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

>  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

> 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)

"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 

>>
>>
>
> 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 

>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?

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

>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!