DC fans stopped working

[vinz]

I hope someone with electrical/electronics training can shed some light on this.

I have four DC fans (0.something Amp each) connected to a AC->DC transformer (12V, 1.5A). The total Amp for the four fans do not exceed the transformers Amp rating. The fans are 12cm square, brushless and are less then a year old.

The problem:
When I first set them up, I have no problems getting them to work. They were set to run only when the lights were on, via timer. No problems with them re-starting by themselves every morning.

A few months back I took them off the timer and had them running 24hrs a day. Once I turned them off to do some maintainance on the tank, but had trouble getting them restarted. I had to spin the blades manually, and eventually they started spinning after sometime.

Recently, I've noticed that they've slowed down. Thinking its the accumulated dirt, I cleaned them last night. After that, I couldn't start them up again. I did some troubleshooting and found that I can get each fan running by itself if I disconnected the other 3 fans. I tried connecting just 2 fans and they wouldn't work most of the time. When I could get 2 fans working at the same time, the air current is noticebly weaker (when newly setup, with all 4 fans connected together, there was no noticeble drop in the air current).

What has gone wrong? Some kind of residue electrical effect from running 24hrs continously? Will resting the transformer for a few hours/days solve the problem? Or is it simply that the fan parts being less smooth and thus required more power to spin? Does the fact they are connected in parallel have anything to do with it? Will connecting in series make a difference?

[bigjohnstud]

Hey Vinz, I experienced the same problem 2 weeks ago. 2 of the dc fans will start while the other 2 required a 'push off', even then they were noticeably slower. I did what you did, clean the fans and so on but it did not help. I can't explain the problem through circuitry; I took the easy way out : change the transformer and everything returned to normal. I think something just went wrong in the transformer through normal wear and tear.

[tawauboy]

Vinz,

do you have a voltmeter?
if so, check that the voltage is 12v or above. however, i don't think there is a problem with your ac->dc transformer. transformer either works or don't.

when you said clean the fans, i presume you are removing the muck at the fan blade leading edge and the frame. try cleaning the insides of the fan. you'll need an electrical contact cleaner in a spray can. spray into the fan, the gap between the fan blade and the frame. there should be some muck accumulated there after being used for a long time. the muck will increase friction and requires more current to start turning the fan. this should explain why you can get individual fans to work but not all of them simultaneously.

you have to connect the fans in parallel so that each fan is driven by 12v. if you connect them in series, the fans will not work as each fan will have about 3v only.

[Daz]

Understand that you connect them up in parallel and each fan works by itself if all 3 other is disconnect.

In truth, the start up current is higher then running current, thus if all 4 is turn on at the same time, the current could be higher then the stated running current. Thus maybe you can turn to turn on one at a time instead of all 4 at the same time.

A couple of things to check as well, it could be a simple as a loose connection, oxidize copper wire, and such.

[vinz]

Thanks, John, Tauwaboy, Daz.

Newbie question time. Get the cleaner and spray into the gap between the frame and blades. Do I need to (should I) brush it?

[Daz]

Depend on what kind of cleaner. Those pressurized spray? then no need in fact, as the pressure will blow away the dust.

I have used degreaser to clean some portion of my home fan when the dust build up is terrible, so far so good. Word of caution if you are using that, place some used newspaper below as those dirt and solvent mixture will make a mess out of your place when they drip down.

[limsteel]

Same happen to mine, 4inch Computer fan! Mine worked for about 1 month plus and the rotor started tightening until one day the blades siezed. I can't even get the blades to spin freely.

Suspect Mineral built-up (oxidation) or corrosion in the rotor and stator causing the fan failure. Water vapour act as catalyst decreasing the MTF, mean time to failure.

Currently using an industrial fan 5inch++ Diameter, 12VDC, 0.48Amps, super fast, no problem, but agitates the water suspect some CO2 losses. Soon the Natural law of metal oxidation swill set in, and don't know when will the blade siezed.

[nbk3]

apply lubricant or grease ?

[limsteel]

Dude heat generated or the spinning force throws some of these lubes into the tank water, how?

[vinz]

I have an un-used AC->DC transformer sitting around that was meant for my other tanks, so I tried it first. My fans are now running at full power... infact running faster then one fan connected to the old transformer.

So, conclusion is that the old transformer was really out-of-whack. Any theories about what might be wrong?

[tawauboy]

unless you know what is the voltage output of the previous adaptor, we will be guessing only.
right now, i think, it could be the wires to the fans are oxidies badly so increasing the wire resistance. this in turn will reduce the voltage level and current to the fans.

[tawauboy]

----------------
apply lubricant or grease ?
----------------

you can try to find a contact cleaner which has a light lubricant in it. spray sparingly into the fan. this will help.

[robin]

I have same problem.
If your tank is near kitchen or if you folks at home do a lot of oily cooking, the grease in the air gets suck by the fan. End up lots of dirt will be attracted and greased to the fan as well.

I clean off the grease with soap and water then use lighter fluid to wipe again. Works wonders

Robin

[badman]

actually from what i see, the problem lies with the transformer. it seems as if the current is no longer 1.5 A thus, the fans seems to move slower or not moving. as these transformer are not heavy duty type, its not advisable to use them for 24hrs. however, its just my guess only as you will need the voltmeter and ammeter to test.

[nbk3]

why not just get a PC type PSU ?? costs about $10 , provides a whole lot more of power , and still comes with its own coolin fan and whats more , it aint just 2 fans , it should be able to power 20 fans with no problems []

[vinz]

An update... my joy is short lived. Yesterday, I thot the fans seemed quieter, but I thot it was just my imagination. Today came home to find them all stopped or on the verge of stopping.

Interestingly, the new transformer didn't last 3 days.

I'll go get a multimeter and find out more.

[hoppinghippo]

Vinz: It sounds like the prob likes with your transformer and not your motor. If your motor works fine separately then your motor is fine, period, nevermind dust dirt built up or watever, I really doubt enuff dirt can build up to really slow or stop your motor totally, my own 2 fans are chock full of dust and dirt on the outside, but runs the same till now (I hardly clean them at all). If your fans run ok separately but koyak when you hook all together, it's a classic sign of insufficient voltage or current supply. I think you should either get a more powerful adaptor or use one adaptor per 2 fans. I think running it for 24 hrs for a period of time def will kill your adaptor or motor somewhat, cuz the coils in both of them will def be very very heated up causing lots of wear plus increased resistance which in turn might suck off more power etc. Even when I used an industrial grade stepper motor in my finaly year project it couldn't tahan 24hrs. Lastly I think the reason why your fans were ok till you stopped them to do tank cleaning then restarted them but they don't move till you start manually spinning is cuz at the point when you switch off and switch back on again, the adaptor oredi koyak, giving much less power than before, so the power supplied to the motors is only sufficient to run the motors at a slow speed which isn't enuff to overcome the initial rotational inertia, so till you helped to overcome it by manually spinning it, it couldn't start spinning by itself. and this again is classic of an underpowered motor. I"m sure those of us who play with motor cars like radio controlled or tamiya 4WD will know! Cannot move, just push the car a bit, and it'll slowly move on.

[hoppinghippo]

Another point too: our PC fans in our computers are on a lot and NEVER cleaned, imagine how dirty they are, yet they are like energiser bunnies, keep going and going and going, so I really don't think you need to worry about dirt clogging your fan! Enuff power supplied to it sure can spin the fan thru tons of gunk! more power more power!!! like the show Home Improvement... []

[joe]

The most likely case is that the transformer is not able to output the same output power as it was when it is new. Fans thought rated at 0.2A might draw a significant higher current (a few times more) when it starts up. The transformer is also old and no longer as efficient as it was when it is new.

[vinz]

I suppose the transformers crapped out. The interesting bit is that the second one only lasted 3 days, while the old one has been running for months, firstly only for part of the day and since the heat wave, 24hrs a day.

However, the second one is rated 1Amp and I loaded it with 3x0.32Amp. Whereas the old one is 1.5Amp and loaded with 4x0.32Amp.