how to get this PWM DC motor control to handle more power
in [Basics]
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From: causalitist on 29 Oct 2008 14:00 > >"causalitist" <nate53143(a)hotmail.com> wrote in message >news:ls6dnT0v_5Izq5rURVn_vwA(a)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¤t=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...
From: amdx on 29 Oct 2008 15:29 > 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¤t=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
From: amdx on 29 Oct 2008 22:24 >> >> > > 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
From: causalitist on 29 Oct 2008 23:23 >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?
From: Robert Monsen on 30 Oct 2008 01:53
On Wed, 29 Oct 2008 22:23:20 -0500, "causalitist" <nate53143(a)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 |