Miniature thermostat switch in car environment? 6

[knowlittle]

I would like to use a bimetal switch for cooling fan control.

https://www.amazon.com/uxcell-KSD9700-Bimetal-Thermostat-Temperature/dp/B005FULR7A.

It comes with different open/close temperatures at 5 degree C interval. The tip is about 1/4" in thickness. I am concerned about the mechanical stability of the bimetal contact in the automotive environment. Please advise. Thank you. I will use it with a relay/diode.

 

[itsmoked]

know; I'm not sure you have it completely. Maybe you do. The point of PWM is to provide variable fan speed to maintain a constant unvarying temperature. This infers feedback which is the fan speed controlling to a temperature. A temperature sensor is required so the PWM controller can see what it's trying to control. This means a standard automotive temperature sensor (but not a temperature switch). I believe standard automotive sensors are negative coefficient devices as their temp goes up their resistance goes down. It sounds like this is what you PWM circuit is looking for.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[knowlittle]

Hi, IT,
I understand that part of pwm. Arduino reads temperature (rtd or lm35 sensor) and generates a pulse. Many cars use this pulse to drive a power FET module. I can actually buy an FET module for 20-30 dollars. I was asking if I could use the circuit to go between Arduino and the module. I also read a discussion if an SSR can be used instead of FET. If you would answer either or both of my questions, I would appreciate.

 

[itsmoked]

Ah, OK. You can probably use either. But.

and generates a pulse

Should be 'and generates a continuous train of pulses'.

SSR's come in many flavors. In automotive land you would not want a standard SSR but rather a DC SSR. They typically take in 3~20V to trigger them ON but you need to confirm that, on any particular one, before you commit to it. They also have outputs rated for a particular range of voltage like 10~60V, or 90~330V, or such, and you need to make sure that also matches your situation. SSR's all need a way to dump their heat so they often are not a complete solution as how and what they mount to is important as that's what they dump their heat into. They have a maximum current rating that's how many amps they can control. Lastly, they may also have a minimum ON/OFF time that must be less than your PWM pulse widths or the SSR won't keep up and will just appear to stay ON or never even go ON. SSR's work very well and are a solid problem free solution if these five things are attended to.

A FET module is really no different than a DC SSR other than they likely have the mounting and cooling already handled and stated - exceed it and it dies.

They will have the same input signal spec needs and output current and voltage limits that you must not exceed and/or need to operate within.

Figure out which one you plan to use and post a link here and someone can approve it for you. Oh, and provide a link to the fan motor details so we can make sure the power control element will be happy controlling it.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[knowlittle]

Sorry for late reply.
Thank you for the explanation. Regarding the specifications of the motor and power MOSFET module, I don't have any info. Car parts manufacturers simply state their parts are "equivalent to" OEM. But each of two fan motors drew 8A when tested out of the car. Since I haven't dissected the power MOSFET module, I don't know what's inside and how much current it can provide.

 

[JayMaechtlen]

so, if it is 'equivalent to oem', then you can look at the usage in an oem type installation and see how similar it is to your intended use.
I suspect that more cars use pwm for interior ac/heat blower motor control than for cooling fan control, fwiw.
I suspect that a ac/heat blower motor is at least as powerful as a radiator cooling fan. If so, then something that drives a blower motor could drive a cooling fan instead.


Jay Maechtlen

http://www.laserpubs.com/techcomm

 

[itsmoked]

You say the fans are about 8A. That's a fine number. Get a controller that will drive twice the combined current and more, a controller that will 'drive motors' and will control more than 20A. 30A would be great.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[knowlittle]

Thank you for the notes. The power FET module is a dedicated radiator fan controller. It is not shared with AC/heater fan. It has a heat sink and packaged for automotive use. Disadvantage is unpublished current rating, but I plan to get one for a large V8.