pwm contoller

[jmecherul]

Hi all

I am looking on building a pwm controller to control the speed of a dc-motor. I have looked at a bunch of info, but due to being a beginner I am lost. I need something that can:
-regulate the speed from 0-100%
-handle up to 120 amps
-use 5KHz frequency or regulation
-be able to input 12-24v

Any help with a schematic and/or bom would be greatly appreciated. Thank you.
Jmecherul

 

[colin55]

Here is a controller that can be modified to your requirements:

<snip: spam links deleted>

 

[jmecherul]

Hi

Thanks for the schematic, but this looks a little more complicated for my needs as i do not need any receiver, no braking, no inverter etc. Also, what is the purpose of having so many FETs?

Jmecherul

 

[colin55]

Each FET will only pass about 30 amps. But if you de-rate each FET the turn-on voltage across them decreases and the heat generated is less. The total current for the Xenon-9 is 250 amps. You can use any number of FETs according to your current requirement.
You can also use only those parts of the circuit that are needed for your application.
The whole circuit is just a series of "building blocks."

Colin Mitchell
TALKING ELECTRONICS.com

 

[jmecherul]

So, the more FETs you have in "parallel", the lower the voltage across them, the higher the load current?

And, you mean the max load current is 250A. My question is now why would they need a 250A load current for a tiny toy car motor control?

Can you please tell me what exactly would I need out of that schematic? My setup is as follows:
two car batteries (24V) roughly 50A output to the PWM.
the PWM connected to a 24V motor sucking roughly 120 amps

So, I just need to control the motor.

Thank you.

 

[Ubergeek63]

120A Gracie? why not use a 90V motor?

the quantity of FETs is to handle the current with outdated parts. you need a switcher chip, a FET driver, at least double the current capacity of FETs, and a very good heat sink.

motor speed is proportional to motor voltage.

Dan

 

[blueroomelectronics]

What tiny toy car has a motor that draws 120A?

 

[colin55]

If you de-rate the FETs, such as in the Xenon-9 circuit, they do not have to be heatsinked as the turn-on resistance is about 0.02 ohms.

 

[Ubergeek63]

So, the more FETs you have in "parallel", the lower the voltage across them, the higher the load current?

And, you mean the max load current is 250A. My question is now why would they need a 250A load current for a tiny toy car motor control?

Can you please tell me what exactly would I need out of that schematic? My setup is as follows:
two car batteries (24V) roughly 50A output to the PWM.
the PWM connected to a 24V motor sucking roughly 120 amps

So, I just need to control the motor.

Thank you.

250A is for a competition racer.

what you have is appearently a low speed overloaded motor.

how do i know? you have a 24V motor on a 24V supply drawing 120A from batteries supplying 50A. You therefore about 8V on the motor going maybe a quarter of it's rated speed.

of course it is hard to tell for sure without the motor specs in front of me.

Dan

 

[blueroomelectronics]

I take it the batteries don't last long.

 

[jmecherul]

The motor is not for a toy car. it is actually an electric winch motor but it rotates way too fast for my application. i would like to control that with a pwm.

but seriously, 250A for a tiny car?

jmecherul

 

[blueroomelectronics]

Slowing the motor will also reduce torque. Can you put some gear reduction on it?

 

[jmecherul]

the torque is not the problem. i dont need torque, i need rotational speed.

thanks

 

[colin55]

RPM of the motor depends on a number of factors. If you over-drive the motor by increasing the voltage, the RPM will increase. The current demand will also increase and the heating will increase.
These are all factors that you have to address.

 

[jmecherul]

Hi

Yes, I understand. It I hook up the motor directly to the batteries, it has too high of a RPM for my application. I would like to use a PWM to control the RPM to the max I need. The problem is this motor is a "low" voltage high current one. That is why I need a PWM that can handle high currents.

I will try to give more info once I get a hold of it.

My understanding that two op-amps can be used to create a saw shaped wave and a comparator in order to create the pulse modulation. I just am not a circuit design person, so I am lost.

Jmecherul

 

[Hero999]

Yes, all that's needed is a couple of op-amps.

Of course Tr1 would need to be replaced with a huge MOSFET or loads of paralleled MOSFETs and D1 and D2 would need to be removed.

 

[smilem]

You could try to build this easy PWM I just made.

https://www.electro-tech-online.com/threads/need-help-with-pwm-mosfet.88471/

It's more easy to make features 5KHZ frequesncy adjust, etc PWM Range 0 to 100%.

 

[Ubergeek63]

Hi

Yes, I understand. It I hook up the motor directly to the batteries, it has too high of a RPM for my application. I would like to use a PWM to control the RPM to the max I need. The problem is this motor is a "low" voltage high current one. That is why I need a PWM that can handle high currents.

I will try to give more info once I get a hold of it.

My understanding that two op-amps can be used to create a saw shaped wave and a comparator in order to create the pulse modulation. I just am not a circuit design person, so I am lost.

Jmecherul

Or just use a voltage regulator chip.

The speed of the motor is proportional to the voltage across the armature minus the voltage on the armature resistance.

Good control is only achieved when the commanded motor voltage has the motor current times the motor DC resistance added to it.

Dan