Problems with H-Bridge for High Torque

[thir13enth]

Purpose: Self-Balancing Scooter
3 Inputs: Low, High, and PWM
Weight: ~60-100 kilos
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Hello, I have a problem regarding on what H-Bridge to use. I have an L298N and it says on the datasheet that 1 L298 can drive a motor at 3.5A.

My problem is, will it be able to handle an ~60-100 kilos weight?

If not, do you have any suggestions on what I can still possibly use for my project?

Regards,
Gello Mark C. Vito

 

[WimRFP]

Hello,

Just current isn't sufficient; you need to think in power torque, gear box ratios acceleration, deceleration and speed.

If you use 24V bus voltage, you power available is about 3*24=72W. Assuming 80% motor efficiency gives you 58W mechanical power. You may want to climb hill also. If you would like to climb a 10% slope. Your maximum speed will be (total weight 120 kg) about 0.5m/s. (P = F*v, F = 0.1*120*9.81). Air resistance ignored

For the balancing action you need power reserve. If you lean forward (during forward speed), the unit has to accelerate to get your CG above the wheels again.

Note that you need a 4-quadrant bridge as during braking (speed reduction), the motor delivers energy to the bridge. This energy has to be stored (battery) or dissipated into resistors.

As this type of projects is nice and challenging, searching the Internet will give you useful information.

I assume you will run some simulation to play with the control parameters. You may also include instantaneous power to get some idea of the powers involved.

 

[thir13enth]

Thank you WimRFP.

As for the balancing feature, I am using an accelerometer and gyroscope for automatic acceleration and deceleration upon leaning.

We have implemented a sprocket with our DC motors along to drive the wheels.

I have been searching the internet using the keywords: high torque h-bridge, high current h-bridge, and relay h-bridge yet I found no relevant results.

If you have any resources which I could read and review, please do share them. More suggestions are also welcome.

Thanks,
Gello Mark C. Vito

 

[WimRFP]

Hello,

There is no high torque H-bridge. A H-bridge is just an electronic topology to convert a DC bus voltage into a controllable DC voltage that you apply to a motor. The H-bridge enables you to generate both positive and negative voltage from a single positive bus voltage. The current that the motor will draw, depends on the torque that the motor has to deliver.

To avoid damage to the motor and the H-bridge, real time current measuring is carried out and appropriate action is undertaken to limit the current.

In your case, 3A from a 24V bus voltage is about 72W, but the same 3A from a 100V bus is 300W. You can imagine that you can generate more torque in the last case (given certain RPM). You may know P = torque*RPM (torque in Nm, RPM in revolutions per minute).

If you want this project to be a success, try to get in touch with a student that has experience in power electroncs.

 

[thir13enth]

Thank you for the reply WimRFP.

I know that there is no high torque h-bridge, the reason why I entitled my topic as "Problems with H-Bridge for High Torque."

I do not really need some calculations regarding power, yet I am trying to get an answer on what components should I use in order to handle a large current or voltage which I will be using for driving my motors which will be subjected with a high torque.

Thanks,
Gello Mark C. Vito

 

[WimRFP]

Hello,

Nowadays many power components and drivers are available for making a motor driver.

If you stay below 100V, mosfets are the first choice (current > 50A). A popular All N-mosfet driver (max 80V) is the HIP 4080A or 4081A.

Up to about 300V, IGBT and mosfet can be used. Fully integrated drivers are available without the need of making transformer- or optics-based driver circuits. For more power >300V, >50A, IGBT outperforms mosfet, except for maximum switching frequency.

Fast shottky rectifiers with reverse voltage > 100V are available (Si and SiC) with current handling capability > 50A.

The challenge is mostly not in getting the semiconductors, but making a good design, respecting limits of passive components, good PCB layout and to stay within acceptable emission limits.

 

[thir13enth]

For that, I guess I should stick to a mosfet since I have a PWM as an output. I would be needing 12V/24V supply but current should be around 50A. In this case, should an N-mosfet like HIP 4080A or 4081A applicable?

BTW, I am also considering the heat for long durations like ~4-5 hours.

Thanks,
Gello Mark C. Vito

 

[WimRFP]

Hello,

the HIP 4080A is a chip that is in between the mosfets and your PWM output. It provides the voltages and peak currents to turn-on and turn-off the mosfets. The chip on its own cannot be used to drive a motor. You need 4 suitable mosfets. For your voltage, current range, many cheap devices are available (1 euro range or less). If you plan to use very high switching frequency, you need mosfets with a fast internal diode.

 

[thir13enth]

Are you familiar with hose mosfets? Can you name some of them?

 

[cubanflyer]

Are you familiar with hose mosfets? Can you name some of them?

Try this link it explains how a mosfet works. If you are going to trigger the mosfet from the micrcontroller directly you will need a logic level gate mosfet.

Metal Oxide Semiconductor MOSFET Tutorial

 

[WimRFP]

Hello,

Best is to check the catalogs of your local suppliers as there are >50 N channel mosfet devices that can operate under 24V/50A load.