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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?

Is it a snap action switch? If so then that will help prevent mechanical bouncing.
Otherwise you will need a lot of delay in the electronics to prevent rapid cycling from mechanical effects.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Miniature thermostat switch in car environment?

(OP)
I don't know if it is snap action or not. Since it is not the disc type and small, it may not be. I will look into disc type. Thank you.

RE: Miniature thermostat switch in car environment?

Amazon description says it's snap action, but I'd look up a mfgr. data sheet to be sure.

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?

From a data sheet, www.es.co.th/Schemetic/PDF/KSD1-90.PDF :

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?

Isn't this backwards from what you would want for turning ON a fan when the temperature is too warm? The description states "the contacts open as the bimetal disc deforms to jump when being heated, then the circuit is cut off to control the temperature ."

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: Miniature thermostat switch in car environment?

(OP)
Thank you for the notes. The description is for Normally Closed, but Normally Open is also available, which is what I am going to use. I didn't know these switches drift away from set point with age. I thought about Arduino logic board + Arduino relay board. But electronic control seems to have the disadvantage of resetting upon battery disconnect and constant current draw during engine off.

RE: Miniature thermostat switch in car environment?

"But electronic control seems to have the disadvantage of resetting upon battery disconnect and constant current draw during engine off."

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.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Miniature thermostat switch in car environment?

(OP)
I didn't know - as always - Arduino does not lose program on power-off. I am now interested in Arduino-based radiator fan control. Please critique my plan:

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?

High temperatures will cause the LM35 to age pretty quickly, though as long as you aren't putting it in the oil or coolant stream it might do ok. An RTD might hold up better.

RE: Miniature thermostat switch in car environment?

(OP)
btrue,
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?

I would think using pressure would be better suited to control the fans based on the AC operation.

RE: Miniature thermostat switch in car environment?

The LM35 is rated for operation up to 150°C junction temperature

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.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Miniature thermostat switch in car environment?

(OP)
LionelH,
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?

What does the AC system pressure have to do with vehicle speed? It's typically recommended by the aftermarket AC guys to use a trinary pressure switch to control the cooling fans.

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?

(OP)
Thank you, LH, for the note. I think doing PWM control on my own is above my level. I understand PWM but don't have the working knowledge. I googled PWM radiator fan control but found nothing. My 2008 Chevy has 2 fans with 3 relays for series (low speed) and parallel (high speed). I think I can handle this method on my project car.

RE: Miniature thermostat switch in car environment?

Any suitable DC PWM circuit would work. Lots of examples on the internet.

RE: Miniature thermostat switch in car environment?

(OP)
Your encouragement revived my interest in PWM radiator fan control. Honestly, I attempted PWM control once before. I got a circuit from internet and started testing on a breadboard. Day 1 it worked well. Day 2 it stopped working. I must have done something to kill the IC but didn't know how I killed it. That's when I gave up. Now Arduino generates PWM output. PWM fan controller modules are available on internet. https://www.partsgeek.com/gbproducts/DC/1899-05220.... I think these modules can generate 20 to 30A. AFAIK many PWM fan modules run on LOW signal. Higher fan speed on longer LOW signal. Since Arduino cannot sink current, I will need something to sink the current from PWM module. Can I use the attached transistor switch circuit? If yes, which transistor and what R values? Thank you.

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?

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

RE: Miniature thermostat switch in car environment?

(OP)
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.

RE: Miniature thermostat switch in car environment?

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

Quote:

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

RE: Miniature thermostat switch in car environment?

(OP)
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.

RE: Miniature thermostat switch in car environment?

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

RE: Miniature thermostat switch in car environment?

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

RE: Miniature thermostat switch in car environment?

(OP)
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.

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