Water vortex (control bilge pump motors 24V,8A)

Other Hardware Motors, Mechanics, Power and CNC
1

Dear all

I am building my own water vortex and i would like to control two large bilge pumps 24V8A via pwm.

So far i have fried some mosfets that are regulated for 24V/15A (the mosfets got destroyed when i switch off the motor, so i assume it is because of motor reverse polarity).

My question is

  1. Does an h-bridge offer reverse polarity protection?
  2. if a motor is rated to work at 8A what is the max current i am supposed to anticipate ?
  3. Should i use ceramic capacitor in paralled to the motor for protection? (what capacity? so it doesnt interfere with pwm signal)
  4. Should i use a diode in parallel to the motor for protection?

The video: https://www.youtube.com/watch?v=aLMRviTHq8A&t=9s

I sorry for the long post , but i really cant afford to burn more equipment

Thanks in advance!!!

2

If the motors run in only one direction, you do not need an H-bridge. You MUST have an inductive kick diode, and noise suppression caps are a good idea.

An 8A motor can draw up to 80A when starting, so use MOSFETs rated at 160A or greater, and a MOSFET gate driver for fast turn on.

3

Or Relays would maybe suit better in this instance and be easier to implement.

However you would still want to employ some protection on the relay coils to prevent damage to the Arduino.

4

Thank you for the answers.

I have bought two h-bridge rated for 43A (one for each motor) . Motors will run in a certain direction only . I believe that h - bridge offers extra protection due to the solid diodes they use. I also need PWM control so Relays are not a good option.

If you can suggest me any good equipment to buy or build please let me know!

p.s. I will slowly turn on and off the motor using time delay PWM (i hope this will help)

5

Most regular h-bridges can be power hungry.

A direct link to the ones you have picked may help others to decide if they are suitable or need anything extra.

Might I suggest the two links below be of use to you.

Could you take a few moments to Learn How To Use The Forum.
It will help you get the best out of the forum in the future.
Other general help and troubleshooting advice can be found here.

6

nsansen:
Dear all

I am building my own water vortex and i would like to control two large bilge pumps 24V8A via pwm.

So far i have fried some mosfets that are regulated for 24V/15A (the mosfets got destroyed when i switch off the motor, so i assume it is because of motor reverse polarity).

Without a free-wheel diode, inductive load instantly destroys all semiconductors its connected to!! A heavy motor can generate many 100's of V of kickback without the slightest difficultly, free-wheel diodes are mandatory and go across the motor if a single switching device is employed.

My question is

  1. Does an h-bridge offer reverse polarity protection?

Not usually, you are expected not to make such basic errors...

  1. if a motor is rated to work at 8A what is the max current i am supposed to anticipate ?

80A to 200A stall, or even more if you reverse it rapidly. Yes, you read right, vast currents are possible if the supply can actually produce them. Large low-voltage DC motor windings are thick copper wires with a few milliohms of resistance. PWM can really help reduce inrush currents by ramping up the drive to match the back-EMF.

  1. Should i use ceramic capacitor in paralled to the motor for protection? (what capacity? so it doesnt interfere with pwm signal)

Not for protection. It reduces EMI from the arcing brushes. 10nF ceramic or so - to be useful they have to be as close to the brushes as physically possible.

  1. Should i use a diode in parallel to the motor for protection?

For single-ended drive this is a requirement whether switching the motor with relay, switch, MOSFET or whatever. With a MOSFET H-bridge the bridge itself always provides the 4 diodes needed. Other kinds of H-bridge may require an additional 4 diodes.

7

BTW For high power a motor driver will always have current-sensing and automatic shutdown on over-current, otherwise the driver will die rapidly in real-world use, popping MOSFETs and maybe more.