how to get this PWM DC motor control to handle more power

[causalitist]

this is the circuit in question, page 3 is the part I'm asking about, not
the PWM circuit on page 1,2:
http://kitsrus.com/pdf/k166.pdf

The IRF4905 and IRFZ44 limit current to 74A and 49A respectively.

The LM324 Quad op-Amp limits Voltage to 32V

What is an op-amp that will work here, but be able to handle 100v or maybe
55v min?

As far as current and total wattage , I'm looking for min 100A , ideally
500A
As far as Wattage/practical heat dissipation, obviously ideal Wattage
would be (500A*100V) , I would think many many mosfets working together
would be the only practical solution to heat dissipation/wattage.

I'm a 1rst year EE major, we haven't covered this stuff at all, I made the
original circuit, but want it to handle more power.
I've wanted to make this circuit since I was 13 years old, I've been
saving this huge brushed DC motor since I was 13

Thank you so much!

 

[Tim Wescott]

causalitist wrote:

this is the circuit in question, page 3 is the part I'm asking about, not
the PWM circuit on page 1,2:
http://kitsrus.com/pdf/k166.pdf

The IRF4905 and IRFZ44 limit current to 74A and 49A respectively.

The LM324 Quad op-Amp limits Voltage to 32V

What is an op-amp that will work here, but be able to handle 100v or maybe
55v min?

As far as current and total wattage , I'm looking for min 100A , ideally
500A
As far as Wattage/practical heat dissipation, obviously ideal Wattage
would be (500A*100V) , I would think many many mosfets working together
would be the only practical solution to heat dissipation/wattage.

I'm a 1rst year EE major, we haven't covered this stuff at all, I made the
original circuit, but want it to handle more power.
I've wanted to make this circuit since I was 13 years old, I've been
saving this huge brushed DC motor since I was 13

Thank you so much!

You'll need an industrial-strength power line to fire it up! You

definitely need to investigate a career in power electronics if this
sort of thing turns you on.

The op-amp solution is slow, weird (op-amps don't make good
comparators), and subject to shoot-through. The generally recognized
way to do this, unless you are intent on saving money on the circuit at
the expense of a protracted design cycle, is to use a gate driver on the
MOSFET. Something like a HIP4082 will let you use N-channel MOSFETS (or
NPN IGBTs) while taking care of at least some of necessary MOSFET drive
issues.

You won't be dissipating 50kW. If you assume an 80% efficient motor
drive then you'd be dissipating "only" 10kW, but you can probably do
better than that if you hold the PWM frequency down. You can get some
pretty big MOSFETs (and some astonishingly large IGBTs), so the "real"
problem is finding a heatsink that will work on your budget.

I'd keep doing web searches for circuits, and maybe get a book on power
electronics.

Good luck. If you work at it long enough it'll be your senior project.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[Robert Monsen]

On Tue, 28 Oct 2008 10:58:38 -0500, "causalitist"
<nate53143@hotmail.com> wrote:

this is the circuit in question, page 3 is the part I'm asking about, not
the PWM circuit on page 1,2:
http://kitsrus.com/pdf/k166.pdf

The IRF4905 and IRFZ44 limit current to 74A and 49A respectively.

The LM324 Quad op-Amp limits Voltage to 32V

What is an op-amp that will work here, but be able to handle 100v or maybe
55v min?

As far as current and total wattage , I'm looking for min 100A , ideally
500A
As far as Wattage/practical heat dissipation, obviously ideal Wattage
would be (500A*100V) , I would think many many mosfets working together
would be the only practical solution to heat dissipation/wattage.

I'm a 1rst year EE major, we haven't covered this stuff at all, I made the
original circuit, but want it to handle more power.
I've wanted to make this circuit since I was 13 years old, I've been
saving this huge brushed DC motor since I was 13

Thank you so much!

The only practical way to do this would be using a microprocessor to
monitor current and voltage levels, generate the pwm outputs, and to
set the precise duty cycles required for the load. 500A out of a bank
of lithium ion batteries will cause your mosfets to smoke is a
millisecond if not controlled very precisely. In addition, you need to
worry about the inductive effects of the motor, which will can cause
huge spikes which will violate the voltage restrictions on the mosfets
when the current is changed. You'll also need big heatsinks.

I'd start small, maybe 20A, and see where that takes you. You'll learn
as you blow things up.

You can get really cheap parts to smoke at the various online surplus
electronics outlets, like goldmine-elec.com. Pick up a bunch of P and
N hv mosfets, and a bunch of shottky diodes (which you'll use to
protect the mosfets). For $50, you can get way more parts than you'll
need during the learning process. Once you figure out the gotchas, you
can buy real parts at digikey or mouser.

How big is the motor? Are you building a car?

Regards,
Bob Monsen

 

[Tim Wescott]

Robert Monsen wrote:

On Tue, 28 Oct 2008 10:58:38 -0500, "causalitist"
nate53143@hotmail.com> wrote:

this is the circuit in question, page 3 is the part I'm asking about, not
the PWM circuit on page 1,2:
http://kitsrus.com/pdf/k166.pdf

The IRF4905 and IRFZ44 limit current to 74A and 49A respectively.

The LM324 Quad op-Amp limits Voltage to 32V

What is an op-amp that will work here, but be able to handle 100v or maybe
55v min?

As far as current and total wattage , I'm looking for min 100A , ideally
500A
As far as Wattage/practical heat dissipation, obviously ideal Wattage
would be (500A*100V) , I would think many many mosfets working together
would be the only practical solution to heat dissipation/wattage.

I'm a 1rst year EE major, we haven't covered this stuff at all, I made the
original circuit, but want it to handle more power.
I've wanted to make this circuit since I was 13 years old, I've been
saving this huge brushed DC motor since I was 13

Thank you so much!




The only practical way to do this would be using a microprocessor to
monitor current and voltage levels, generate the pwm outputs, and to
set the precise duty cycles required for the load. 500A out of a bank
of lithium ion batteries will cause your mosfets to smoke is a
millisecond if not controlled very precisely. In addition, you need to
worry about the inductive effects of the motor, which will can cause
huge spikes which will violate the voltage restrictions on the mosfets
when the current is changed. You'll also need big heatsinks.

I'd start small, maybe 20A, and see where that takes you. You'll learn
as you blow things up.

You can get really cheap parts to smoke at the various online surplus
electronics outlets, like goldmine-elec.com. Pick up a bunch of P and
N hv mosfets, and a bunch of shottky diodes (which you'll use to
protect the mosfets). For $50, you can get way more parts than you'll
need during the learning process. Once you figure out the gotchas, you
can buy real parts at digikey or mouser.

How big is the motor? Are you building a car?

Regards,
Bob Monsen

Everything Bob says, except the microprocessor is optional. A good
analog controller will do just fine.

Of course, it may be _easier_ to do with a micro, but it's not _necessary_.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[Jasen Betts]

On 2008-10-28, causalitist <nate53143@hotmail.com> wrote:

this is the circuit in question, page 3 is the part I'm asking about, not
the PWM circuit on page 1,2:
http://kitsrus.com/pdf/k166.pdf

The IRF4905 and IRFZ44 limit current to 74A and 49A respectively.

The LM324 Quad op-Amp limits Voltage to 32V

What is an op-amp that will work here, but be able to handle 100v or maybe
55v min?

you may have to build your own. 100v signal transistors are fairly common



Bye.
Jasen

 

[Huff]

On Oct 29, 2:58 am, "causalitist" <nate53...@hotmail.com> wrote:

this is the circuit in question, page 3 is the part I'm asking about, not
the PWM circuit on page 1,2:http://kitsrus.com/pdf/k166.pdf

The IRF4905 and IRFZ44 limit current to 74A and 49A respectively.

The LM324 Quad op-Amp limits Voltage to 32V

What is an op-amp that will work here, but be able to handle 100v or maybe
55v min?

As far as current and total wattage , I'm looking for min 100A , ideally
500A
As far as Wattage/practical heat dissipation, obviously ideal Wattage
would be (500A*100V) , I would think many many mosfets working together
would be the only practical solution to heat dissipation/wattage.

I'm a 1rst year EE major, we haven't covered this stuff at all, I made the
original circuit, but want it to handle more power.
I've wanted to make this circuit since I was 13 years old, I've been
saving this huge brushed DC motor since I was 13

Thank you so much!

The circuit that you have is only suitable for flea power compared
with what you are talking about. It would be hpelessly inefficient at
high power levels
As some of the other contributors suggest, browse the applications
information of the Power Electronics companies like IR.
I'd suggest that you use a High and Low side driver like an IR2110
with a separate 12 or 15V power supply for the control circuit. Use
all N-channel MOSFETs - they are cheaper for a given current and
voltage. Make sure in an H-bridge with an inductive load like a motor,
that the voltage rating of the FETs is at least 2x the supply voltage
due to the parasitic transistor dV/dT breakdown phenomenon. Make sure
the main power supply has good bypassing - big capacitors with short
leads.
What you are attempting is difficult and dangerous. You will certainly
create some smoke from failed devices. Learn but please do not die
trying.

Cheers, Hugh.
25 years of Power Electronics!

 

[amdx]

"causalitist" <nate53143@hotmail.com> wrote in message
news:ls6dnT0v_5Izq5rURVn_vwA@giganews.com...

this is the circuit in question, page 3 is the part I'm asking about, not
the PWM circuit on page 1,2:
http://kitsrus.com/pdf/k166.pdf

The IRF4905 and IRFZ44 limit current to 74A and 49A respectively.

The LM324 Quad op-Amp limits Voltage to 32V

What is an op-amp that will work here, but be able to handle 100v or maybe
55v min?

As far as current and total wattage , I'm looking for min 100A , ideally
500A
As far as Wattage/practical heat dissipation, obviously ideal Wattage
would be (500A*100V) , I would think many many mosfets working together
would be the only practical solution to heat dissipation/wattage.

I'm a 1rst year EE major, we haven't covered this stuff at all, I made the
original circuit, but want it to handle more power.
I've wanted to make this circuit since I was 13 years old, I've been
saving this huge brushed DC motor since I was 13

Thank you so much!


Check out these forums, there is usually a thread running about how to

build
high power PWM motor speed controllers.

http://www.diyelectriccar.com/forums/

http://www.evforum.net/forums/

http://visforvoltage.org/

Mike

>

 

[amdx]

"causalitist" <nate53143@hotmail.com> wrote in message
news:ls6dnT0v_5Izq5rURVn_vwA@giganews.com...

this is the circuit in question, page 3 is the part I'm asking about, not
the PWM circuit on page 1,2:
http://kitsrus.com/pdf/k166.pdf

The IRF4905 and IRFZ44 limit current to 74A and 49A respectively.

The LM324 Quad op-Amp limits Voltage to 32V

What is an op-amp that will work here, but be able to handle 100v or maybe
55v min?

As far as current and total wattage , I'm looking for min 100A , ideally
500A
As far as Wattage/practical heat dissipation, obviously ideal Wattage
would be (500A*100V) , I would think many many mosfets working together
would be the only practical solution to heat dissipation/wattage.

I'm a 1rst year EE major, we haven't covered this stuff at all, I made the
original circuit, but want it to handle more power.
I've wanted to make this circuit since I was 13 years old, I've been
saving this huge brushed DC motor since I was 13

Thank you so much!

I read the circuit oscillates at 270 hz, I've noted most commercial

controllers
oscillate at a higher frequency so you don't have to listen to them sing.
I've seen
18khz used. I couldn't get the LM324 to work at 18 khz with the circuit I
tried.
Mike
P.S. Here's how I used my huge brushed DC motor!
http://s395.photobucket.com/albums/pp37/Qmavam/?action=view&current=gokartreduced.jpg

 

[causalitist]

MORE INFO:
Thanks so much guys. the motor is about 3.3" diameter, 7 inches long.
it's rated at 24v, but it was taken out of a handicap mobility chair. Says
CIM EM801-003 on it. I know the 24v rating is very very conservative.. i
ran 36v through it last night, (3, 12v lead acids) was cranking pretty
good,
the wire welded to the battery terminal on startup.. but I let it run 1
hour, and it was barely warm.. doesnt seem to draw too much current once
spinning.
i ended up buying a different kit, http://www.kitsrus.com/pdf/k67v3.pdf
along with a few handfuls of
IRFB3206 Pd=300w, Rds=4.1 mOhm max, 75v, 120-170nC Qg
(will use these after i burn up the cheap ones)
and I took your advice and got a bunch of FQP55N06 and IRF530 from that
surplus site you gave me.

A REASONABLE HEAT MANAGEMENT/WATTAGE GOAL?:
So given the schematic AT http://www.kitsrus.com/pdf/k67v3.pdf,
apparently the only way i will get near at least 1000watts is to put many
mosfets in parallel, and buy a long, high surface area copper heat sink
that they all bolt to, and a good fan. I CANT FIND A LONG COPPER HEATSINK
TO BOLT THEM TO .. i cant even find any copper heat sinks for t0-220.

so with 85% efficiency, 1000w = 150watts i need to dissipate.. if i use 5
of the IRFB3206, with an awesome copper heat sink they all mount to (which
hopefully you guys know where to get) .. that should do it right??


QUESTIONS ABOUT MY CIRCUIT, AND PARALLELING MOSFETS:
I am not told that the number of mosfets i put in parallel is restricted
by the total gate charge of all added together, and if the PWM signal is
too low in current, they will switch slower/get hotter.
So i need, or eventually will need to increase the current of my PWM
signal. i with the kit67, I intend to give the PWM and motor/mosfet
circuits different power supplies.
why then couldnt i just use this stock kit67, mosfet and all, as my PWM
generator.. meaning: give the kits PWM circuit a small power source... then
give the one mosfet in the circuit 5v, but a power supply capable of say,
an amp?? so i would then have a higher current pwm signal, that i could
use to switch alot of high amp mosfets in parallel.... ?

would that work?


also, when paralleling mosfets, gate resisters are needed (i'm told) to
help get them in sync.. how do I choose these?

"causalitist" <nate53143@hotmail.com> wrote in message
news:ls6dnT0v_5Izq5rURVn_vwA@giganews.com...
this is the circuit in question, page 3 is the part I'm asking about,
not
the PWM circuit on page 1,2:
http://kitsrus.com/pdf/k166.pdf

The IRF4905 and IRFZ44 limit current to 74A and 49A respectively.

The LM324 Quad op-Amp limits Voltage to 32V

What is an op-amp that will work here, but be able to handle 100v or
maybe
55v min?

As far as current and total wattage , I'm looking for min 100A ,
ideally
500A
As far as Wattage/practical heat dissipation, obviously ideal Wattage
would be (500A*100V) , I would think many many mosfets working
together
would be the only practical solution to heat dissipation/wattage.

I'm a 1rst year EE major, we haven't covered this stuff at all, I made
the
original circuit, but want it to handle more power.
I've wanted to make this circuit since I was 13 years old, I've been
saving this huge brushed DC motor since I was 13

Thank you so much!

I read the circuit oscillates at 270 hz, I've noted most commercial
controllers
oscillate at a higher frequency so you don't have to listen to them sing.

I've seen
18khz used. I couldn't get the LM324 to work at 18 khz with the circuit I

tried.
Mike
P.S. Here's how I used my huge brushed DC motor!
http://s395.photobucket.com/albums/pp37/Qmavam/?action=view&current=gokartreduced.jpg

 

[causalitist]

"causalitist" <nate53143@hotmail.com> wrote in message
news:ls6dnT0v_5Izq5rURVn_vwA@giganews.com...
this is the circuit in question, page 3 is the part I'm asking about,
not
the PWM circuit on page 1,2:
http://kitsrus.com/pdf/k166.pdf

The IRF4905 and IRFZ44 limit current to 74A and 49A respectively.

The LM324 Quad op-Amp limits Voltage to 32V

What is an op-amp that will work here, but be able to handle 100v or
maybe
55v min?

As far as current and total wattage , I'm looking for min 100A ,
ideally
500A
As far as Wattage/practical heat dissipation, obviously ideal Wattage
would be (500A*100V) , I would think many many mosfets working
together
would be the only practical solution to heat dissipation/wattage.

I'm a 1rst year EE major, we haven't covered this stuff at all, I made
the
original circuit, but want it to handle more power.
I've wanted to make this circuit since I was 13 years old, I've been
saving this huge brushed DC motor since I was 13

Thank you so much!

I read the circuit oscillates at 270 hz, I've noted most commercial
controllers
oscillate at a higher frequency so you don't have to listen to them sing.

I've seen
18khz used. I couldn't get the LM324 to work at 18 khz with the circuit I

tried.
Mike
P.S. Here's how I used my huge brushed DC motor!
http://s395.photobucket.com/albums/pp37/Qmavam/?action=view&current=gokartreduced.jpg

oh ya... as for the diode across the motor.. what specs do you guys think
i need? whats the model # of a huge one ?

also, as the motor draws massive amps upon startup, i need a huge
capacitor
from its + to ground right? how the heck does this work? its
discharged, then you give the motor power, motor draws alot of amps, as the
capacitor charges?? it wouldnt serve the purpose.. the capacitor should
be charged, waiting.. then somehow be applied to the motor right when the
motor is given power...

 

[amdx]

but I let it run 1
hour, and it was barely warm.. doesnt seem to draw too much current once
spinning.

Note: there is no load on the motor so it won't draw a lot of current and it
won't get very warm.
Put it on a scooter or cart and it will get warm.

i ended up buying a different kit, http://www.kitsrus.com/pdf/k67v3.pdf
I CANT FIND A LONG COPPER HEATSINK
TO BOLT THEM TO .. i cant even find any copper heat sinks for t0-220.

An aluminum heatsink will be fine.

so with 85% efficiency, 1000w = 150watts i need to dissipate.. if i use 5
of the IRFB3206, with an awesome copper heat sink they all mount to (which
hopefully you guys know where to get) .. that should do it right??

I'm a little confused, 1000 watts at 36 volts is only 28 amps. And (28amps
squared ) times 4.1mOhms is
only 3.3 watts.
I think you need to get some data on your motor, and decide what you
really need or want to build.

The picture I posted:
http://s395.photobucket.com/albums/pp37/Qmavam/?action=view&current=gokartreduced.jpg
has a 2 hp motor, 28v, 62amps at 2600rpm. I ran it at 36volts, on a hard
acceleration it draws 160 amps
but comes down quickly as the kart gains speed. It cruises at about 30 amps.
Mike

 

[causalitist]

I'm a little confused, 1000 watts at 36 volts is only 28 amps. And
(28amps
squared ) times 4.1mOhms is
only 3.3 watts.
I think you need to get some data on your motor, and decide what you
really need or want to build.

The picture I posted:
http://s395.photobucket.com/albums/pp37/Qmavam/?action=view&current=gokartreduced.jpg
has a 2 hp motor, 28v, 62amps at 2600rpm. I ran it at 36volts, on a hard

acceleration it draws 160 amps
but comes down quickly as the kart gains speed. It cruises at about 30
amps.

I was just going by the other guy assuming 80% efficiency(i'm optomistic,
hence 85%) .. and running 1000w .. would imply 150w being used up as heat
(what else ) .. but i don't know about this stuff, and thats why i'm
here.

the 1000w figure was just something i was going to start with, with the
motor under no load.
your saying theres no more to it but I^2*R = W .. R being of mosfet, W
being heat generated? just like anything else.. how nice!

what mosfet or other are you using for your speed control? how many?

your motor is bigger than mine .. but i intend to beat the crap out of
mine... mine is being put on a bicycle so i would imagine your specs are a
good starting place.

"28v, 62amps at 2600rpm. I ran it at 36volts, on a hard

acceleration it draws 160 amps"

with your circuit, are you required to use a big capacitor or anything,
for right off the line? .. aka the instantaneous initial short ?

right now, it sounds like I need a speed control like yours.
your kart @90 amps average amps, if you were using one Irfb2306,
you would only need 33.3 watts of dissipation .. thats not much!.. it's
alot for such a small item, but alot more do-able than i thought.

that go kart is soo cool. i'm very very curious:
1. what type, how many mosfets you use.
2. do you think my selection of Irfb2306 mosfets would work for your
scooter?
3. if so, how many would you use in your circuit?
4. do you think "kit67" could run the mosfet(s) i require? (replacing the
crappy mosfet with however many good ones I need, using a seperate circuit
board for the high power circuit)

 

[amdx]

"causalitist" <nate53143@hotmail.com> wrote in message
news:wrqdnZBvAIXBQpXU4p2dnAA@giganews.com...

I'm a little confused, 1000 watts at 36 volts is only 28 amps. And
(28amps
squared ) times 4.1mOhms is
only 3.3 watts.
I think you need to get some data on your motor, and decide what you
really need or want to build.

The picture I posted:
http://s395.photobucket.com/albums/pp37/Qmavam/?action=view&current=gokartreduced.jpg
has a 2 hp motor, 28v, 62amps at 2600rpm. I ran it at 36volts, on a hard

acceleration it draws 160 amps
but comes down quickly as the kart gains speed. It cruises at about 30
amps.

I was just going by the other guy assuming 80% efficiency(i'm optomistic,
hence 85%) .. and running 1000w .. would imply 150w being used up as heat
(what else ) .. but i don't know about this stuff, and thats why i'm
here.


the 1000w figure was just something i was going to start with, with the
motor under no load.
your saying theres no more to it but I^2*R = W .. R being of mosfet, W
being heat generated? just like anything else.. how nice!

what mosfet or other are you using for your speed control? how many?

I didn't build a controller, I bought one.

your motor is bigger than mine .. but i intend to beat the crap out of
mine... mine is being put on a bicycle so i would imagine your specs are a
good starting place.

"28v, 62amps at 2600rpm. I ran it at 36volts, on a hard
acceleration it draws 160 amps"

with your circuit, are you required to use a big capacitor or anything,
for right off the line? .. aka the instantaneous initial short ?

That would be normal to have a big capacitor across the DC line.

right now, it sounds like I need a speed control like yours.
your kart @90 amps average amps, if you were using one Irfb2306,
you would only need 33.3 watts of dissipation .. thats not much!.. it's
alot for such a small item, but alot more do-able than i thought.

Check out Alltrax, http://www.alltraxinc.com/

that go kart is soo cool. i'm very very curious:
1. what type, how many mosfets you use.
2. do you think my selection of Irfb2306 mosfets would work for your
scooter?
3. if so, how many would you use in your circuit?
4. do you think "kit67" could run the mosfet(s) i require? (replacing the
crappy mosfet with however many good ones I need, using a seperate circuit
board for the high power circuit)

I bought the Alltrax and ya the kart is very cool. I popped the

controller though, it's in for repair.
I caused the controller problem, it wasn't the Alltrax's fault. Only got to
drive it 4 days before I
caused the defect.
Mike

 

[amdx]

oh ya... as for the diode across the motor.. what specs do you guys think
i need? whats the model # of a huge one ?

also, as the motor draws massive amps upon startup, i need a huge
capacitor
from its + to ground right? how the heck does this work?

The cap is on the input of the motor controller, basically across the
battery.
BUT, after the power leads and as close to the Mosfet as possible.

its discharged, then you give the motor power, motor draws alot of amps, as
the
capacitor charges?? it wouldnt serve the purpose.. the capacitor should
be charged, waiting.. then somehow be applied to the motor right when the
motor is given power...

Ya, it is setting there charged.

Mike

 

[causalitist]

Check out Alltrax, http://www.alltraxinc.com/


that go kart is soo cool. i'm very very curious:
1. what type, how many mosfets you use.
2. do you think my selection of Irfb2306 mosfets would work for your
scooter?
3. if so, how many would you use in your circuit?
4. do you think "kit67" could run the mosfet(s) i require? (replacing
the
crappy mosfet with however many good ones I need, using a seperate
circuit
board for the high power circuit)

I bought the Alltrax and ya the kart is very cool. I popped the
controller though, it's in for repair.
I caused the controller problem, it wasn't the Alltrax's fault. Only got
to
drive it 4 days before I
caused the defect.
Mike

ok, which one did you buy, so i can buy a better one.. unless it burnt out
from being dropped or something.

anyone have any answers to my specific questions?

particularly about using the "kit67" i bought , as my PWM source, going to
the gates of 4-10 mosfets? .. the kit being supplied and outputting 5v of
course.

will someone else confirm that the power that needs to be dissipated from
a mosfet is solely a function of the mosfets resistance? given the gate
current is sufficient of course.

most importantly: with a given gate charge, how does one roughly determine
the current needed to operate the irfb3206 .. how many would be too many
for this circuit?

 

[Robert Monsen]

On Wed, 29 Oct 2008 22:23:20 -0500, "causalitist"
<nate53143@hotmail.com> wrote:

Check out Alltrax, http://www.alltraxinc.com/


that go kart is soo cool. i'm very very curious:
1. what type, how many mosfets you use.
2. do you think my selection of Irfb2306 mosfets would work for your
scooter?
3. if so, how many would you use in your circuit?
4. do you think "kit67" could run the mosfet(s) i require? (replacing
the
crappy mosfet with however many good ones I need, using a seperate
circuit
board for the high power circuit)

I bought the Alltrax and ya the kart is very cool. I popped the
controller though, it's in for repair.
I caused the controller problem, it wasn't the Alltrax's fault. Only got
to
drive it 4 days before I
caused the defect.
Mike





ok, which one did you buy, so i can buy a better one.. unless it burnt out
from being dropped or something.

anyone have any answers to my specific questions?

particularly about using the "kit67" i bought , as my PWM source, going to
the gates of 4-10 mosfets? .. the kit being supplied and outputting 5v of
course.

will someone else confirm that the power that needs to be dissipated from
a mosfet is solely a function of the mosfets resistance? given the gate
current is sufficient of course.

most importantly: with a given gate charge, how does one roughly determine
the current needed to operate the irfb3206 .. how many would be too many
for this circuit?

Regarding using the PWM controller to drive the gates, I think your
plan works. The amount of current needed can be determined by using
the capacitance of the mosfet gate, and uaing the voltage swing of the
drain divided by the time it takes to get up (or down). The formula
is I = C * dV/dt. So, if you have a 1000pF gate capacitance, and you
want to make a 100V swing in 1 microsecond, you'll need a current of
100mA while the change is occuring. If you have 10 of these, you'll
need an amp. Ballpark.

Using gate charge diagrams can work to find the required current as
well, but it is easier to use the gate-drain capacitance, Crss.

Regards,
Bob Monsen

 

[causalitist]

On Wed, 29 Oct 2008 22:23:20 -0500, "causalitist"
nate53143@hotmail.com> wrote:


Check out Alltrax, http://www.alltraxinc.com/


that go kart is soo cool. i'm very very curious:
1. what type, how many mosfets you use.
2. do you think my selection of Irfb2306 mosfets would work for your
scooter?
3. if so, how many would you use in your circuit?
4. do you think "kit67" could run the mosfet(s) i require?
(replacing
the
crappy mosfet with however many good ones I need, using a seperate
circuit
board for the high power circuit)

I bought the Alltrax and ya the kart is very cool. I popped the
controller though, it's in for repair.
I caused the controller problem, it wasn't the Alltrax's fault. Only
got
to
drive it 4 days before I
caused the defect.
Mike





ok, which one did you buy, so i can buy a better one.. unless it burnt
out
from being dropped or something.

anyone have any answers to my specific questions?

particularly about using the "kit67" i bought , as my PWM source, going
to
the gates of 4-10 mosfets? .. the kit being supplied and outputting 5v
of
course.

will someone else confirm that the power that needs to be dissipated
from
a mosfet is solely a function of the mosfets resistance? given the gate
current is sufficient of course.

most importantly: with a given gate charge, how does one roughly
determine
the current needed to operate the irfb3206 .. how many would be too
many
for this circuit?


Regarding using the PWM controller to drive the gates, I think your
plan works. The amount of current needed can be determined by using
the capacitance of the mosfet gate, and uaing the voltage swing of the
drain divided by the time it takes to get up (or down). The formula
is I = C * dV/dt. So, if you have a 1000pF gate capacitance, and you
want to make a 100V swing in 1 microsecond, you'll need a current of
100mA while the change is occuring. If you have 10 of these, you'll
need an amp. Ballpark.

Using gate charge diagrams can work to find the required current as
well, but it is easier to use the gate-drain capacitance, Crss.

Regards,
Bob Monsen

thanks!