12v DC Thermostat Burns Out 12v DC 90mm Cooling Fan  - Page 1
Forum section: electronics / beginners

author: Omargosh
author_rank: Contributor
timestamp: March 12, 2025, 11:06:43 pm
content: Hello! I'm at my wits end and any help would be greatly appreciated!I have a cheap DC 12v thermostat from Amazon (https://a.co/d/92qodHr) that's getting it's power from a charge controller and it's supposed to turn on a DC 12v 0.2A 90mm cooling fan when it gets hot enough. The fan will work for about 5-10 seconds and then burns out, doomed never to work again. I've gone through 3 thermostats and 4 fans. So I think I'm just doing something wrong or I'm missing a component.The instructions have 2 options of how to connect the power going to the thermostat and how to connect the cooling fan to the thermostat. The straight forward way (2 terminals to power the thermostat and the other 2 to power the fan) was not working. The other way with bridged terminals seemed so strange, but that worked to power the fan.I only tested for voltage. The thermostat is getting 13.9v and it's giving 13.89v to the fan.One of the pics I included shows how the Amazon seller has their fan wired and I don't know what that extra wire is that they're using.Even if it sounds like I might have an inkling of an idea of what I'm talking about, I don't. So feel free to explain it to me like I'm a 5yr old. So what is this thing called electricity and why is it so spicy when I touch it? Lol!Not sure if this is relevant, but this is for an electrical box. I have solar going to a grid tie inverter and a charge controller. The controller is powered by a 12v battery and the controller turns on the thermostat at sunrise. All of that is working fine, I just need this fan to keep everything cool enough during the summer days.Thank you!!!!!

author: edavid
author_rank: Super Contributor
timestamp: March 13, 2025, 12:05:53 am
content: The problem is that the output voltage of the charge controller is too high. The thermostat does not regulate the fan voltage.You need to supply the fan with no more than 12V.

author: Omargosh
author_rank: Contributor
timestamp: March 13, 2025, 12:18:37 am
content: Thank you for the reply! So is there a resistor or some component that I can add to the circuit between the thermostat and fan so that it doesn't go above 12v?

author: edavid
author_rank: Super Contributor
timestamp: March 13, 2025, 12:43:48 am
content: If we believe the current rating on the fan, you could try a 15 ohm 1W resistor. It would be best to measure the actual fan current at 12V to calculate the resistor value.You could also use 4 1N4001 diodes in series.

author: antenna
author_rank: Frequent Contributor
timestamp: March 13, 2025, 12:47:41 am
content: edavid beat me to it, but I think just three 4001's would do it. 13.9v - 12v = 1.9v and .65v x 3 = 1.95v

author: edavid
author_rank: Super Contributor
timestamp: March 13, 2025, 12:52:23 am
content: Nice to have a little margin for error, when we don't know the worst case output from the charge controller, but we do know that the fans are easy to fry

author: Omargosh
author_rank: Contributor
timestamp: March 13, 2025, 02:43:52 am
content: You guys are awesome!Ok, I think my cerebellum might be going the same route as my last 4 cooling fans, but I Googled the diodes you recommended and if I'm understanding correctly...I can soder 3 of them in series, right? Then I can soder the now one long wire of 3 diodes in line on the positive wire between the thermostat and the cooling fan, right?Gotta give the kid a bath and get her to bed, but I'll see if I can draw and post a diagram to make sure I'm understanding correctly.I seriously appreciate all the help!!!!!!!!!! 🙂-Omar

author: Omargosh
author_rank: Contributor
timestamp: March 13, 2025, 02:50:59 am
content: Oh, and is there no device online that has the same function as those 3 diodes? I can soder, I'm just lazy 😂

author: Analog Kid
author_rank: Super Contributor
timestamp: March 13, 2025, 04:17:39 am
content: That device would be a triple diode, but no, there's no such device, at least not commonly available.If you put the diode string in line with the positive lead of the fan motor, be sure that the cathodes of the diodes--that's the end with the line around the diode--are all pointing towards the motor.

author: rteodor
author_rank: Frequent Contributor
timestamp: March 13, 2025, 05:06:15 am
content: Quote from: Omargosh on March 13, 2025, 02:50:59 amThere are, namely "DCDC buck-boost converter". Or just "buck converter". But the solution with the diodes is simpler and cheaperifyou know that input voltage won't go higher.Is there is a solar charger supplying the battery (and the thermostat in consequence) during the day ? Is the charger of PWM type or MPPT ? Depending on the battery temperature and type the charging voltage might not be constant. Worst case is if you have a cheap PWM charger. Do several measurements during the day to check that voltage.

author: antenna
author_rank: Frequent Contributor
timestamp: March 13, 2025, 06:57:51 am
content: They do have packages with three diodes in one, commonly used in cb radios like the KB363. That one, however, is discontinued.There are modern diodes with higher forward voltage drops such as the BY20312, which at .2A has a forward voltage drop of about 2.4v per the datasheet. Mouser has them in stock, under a dollar (but shipping will get you).Edit: just for the record, there are diodes currently being made with multiple diodes inside, such as the CMXSTB400, it has 4 diodes in series and pinouts for each junction. But the current rating is only .35A, so that's cutting it close.Edit2: well, they discontinued that one too it seems, but can be found if desperate. Cool parts sure don't stick around long.Edit 3: ignore edit 2, digikey has a whole category called "diode arrays"And their shipping is much better.

author: Zero999
author_rank: Super Contributor
timestamp: March 13, 2025, 08:40:07 am
content: What kind of 12V fan burns out at 13.9V?I recommend buying a higher quality fan. Choose something with an maximum voltage rating of no less than 14.5V. Read the data sheet carefully.EDIT: It turns out that most fans are rated to 13.8V, except forebm-papst, but then you only need a single 1N4001. There's no need for multiple diodes or anything fancy.

author: SteveThackery
author_rank: Super Contributor
timestamp: March 13, 2025, 10:24:21 am
content: I think there might be more going on. I'm with @zero999: I don't believe a 12V fan will burn out at 13.9V. At least, not as reliably as the OP reports.

author: antenna
author_rank: Frequent Contributor
timestamp: March 13, 2025, 11:22:30 am
content: 3rd that. Ive ran fans like that way higher. I see that many of the fans with that part number come back ti 24v fans rated around .25A. Having a fan with the same part number using half the power seems odd to me.

author: Zero999
author_rank: Super Contributor
timestamp: March 13, 2025, 11:31:59 am
content: Quote from: antenna on March 13, 2025, 11:22:30 amI didn't look up the part number. If the fan is designed for 24V, then that might be the problem. If it's cheap and doesn't have any protection against stalling, then it might overheat, if the supply voltage is too low for it to start reliably, yet still high enough for a significant current to flow.

author: Omargosh
author_rank: Contributor
timestamp: March 13, 2025, 02:08:30 pm
content: Honestly don't know enough about the controller to answer that question. I attached the pic that Amazon has and this is the link, but unfortunately now it directs to a newer model.https://a.co/d/eJBoj37The 12v battery keeps the controller on at all times. During the day the controller tops off the battery and any remaining power goes to the grid tie inverter. I have the controller set so that it turns the thermostat on during the day and then shuts it off at night. The fan burns out only 5-10 seconds after I test it. So it doesn't even have a chance to through any voltage variations, but I can still try to get multiple readings at different times during the day when I'm off again. Thank you!

author: Omargosh
author_rank: Contributor
timestamp: March 13, 2025, 02:11:46 pm
content: Thank you!!!! I would not have known which way to point them otherwise! 👍

author: Omargosh
author_rank: Contributor
timestamp: March 13, 2025, 02:15:59 pm
content: Thank you for the suggestion! I looked it up on DigiKey, but I think my noob brain is a little too intimidated by which one to get and how to connect it. So I think I'll go the triple diode route, but thank you anyway!

author: Omargosh
author_rank: Contributor
timestamp: March 13, 2025, 02:31:39 pm
content: Ok, first of all thank you to everyone for all the replies!I think I'll go with the in-line diodes route. I already ordered a pack of them and another fan. I think I'll first try 3 and if that works, great! If not then I'll reduce one at a time and see how it goes. Hopefully that will avoid the purchase of yet another fan.I drew and attached a diagram and to semi quote Doc Brown, please excuse the crudity of this diagram. I didn't have time to draw it to scale. I included where the line on the diodes is supposed to go.Let me know if I got anything wrong. Otherwise I'll test it out when I get the parts and let you know how it goes! 🤞🏻🤞🏻Thank you all!!

author: rteodor
author_rank: Frequent Contributor
timestamp: March 13, 2025, 05:39:56 pm
content: Maybe check your charger and battery wiring. I'm guessing the fan might had a taste of the full 18...21V from the solar panel (typical) and for some reason you did not measure that !? ... (either wrong measurement or the charger does some funny stuff that your meter can't catch).Hint: if you have some other load (a 50 ohm power resistor for example) - try putting that instead of the fan until you find out the problem.

author: Gyro
author_rank: Super Contributor
timestamp: March 13, 2025, 06:38:34 pm
content: Try powering the thermostat and fan via an LM2940CT-12 linear regulator (use the typical application circuit in the datasheet). It has a dropout voltage of around 150mV @ 200mA and very predictable dropout behavior. It also has automotive grade input transient and reverse polarity protection...https://www.ti.com/lit/ds/symlink/lm2940c.pdf.If the controller really is putting out 13.9V then it won't need a heatsink. If there are transients (of less than 45V), it should mop them up.

author: floobydust
author_rank: Super Contributor
timestamp: March 13, 2025, 07:08:44 pm
content: I don't think the problem is quite known.I would speculate line inductance and the high inrush current with a battery, making voltage spikes.The PWM charge controller could also be making hash.But why the fans die after "5-10 seconds" makes no sense- they should be smoking right away if transients killed them.Unless these are mislabeled or dud 5V fans? I'd take one apart and see what's inside, what failed.

author: tooki
author_rank: Super Contributor
timestamp: March 13, 2025, 07:46:23 pm
content: Quote from: antenna on March 13, 2025, 11:22:30 amIt's not odd at all, insofar as "YD9225HSL" is not a part number. It's a series number, with that and the voltage comprising the "part number". 9225 is simply the dimensions: 92x92x25mm.Anyhow, I concur with everyone else who suspects the root cause is something else, since 14V is still within tolerance for most 12V fans.OP: I suggest not buying no-name el cheapo parts/modules. They are "cheap" but the lack of datasheets and reliability wastes your time and money.

author: Zero999
author_rank: Super Contributor
timestamp: March 13, 2025, 07:48:32 pm
content: Quote from: Omargosh on March 13, 2025, 02:15:59 pmThis fan is rated to for from 8 to 15V. It's probably more pricey than the one you have, but ebm-papst are a premium brand.https://www.digikey.co.uk/en/products/detail/ebm-papst-inc/3412NGH/441252

author: Omargosh
author_rank: Contributor
timestamp: March 14, 2025, 03:28:06 am
content: Oh! I really like the idea of using this fan! The biggest that will fit in there is 90mm. I looked in DigiKey and is it just me or do they not sell a 90mm fan?

author: Omargosh
author_rank: Contributor
timestamp: March 14, 2025, 03:57:38 am
content: And here's a look into one of these Cheapos R Us Matell fans.

author: Stray Electron
author_rank: Super Contributor
timestamp: March 14, 2025, 02:44:27 pm
content: Quote from: Omargosh on March 13, 2025, 02:50:59 amWhy not just use a 7812 12 volt regulator? It's just two wires in and two wires out (one wire, the negative, is shared so it only has three pins) and if you attach it to some metal bit to use as a heat sink the real 7812s (not the fakes) are good for up to an amp.I agree that 12.9 volts should not burn out a fan but given the very poor quality of many imported electronic devices today, I can't say that I'm surprised." is there no device online that has the same function as those 3 diodes?"Three diodes operate differently then a single 7812. A 7812 regulates (limits) the output voltage to 12 volts regardless of the input voltage (within certain limits, see the spec sheet). But a silicon diode is simply a 0.6 (nominal) volt drop so three diodes would give you a 1.8 volt drop regardless of the input voltage (they will operate up to 400 volts or so depending on the diode). That's fine if your PSU outputs 13 VDC but if it happens to output say 16VDC then the output after the diodes will still be 14.2 VDC.A 7812 regulates the voltage but diodes are simply a fixed voltage drop.I've used both in circuits but for a poorly regulated input and for a fraction of an amp I prefer to use a 7812. The 7812 and similar regulators will also shutdown if the current is too high and they over heat so they do add a bit of protection. The 7812s (and similar) operate by switching the power off and on at high frequency (pulse modulation) so they do generate some electrical noise on the output, and usually, you need to add input and output filter capacitors to them to reduce the electrical noise but for a mechanical device such as a fan, you shouldn't need them.PS 7812s are very common and are used in many devices so if you're operating on the cheap, you can easily find 7812s in things like wall warts. electric clocks, transistor radios, timer boards for washing machines etc and they're also very widely available as surplus. In the US it's not hard to find partial rolls (end of the reel) of brand newhigh qualityones for a few cents per part.

author: themadhippy
author_rank: Super Contributor
timestamp: March 14, 2025, 02:53:10 pm
content: QuoteDont they have a 2v minimum drop out voltage?

author: Stray Electron
author_rank: Super Contributor
timestamp: March 14, 2025, 03:06:34 pm
content: Quote from: themadhippy on March 14, 2025, 02:53:10 pmI think that all of the ones made for a long time now have a drop out voltage of about .6 volts and I think that some of the newest have a drop out that is less than that. They are made by many companies and in a wide range of specs. I would look up the data sheet for anything that I was considering using and see what all of the specs (current, heat sinking etc) are before using it. And also a fan would probably operate just fine even if the output dropped below 12 VDC.

author: Zero999
author_rank: Super Contributor
timestamp: March 14, 2025, 06:14:14 pm
content: Quote from: Omargosh on March 14, 2025, 03:28:06 amHow about filing it down to size? You should be able to get away with taking 1mm either side off.90mm doesn't appear to be a standard size. 92mm is very common. Perhaps it's imperial. 92mm = 35/8inches.Quote from: themadhippy on March 14, 2025, 02:53:10 pmSo what?The output voltage might be a little below 12V, but it will still work.Heck, the fan draws only 0.2A whilst the 7812 is rated to over 1A, so it'll probably still output 12V. The graph on the data sheet shows a dropout voltage of under 1.75V, with an output current of 500mA, so at 200mA, it'll be even better.https://www.ti.com/lit/ds/symlink/lm340.pdf

author: TimFox
author_rank: Super Contributor
timestamp: March 14, 2025, 08:33:00 pm
content: Actual TI 7812 regulators are rated for typical dropout voltage of 2 V, and recommended minimum operating input voltage of 12 + 2.5 V.https://www.ti.com/lit/ds/symlink/ua78.pdf?ts=1741961745062&ref_url=https%253A%252F%252Fwww.google.com%252FThere are other regulator ICs, with very different insides, that have lower dropout voltage.

author: Gyro
author_rank: Super Contributor
timestamp: March 14, 2025, 08:41:31 pm
content: Hence the LM2940 suggestion.Quote from: Gyro on March 13, 2025, 06:38:34 pm

author: TimFox
author_rank: Super Contributor
timestamp: March 14, 2025, 08:47:54 pm
content: I was referring to the post above (by StrayElectron) about 7812s having 0.6 V dropout.

author: Zero999
author_rank: Super Contributor
timestamp: March 14, 2025, 09:07:18 pm
content: Quote from: TimFox on March 14, 2025, 08:33:00 pmDid you not read my other post?1) The dropout voltage will be much lower at only 250mA out. 2V is specified at 1A.2) It doesn't matter if it goes into dropout, because a regulated power supply is not required for a fan, which will still work at 11V.3) Just use any plain old µA7812 or LM7812.

author: Stray Electron
author_rank: Super Contributor
timestamp: March 14, 2025, 09:07:50 pm
content: Quote from: Stray Electron on March 14, 2025, 02:44:27 pmWhat I had in mind, and should have said more clearly, was a 7812 type3-terminal voltage regulator. They are made by a large number of companies today and most newer parts are a great improvement over the original 7812 and I'd sure that the OP can find one that will suit his purposes.

author: floobydust
author_rank: Super Contributor
timestamp: March 14, 2025, 09:26:49 pm
content: From the disassembly pic, fan controller IC OCS477H (same as OCH?) rated for 24V use BUT it must have an input capacitor. There is none on the PCB."In the 3~18V application in the right figure, C2 is an optional capacitor to improve IC reliability."I would say the fan is not overvoltaged but is getting killed from the turn on spike/line inductance, the lack of input capacitor.PS -> The axle C-clip is behind the sticker usually, no need to karate the blades off.

author: TimFox
author_rank: Super Contributor
timestamp: March 14, 2025, 10:37:03 pm
content: Quote from: Stray Electron on March 14, 2025, 09:07:50 pmDon't say "7812-type" if you mean a low-dropout linear regulator, which arenot7812-type and should not have 7812 part numbers.Both 7812s and low-dropout regulators have their uses, but should not be confused.

author: Omargosh
author_rank: Contributor
timestamp: March 15, 2025, 09:05:28 pm
content: Thanks for the reply! Don't forget these are the cheapo Barbie fans. No clip under the sticker on either side. It's like they were molded like that. So I drilled away just enough so I could break away in mostly one piece. But either way, where's the fun in no karate?Thanks anyway, though!

author: Omargosh
author_rank: Contributor
timestamp: March 15, 2025, 09:19:59 pm
content: Ok, big reveal. Drumroll please .......IT WORKS!! Well, hopefully I didn't jinx it just now. Lol! But I connected while load out from thermostat was switched off. Triggered it on with the sensor, left it on for 5 min. It's a bright and sunny day and voltage to the fan (past the diodes) was very steady at 11.27. Triggered on/off 3 more times and still works.So I'll clean it up some by shortening the diode contacts, resoldering and insulating it.If there are any further developments I'll let you know. Otherwise....THANK YOU SO MUCH!!!! ALL of you! Sure, some of it sounded like Huttese to me due to my lack of knowledge in this field. Lol! But I genuinely appreciate all of you for taking the time to read, discuss, and guide me!! I was completely lost. So again, THANK YOU!!!! 🙏🏻May you all have a wonderful day!

author: floobydust
author_rank: Super Contributor
timestamp: March 16, 2025, 06:18:11 pm
content: I'm not sold on it, I think the fan needs the input capacitor- but time will tell. Because it's a mosfet H-bridge drive and the back-EMF has no where to go when the relay contacts open. Hopefully I'm wrong. Or ignore me and load up on champagne lolAlways have a fuse just for this thermostat/fan circuit anyhow because battery power and skinny wires does not go well.