't tell you without looking at it. I hope you have layed out a schematic on the stock set-up and understood that before building your own. Otherwise, you're just asking to burn something.

[mod_o_matic]

FEW!!! It worked! I did not notice any smoke! The motar worked perfectly (mini-t motar that is ) One thing is, the fets got warm but not hot...the were 10A and i belive a 280 sized motar runs under 10A?!?! How can i see how much Apage the motar is drawing?
If this helps:
FETS:
ST 9718
MOROCCO
MJE30
55T

and,

ST 9701
MOROCCO
MJE29
55T

I used the "MJE29" first...i am useing the circut shown in this thread, thing is..dose it matter if i got the N or P channel fets switched into the wrong places?
Thanks for the help!!

[Jshwaa]

Good work on getting it going. You can put the motor in series with an ammeter and read the current. Please tell me that you got a digital multimeter. How in the hell are you going to be building h-bridges on xmods without a multimeter?

[mod_o_matic]

Heh, i have a multimeter, but don't know how to use it..:P YET, i still made the h-bridge (i thought it was a fet upgrade..meh!) But it works and i am happy..when i go to my LHS today i will see if they can help with the ampature thingy!!...

[Jshwaa]

when i go to my LHS today i will see if they can help with the ampature thingy!!...

Gotcha covered. First put the red probe in a hole which is labeled 20A, or 10A(fused), etc. Generally the ammeter connector is on the bottom left, and labeled A or mA(not V). Then put the multimeter setting on mA, A, etc. The abreviation next to the hole, that you plugged the red probe into, should be the same as the abreviation that is at the setting you set the multimeter to. Simple enough, eh?

Ok, now you have to put the ammeter in "series" with your current flow. In other words, treat the ammeter like a wire in your circuit, and have current flow through it and to the motor/h-bridge, etc.(or whatever you're wanting to monitor current to). If you have current flow into the red probe and out the black probe, you will get a positive current reading. If you have current flowing into the black probe and out the red, then you'll have a negative current reading. Have fun, and good luck.

[mod_o_matic]

AHHH, i see..thats how..thanks!

Problem now
It seems that not enough power is getting to the motar...what happens is like 0.8 volts or something gose to the motar, YET 4.8 v go to the ECS of the Xmod...basically, i am looseing power somewhere. i have checked all the connection, and its all good, but i just dont know what is wrong..

I am running something like a mini t motar which is 280 sized...HELP ME!!

ALSO..i think i messed up the circut, so what FETS should i get? I can get basically anyhting on this siteL http://www.e-sonic.com

[Jshwaa]

Problem now
It seems that not enough power is getting to the motar...what happens is like 0.8 volts or something gose to the motar, YET 4.8 v go to the ECS of the Xmod...basically, i am looseing power somewhere. i have checked all the connection, and its all good, but i just dont know what is wrong..

I'll quote myself from a couple posts up. I specifically addressed this.

quote:
--------------------------------------------------------------------------------
What does that do, and is it necssary?
--------------------------------------------------------------------------------



An opto isolator with NPN outputs works by utilizing light to bias on/off transistors. The 4 FET control signals are connected to the anodes of the LED's at the input of the opto-isolator. The LED's then turn on their respective NPN transistor at the output of the opto-isolator. The NPN's are then used to amplify the signal and provide an adequate amount of gate voltage to fully turn the FET's on/off.

Is it necessary? Well, if you don't have a method of stepping up the voltage from IC1, you only have 3.4V to drive a mosfet transistor that wants 10V(with some power MOSFET's). So with an H-bridge that's driven by mosfets that never get fully turned on/off, you have serious losses in power which shorts the MOSFET's and your cells. I'd say it's pretty necessary, but there are other ways to do what I'm doing with the device that I've chosen. There are mosfet transistor driver IC's which do about the same thing but with a CMOS/TTL type device. ph2t was telling me about it once, but I forgot the part number. Ask him, I think he's using it on his newer nelly turbo.

Also.....

quote:
--------------------------------------------------------------------------------
Beacuse i am not sure which of my FETs are what channel, i might have to mess around on which IC5/6 pin goes to what pin on the fet...if i get it wrong, will it "burn up" or something?
--------------------------------------------------------------------------------



YES!! If you don't have your logic set up right, you will directly short your cells through the FET's. You won't have any current channeled through the motor, just through the FET's, which will burn your FET's and/or your cells. Make sure you have that right. I don't know how you have your H-bridge set up, so I couldn't tell you without looking at it. I hope you have layed out a schematic on the stock set-up and understood that before building your own. Otherwise, you're just asking to burn something.

[mod_o_matic]

It WAS working...but seemingly...not now..Its very odd..the first time i tested it, i used two seperate power supllies...6V for the main ecs and 9 volt for the FETs...so i gess i need more power!?!?!

Well, this is now showed me that it is harder then what i thought it would be. I have the wireing set up proparly for sure, becasue it did work at a time :P So now what? What can i do? What should i look for? Is there other FETs that dont require that much energy? I NEED HELP!!

P.S: But, i used 4.8 volts to run the FETs before, and it did work..or did i just kill the FETS?

[Jshwaa]

It's really hard to say, because again, I would have to see the circuit. You say that you have it hooked up right "for sure", but something is definitely wrong, or else we wouldn't be even posting about it.

When you tested it earlier, and it worked, did you have a load on the motor? If not, then that could explain why you thought it was working fine. Was it loaded when you noticed problems? If so, then you definitely have either mistakes in wiring, logic levels at the gates of the FET's, or half-driven FET's.

[mod_o_matic]

Do you have MSN? If so add me ez_icz_is@hotmail

I think i found something out. Is it possible that becsaue i have the N channel fets getting NEGATIVE from the cells and vise versa it can effect the set up?

I think this is it..i tryed it out and the motar actaully started to move..now all i need is more pwoer, like possible 8.4 volts or something to get it moveing...