> A few questions abouts leds and batteries and smoke again
|
|
|
JAGUAR |
|
Class : Apprenti
Posts : 12
Registered on : 24/04/2009
Off line
|
Hi again, my 3 point cap is almost finished, I tested the 1 single point with DCS blackShark and works incredible, and the 3 point works good, but I need to play more with the configuration with this. Everything is great except for a little thing, it's still coming smoke from the battery case.
I'm using a switch to turn on/off the leds, but curiously they turn on, only in the off position of the switch, I tried changing the position of the cables on the connectors of the switch and nothing, I got the same result, but that's ok, the real problem is that when I turn the leds on, everything works fine, but when I turned them off, the smoke begin to appear in the battery case.
Again resistors are not being used, because the voltage provided by the batteries are lower than the required by the leds, each led need a minimun of 3.5V and the batteries are providing 2.4V.
Even in this situation resistors be used?
And two more questions?
1- Why there is smoke in the battery case when I used the switch, when I tested without the switch on a test board it works fine with no smoke?
3- Just for curiosity, Karin mention that if I don't use resistors, the batteries could be damage, but only damaged, or something worse like exploding? (I hope not)
Thanks in advance, sorry if I bother you guys with the same questions about resistors, with smoke or not I will post the pictures of my 3 point cap as soon as posible.
|
|
Mustaine |
|
Class : Apprenti
Posts : 9
Registered on : 11/05/2009
Off line
|
Have you tried changing the battery...?
|
|
JAGUAR |
|
Class : Apprenti
Posts : 12
Registered on : 24/04/2009
Off line
|
Hi, yes I tried changing the batteries, for a cheap one non rechargeable, that's the only one available on sunday, and the result was that they work without smoke in any position of the switch, but they do it only for a few hours, they don't last too much.
It's curious because I used that same batteries, on a remote control and they lasted weeks.  |
|
DrSnow |
|
Class : Apprenti
Posts : 39
Registered on : 11/08/2008
Off line
|
You most likely have short circuit when switch is turned off. Measure the switch, on and off positions. i could bet you have "on-on " switch where one of positions is short circuit ...or the switch is broken. If its ok, measure the circuit.
Edit.Was in too hurry and didn't read whole post.the What kind of leds you are you using? What are the specs for them? 3.5V sounds strange. (This edit doesn't make above irrelevant, i still bet on short circuit.)
Edited by DrSnow on 12/05/2009 at 06h59. |
|
JAGUAR |
|
Class : Apprenti
Posts : 12
Registered on : 24/04/2009
Off line
|
This are characteristics of the led
0.19 in (5 mm), ultra-bright red light LED. GAN (Galium Nitrogen) composition. Ideal for LED displays, electronic projects, repairing instruments, etc.
Voltage: 3.5 to 4 VDC
- Lighting: 1300 to 1600 mcd
- Current: 20 mA
- Wave length: 635 nm
- Lighting angle: 30°
- Diameter: 0.19 in (5 mm)
- Long: 0.33 in (8.6 mm)
What are the correct values the voltimeter should show when I measure the circuit with the positions of the switch?
|
|
DrSnow |
|
Class : Apprenti
Posts : 39
Registered on : 11/08/2008
Off line
|
Ok,
Lets start with the switch. if you dont want to heat up the battery again, i recommend that you turn your multimeter to ohm area. Like 200 or 2kohm or so.
(recommend disconnecting the switch from the circuit)
Put the switch to on position the meter should give you 0. If you did not disconnect the switch it gives you a very small resistance value from the other components.
Put the switch to off position meter should not give you a reading at all. (resistance is too big to measure because there is no circuit.)
If both above mentioned are true, then the switch is ok, and fault is elsewhere.
Basicly leds must always have resistor before them. And normally forward voltage is 1.5V. So 4 volts sound more like reverse voltage.If this is true in this case also i think you need as serial connected with 20mA current and your 2,4 volt batteries a 120 ohm resistor before leds.
And you dont need 20 mV, 15 will do just fine. (saves battery and leds also.) Use the calculator to get correct value.
Hope this helps somehow. And also the handbook and FAQ's are good things to read carefully, there's so much other info which might help you and i forgot to say / or don't know.
Edited by DrSnow on 12/05/2009 at 20h56. |
|
JAGUAR |
|
Class : Apprenti
Posts : 12
Registered on : 24/04/2009
Off line
|
I remove the switch and no more smoke, but now the leds are really hot. I used the led wizard to know what resistance should be used, but with the first leds, it don't give me any info, so I will try with another type of led.
The specifications of the new one are 2.1V and 15mA and the resistance according to the led wizard is 20 Ohms 5%.
What do you think guys, this resistance looks good for the kind of led and the power provided by the batteries?
|
|
DrSnow |
|
Class : Apprenti
Posts : 39
Registered on : 11/08/2008
Off line
|
What forward voltage did you use in the wizard with the 1. setup?
|
|
JAGUAR |
|
Class : Apprenti
Posts : 12
Registered on : 24/04/2009
Off line
|
I selected the 3 leds setup, with a forward voltage of 2.1 V and a current forward of 15 mA for the leds and 2.4 V for batteries.
The wizard show that 20 ohms resistors should be used, but I don't find them in the store, so I have to buy 22 ohms resistors, hope this one works well.
Edited by JAGUAR on 13/05/2009 at 19h09. |
|
EDcase |
|
Class : Apprenti
Posts : 11
Registered on : 05/05/2009
Off line
|
Resistors MUST ALWAYS be used to control the current through the LED even if the battery voltage is below the LED spec.
This is a good utility for wiring LEDs
http://led.linear1.org/led.wiz
As for the smoke, that must be a short at the switch.
Edited by EDcase on 13/05/2009 at 13h24. |
|
JAGUAR |
|
Class : Apprenti
Posts : 12
Registered on : 24/04/2009
Off line
|
The page you sugested is cool, but there is something that confuse me, if I'm not wrong, the led wizard says the resistors must be conected to the positive pin of the led, and the page that shows the diagram says it must be conected to the negative pin.
Which one is the correct?  |
|
Karin |
|
Class : Apprenti
Posts : 25
Registered on : 17/03/2009
Off line
|
Both are correct. You can connect resistors to the positive or the negative end of the LED and it will work the same way. I'm pretty sure that as long as the properties of each part of your circuit remain the same (resistance, voltage, current) the order of the resistor relative to the LED doesn't matter.
|
|
JAGUAR |
|
Class : Apprenti
Posts : 12
Registered on : 24/04/2009
Off line
|
Good, I will start inmediatly to work in the circuit. This time I'm sure it will work as it should. I will post the result in a few hours.  |
|
JAGUAR |
|
Class : Apprenti
Posts : 12
Registered on : 24/04/2009
Off line
|
It works really great, no more smoke from the battery case, and the leds are fresh like a lettuce. I tested for more than 1 hour and they were completely fresh.
Thank you so much guys you really help me a lot with this, and this is the link to the post where are the pics of my 3 point cap design.
Cheers |