Limited experience - Trying to fix a Christmas inflatable

Thread Starter

Ben S.

Joined Nov 30, 2019
5
I have a lawn inflatable that lights up and plays music. One of the LEDs is not working. The power supply is labeled as 12V 1.5A. I know power is getting to the LED but it doesn't light up. I was hoping I could splice in a different LED but the ones I have tried fried immediately. Here's a pic of the original:IMG_20191130_203150576.jpg

I only see one other component on the board. I take it that is stepping something down to what the LED can handle?

I also have this LED night light that plugs into the wall:

IMG_20191130_203454897.jpg

IMG_20191130_203511132.jpg

IMG_20191130_203522018.jpg

I tried just clipping the leads from the inflatable to the outlet prongs but it didn't light up. Can this little board be modified so the LED will work in this application? Thanks!
 

dendad

Joined Feb 20, 2016
3,190
That mains powered LED driver is a killer!
Stay away from it!
DO NOT PLAY WITH IT WHEN POWERED!!!!
Do not try to connect extra LEDs to it. In fact, toss it in the bin!

Use a 12V plug pack, like off an external hard drive, or some other device.

It could be the wires to your suspect LED are broken, or it may have been connected in reverse and be fully dead.
An extra LED can be added to your 12V supply as long as you include the correct rated series resistor.
Read up on some basic electronics.
http://www.learnabout-electronics.org/ is one site.
Also, here... https://www.allaboutcircuits.com/education/
 
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DickCappels

Joined Aug 21, 2008
6,015
Good advice about the mains powered LED. If it stops working, replace it.

As for the LED for the inflatable, the small black part is a 120 ohm resistor. Yes, you are right - it is a necessary part of the circuit that limits the current to the LED.

A replacement LED will also need to have a resistor in series with it. If you match the color and the wattage, as suggested by the physical size, then is pretty safe, though not absolutely safe, to use the same value resistor to protect the new LED.
 

Thread Starter

Ben S.

Joined Nov 30, 2019
5
Thank you for the helpful responses. I'm not clear on what you're saying about the "mains powered LED." I'm not familiar with that term. Could you explain a little more? I think I do follow what you're saying about the resistor though. I just need a 120 ohm resistor in series with the LED and it should work. I'll proceed experimenting with that info. Thank you!
 

DickCappels

Joined Aug 21, 2008
6,015
I misunderstood what you intended for the night light. It is operated from the AC Mains and is therefore dangerous to work on. I now see that you were asking whether you can use that LED. Yes, you probably can but it looks smaller than the original LED. What color is it?

The voltage the LED takes with vary according to the color of the LED so try and get the same color LED as the one you are replacing. Also it is important that the replacement LED be able to hand the same amount of power as the original, otherwise you would need to use a larger resistor.
1575198276986.png
What color was the original LED?

Knowing the colors of the LEDs we can suggest resistor values for an almost-exact replacement and the one from the night light in more detail.
 

dendad

Joined Feb 20, 2016
3,190
I too thought you may be wanting to use the night light, maybe to power the other LEDs.
Those transformer-less devices are extremely dangerous if there is any possibility of coming in contact with the circuitry and are best to be not used.
And your posting message title "Limited experience " raised a flag to me so I was quite concerned for your safety.
 

Thread Starter

Ben S.

Joined Nov 30, 2019
5
Oh ok. Thank you for the warning. Both of the LEDs are a cool white color. The original does look bigger but it's potted in that epoxy or whatever so I was thinking that might be distorting it's apparent size.
 

DickCappels

Joined Aug 21, 2008
6,015
The original may be on a metal core PCB which will carry away heat much better than a simple fiberglass board like the night light.

For white LEDs we can take the forward voltage to be 3.0 to 3.5 volts when driven conservatively. With a 12 volt power supply that leaves about 8.5 volts across the resistor. to get 30 ma, which might be pushing it with that small package try a 300 ohms 1/2 watt resistor.

You can put two 620 ohm 1/4 resistors in parallel to make the 300 ohm 1/2 watt if that is easier.

Please separate the mains plug from the LED before you connect it to your 12 power supply just to avoid accidents.
 

Wolframore

Joined Jan 21, 2019
1,486
My wife has a bunch of these on our lawn and I keep telling her I will fix the lights... all the ones I have run on 12 VDC. I swear they’re being run high current to burn out in about a year.

the original led shows a 120 ohm resistor indicating about 70 mA and just under 1/4 watt Assuming 3.5v Vf. The resistor is 1206.

the LEDs are 5050 with 3 LEDs at 20mA each, it’s unclear how they’re wired. I would assume series which changes the calculation. In any case they are not designed well.
 
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Thread Starter

Ben S.

Joined Nov 30, 2019
5
@Wolframore mine has three LED boards. One went out. You make me think I should replace all three so the others don't go out mid-season. I ordered this kit to experiment with. We'll see how it goes.
 

Wolframore

Joined Jan 21, 2019
1,486
no that won't help... it will be great to play with for learning but not for your situation. Ugh I promised my wife I would fix ours also... It will save money on replacing them otherwise we keep 3 each each year. I'll keep you updated, I started with some inexpensive 12V LED bulbs that have the same SMD led on them... The issue I have is they need to get waterproofing.
 

Wolframore

Joined Jan 21, 2019
1,486
I found a few of these in a drawer in my garage. I believe it I got them to put lights on a bicycle. They only work in one direction. I pulled the base off by bending the pins straight. Then soldered leads and heat shrink. It needs waterproofing. Either clear silicone or epoxy. But that’s as far as I got. Since the system works on 12v from the switching supply any 12v led light will work without having to reinvent the wheel.
https://www.amazon.com/AMAZENAR-Replacement-194-Interior-Dashboard/dp/B01GYXGEAQ/ref=sr_1_8?keywords=12v+led&qid=1575600888&rnid=2941120011&s=automotive&sr=1-8

one more thing, it may be tempting to use brighter lights but these bulbs will be a huge improvement. If you go brighter you have to make sure your power supply can handle the pump motor and the additional lights.
 
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Wolframore

Joined Jan 21, 2019
1,486
Sorry it's taken another reminder from my wife to get to this... here's what I did so far. Now I need to waterproof them and get them wired and mounted in the inflatables. Another thought... a few of these would work as well... but I'm using what I got.

1575648483233.png

I'll bring in one of our smaller dim ones and test first but seeing how it has 5 5050 LED's it should be quite bright... It also lights up in several directions which will help with the overall lighting. I will mix some clear epoxy resin and dip them for waterproofing. I suppose I should get going on this, You can save his step by starting was something that's already enclosed like the accent lighting modules like the one above.

LED.jpg
 
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Wolframore

Joined Jan 21, 2019
1,486
Clear 5 min epoxy - takes an hour to set completely. Should be able to get them in the inflatables soon. OK one soldered in place and we will see tonight how bright it is.

IMG_1640.JPG
 
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MisterBill2

Joined Jan 23, 2018
4,615
You can also find a fair selection of automotive LED bulbs at Wallmart. They were cheap but not any more. BUT they are rugged and durable and simple to solder to and they are made for 12 volts with no external anything. So there you have another option that can work quite well. Also they deliver a lot more light.
 
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