Meanwell clone- AD488.3-400W power supply mods

[ElectronMan]

Mine looks a bit different. I bought mine to run my ebike from a small gas generator for long trips.
The regenerating effect of braking, blew up the mosfet despite of having a blocking diode at the output!
I like to fix this and make it 24V instead of 48V which should be easy tweaking the TL431.
Can any one tell me the value of the 2 power resistors marked with a red arrow?
They are the source resistors for the mosfet 20N603C3. Some other passives are blown but that is not a problem for me.
Anyone know the value of these 2 resistors? they are not the same resistors being paralleled.

 

[fechter]

Well, my 400W clone suddenly stopped working. I opened it up and the problem was obvious.



This is the NTC inrush current limiter. Looks like it just burned up. This part goes in series with the AC line and limits the current when you first turn on the supply. Once the supply starts pulling some current, this part heats up, which lowers its resistance. If your supply has no on/off switch and you just plug into the wall to turn it on, this part could just be replaced with a jumper. But mine has a switch and I want the switch to keep working.

I dug around my junk box and found one of these from a larger (dead) power supply. The part I used is about twice the size as the original, so I hope this makes it last longer. If I had to buy one, there are lots on DigiKey or Mouser and they are cheap, but the original markings burned off, so no clue as to the exact rating. Looking at the datasheets for similar parts, there are some nice charts showing the maximum working current and maximum capacitor size for various part numbers, so it would be easy enough to figure out a part that would work well.

 

[TheBeastie]

Well, my 400W clone suddenly stopped working. I opened it up and the problem was obvious.

Burnt NTC.jpg

This is the NTC inrush current limiter. Looks like it just burned up. This part goes in series with the AC line and limits the current when you first turn on the supply. Once the supply starts pulling some current, this part heats up, which lowers its resistance. If your supply has no on/off switch and you just plug into the wall to turn it on, this part could just be replaced with a jumper. But mine has a switch and I want the switch to keep working.

I dug around my junk box and found one of these from a larger (dead) power supply. The part I used is about twice the size as the original, so I hope this makes it last longer. If I had to buy one, there are lots on DigiKey or Mouser and they are cheap, but the original markings burned off, so no clue as to the exact rating. Looking at the datasheets for similar parts, there are some nice charts showing the maximum working current and maximum capacitor size for various part numbers, so it would be easy enough to figure out a part that would work well.

I don't know how much this helps but you can see the labelling of a very similar component for my power supply in this photo here. NTC 2.50-15
https://photos.app.goo.gl/y2i7C6jtWwq3s2mQ8

 

[flippy]

NTC rating is very important. wrong rating and it will either simply not work or burn up lots of power.

 

[fechter]

NTC rating is very important. wrong rating and it will either simply not work or burn up lots of power.

I'm sure that's true. I have seen plenty of power supplies that don't have one at all and they seem to work. If the supply is powered through a switch, the switch contacts might fail if the NTC is bypassed or too low of a resistance. The datasheet I was looking at had a pretty good chart to select the right part.

 

[flippy]

the NTC is to prevent massive inrush currents that destroy the contact area of whatever you are using it power it (a plug or switch) and the prevent the RCD from popping.
not using them will degrade wall sockets and after repeated use it will cause wonky sockets that will burn houses down.

the reason why some have it and some dont is due to the capacitence and iductance of the input stage (aka: coils, capacitors and transformers), depending on the size of them you either do need them or not.

anything with a CE or TUV UL listing or whatever will usually have them in order to pass inspection.