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Old Dec 22, 2011, 03:55 AM
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hobbyking 540w ps fans not working

i opened another thread asking for the minimum load of the hobbyking 540w power supply. because it gets hot when there is no (or minimal) load connected.

http://www.rcgroups.com/forums/showthread.php?t=1546407

when i hook up a 6s lipo to my charger fans start turning after a little time. but while charging/discharging 4nimh cells the case just gets hot, and fans don't turn. when i disconnect the charger from the power supply, fans start turning full power for some seconds, and then turn off.

i now opened the power supply to see what gets hot inside. it's not the power mosfets where the temp sensor is connected to, it some ceramic resistor which gets REALLY hot within a minute.

i measured over 100C (= 220F) while the temp sensor stayed cool (of course - because it's attached to the mosfets).

so: what should i do? i don't think that temps that can boil water are a healthy temp for any electronical device.

install a second temp probe in parallel? this will change resistor values ...



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Old Dec 24, 2011, 06:58 AM
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may anyone tell me what that resistor is for?
i detached the termal probe from the heat sink and attached it to the resistor. now the fans start to turn as expected. but of course the will not spin when charging big packs (i did that for testing only)
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Old Feb 23, 2012, 05:40 AM
Yes, I know it's upside down.
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Originally Posted by ize.man View Post
may anyone tell me what that resistor is for?
i detached the termal probe from the heat sink and attached it to the resistor. now the fans start to turn as expected. but of course the will not spin when charging big packs (i did that for testing only)
I think you did the wrong thing. Now when you are charging a really big pack, the MOSFETS will get hot, and the resistor maybe not so hot, and the fan will not run fast. I'd change it back. 100C is not very hot for a ceramic resistor. Think of a bar radiator. They are a couple of hundred degrees at least and can do that for years.

Anyway, at least yours works. I just received mine, and it is blowing up fuses instantly.
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Old Feb 23, 2012, 05:45 AM
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hmmm. i thought that too. and of course i charged some 6s 5000mah blocks as well - monitoring temps during the whole time. fans start running and the case just becomes a bit above ambient. so i may be the better solution.

afaik resistors change value, at least to some degree, when operated outside their ranges. but the real "problem" was that the power supply did smell bad when used. you know: the smell of hot electronic parts. it just doesn't seem right to me
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Old Feb 23, 2012, 07:34 AM
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Without a schematic, it is hard to say for sure...But from the pics you provided, the resistor is on the output side of the switching supply. Switching power supplies require a load....I believe that this resistor is the load, and will get very hot when no load is on the supply.

If you want to make sure all is ok....here is the test. Be careful, there are some VERY high voltages inside this thing....Mostly on the other side of the switching transformer....Also, the big caps on the other side can stay charged long after the supply is shutdown. That said...
Find all the values on the resistor (Resistance, Wattage)

Measure the Voltage across the 2 leads of the resistor with No Load. Use a good quality meter and use as many places after point as you can. If you really want to check with VERY accurate measurements, remove the resistor and measure the resistance. But the value on the resistance should be close enough. Now get out your calculator.

Watts = Volts X (Volts/Resis)

If the WATTs above is less than Wattage printed on the resistor, you can relax and not worry...10% less or more would be best.

Have a good one.

Sts41
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Old Feb 23, 2012, 08:13 AM
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that's a good explanation. i could be the load! i could have thought of that as well
it's just wasting energy to power on the power supply. i must say that this is not a very high sofisticated way of doing it, but maybe the standby current of a charger is not enough.
what definetly is a design error is, that the fans are not turning to cool the resistor. even though it's capable of +100C it's not nice when you discharge a big pack (almost no load on the powersupply, and no load on the mosfets), leave the room and come back after some time and smell burned stuff.

thanks for your help!
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Old Feb 23, 2012, 10:10 AM
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First, Do not leave the Power Supply un attended while charging.

The only real drawback with a switching power supply is that it requires a load to operate properly, and normally the bigger the power supply, the bigger the load.
When connected to a charger that does not require much power (During Discharge). The load resistance is going to be working overtime.

Here are the advantages...
Effeciency 90% or better compared to Linear at 30%
Weight 500 Watt switching power supply maybe a pound, linear.VERY Heavy.

And this one may be hard to believe...But they run Much cooler, explanation, most power supply's are designed to supply a certain amount of power to a circuit, and that power is constent...We in the RC biz are using the power supplies in a way that goes against their design. High power needs sometimes....Very little power other times.

Most computer power supplies will not turn on if they are not connected to the circuit board...That is why we mod them, and that is why RC switching power supplies have the resistor.

Solution:

Well, there is a simple solution, from your first post, you mention that this is a 540W supply...How much power do you need for the charger?....Add an incandescent light in parallel with your charger...This will move a lot of the heat to outside your power supply....Add a switch, and when you really need the full 540W...open the switch, or unscrew the bulb.

Hope this helps

sts41
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Old Feb 23, 2012, 10:25 AM
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Also....If you don't mind the fan running, compared to power supply burning , You can connect the fan to the 12V out and have it run all the time at full speed.

sts41
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Old Feb 23, 2012, 03:42 PM
Yes, I know it's upside down.
Sydney, Australia
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sts41 is spot on with everything he has said.

I bought the 240v unit because I live in Australia, but I have a feeling that it has the 110v circuit board inside. It lasted about 15 seconds before the first fuse blew, and now the fuse is blowing instantly. The two large capacitors on the supply side are rated at 200 volts on my unit. A 240v power supply has a peak of 340v, so either these are wired in series (which would be a poor design), or as I suspect they are designed for the 110v supply.

Could you please tell me if you have a 110v or 240v unit, and what the voltage rating of the two large caps near the mains power plug are? (ie. the ones not in your photo.)

Thanks,
Harrow.
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Old Feb 24, 2012, 07:18 AM
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Originally Posted by Harrow View Post
sts41 is spot on with everything he has said.

I bought the 240v unit because I live in Australia, but I have a feeling that it has the 110v circuit board inside. It lasted about 15 seconds before the first fuse blew, and now the fuse is blowing instantly. The two large capacitors on the supply side are rated at 200 volts on my unit. A 240v power supply has a peak of 340v, so either these are wired in series (which would be a poor design), or as I suspect they are designed for the 110v supply.

Could you please tell me if you have a 110v or 240v unit, and what the voltage rating of the two large caps near the mains power plug are? (ie. the ones not in your photo.)

Thanks,
Harrow.
It has been a long time since I repaired Switching Power supplies...But I believe the input caps need to be 480V (I say 480 because it was the value I saw most often)....Make sure the rectifiying Diodes can handle the reverse polarity also....And then theres the switching transistor. But honestly, either get a 240v unit, or an adapter....I know in Canada we have adapters to plug in our stuff when we vacation....not sure how much power they can handle though.

There are lots of power supplies that do both 110 and 240...and they centertap the input to supply the same voltage to switching transistor....If you can re design the input circuit to supply 170V of rectified voltage to the input of the switching transistor...you should be good.

Do I recommend doing any of this?????? NO....
But if you have the engineering education and know how a Switching power supply works....It can be done...just doubt that buying all the parts needed would be cheaper than the proper supply

I have seen these things blow up so violently...and spew shrapnel all around the room....Keep this in mind when working on them....and always wear safety glasses.

sts41
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Old Feb 24, 2012, 04:47 PM
Yes, I know it's upside down.
Sydney, Australia
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Actually, I designed and scratch-built a switching power supply for my final year engineering thesis. (and got a High Distinction for it. ) That was a looooong time ago when you couldn't buy one off the shelf of you local store for $29.99.

Yep, I covered the whole thing with plexiglass before I powered it up the second time with the cover removed.

I've only looked at it from the top, since I can't see the bottom of the board without undoing all the loctited nuts, (which would probably void my warranty claim.) The input power stage of the HK design looks to be a standard full wave rectifier connected to the power caps. For 240 RMS input, that's a 340v peak, so I'd expect to see 360v or 390v rated caps there, not 200v. (Thus my suspicion it's the 110v design.)

Anyway, at least with the Aussie warehouse, I only need to mail it local for a warranty claim.

I just noticed that last night another Aussie posted on HK website that his blew up the moment he turned it on as well. I expect they're going to see a lot of these coming back soon!
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