High Current 12V DC motor speed control

[paatohjul]

TL;DR Summary

High Amp 12V DC motor running a pump.

Hi.
I am new here.
I have a question on how to speed control a DC motor running a pump. The pump is a seawater cooling pump cooling a large V8 motor.
Therefore I need to control the RPM, based on the temp of the V8 Motor.

Any ideas?

 

[anorlunda]

A BLDC motor with it's controller sounds appropriate. You do not say how much power you need, or whether you need to reduce the speed to near zero.

https://en.wikipedia.org/wiki/Brushless_DC_electric_motor

 

[trurle]

Summary: High Amp 12V DC motor running a pump.

Hi.
I am new here.
I have a question on how to speed control a DC motor running a pump. The pump is a seawater cooling pump cooling a large V8 motor.
Therefore I need to control the RPM, based on the temp of the V8 Motor.

Any ideas?

Standard (low-performance, low-cost) way is to use a hysteresis controller to switch motor on and off at two preset temperatures of coolant. Temperature will ripple, but it is frequently acceptable. Low end controllers of this type have just bimetallic switch as combined sensor and relay and no electronics at all, high end controllers have a single temperature sensor with programmable hysteresis, and integrated relay or silicon switch for motor, sometimes with PWM. Keeping temperature of coolant at stable level is more advanced task, you need servo controller connected to BLDC or synchronous motor of pump as @anorlunda suggested.

 

[paatohjul]

Thanks to @anorlunda and @trurle for the quick reply, and sorry for the lack of information I have provided.

1. The motor is a 12V/55A brush motor, directly connected to a seawater pump.
2. I tried to control a SSR from an Arduino, where i used the water temp NTC sensor as reference. This worked fine for about 2 min... and I blew the SSR...
3. I have bee looking into using MOSFET, but I have not found any suitable circuits and parts.

The reason why I do not want the motor/pump running at full speed while the V8 is idling, is that the cooling is to high and causes condensation inside the exhaust pipes. The condensation will cause the lambda sensor to break down.

With regards

Knut

 

[Windadct]

Probably too heavy switching duty for the SSR. What you need is a ~100A / 60V Mosfet properly setup with heatsink, DC Cap and Freewheeling diode.

https://www.arduino.cc/en/Tutorial/TransistorMotorControl

 

[trurle]

Probably too heavy switching duty for the SSR. What you need is a ~100A / 60V Mosfet properly setup with heatsink, DC Cap and Freewheeling diode.

https://www.arduino.cc/en/Tutorial/TransistorMotorControl

Plus varistor at output. The large motors are well-known killers of switching control circuits.

 

[essenmein]

Are you looking for off the shelf or DIY?

If comfortable with arduino etc, and electronics, you could build a PWM motor controller, these are pretty basic for a brushed machine. From quick internet search the Arduino boards use an Atmel ATmega MCU, these have pretty powerful timer counter units that can generate 3 phase PWM if you want, but a single output is all you need. Get yourself a half bridge gate driver (something basic like IR2301 is more than adequate), couple of Nch fets, current sense resistor (want to make sure you current limit in case of fault etc), then vary duty cycle based on temp, etc.

If that sounds to complicated, i'd get an off the shelf brushed motor speed controller (eg amazon has a pile to chose from).

Also not sure how much you want to tinker/change things, but usually the coolant pump turns constantly with the engine, and a thermostat determines how much coolant is recirculated and how much is sent to the radiator (in case of a car at least). If worried about corrosion in exhaust due to over cooling/condensation but not worried about corrosion from direct seawater cooling? Maybe a closed circuit thermostat controller cooling loop with a seawater heat exchanger is the better route? Then you can run glycol coolant in the engine to prevent internal corrosion and silt build up at bay, as well as keep it at happy temperatures.

One of the reasons coolant pumps are run higher rather than lower is faster coolant flow also reduces temperature gradient across the engine, so with a closed loop you can run the coolant at good flow rate keeping even temps in the cylinders, and you control the temperature of the circulating coolant with a thermostat.