Miniature thermostat switch in car environment?
Miniature thermostat switch in car environment?
(OP)
I would like to use a bimetal switch for cooling fan control. https://www.amazon.com/uxcell-KSD9700-Bimetal-Ther.... 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.





RE: Miniature thermostat switch in car environment?
Otherwise you will need a lot of delay in the electronics to prevent rapid cycling from mechanical effects.
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P.E. Metallurgy, Plymouth Tube
RE: Miniature thermostat switch in car environment?
RE: Miniature thermostat switch in car environment?
I don't know of any snap-action bimetal switches that don't wear out (the temperature setpoint starts to drift fairly significantly) within a few thousand cycles or so, it is the drawback to their simplicity.
RE: Miniature thermostat switch in car environment?
Active temperature :90+/-5C, Reset temperature:70+/-10C
Structure and application: KSD9700 series product is a kind of thermostat which adopt the bimetal disc as the temperature sensing element. The bimetal disc is in free state and the contacts are closed when the electrical appliance is working in normal condition. When the ambient temperature raises to the preset operating temperature, the contacts open as the bimetal disc deforms to jump when being heated, then the circuit is cut off to control the temperature .Then the contacts will close automatically to cut on the circuit when the electrical appliance is cooled down to the reset temperature. This product is widely used in home appliance’s motor and electrical equipment, such as air conditioner motor, transformer, thermal appliances, etc.
It looks like an over-temperature protection switch not a temperature regulation switch.
RE: Miniature thermostat switch in car environment?
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RE: Miniature thermostat switch in car environment?
RE: Miniature thermostat switch in car environment?
Neither needs to be true. A normal Arduino processor would have some amount of non-volatile store, such as the memory required to store the actual program, which retains its information when power is off. Otherwise, you'd need to connect a PC to an Arduino every time you turned the power off. Since the Arduino has non-volatile memory, there is no need to maintain power when the engine is off.
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RE: Miniature thermostat switch in car environment?
https://www.summitracing.com/int/search/part-type/...
At the low end, they are not much more than the switch you linked.
RE: Miniature thermostat switch in car environment?
RE: Miniature thermostat switch in car environment?
Parts list: Arduino board, relay board (to turn on fan relays), LM35 temperature sensor, automotive fan relays
I will tape LM35 temperature sensors to radiator outlet and AC condenser outlet. If either exceeds preset temperature, turn on low fan. If radiator outlet exceeds a higher preset, turn on high fan. Also a question. Can Arduino board be powered directly from battery? Or via USB?
LionelH,
I need to use AC condenser outlet temperature for fan control. That's why I cannot use a commercial controller.
RE: Miniature thermostat switch in car environment?
RE: Miniature thermostat switch in car environment?
Both AC condenser outlet and radiator outlet reach 60, maybe 70 deg C. Would you still recommend RTD? I plan to tape LM35 to the outlet. It will not see the fluid directly.
RE: Miniature thermostat switch in car environment?
RE: Miniature thermostat switch in car environment?
Per datasheet: http://www.ti.com/lit/ds/symlink/lm35.pdf its 1000-hr stability at 100°C junction temperature is ±0.08°C. While 1000 hr isn't particularly long, for 2 hr operation per day, it represents over a year of normal operation, and it'll be many years before the stability error exceeds its ±1°C error at 150°C max operating temperature.
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RE: Miniature thermostat switch in car environment?
When vehicle is moving, AC condenser cools to near air temperature at the outlet. According to my measurement, not even 10 deg C above air temperature. Tying fan operation to vehicle speed would be ideal but I don't know where vehicle speed wire is or what format signal is available. That's why I am going to use AC condenser outlet temperature.
Thank you, IRStuff, for the LM35 data interpretation.
RE: Miniature thermostat switch in car environment?
Temperature sensors on both sides of the condenser to measure the differential would likely work OK.
You need to run the fans at a minimum speed all the time with the AC on unless the vehicle is moving something like 25mph or more. If you have 2 speed fans then the low speed would be appropriate for this.
Also, since you're going Arduino, might as well do PWM control of the fans as well.
You should be able to find the info for speed signal if you search forums related to the car. People often install aftermarket stuff that needs the speed signal.
RE: Miniature thermostat switch in car environment?
RE: Miniature thermostat switch in car environment?
RE: Miniature thermostat switch in car environment?
Another approach I have seen on internet is Arduino + SSR. This looks very simple.
EDIT: The PWM module has 4 terminals, Ground, PWM input, PWM output to motor and +12V. The only circuit I have to build is the switch to reverse the signal.
RE: Miniature thermostat switch in car environment?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Miniature thermostat switch in car environment?
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.
RE: Miniature thermostat switch in car environment?
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
RE: Miniature thermostat switch in car environment?
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.
RE: Miniature thermostat switch in car environment?
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
RE: Miniature thermostat switch in car environment?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Miniature thermostat switch in car environment?