Im not sure how efficient the motor is...it's big and heavy being a permanent magnet brushed dc rated for 1000 watts. It came out of a 24VDC 50 amp lawnmower.
My trouble is in designing a PWM from scratch. PWM ICs are made to order so getting one with a high and a low output is easy. I have never seen a 555 PWM circuit with a high and low. Not that I want to use a 555. I have a lot of spare parts and ICs from things I have taken apart and so far I have no gate drivers yet but I did find a PWM IC called KA7500B. There is a circuit on the datasheet used in a typical application but I only see two outs which are the positive rail and the negative. How might I get a high PWM out and a low PWM out from this IC? I also have another IC called HD74LS221P a dual monostable multivibrator. Sounds like this might make a good PWM?

 

Thanks for the patience everyone. This is a slow process for me because if I can use existing ICs for my project then I can keep costs down. If I can't use the KA7500B or the HD74LS221P for the PWM then I will use the ones suggested by Wookie. I need a PWM IC capable of a LOW and HIGH output to drive a half bridge gate driver IC like the IR2184S or the IR2101S. Once I have all of my parts I can begin to draw an LSpice circuit for everyone to see but for now Im still in the 'feedback' stage so thanks for all of the help.

PS -I also have a LM358N and an LM324N. If I can use any combination of these for a PWM and a Gate Driver for my mosfets that would be nice.

 

Ok forget the old parts. I will buy new except the mosfets. I have the PWM I want to use that gives 100% duty cycle and it is a MC34060AP. I would like to use the HCPL-3120 but as you say Wookie, it needs a minimum of 15 volts to operate. I would like it to be 10 but I can't find an opto capable of 2.0 amps output that operates less than 15 volts. I could use a different gate driver IC but I like the idea of keeping the circuit isolated. At http://web.mit.edu/first/kart/controller_rev1.pdf, they are driving the HCPL-3120 with a dc/dc converter called DCP021212. Do I need to do this? Can I just drive the opto with the PWM or do I need to drive the dc/dc converter with a PWM first? Here are my parts as I understand it:
(MC34060AP)PWM--->(DCP021212)DC/DC Isolated Supply--->(HCPL-3120)Opto/Driver--->(RFG70N06)(RFG45N06)Mosfets--->1200 watt Brushed DC Motor.
I'll wait for feedback before I order to make sure I'm on the right track.

 

Im not sure how efficient the motor is...it's big and heavy being a permanent magnet brushed dc rated for 1000 watts. It came out of a 24VDC 50 amp lawnmower.
My trouble is in designing a PWM from scratch. PWM ICs are made to order so getting one with a high and a low output is easy. I have never seen a 555 PWM circuit with a high and low. Not that I want to use a 555. I have a lot of spare parts and ICs from things I have taken apart and so far I have no gate drivers yet but I did find a PWM IC called KA7500B. There is a circuit on the datasheet used in a typical application but I only see two outs which are the positive rail and the negative. How might I get a high PWM out and a low PWM out from this IC? I also have another IC called HD74LS221P a dual monostable multivibrator. Sounds like this might make a good PWM?

You can't get a high and a low pwm out of that controller, it was not designed for that, furthermore you need to make sure the current does not reverse directions when the low side switch is held on too long.
You need to use a chip designed for driving dc servos or use one designed for buck regulators, one that can operate in discontinuous and continuous mode.

My advice is stick to a traditional single switch and diode buck regulator, and use a ka7500 or tl494 and get familar with its limitations, then work on adding a low side fet and controling it.
Keep the frequency low, like 1khz or so.

 

I thought I needed the frequency to be above 20KHz so I can't hear it? Say maybe 100 KHz or so? Is that too fast for the motor in that it will cause too much heat in the windings? Thanks for all of the feedback. I'm learning alot researching the specs for these IC's. The answer Im really looking for at the moment though is asked in my previous post aaand that is, do I need to power the optocoupler with a DC/DC IC or can I just power the Opto with the PWM without using the expensive DC/DC chip?

 

I became a member of this forum to get help on a project of mine since I am no electronics whiz. I am really hoping to get an answer on this so I can begin my work. My questions once again are...Do I have the right parts now? Will they work together?
1) PWM IC-MC34060 AP
2)DC/DC power isolator IC-DCP021212
3)optocoupler driver- HCPL3120
4)parallel mosfets -RFG70N06

I don't really know if the DC isolator is needed but it was used in MIT's CapKart project. Maybe I can just power the driver with the PWM? I think I am following the right steps. I have looked up all of these parts, I think they will work but I'm a beginner so I would appreciate any help.

 

OK, I just came across this thread and I see one thing that has been missed rather completely. That is about "back EMF', the voltage generated by the motor spinning. There are 2 different conditions for that EMF generated by the spinning of the motor: When the motor is not being driven, that voltage and power can be recovered and much of it can be returned to the battery or other power source. That is regenerative braking or dynamic braking and it is done a lot. Unfortunately, as the motor slows that voltage drops, and at some point it gets really complicated to try to recover that last bit of energy. The second condition for back EMF, or counter-emf, iis while the motor is being powered and is delivering work to some load. Then the back emf acts in opposition to the applied power and serves to limit the current flowing into the motor. THAT emf is real, but it is not accessible. THAT may be the "free energy" that was mentioned at the start of this thread. A very deep study of electric motor theory will give a much more detailed explanation, but I have explained what is needed here.
Good luck with your project!

 

OK, I just came across this thread and I see one thing that has been missed rather completely. That is about "back EMF', the voltage generated by the motor spinning. There are 2 different conditions for that EMF generated by the spinning of the motor: When the motor is not being driven, that voltage and power can be recovered and much of it can be returned to the battery or other power source. That is regenerative braking or dynamic braking and it is done a lot. Unfortunately, as the motor slows that voltage drops, and at some point it gets really complicated to try to recover that last bit of energy. The second condition for back EMF, or counter-emf, iis while the motor is being powered and is delivering work to some load. Then the back emf acts in opposition to the applied power and serves to limit the current flowing into the motor. THAT emf is real, but it is not accessible. THAT may be the "free energy" that was mentioned at the start of this thread. A very deep study of electric motor theory will give a much more detailed explanation, but I have explained what is needed here.
Good luck with your project!

You're over 10 years late, Mr. Bill.

 

You're over 10 years late, Mr. Bill.

OK, if this is an old thread why did it just appear on the list? is somebody recycling threads??

 

OK, if this is an old thread why did it just appear on the list? is somebody recycling threads??

Maybe -- as a grand finale -- 2020 is recycling all the way back to 2010.

 

The tread was reawakened by somebody who posted an impolite comment yesterday -they are the one that answered 10 years too late.

 

The tread was reawakened by somebody who posted an impolite comment yesterday -they are the one that answered 10 years too late.

OK, I guess. Probably there should be a note: "Impolite comment removed" put in place to remind those like me to check the dates.

 

Good idea