Basic adapter no output

[pharaon]

The diodes are fine not shorted
But no output
What could be the reason

 

[davenn]

do you have AC across my marked locations ??

if you don't then ......

most of these transformers have a thermal fuse on the mains AC side
with the PSU unplugged from power use continuity tester or multimeter in Ohms range and look for resistance in the 500 to 1500 Ohms range across than mains plug

if you get open circuit, throw it out and get a replacement plugpack



Dave

 

[pharaon]

I open it found this white thing i think its the problem can any one tell me what is
If i can't find similar part what would be a god replacement for it
The numbers on it is
323 umi
1A 130C
250 V~K1
(ps)E jet

 

[pharaon]

i went to buy another one it's not available only ,temperature resistor
i would like to know what ohm and what i should get the replacement resistor

 

[Alec_t]

Something here should do as a replacement fuse.

 

[duke37]

This looks like a fuse as suggested and not a resistor thus it should have a very low resistance. It is rated to 130 degrees C.
Why did it blow? Was there overload of the output or did the primary winding fail with a shorted turn?
If the winding is faulty, can you rewind it?
Can you solder in a replacement without it failing? I have never managed it.

 

[pharaon]

Why did it blow? Was there overload of the output or did the primary winding fail with a shorted turn?
If the winding is faulty, can you rewind it?

the primary winding didn't fail..i don't know why that thermal fuse fails maybe overheat

Can you solder in a replacement without it failing? I have never managed it.

well i can't find thermal fuse in my area so i'm wondering what could be another good protection part to use rather than thermal fuse

 

[duke37]

You could fit a very low current fuse but may not find anough space to fit it.
Try connecting across the fuse and, without load, check whether the transformer heats too much. Do not leave it unattended and do not touch any mains terminals.

 

[HellasTechn]

most of these transformers have a thermal fuse on the mains AC side

It is not just a fuse. It is a thermal fuse. like davenn said.

 

[davenn]

It is not just a fuse. It is a thermal fuse. like davenn said.

exactly, you cannot use anything other than a thermal fuse, else you will not have protection
if you cannot get a thermal fuse, then bin the plugpack as I originally told you


Dave

 

[HellasTechn]

A thermal fuse is a fuse that would blow not only if you draw excessive current but also if temprature climbs up to the specified point.
So by not useing the same rating thermal fuse you risk overheating the coil and fire.

Remember there was a reason that made the original fuse blow in the first place (if the fuse is blown ofcource).

 

[pharaon]

ok correct me if im wrong in this idea
what will make the primary winding be overheating is more voltage than what it's design to work on
so if i make sure the voltage and the current that is going to the AC side never exceed the coil specification then it wont get overheated..

so why don't i use regular fuse that will shut if it get overload voltage or current..so that the AC coil will always remain in it's regular temperature

 

[pharaon]

73's de Edd
hope to know what do you think about that

 

[HellasTechn]

so why don't i use regular fuse that will shut if it get overload voltage or current..so that the AC coil will always remain in it's regular temperature

You are wrong. First because you are not taking into consideration ambient temprature variations and second changes in magnetic flux within the transformer will cause temprature variation on the coil.

Besides why dont you just replace it with an other transformer of same specs and stay safe ?
Or find the same type of thermal fuse ?

 

[HellasTechn]

so if i make sure the voltage and the current that is going to the AC side never exceed the coil specification

That sounds as a much more expensive way to deal with this issue than just replace the transformer.

 

[davenn]

ok correct me if im wrong in this idea
what will make the primary winding be overheating is more voltage than what it's design to work on

not quite right

2 main things that will cause the transformer to overheat and the thermal fuse to operate

1) excessive current draw on the secondary side, which will increase the current on the primary side as the transformer tries to supply the extra current
2) large voltage spike / surge on the primary side

we have no easy way of telling which of those 2 may have caused the failure, tho if there is a lack of other failed devices around the house
then #1 would be the most likely reason

again ... a correctly rated thermal fuse is your ONLY safe option


Dave

 

[duke37]

The thermal fuse takes into account the dissipation in the transformer. An external fuse can never do this.
You seem to think that the transformer is basically OK. One likely fault is that there are shorted turns. The wire has a very small diameter and the insulation is very thin. If two turns are shorted, then the transformer will heat the shorted turns. These transformers are scramble wound without interlayer insulation.
That was why I suggested testing the transformer without a load.

Putiing a new thermal fuse in can be difficult, get it over 130 C and it is dead.

 

[davenn]

@pharaon

I'm going to close this thread now
you have been given good advice to keep you safe. Please take it


Dave