Common Mode Choke / inductor filter getting too hot

Thread Starter

Lumenosity

Joined Mar 1, 2017
636
Greetings,
I am experimenting with a Switch Mode Power Supply, a rather cheap one actually, and I have found that the Common Mode Choke / inductor Filter may be running too hot. It is a 60v 10Amp unit.

With a laser thermometer I measured 237F at the coils.
This is when running the PSU at 5Amps. I didn't dare run it at the full 10Amps due to the possibility of releasing the magic smoke.
In the image below you can see the PSU in question and the Common Mode Choke circled in red. It seems too small for the application.
I was running a 48v inverter with it and had a 5Amp load attached to the inverter.

How difficult is it to calculate the correct choke for this application? I do realize that sending it back is easier, but I am trying to learn electronics and this is a challenge.

Thanks in advance.

60v 10A SMPS_3.jpg

60v 10A SMPS_1.jpg
 
Last edited:

ronsimpson

Joined Oct 7, 2019
1,630
Do you have a part number on the filter transformer?
Many companies make that type. We could switch it for the next higher current/lower inductance version.
Warring; any changes in the power supply voided its UL, VDS, CSA certifications. But if you don't care......
The other thing is are you certain it is actually that hot?
Power line voltages in that area. Be careful.
1624495478984.png
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
636
Do you have a part number on the filter transformer?
Many companies make that type. We could switch it for the next higher current/lower inductance version.
Warring; any changes in the power supply voided its UL, VDS, CSA certifications. But if you don't care......
The other thing is are you certain it is actually that hot?
Power line voltages in that area. Be careful.
View attachment 242037
Hi Ron,
I don't see any part numbers on it. But I haven't removed it.
It measures ~17mm x ~17mm x ~17mm

I measured the coils themselves from about 8 inches away with a laser thermometer at 237F. Too hot I think.
The Common Mode Filter is very very small. Smaller than those I see on other better quality SMPS units I have.
I'm fairly certain this thing will fail after a very short time due to heat. I didn't detect any other components this hot.

I looked over a wide variety of them at Mouser and around 200F was as high a temp for this application seemed to be evident.

Do you think switching it for the next larger size would help with the thermal problem?
There seems to be room on the sides and vertically but not laterally.
But it's a single sided board so adding connections underneath is a possibility.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
636
I was also wondering what was "the worse" that can happen if it does overheat?

I don't think it can really "short out" because it's just a point to point wire.
as it overheats I would think the protective coating on the wire will break down resulting in lower resistance changing the filtering capability of the inductor until it separates, leaving an open circuit and thereby shutting down the power supply since current will no longer pass through the circuit.

Am I correct?
 

ronsimpson

Joined Oct 7, 2019
1,630
Prob
Am I correct?
probably correct. I have seen parts get so hot they melt solder and fall out of the board.

Do you have a inductance meter? If I know the inductance and resistance I could find the part. Then we could get a better part.
I don't trust your temperature meter. Is the part too too too hot to touch?

It could be some one put the wrong part in the board.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
636
Prob

probably correct. I have seen parts get so hot they melt solder and fall out of the board.

Do you have a inductance meter? If I know the inductance and resistance I could find the part. Then we could get a better part.
I don't trust your temperature meter. Is the part too too too hot to touch?

It could be some one put the wrong part in the board.
Hello Ron and thanks for your assistance.

I do not have an inductance meter yet but I'm ordering one. MESR-100 and Should have it in a week.

May I ask why you don't trust the Later thermometer? It has always been very reliable and very accurate.
Is there something special in the coil that may give it a false reading? inductance maybe? Magnetic fields?

I will try touching it when the thermometer reads high temperature and see if the heat feels to correspond with the thermometer.

Thanks again.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
636
Ok,
I fired it back up and ran it at 7A for 1 minute and I began to smell a burning smell.
When I touched the top frame of the Common Mode Filter it was indeed getting hot.

Would a larger Common Mode Filter solve this issue? Maybe the windings are just too small for the current?

60v 10A SMPS_2.jpg
 
Last edited:

ronsimpson

Joined Oct 7, 2019
1,630
why you don't trust the Later thermometer?
On some surfaces it is wrong.
Would a larger Common Mode Filter solve this issue? Maybe the windings are just too small for the current?
The core and bobbin is the same for several different filters. They just change the size of the wire and number of turns. So 2x the wire size and 1/2 the turns makes a much cooler filter. But it has 1/4 the inductance.

For now you could short across the windings. Both sides. The supply will send RF noise back into the power line and all over hour house. But the filter transformer will not be hot. lol (If you short the wrong direction the fuse will pop!)
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
636
On some surfaces it is wrong.

The core and bobbin is the same for several different filters. They just change the size of the wire and number of turns. So 2x the wire size and 1/2 the turns makes a much cooler filter. But it has 1/4 the inductance.

For now you could short across the windings. Both sides. The supply will send RF noise back into the power line and all over hour house. But the filter transformer will not be hot. lol (If you short the wrong direction the fuse will pop!)
Thanks Ron.
You've been a lot of help and it is appreciated.
 
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