Soldering cable question

[KeepItSimpleStupid]

Nice Job!

 

[skmdmasud]

Once for jumper wire I tried to use a type of thin wire which are found inside those surgical mask which can be bend and retains its shape. I still dont know why it did not stick leads no matter how much i heat it. it was like soldering proof lol.. when thinks dont work out i use lots of flux and use a knife to clean the surface to be soldered.

 

[KeepItSimpleStupid]

I still dont know why it did not stick leads no matter how much i heat it. it was like soldering proof lol.. when thinks dont work out i use lots of flux and use a knife to clean the surface to be soldered.

Lots of things don't solder well. What may have been in the mask is Stainless Steel. That won't solder well. Resistance wire won't either. Neither will tungsten tantalum or molybdenum. Indium solder sticks to nearly everything, but it melts close to room temperature.

Now, you can braze or "silver solder" stainless steel.

 

[skmdmasud]

Lots of things don't solder well. What may have been in the mask is Stainless Steel. That won't solder well. Resistance wire won't either. Neither will tungsten tantalum or molybdenum. Indium solder sticks to nearly everything, but it melts close to room temperature.

Now, you can braze or "silver solder" stainless steel.

I ditched it. copper wires are good enough for jumper cables.

 

[nicksydney]

Continuing on this topic just want to ask somewhat related question. I notice at the back of the power supply it says that the output is 5.7v 800mA does this means that the total wattage delivered from this power supply is around 4.5W (5.7v x 0.8A) ?

Thanks

 

[skmdmasud]

Continuing on this topic just want to ask somewhat related question. I notice at the back of the power supply it says that the output is 5.7v 800mA does this means that the total wattage delivered from this power supply is around 4.5W (5.7v x 0.8A) ?

Thanks

yep W = V X I. Some times the power supply are over rated specially ac transformers in my case.

 

[audioguru]

A manufacturer who over-rates a power supply or power transformer should be jailed.

 

[nicksydney]

I've tried using the power supply in my breadboard and notice that when I test using a resistor and after few seconds it became very hot (and also heard a high pitch sound) and when I try to understand why the resistor become very hot, it clicked my mind that it must be something got to do with the power supply which is delivering 800mA. Checking the resistor that I have seems like it can only take 1/2W. Looks like from this exercise if I want to use the power supply for the breadboard I will need to reduce the current.

 

[davenn]

I've tried using the power supply in my breadboard and notice that when I test using a resistor and after few seconds it became very hot (and also heard a high pitch sound) and when I try to understand why the resistor become very hot, it clicked my mind that it must be something got to do with the power supply which is delivering 800mA. Checking the resistor that I have seems like it can only take 1/2W. Looks like from this exercise if I want to use the power supply for the breadboard I will need to reduce the current.

what is the resistance value of the resistor ?
was it the only component across the power supply ?

If it was relatively low value ~10 Ohms or less then yes it will get hot, cuz you are basically putting a short circuit across the power supply
and its going to draw lots of current, to whatever the PSU can deliver

Dave

 

[nicksydney]

what is the resistance value of the resistor ?
was it the only component across the power supply ?

The value of the resistor was 1000ohms and it was the only component I tested out with the power supply.

 

[davenn]

The value of the resistor was 1000ohms and it was the only component I tested out with the power supply.

OK do some Ohm's law

5.7V / 1000 Ohms = 0.0057A = 5.7 milliAmps
5.7V x 0.0057A = 0.0325 W 32.5 milliWatts

that isnt going to make a 1/2 Watt resistor warm let alone hot
so it begs the question, did you read the resistance correctly ?

Dave

 

[nicksydney]

OK do some Ohm's law

5.7V / 1000 Ohms = 0.0057A = 5.7 milliAmps
5.7V x 0.0057A = 0.0325 W 32.5 milliWatts

that isnt going to make a 1/2 Watt resistor warm let alone hot
so it begs the question, did you read the resistance correctly ?

Dave

The output of the power supply (reading from the back cover of the power supply) says that the output is 5.7v 800mA, doesn't that equates to more what the resistor can handle in terms of Watts ?

 

[audioguru]

Ohm's Law says that 5.7V/800mA requires a resistor that is (5.7/0.8=) 7.125 ohms. The power in that resistor is (5.7V x 0.8=) 4.56W.
1000 ohms draws a current of only (5.7V/1000=) 5.7mA, not 800mA. It draws power that is (5.7V x 5.7mA=) 32.49mW.

A power supply does not force its maximum current on every load, its load draws whatever current it needs.

 

[nicksydney]

Tried again last night with 4.7k resistor and went without any problem even I tried using the power supply with a transistor and LED and went without any heat problem. I think I have done something wrong previously but not sure what was different. I measured the current through the 4.7k and I'm getting 1.2mA.

Thanks all for the help.