Chinese power supply LM317 overheating.

[NeedsMoreFlux]

I have a 2 amp Chinese power supply with a LM317 on a heat sink.

It's only running a 6(of the planned 10) 120mm CPU fans(all between 0.10-0.20-in parallel) on my home made solder filter.

I don't know if it is over heating due to back EMF. I wrapped the output wire around a torroid a few time-no change.

I'm thinking about upgrading the LM317 to a better transistor if anyone can recommend a better one(I have tons in my spares box).

The KBL404 bridge rectifier gets pretty hot too. If anybody can recommend a higher amp alternative for that as well.

If not; I'll have to hack some other power supply. I've got a few CPU supplies around. But I like the small size of this one, and the selector switch.

[eccerr0r]

Re: Chinese power supply LM317 overheating.

What specific PSU do you have?

LM317 is an IC. To upgrade it, you either have to go to a LM338 or LM350 or add a pass transistor. I'm not sure how well LM317s respond to being parallelized. Likely you'll get the same amount of heat, can't get around that.

Depending on the voltage differential between input and output of the LM317 will determine how how it will get. It seems that you're drawing a significant amount of current. Most LM317 were design limited at 1 to 1.5 amps, which you're fairly close.

The KBL404 should be enough for whatever you're drawing through the LM317. Unless there's some other problem, upgrade the LM317 first.

[stj]

Re: Chinese power supply LM317 overheating.

6fans at 200-300ma each = 1.2 - 1.8a
what's your input voltage and output voltage?

[NeedsMoreFlux]

Re: Chinese power supply LM317 overheating.

I have an MW122A

https://www.ebay.com/itm/3-12-VDC-2-...IAAOSw3mdZci-Z

[NeedsMoreFlux]

Re: Chinese power supply LM317 overheating.

6fans at 200-300ma each = 1.2 - 1.8a
what's your input voltage and output voltage?

The voltage coming out of it is 11.98 volts.

The fans are in parallel. Should I measure the voltage with the fans running, is that what you mean?

[NeedsMoreFlux]

Re: Chinese power supply LM317 overheating.

What specific PSU do you have?

LM317 is an IC. To upgrade it, you either have to go to a LM338 or LM350 or add a pass transistor. I'm not sure how well LM317s respond to being parallelized. Likely you'll get the same amount of heat, can't get around that.

Awe, so it is a cheap under powered unit. I figured. well, I'll still look at the numbers you recommended, because it is smaller and cleaner looking onmy desk.

I pulled another CPU PS out of another old comp I was throwing away. So much dust that I had to clean it with water, lol!

I'll let it dry for a few days in front of the heater. While I figure out the connector I want to use.

I'll try to get some pictures of my filter up.

[budm]

Re: Chinese power supply LM317 overheating.

The voltage coming out of it is 11.98 volts.

The fans are in parallel. Should I measure the voltage with the fans running, is that what you mean?

So what is the input Voltage feeding the LM317?
The Voltage drops between the input and output pins of the LM317 x the load current = Power dissipation for the LM317.

[eccerr0r]

Re: Chinese power supply LM317 overheating.

The voltage coming out of it is 11.98 volts.

The fans are in parallel. Should I measure the voltage with the fans running, is that what you mean?

Yes you should measure the input and output voltage of the LM317 with the load connected. The "input" you can measure the voltage across the KBL404 bridge rectifier DC output (two outer pins).

Note that cheap chinese transformers may also generate a significant amount of heat and was never meant to run 24/7. See how hot the PSU gets when you have no load.

[NeedsMoreFlux]

Re: Chinese power supply LM317 overheating.

Oh, doy!

I thought you mean what voltage the output of 12v dropped to when under load.

I'm working on a tv, but I'll get to that a little later today.

Thank you for your time guys. It's an interesting puzzle(to me atleast).

[NeedsMoreFlux]

Re: Chinese power supply LM317 overheating.

Yes you should measure the input and output voltage of the LM317 with the load connected. The "input" you can measure the voltage across the KBL404 bridge rectifier DC output (two outer pins).

Note that cheap chinese transformers may also generate a significant amount of heat and was never meant to run 24/7. See how hot the PSU gets when you have no load.

Under no/light load it stays pretty much room temp(I believe). I'll have to check it with my finger again.

[budm]

Re: Chinese power supply LM317 overheating.

Oh, doy!

I thought you mean what voltage the output of 12v dropped to when under load.

I'm working on a tv, but I'll get to that a little later today.

Thank you for your time guys. It's an interesting puzzle(to me atleast).

No puzzel, basic Power calculation: E x I = Power, so all you have to do is to measure the Voltage between Input pin and Output pin and multiply that by the current draw by the load, no load = no current draw = no heat.

[NeedsMoreFlux]

Re: Chinese power supply LM317 overheating.

True. I was more referring to the problem solving on this tv and the problem solving of hacking to fix the over heating on the power supply. as I assume I will have to do alot more than just replace the under rated lm317 and rectifier.

Though I hated math in high school, I did enjoy it MUCH more in college and went much further than I thought I could when in college it was of my own free will.

And thank you for the calculation formula.

(BTW: running on no sleep. I try to flip the negative into a positive.)

[stj]

Re: Chinese power supply LM317 overheating.

the difference between the input voltage and output voltage is converted into heat.
pretty crude - but simple.

i suspect you really need a buck convertor from ebay.

[eccerr0r]

Re: Chinese power supply LM317 overheating.

The LM350 and LM338 should mostly be drop-in replacements; though you still need to remove that heat away. The main difference with the LM350 (3A) and LM338 (5A) is that they have beefier internal pass transistors than the LM317 (1.5A). Reading the datasheet for the LM317, it looks like at 12V output and you're close to minimum dropout, you can get 2.2A or possibly more safely.

Remember you will still produce the same amount of heat - there's no way to get around it without a different circuit topology. However, the IC will last longer.

[PeteS in CA]

Re: Chinese power supply LM317 overheating.

1. Fans draw current in pulses. The label gives the average current.

2. In power electronics heavy metal is usually your friend.

3. Maybe next time take a really dusty PSU to a gas station and use their air hose. Wear a dust mask.

[NeedsMoreFlux]

Re: Chinese power supply LM317 overheating.

Right. I assume youre referring to back emf? Oh, I reread it. How much higher could it spike on each pulse?

By heavy metal do you mean for the heat sink? it has a pretty decent one.

I blew it out with a compressor, but it still had alot caked on from years of neglect-NOT BY ME! lol.

[eccerr0r]

Re: Chinese power supply LM317 overheating.

BTW what do you mean when you say "hot"? Warm is expected, as long as the metal part of the LM317 isn't uncomfortably hot, it shouldn't be a problem.

If it is uncomfortably hot, then that means the thermal interface material is bad or the heatsink is too small. Both these problems apply to the LM350/LM338 even if you replace the IC but not the heatsink solution.

You need a switching power supply if you don't want to deal with the heat.

[PeteS in CA]

Re: Chinese power supply LM317 overheating.

NMF, it's been a long time since I last looked at the current waveform for a DC fan, so I'm afraid I can't be helpful.

Yes, I do mean a hefty heatsink is usually a good thing, in proportion to the device(s) mounted on the heatsink.

Maybe the dust from the past drought years got a little moisture from last winter's rains.

IIRC, older ATX PSUs had ~6A 12V outputs. A ~2A load on the 5V output might be enough to have the 12V output close to in regulation. Got any ancient junker ATX PSUs packratted away?

[Relayer]

Re: Chinese power supply LM317 overheating.

Hello NeedsMoreFlux,
When the LM317 is fairly hot, how hot is the transformer?
Regards,
Relayer

[eccerr0r]

Re: Chinese power supply LM317 overheating.

This is what one fan looks like...


Dammit. I need to get screen capture working someday, alas, need to do it over GPIB...

BTW, 1mV=1mA for this fan as the current sense resistor is 1 ohm.

Also I tried a couple of computer fans. They all drop to zero during part of the cycle but never goes below 0. Just this one significantly shoots up. I suspect the circuitry inside the fan is snubbing the kickback that people would expect from motors/inductive devices.