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  • OT Electrical Problem/Question on LEDs

    My question is an electrical one. I bought 5 LED bulbs, each rated at 24 volt. I have connected them in series, so the voltage drop across all 5 is 120 volts. They won't light. What did I do wrong? I check the resistance across each bulb and it is infinite. Are the bulbs bad? Did I screw up? Appreciate any wisdom.
    Bill

    Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

    Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.

  • #2
    We need more infomation, perhaps take a picture of the setup and we can go from there.

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    • #3
      A link to the bulb specs would also be helpful. If these LED bulbs are rated for AC, then I suspect there are power supplies in each bulb that will not allow it to work this way.
      Definition: Racecar - a device that turns money into noise.

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      • #4
        Originally posted by browne92 View Post
        A link to the bulb specs would also be helpful. If these LED bulbs are rated for AC, then I suspect there are power supplies in each bulb that will not allow it to work this way.
        Probably the most exciting part is a resistive thing like an old fashioned light bulb doesn't care (much) about DC vs RMS but a LED probably will.

        120V AC RMS is more like 170V AC peak.

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        • #5
          You did not state if using 120vAC?
          Simple 24v LED's are usually rated for 24vdc, they have a suitable resistor internally, but they are not designed for AC if this is what you powered them with?
          Max.

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          • #6
            Yes more info is needed. AC or DC rated voltage for the lights? Got a link to these things?

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            • #7
              I suspect that you have just blown out 5 LED's, because if they were for 24 VDC, they just got that in reverse when you connected them to 120 VAC (as I'm suspecting). Hope they didn't cost you much.
              Amount of experience is in direct proportion to the value of broken equipment.

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              • #8
                Originally posted by BigBoy1 View Post
                My question is an electrical one. I bought 5 LED bulbs, each rated at 24 volt. I have connected them in series, so the voltage drop across all 5 is 120 volts. They won't light. What did I do wrong? I check the resistance across each bulb and it is infinite. Are the bulbs bad? Did I screw up? Appreciate any wisdom.
                Please post the model number of what you bought and we can reverse engineer it for you. It might be something as simple as a grounded case on the body of the "bulb".

                LEDs are interesting in that they do not light at all until the voltage reaches a threshold. As the voltage rises above that they quickly reach full brightness, then very quickly hit overload. Did you measure the voltage drop across each one?

                Lastly, the term BULB implies a ready to use fixture( often with electronics) , as opposed to an LED, which is a discrete component.

                Dan
                At the end of the project, there is a profound difference between spare parts and extra parts.

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                • #9
                  Probably one is dead (open) so that stops current to the whole string.
                  I'm not sure, but, possibly for a fraction of a second when you first apply power, one of the LED's gets too much voltage and opens.
                  LED are not purely resistive and I can see this happening.
                  Try using a single LED with a resistor for 120V. (doesn't matter if AC or DC).
                  Then parallel several of these circuits for the desired brightness.
                  This is not a very efficient circuit.
                  If it were me, I'd use a small low-voltage transformer and design from it's voltage.
                  Tom M.

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                  • #10
                    You cannot run LED bulbs like that. 24 volts is an odd rating for LEDs bulbs but they do make them for use in China. Many cars and most trucks in China have 24 volt electrical systems but they are DC.

                    If you are trying to run them on AC you may have cooked them all. Most AC LED bulbs will not read anything other than open circuit. They use internal switch mode power supplies or on the cheap ones capacitor current limiters. DC LED bulbs may or may not read open circuit depending on how they are powered internally.

                    This is all changing quickly. The next step in AC LED lighting will come out next year. These are LEDs with multiple emitters on one die along with rectification. They run directly from 110 vac or 240 vac.

                    BTW, the current LED champion is a 300 watt unit about 1.5 inches square. It puts out somewhere around 30,000 to 35,000 lumens.
                    Last edited by Evan; 12-05-2012, 03:58 PM.
                    Free software for calculating bolt circles and similar: Click Here

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                    • #11
                      More Information

                      Here are the spec. for the bulbs I purchased.


                      24 Volt.T3 1/4 Miniature Screw (E10) LED Light Bulb 0.72 Watt Color White

                      Product ID# LM1024MS-W
                      LED BULB
                      T3 1/4 Mini Screw LED
                      Color: White
                      Plastic Envelope Shape: T-3 1/4
                      Max. Bulb Diameter (in): 13/32
                      Base Type: Miniature Screw (E10)
                      Design Volts: 24.00
                      Mili Amp (mA): 30.00
                      Design Watts: 0.72
                      Bi-Polar: Yes
                      Viewing Angle Degree: 360
                      Luminous Flux: 3.10
                      Wave Length: 0
                      Average Life Hours: 100,000
                      1–5 units 6 & Above
                      $8.00 $7.60

                      The wiring was to place the five LEDs in electrical series so that each bulb is a candle in a candelabra. The bulbs in the picture are the old bulbs, NOT the LEDs. The white power cord plugs into 120V AC.

                      Last edited by BigBoy1; 12-05-2012, 04:04 PM.
                      Bill

                      Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

                      Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.

                      Comment


                      • #12
                        The bulbs are "bipolar" which means they are designed to run on ac. HOWEVER, it also means they have a rectifier of some sort as well as a current limiter. The bulbs will not present a pure resistive load and cannot be run in series with predictable results.

                        The product is here: http://pearlandlighting.com/proddeta...rod=LM1024MS-W

                        Those bulbs are rated at what looks like 3 lumens. That isn't even as bright as a night light. The bulb form factor is so small that there is only room for a diode and resistor in series with the LED.
                        Free software for calculating bolt circles and similar: Click Here

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                        • #13
                          Doesn't a 'Bi-Polar LED' contain two LEDs back to back (in parallel) rather than additional rectification ?

                          If these ones are 24v 30mA they they may just have an internal ~700ohm resistor in series.

                          Putting 5 of these in series would then be effectively the same as 3500 ohms in series with a chain of 5 LEDs - i.e. should work o.k. at 120v - for a while at least. They may however be susceptible to mains transients (voltage spikes).

                          They should light up enough with a 12v battery to check if they still work (testing each one both ways round )...

                          Cheers

                          .

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                          • #14
                            LED stands for Light Emitting DIODE. Emphasis on the word "DIODE". A diode will only conduct in one direction. So if you connect it to AC, it will act exactly like a rectifier and only conduct (and light) when the Voltage/current is flowing in one direction. On the other half cycles, when it tries to flow in the other direction, it will not conduct and it will not light. LEDs can be connected to AC and they will work: like all other diodes, they simply block conduction in the reverse direction. This does not burn them out unless the reverse Voltage is greater than the rated reverse Voltage of the LED.

                            My first thought is if you are running them in series, they MUST all be connected in the same polarity. That means all of the plus (+) terminals on the LEDs must be connected to minus (-) terminals on the next one (cathode to anode). Just like batteries. Even if only one of them is connected in the reverse polarity, they will not conduct and none of them will light. Since you are using screw based sockets, this SHOULD mean that the center terminal on one socket is connected to the outer terminal on the next. Recheck your wiring and try it again. Chances are you have not destroyed any of the LED lamps.

                            All the above being said, you may still have some problems. There is no guarantee that the forward current or conduction (the inverse of resistance) rating of each individual LED lamp is the same as the next. If they are sufficiently imbalanced the actual Voltage across the individual ones in a series circuit will not be the same: some will be higher than 24 Volts and others will be lower. Since it is a series circuit, the current will be the same for all of them, but it may be low and that would mean all of them may be dim.

                            BTW, you can not check a 24 Volt LED with an ordinary Ohm meter because most Ohm meters use a 1.5 or 3 Volt battery to check the resistance. Those Voltages will not be enough to turn on a 24 Volt LED so no conduction will occur in either polarity. It will read very high or infinite resistance. You would need a meter with a higher test Voltage, at least 24 Volts. I do not know of any such meter. 9 Volts if the highest I have ever seen except for meggers.
                            Last edited by Paul Alciatore; 12-05-2012, 05:29 PM.
                            Paul A.
                            SE Texas

                            Make it fit.
                            You can't win and there is a penalty for trying!

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                            • #15
                              A door bell style transformer will provide you with 24v AC so you can run them in parallel. That's your best bet.

                              Dan
                              At the end of the project, there is a profound difference between spare parts and extra parts.

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