Announcement

Collapse
No announcement yet.

repairing corn cob led bulbs

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    Can't really tell from the picture, but the analog current regulator chip could be there- it's about the same size as the bridge rectifier you do see.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

    Comment


    • #17
      thanks everybody for the input. i found the obvious solution to the problem. however i would still like to understand what is going on with these lamps.

      for working lamp:

      supply: 230 vac
      each array: 8.3 vdc
      brown cap: 190 vac
      electrolyt: 100 vdc
      11 arrays
      max. between any 20 points: 66 vdc (no acces to top array)
      max. of any point to earth: 48 vdc

      so i would have thought these to be 11 arrays in series for 110 vac providing 14 vdc to each array with the cap added for 230 vac? but probably not. does the cap reduce voltage to 71 vac resulting in 100 vdc on elecrolyt? 100/11 = 9.1 and 8.7 vdc is lost somewhere? but why the 66 and 48 vdc is beyond me.

      interestingly i am not able to measure any voltage accross the single leds.

      the current through the jumper is 104 ma (@8.3 vdc), so 0.9 w? no idea how this fits in the picture. the lamp puts out around 2000 lm and was advertised as 20-30 w. so 25 w/165 should be around 0.15 w per led or 2.25 w per array. i dont think these leds put out 150 lm/w.

      the lamp is similar to this:

      https://www.ebay.com/itm/E27-E14-E12...sAAOSwe0hc5lge

      edit: besides the arrays are somehow in series, so the current measurement makes even less sence.




      Click image for larger version  Name:	0 115.jpg Views:	0 Size:	3.18 MB ID:	1905153 Click image for larger version  Name:	0 116.jpg Views:	0 Size:	2.98 MB ID:	1905154

      Last edited by dian; 10-16-2020, 08:01 AM.

      Comment


      • #18
        I agree that the PCB for those bulbs is mighty sparse, but off-line PWM controllers can be in pretty tiny packages, and don't require many external components. Check out the HV9922 in a TO-92 or tiny SOT-89 three lead package which can run on 85-264 VAC (through a bridge rectifier) and drive dozens of high power LEDs in series at a current of 50 mA. The only other components are one large and one small capacitor, a small diode, and an inductor. It has an efficiency of 70-80%.

        I seriously doubt that a high power LED lamp like this would use a linear current regulator, especially if it is expected to operate on a normal range of voltage. Consider that it has a power draw of about 50 watts, probably 90 volts at 750 mA, and at 220 VAC or nearly 300 VDC peak, a linear regulator would have to drop 210 VDC at 750 mA or 157 watts! Even if enough LEDs are put in series to drop 270 volts at 185 mA, the linear regulator would need to dissipate 30 volts * 0.185 = 5.5 watts. The ALS5890 is a linear regulator with a fixed current of 10, 15, 20, 30, or 40 mA, but maximum power dissipation is 3.85 watts in the rather large TO-252 package although a large heat sink can greatly increase that. But obviously the PCBs for the lamps being discussed do not have such large components and heat sinking.
        http://pauleschoen.com/pix/PM08_P76_P54.png
        Paul , P S Technology, Inc. and MrTibbs
        USA Maryland 21030

        Comment


        • #19
          Now that I can see the components more clearly, it looks like the circuit consists of a series AC capacitor (large brown one) which acts as a capacitive reactance into the bridge rectifier and electrolytic capacitor to the LED strings. This is a "cheap and dirty" solution to avoid wasting power in a resistive (linear) regulator, but it will have poor power factor and the LED brightness will vary with input voltage. However, that may be desired if you want to run the lamp on a dimmer.

          [edit] The 8.3 VDC is probably three LEDs at 2.8 VDC each. The 66 VDC is probably two banks of 12 LEDs in series, and there is a third bank of 33 VDC, for a total of 99 VDC. The 48 VDC to earth is probably just leakage or capacitance.
          Last edited by PStechPaul; 10-16-2020, 07:44 AM.
          http://pauleschoen.com/pix/PM08_P76_P54.png
          Paul , P S Technology, Inc. and MrTibbs
          USA Maryland 21030

          Comment


          • #20
            so 66 = 8 x 8.3, 3 arrays left, 3 x 8.3 = 25. ?

            Comment


            • #21
              Originally posted by PStechPaul View Post
              This appears to be something like a 100 watt actual power bulb (about 300 watt halogen equivalent) which costs nearly $200:
              The bulb you have listed is intended to replace a mogul base HPS or Metal Halide bulb in a commercial lighting fixture. Not some like the bulb the OP has shown.
              Apples and Oranges.

              The 100w bulb Dian linked to is 99 cents USD.
              Last edited by reggie_obe; 10-16-2020, 11:29 AM.

              Comment


              • #22
                well, as i said they are supposed to be 20-30 w (i dont remember what i bought at that time) and is around $6 as in the link.

                so i fixed quite a number of these bulbs, didnt take that long, you see the faulty array right away, leds have black dots.

                now a new mystery: i noticed there are 315 vdc on the electrolyt if the bulb is connected to supply with one array not working. ???

                Comment


                • #23
                  to be honest, with cheap Chinese LED lights of any variety actual output is typically about 1/4 to 1/3 of what's claimed. So I wouldn't go off any number that they're supposed to be, but work it out from the basics. Looks like 12 arrays of 3S5P LEDs. So 8.3Vf x 12 x 0.1A = 10W. Efficiency of those cheap LEDs is probably around 70-80lm/W at 20mA per LED (maybe a bit higher, but not by much) so output is probably around 700-800lm. All of which matches pretty well the LED density and lack of heatsinking.

                  Comment


                  • #24
                    sorry, no, they produce around 2000 lm, are as bright a 150 w halogen bulb. thats why i have been using them for several years now.

                    three of the bulbs blew the electrolytic cap (4.7 µf, 250v). why would the cap blow? i thought because the other cap gave up the ghost and it was fed 325 vdc. but: i fixed one of them as i did the other ones and it now runs happily without the electrolyt. there is 82 vdc and 20 vac beteen the legs (remnants of the cap). if a cap is added voltage goes to 90 vdc without the slightest change in light output. and no, it doesnt flicker. so why are the leds actually not run on ac?

                    Comment


                    • #25
                      From my experience, the cheap bulbs overdrive the LEDs to get higher output but this results in early failure (and more sales for the supplier). This bulb appears to be what is listed on the eBay link as 136 LEDs and 140 watts, or about 1 watt per LED, and costing $3.69. This would require 357 mA per device, so if they are indeed 150 mA rated, they are driven to 2.4 times rating. But that seems to be an equivalent rating, so the OP's measurement of 104 mA would correspond to about 10 watts actual power (based on 99 VDC on string). That is typical for bulbs rated at 60-75 watt equivalent. And that would be about 20 mA per LED, which is typical for tiny 0805 devices.

                      Sorry if this seems like rambling - on my first cup of coffee.

                      With any bank of LEDs missing from the array, this will present an open circuit which will charge the capacitor to 220 VAC * 1.414 = 311 VDC.

                      Ordinary 60W equivalent LED lamps are selling locally in stores for less than $1 each on sale, and appear to be much higher quality than these Chinese contraptions. If you have experienced multiple failures, "repairing" these with jumpers may be a fool's errand and you will get poor reliability and short life, as well as probably poor light quality. These LEDs appear to be unreliable and will continue to degrade and burn out. There is also perhaps a fire hazard if the capacitor is not rated for the 315 volts it will see when the string opens, and the film capacitor across the line may not be properly rated for safety.
                      http://pauleschoen.com/pix/PM08_P76_P54.png
                      Paul , P S Technology, Inc. and MrTibbs
                      USA Maryland 21030

                      Comment


                      • #26
                        OK, you want to jump one 15 LED section out of the circuit and use the rest at their original current. I am jumping on two numbers here. The 66 Volt measurement which is probably two 15 LED groups in series. So each LED group is dropping 33 V (about 2.2 V per LED which is a reasonable value).

                        The other number is the 104 mA reading through your jumper. Since the power supplied to the LEDs does not appear to be have current regulation this will be an approximate starting point. I am going to use the approximate value of 0.1 Amps.

                        Using Ohms law, R = E/I = 33/0.1= 330 Ohms

                        and for power rating:

                        P = VI = 33 x 0.1 = 3.3 Watts. You will probably need to step up to a 5 W rating on the resistor.

                        That's just a STARTING point. After substituting a 330 Ohm, 5 W resistor for your jumper, take Voltage readings across that resistor and the other, working 15 Led groups. The 330 Ohm resistor will probably have a higher Voltage reading. You can then adjust the value of that resistor, probably downward, until the Voltage readings match.

                        If my numbers above are a good approximation of the actual values needed, you can see that the power rating of the resistor can be a very important factor. You should do a new power calculation for each new resistor value that is tried.

                        I am sorry that this is a cut and try thing, but without access to the actual bulb it may be the best I can do.

                        You can use nine 1/2 Watt, 330 Ohm resistors in a parallel - series arrangement to get a 4.5 Watt rating. You would make three groups of three 330 Ohm resistors in parallel in each group. Then connect those three groups in series. I would assemble them with a maximum area of the resistors exposed to the air. The parallel groups would be arranged side by side instead of using an triangular arrangement where each of the three resistors is in contact with the other two. And the series configuration would have the three groups spaced from each other, again for good air circulation.
                        Paul A.
                        SE Texas

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

                        Comment


                        • #27
                          Originally posted by PStechPaul View Post
                          From my experience, the cheap bulbs overdrive the LEDs to get higher output but this results in early failure (and more sales for the supplier). ..........

                          Ordinary 60W equivalent LED lamps are selling locally in stores for less than $1 each on sale, and appear to be much higher quality than these Chinese contraptions. If you have experienced multiple failures, "repairing" these with jumpers may be a fool's errand and you will get poor reliability and short life, as well as probably poor light quality. These LEDs appear to be unreliable and will continue to degrade and burn out. There is also perhaps a fire hazard if the capacitor is not rated for the 315 volts it will see when the string opens, and the film capacitor across the line may not be properly rated for safety.
                          Those $1 bulbs are the same cheapo chinese "contraptions" as you suspect this one is, maybe a different layout, but same crap.

                          If you can actually find a bulb that does not appear to be made in china, and it costs under $8 per each, look again. I think every LED bulb around is made in china, at least I have not found any consumer LED bubs, tubes, etc that are not.

                          Even CREE, who make their own LEDs, unlike most, still have the bulbs assembled overseas, although the design is much better, and they use Power Integrations chips in the power supply.

                          As for that device in the pics......

                          If it is a capacitive dropping system, as it superficially looks to be (there is that slot in the PWB, more typical of an SMPS), then it is dropping about 130V or so. At 357mA, and 130V, the impedance has to be about 350 ohms.

                          That comes out to 9 uF, which I believe I can reliably say that brown capacitor is probably not rated at. At least it would be "very surprising".

                          There may be some simple form of SMPS on the reverse side of the PWB we see in the pic.
                          Last edited by J Tiers; 10-16-2020, 07:12 PM.
                          1601 2137 5683 1002 1437

                          Keep eye on ball.
                          Hashim Khan

                          If you look closely at a digital signal, you find out it is really analog......

                          Comment


                          • #28
                            Again, why bother with a resistor? This is essentially a current limited circuit based on 190 VAC across a film capacitor. If the current is 100 mA, the capacitive reactance is 1900 ohms, and at 50 Hz that calculates to 1.67 uF. Shorting one out of the 12 LED columns will just lower the load resistance by about 8%, resulting in about 8% higher current. That would probably be perfectly OK, although it may shorten the life of the remaining LEDs. The heat from an equivalent resistor might have even more deleterious effect.

                            If there are several strings in parallel, balancing the current will be more important. But from the evidence presented, an open circuit in one column causes the lamp to extinguish, with 312 volts on the 250V 4.7 uF capacitor across the load. So balancing is not needed.

                            [edit] The cheap (but more than $1) lamp I took apart five years ago had a switching supply circuit, as did another one (probably $1 type) I cracked open more recently. I have never seen one with the minimal circuitry found in the OP's lamps.

                            Click image for larger version

Name:	LED_Lamp_1929.jpg
Views:	61
Size:	80.0 KB
ID:	1905261
                            Click image for larger version

Name:	LED_Lamp_1932.jpg
Views:	59
Size:	97.4 KB
ID:	1905263
                            Click image for larger version

Name:	LED_Lamp_1933.jpg
Views:	59
Size:	91.4 KB
ID:	1905262
                            Click image for larger version

Name:	LED_Lamp_1936.jpg
Views:	59
Size:	119.6 KB
ID:	1905265
                            Click image for larger version

Name:	LED_Lamp_1939.jpg
Views:	58
Size:	80.2 KB
ID:	1905264
                            A short video of the analysis:
                            http://enginuitysystems.com/pix/elec..._Lamp_1938.AVI
                            And a short clip showing the symptoms of a second lamp which failed later:
                            http://enginuitysystems.com/pix/elec..._Lamp_2350.AVI
                            Last edited by PStechPaul; 10-16-2020, 07:21 PM.
                            http://pauleschoen.com/pix/PM08_P76_P54.png
                            Paul , P S Technology, Inc. and MrTibbs
                            USA Maryland 21030

                            Comment


                            • #29
                              Originally posted by dian View Post
                              and no, it doesnt flicker. so why are the leds actually not run on ac?
                              It's flickering, you just don't see it. You bought cheap, you got cheap, the caps failed because they were they cheapest they could source.
                              On A/C, since they are a diode, they would conduct in one direction and only illuminate on half of the waveform (if they lit up at all).

                              Comment


                              • #30
                                Originally posted by PStechPaul View Post
                                Again, why bother with a resistor? This is essentially a current limited circuit based on 190 VAC across a film capacitor. If the current is 100 mA, the capacitive reactance is 1900 ohms, and at 50 Hz that calculates to 1.67 uF. Shorting one out of the 12 LED columns will just lower the load resistance by about 8%, resulting in about 8% higher current. That would probably be perfectly OK, although it may shorten the life of the remaining LEDs. The heat from an equivalent resistor might have even more deleterious effect.

                                If there are several strings in parallel, balancing the current will be more important. But from the evidence presented, an open circuit in one column causes the lamp to extinguish, with 312 volts on the 250V 4.7 uF capacitor across the load. So balancing is not needed.
                                If they are all in series, and at a lower current, then it does become more practical. In an earlier post it was suggested they were parallel......

                                Tear apart a bad one and settle the matter!
                                1601 2137 5683 1002 1437

                                Keep eye on ball.
                                Hashim Khan

                                If you look closely at a digital signal, you find out it is really analog......

                                Comment

                                Working...
                                X