LED getting hot

[ghost]

I built a series parallel circuit using IR LEDS the led specs are 1.5 -1.6 fv 140ma current 5 rows and 7 leds in each row and a 12ohm 1/2 watt resistor at the end of each row . I am power it with an 120v power supply with a 12vdc output for indoor use . Then Iam using a power pack that is putting out 13.2 vdc I put a stepdown regulater in line to lower it to 12vdc . But when when I use the wall xformer it gets warm , But when I use the power pack it gets hotter any way to help control this.
Any help would be helpful.

 

[Robert_fay]

What are the specifications on the wall transformer. You are pulling some pretty good power out of a wall wart. I think I calculated about 9W.

 

[kellys_eye]

Why step down from 13.2V to 12V? The circuit should operate on both voltages with only a very slight difference in LED forward current.

But at the same time, there are only a few types of regulator that can work with such a small difference between in/out voltages - which version are you using?

What are the CURRENT ratings of the power packs? You need a MINIMUM of 700mA so a 1A output is what you need to aim for.

 

[ghost]

What are the specifications on the wall transformer. You are pulling some pretty good power out of a wall wart. I think I calculated about 9W.

its 2 amp

 

[Robert_fay]

its 2 amp

Since you are using half of the max output you should not be having heat issues. This would lead me to believe that there is something else wrong either with the supply or the circuit if it is getting hot.Warm would not not be considered bad as almost all wall warts will get warm changing AC to DC.

 

[ghost]

What are the specifications on the wall transformer. You are pulling some pretty good power out of a wall wart. I think I calculated about 9W.

led strip pwr supply 250v 3a 24 w sorry had to look at paper work.

 

[kellys_eye]

What are you using as a voltage regulator to drop from 13.2V to 12V.

You might be getting oscillation if it isn't designed properly and thereby drawing more current (and producing more heat) than you expect.

 

[kellys_eye]

250V 3a 24 w???

Something wrong with that. Is that 3A at 24V or 3A and 24 WATTS (which would mean an 8V output).

 

[Robert_fay]

led strip pwr supply 250v 3a 24 w sorry had to look at paper work.

Something wrong here. I agree. Is 250V an input? Better yet do you have a pic of the tag?

 

[ghost]

Why step down from 13.2V to 12V? The circuit should operate on both voltages with only a very slight difference in LED forward current.

But at the same time, there are only a few types of regulator that can work with such a small difference between in/out voltages - which version are you using?

What are the CURRENT ratings of the power packs? You need a MINIMUM of 700mA so a 1A output is what you need to aim for.

sorry could not find the current rating it the part number is A-844 and the regulater is a Pololu s18v20f12 12v step-up/step-down 2A it was to see if it made any differance the cords and plug in and wall trans former do not get hot the temp of the leds with the wall xformer is 89 deg f and with the power pack temp goes up to 109 deg f

 

[Robert_fay]

the wall xformer is 89 deg f and with the power pack temp goes up to 109 deg f

The wall wart does not seem that hot to me.

Have you used the power pack prior to this to see what kind of temps it normally runs at?

 

[ghost]

250V 3a 24 w???

Something wrong with that. Is that 3A at 24V or 3A and 24 WATTS (which would mean an 8V output).

sorry 3a at 24watt

 

[ghost]

250V 3a 24 w???

Something wrong with that. Is that 3A at 24V or 3A and 24 WATTS (which would mean an 8V output).

sorry guys that is 2A 24 watts

 

[ghost]

Something wrong here. I agree. Is 250V an input? Better yet do you have a pic of the tag?

sorry 110 vac wall xformer is 2A 24 watt used with 110 ac

 

[ghost]

The wall wart does not seem that hot to me.

Have you used the power pack prior to this to see what kind of temps it normally runs at?

used it but did not seem that hot to me I did not check how hot it was then but checked it last night leds got up to 109 110 deg f

 

[BobK]

That is not what I would call hot.

Bob

 

[kellys_eye]

Much confusion here.....

are you 'complaining' about the LED's getting hot or the POWER PACK getting hot?

 

[ghost]

Much confusion here.....

are you 'complaining' about the LED's getting hot or the POWER PACK getting hot?

Hi the power pack and the cords and the plugins do not get hot just the leds and resistors . I checked the temp of my florescent tubes of my shop lights it was 114 deg F . So maybe I over reacted I checked the voltage on each led run had 12.1 volt 1.4v across each led .

 

[kellys_eye]

At 1.5 to 1.6V (forward volt drop) and 140mA, each LED is dissipating around 200mW.

You've got 35...... so about 7 watts of heat. That's substantial. I've got a 3W LED reading lamp that gets nearly too hot to touch under normal running.

'Warm' is perfectly normal.

 

[ghost]

At 1.5 to 1.6V (forward volt drop) and 140mA, each LED is dissipating around 200mW.

You've got 35...... so about 7 watts of heat. That's substantial. I've got a 3W LED reading lamp that gets nearly too hot to touch under normal running.

'Warm' is perfectly normal.

thanks again