My Motors got me to Tap into Radiant Energy

[sampojo]

Adding in the heavy wires on the MOSFETs

looking at using 12 or 14ga solid house wires on the light blue connections here...



I am supposing I should use 12 rather than 14, but I know it will take a lot more heat to solder, worrying about the components. Guess I can put some more heat sinking action on it like a small damp cloth...

Would 12ga be enough for an Imperial style operation taking 12-18A?

[sampojo]

Heat sink ology

Hello Sam,

If the Heat Sink is supposed to be attached to Ground, and Ground goes to Battery Negative...Then you need to Isolate the Heat Sink from the Drain Contact through the Mica/Bakelite transparent sheets as also a washer/nut that is made of heat resistive plastic for the bolt/nut not to make contact with FET's Drain Plate...Only then you could use the Heat Grease based on White Silicon Compound which is not conductive electrically, only transfers heat.

That is my opinion, however, I have to check again the Monster Driver Diagrams

Regards Sam

Ufopolitics

hmm... So yeah the center pin goes to the drain and to the heat sink and to the negative on the motor, not battery ground. I guess grounding means grounding to battery ground and would be optimal. So mica insulators would be good. Got some pads from the salvaged heat sinks that must do just this job! only 2 though, good for only 1 board, but I at least know what to look for now.

I am tempted to leave them floating and ungrounded but I bet that's a bad idea. Or even attached directly to Drain without an insulator. Again probably a bad idea. I wonder what Dana did?

[iankoglin]

Hello my Dear Friend Kogs,

I believe the above statement tends to confusion...or am I wrong?

The Drain of the MOSFET should go to the Negative Input of Motor, and Not to the Negative of Battery...am I right?

Negative from Battery should go to Source of the FET.


Kind Regards


Ufopolitics

G'day UFO
You are Right The back of the Mosfets is also connected to the centre pin the Drain which when connected to the heat sink, and this is connected to the negative of the Motor


Thanks for picking up my error I should proof read before pushing the submit button

Thanks my friend

[iankoglin]

Hello Sam,

If the Heat Sink is supposed to be attached to Ground, and Ground goes to Battery Negative...Then you need to Isolate the Heat Sink from the Drain Contact through the Mica/Bakelite transparent sheets as also a washer/nut that is made of heat resistive plastic for the bolt/nut not to make contact with FET's Drain Plate...Only then you could use the Heat Grease based on White Silicon Compound which is not conductive electrically, only transfers heat.

That is my opinion, however, I have to check again the Monster Driver Diagrams

Regards Sam

Ufopolitics

G'day UFO and Sampojo
I corrected my post above

The back of the Mosfets is also connected to the centre pin the Drain which when connected to the heat sink, and this is connected to the negative of the Motor

Kindest Regards

Kogs a bit

[iankoglin]

G'day Sampojo
Bidirectional means just that you do not need to worry about polarity
With regard to the diodes that are polarized you will notice that they have a stripe around the circumference one end and if they come taped together the tape on this leg is red colour this is the cathode end the striped end


The back of the Mosfets is also connected to the centre pin the Drain which when connected to the heat sink, and this is connected to the negative of the Motor
I hope this helps

G'day UFO, Sampojo and all others
I wrote the above in a hurry and did not proof read it
UFO I am glad you noticed my error and I have corrected the above post

So as to stop any confusion I will delete this Post in a few Days

Kindest Regards

Kogs has never ever made even one mistake Just 100's of errors and still going

[Ufopolitics]

If...

Kogs, thanks a million! so cool to have a show-stopper problem when you go to sleep at night and have blokes on the other side of the world answer the question for you when you wake up in the AM!

Heres another worry wort problem, can't find my electronic heat conductive grease anywhere but would like to use it on the heat sink, but am concerned it may affect electronic conductivity on the ground connection of the heat sink. Better off grounding it independently then?

Hello Sam,

If the Heat Sink is supposed to be attached to Ground, and Ground goes to Battery Negative...Then you need to Isolate the Heat Sink from the Drain Contact through the Mica/Bakelite transparent sheets as also a washer/nut that is made of heat resistive plastic for the bolt/nut not to make contact with FET's Drain Plate...Only then you could use the Heat Grease based on White Silicon Compound which is not conductive electrically, only transfers heat.

That is my opinion, however, I have to check again the Monster Driver Diagrams

Regards Sam

Ufopolitics

[Ufopolitics]

Drain To Negative of Battery?!

The back of the Mosfets is also connected to the centre pin the Drain which when connected to the heat sink, and this is connected to the negative of the battery

Hello my Dear Friend Kogs,

I believe the above statement tends to confusion...or am I wrong?

The Drain of the MOSFET should go to the Negative Input of Motor, and Not to the Negative of Battery...am I right?

Negative from Battery should go to Source of the FET.


Kind Regards


Ufopolitics

[sampojo]

thanks Kogs! conductive grease anyone?

G'day Sampojo
Bidirectional means just that you do not need to worry about polarity
With regard to the diodes that are polarized you will notice that they have a stripe around the circumference one end and if they come taped together the tape on this leg is red colour this is the cathode end the striped end


The back of the Mosfets is also connected to the centre pin the Drain which when connected to the heat sink, and this is connected to the negative of the battery

I hope this helps

Kogs, thanks a million! so cool to have a show-stopper problem when you go to sleep at night and have blokes on the other side of the world answer the question for you when you wake up in the AM!

Heres another worry wort problem, can't find my electronic heat conductive grease anywhere but would like to use it on the heat sink, but am concerned it may affect electronic conductivity on the ground connection of the heat sink. Better off grounding it independently then?

[iankoglin]

My mouser part from Fairchild does not have a color band on the part to denote the cathode. The datasheet diagram says its supposed to. Can't just hook up a multimeter to see which way the current goes on these. Its says bidirectional. Does that mean it doesn't matter which way it goes?

Any body know a way to tell which side is the cathode on these?

RE post on MOSFETs, thanks cornboy! and thx! Very informative.

G'day Sampojo
Bidirectional means just that you do not need to worry about polarity
With regard to the diodes that are polarized you will notice that they have a stripe around the circumference one end and if they come taped together the tape on this leg is red colour this is the cathode end the striped end


The back of the Mosfets is also connected to the centre pin the Drain which when connected to the heat sink, and this is connected to the negative of the Motor
I hope this helps

[sampojo]

Ground heatsinks for MOSFETs?

Should the heats sinks for the MOSFETs on Monster driver be grounded to board ground?

[sampojo]

PKE250CA transil diode problem on Monster driver

My mouser part from Fairchild does not have a color band on the part to denote the cathode. The datasheet diagram says its supposed to. Can't just hook up a multimeter to see which way the current goes on these. Its says bidirectional. Does that mean it doesn't matter which way it goes?

Any body know a way to tell which side is the cathode on these?

RE post on MOSFETs, thanks cornboy! and thx! Very informative.

[Cornboy 555]

Assembling my OSHpark Monser driver v5.1 boards finally. On the MOSFET, Pin 1 is the gate, Pin 2 the drain and Pin 3 the source. What I am seeing seems a little counter intuitive, is that the "source" pin is hooked up to the board and battery ground then? Is my understanding correct? Here are the diagrams.
Schematic: (Note: R2 value is incorrect, has been changed to 330)


Package diagram


Piece schematic


Using 1 ohm on R3,8

Any input appreciated

Hey Joey, that is correct, source to battery negative, drain to - end of motor coils.

You are simply using these boards as an on/off switch on the low side, or negative side, completing the circuit.

Great to see you building these now.

Regards Friend, Cornboy.

[sampojo]

MOSFET question

Assembling my OSHpark Monser driver v5.1 boards finally. On the MOSFET, Pin 1 is the gate, Pin 2 the drain and Pin 3 the source. What I am seeing seems a little counter intuitive, is that the "source" pin is hooked up to the board and battery ground then? Is my understanding correct? Here are the diagrams.
Schematic: (Note: R2 value is incorrect, has been changed to 330)

(This is now the corrected image, using blogspot instead of photobucket)


Package diagram


Piece schematic


Using 1 ohm on R3,8 Edit: Sorry, threw up my old express PCB schematic, not numbered the same as JS T3001 schematic. It is R7,8 on this diagram and R3,9 on the JS schematic

Any input appreciated

[Farmhand]

Yep I think you got it. Theoretically the basics are simple but getting
it done with the results we want is not always so easy. There is always a "trade off".

Cheers

P.S. When we start talking of capacitors passing AC and not DC we get into an area where we kinda need to define "what is AC and what is DC".

A capacitor will pass direct current but only until it is charged and it passes
displacement current not "electron" current per se. Once the capacitor is
charged if we discharge it we can charge it again with DC, in this situation
the capacitor is being charged and discharged from a DC supply and we could
hardly call it AC but the capacitor is being charged and discharged and in
order to do that current must flow both ways, but it isn't what I would call
"AC as such".

If we take a capacitor and a battery and charge the capacitor then leave it
like that, we have effectively caused the capacitor to pass some DC by
displacement current. The statement that capacitor only pass AC and won't pass DC
is a confusing statement and completely disregards the fact that we can charge a
capacitor with a battery.

A better way would be to say that a capacitor can only pass "displacement current".

..

[Farmhand]

It seems I've blown a U7 MOSFET driver on my circuit board. Here is the source of my confusion from LN004 - PWM DRIVER for ASYMMETRIC MOTORS (V5.1) document:

"R8 [typo S/B R3], R9 shall prevent spurious oscillations at FET side. They grow up along gate capacitance and inductivity of the leads between driver and FET. Therefore it is essential to have them as short as possible. The resistor values need to be determined at the setup itself. You are advised to check before with wire jumpers only."

"You are advised to check before with wire jumpers only" needs a little explaining, I guess. I connected the wire jumpers between the output of the MOSFET driver (U7) and the gate of the MOSFETS. What that does is draw an almost infinite current, the resistance of the jumper being the only resistance. I was assuming the U7 MOSFET driver would handle the current limiting.

I = V / R : Infinite = 12V / 0R
It wouldn't be truly infinite because the wire would have some resistance and it would be limited by the amount the LM7812 and capacitors could supply but for an instant it would be everything they could deliver.

Even with the 1 Ohm value for R3 and R9 given in the schematic it would be 12 amps.
12I = 12V / 1R

My understanding of MOSFET's is that they are voltage driven rather than current driven like BJT's. So it seems they don't need nor do we want much current. Is that correct?

I'm guessing I should have used the "jumper wires" to test different resistor values and they shouldn't have been connected directly from the driver output to the MOSFET gate.

As I said in my earlier post, this is my first power handling circuit. Could someone please tell me the resistances they are using for R3 & R9 and how they came up with the value?

Hi thx1138, Basically the gate of a mosfet is a capacitor, with "N" channel parts,
when the capacitor (gate) is charged to the "turn on" voltage (typically 10 volts) the mosfet is "on",
and when the capacitor (gate) is fully discharged the mosfet is "off". To switch
the mosfet on and off fast requires a fairly high peak current both ways "on" and "off".

Because it's a capacitor it won't allow any continuous direct current to pass once the gate (capacitor) is charged.
The more the current to the gate is restricted the slower the capacitor (gate) will charge
and also cause the mosfet to turn on slower, which in turn causes a longer
amount of time that the mosfet is transitioning through it's resistance range before
it achieves it's full lowest "on" resistance. A TO220 mosfet can have typically
a up to several nF of capacitance to the gate. This capacitance needs to be
charged and discharged to from 0 to over 10 volts and back to zero as fast as
is practical in order to reduce transition resistance losses in the mosfet as
a result of the main current from drain to source heating of the mosfet itself,
due to current through a resistance while the mosfet is conducting but not yet fully "on".

A resistor between the driver and the gate will serve to restrict the current
charging the gate capacitance if it is necessary, and can damp unwanted
oscillations at the gate, but reducing the gate drive current too much is detrimental.

The charging and discharging of the mosfet gate is a "switching" loss.

Here's a PDF from microchip about it.

Driving Power MOSFETs

http://ww1.microchip.com/downloads/en/AppNotes/00786a.pdf

..

P.S. For example, I encountered a particular problem when trying to drive an IRF740
at over 1 mHz with a TC4420 mosfet driver chip, the driver chip heated up
because
it was charging and discharging the mosfet's gate capacitance 1 million times each second,
which meant it had to pass a considerable peak current for a good portion of each second.
The mosfet itself stayed cool but the driver chip got very warm because it was working hard.

..