Announcement

Collapse
No announcement yet.

Ot: Driverless cob led lights

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

  • Ot: Driverless cob led lights

    Sorry if this has already been discussed before, if so I missed it.

    For better or worse I've ordered about a half dozen of a new type of COB led that I plan on re-purposing some old halogen floodlight housings to, using the housing as a passive heatsink. I have some applications both in and outside of the shop for these.

    The beauty of these is that they require no led driver or buck boost converter to power them up. All that's needed is to simply solder them up to 110 or 220 line voltage, depending of coarse on the voltage of the led that one has ordered. Supposedly they have the light output of of a 500 watt halogen in a 50 watt package. Considering this and the extremely low cost of these COB leds, $1.59US, they sound too good to be true. Even if they are DOA at least I won't be out much.

    Just wondering if anybody has some direct experience with these as to their longevity or if I need more than the passive heatsink capability of a typical aluminum halogen light housing's ability to dissipate the required amount of heat generated. Not a problem this time of year so much as in the summer. I do have several led flood lights that use a driver and I have been extremely satisfied with both their longevity and light output.
    Apparently these stand alone COB leds are available from various sources from 10-150 watt, but it's mainly the 50 watters I'm going to be working with for now.

    An Ebay link and a pic from that link to better help illustrate what I'm going to be using.

    https://www.ebay.com/itm/110v-220v-L....c100507.m3226


    Home, down in the valley behind the Red Angus
    Bad Decisions Make Good Stories​

  • #2
    Did you read the feedback on some of those. 20-25W for those sold as 50W. About two negatives per day. Not a good track record.

    Comment


    • #3
      Thanks Ken I hadn't checked in on the negative feedback for that seller. In all fairness to that particular merchant he does have almost a 99% satisfaction rating on a feedback score of over 35,000. However you are right there is a disproportionate negative response feedback to his cob led sales from what I saw.

      Although I left this seller as an example it is not the merchant that I purchased these cob leds from, mine where even less dollars than those in the link. Although they do appear to be the same type so I'm sure that the negative feedback will continue with my particular merchant when I receive mine, as I will take some readings on them when I receive them.

      I was a little concerned about them being of a dubious design quality hence my question as to their longevity. I'll see how they stack up when I get them. Even at 20-25 watts for less than a buck and half a piece and a direct hookup they still aren't all that bad. At least I won't have to worry so much about the heat dissipation issue now.

      Thanks for the heads-up.
      Home, down in the valley behind the Red Angus
      Bad Decisions Make Good Stories​

      Comment


      • #4
        I've done 4 ten watt led chips in one housing and it does get pretty warm. I mounted these on an aluminum plate which I cut to fit within the housing. Mounted that using plenty of goop to help take the heat out of the plate and into the housing material.

        For me it's all about dissipating the heat. For use as a replacement light that's expected to be on for hours at a time, sufficient heat sink is a must. For my 50 watt chips I'm using about 200 sq in of fin area. Can be much smaller if fan cooled but now you can't just wire 110 to it- you need to power the fan (and you get to hear it running probably) and have more stuff to go wrong.

        Many times I've considered mounting those led chips onto aluminum square tubing. If you expose the entire outer surface to air, then for 1.5 x 3 inch tubing you have 9 sq in of area for every inch of length of tube. If air can flow through the tube, that doubles. So a 10 inch length of that sized tubing would give you about 180 sq in of area. That's without adding any fins or mounting it to another heat-absorbing material. The looks would be lacking, but it's workable. The heat sink is always going to be way more expensive than the led chip.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

        Comment


        • #5
          Small liquid heat exchanger and heat up the shop's hot water supply
          Helder Ferreira
          Setubal, Portugal

          Comment


          • #6
            I don't have experience with this particular model - i tried other cheap driverless led module. The damn thing blinked with mains frequency like a stroboscope - barely usable as reading lamp, absolutely unusable around rotating machinery.
            It was a few years ago so your cob may be better suitted (some sort of filtering, longer decay time on phosphorus?).

            Wysłane z mojego GT-N7100 przy użyciu Tapatalka

            Comment


            • #7
              I use those led chips for machine worklights, but the versions with the seperate ac->dc transformer. 20w gives a good light with low voltage outside of the transformer. I've migraged all of my ex lovo machine lamps to them as 80v bulbs are getting hard to find and as I get older, I like a lot of light. In fact the first one I tried, I used a 100w led unit, and it was too much, blinding almost. So I swapped the led itself for a 20w unit.
              But, you do have to add heatsinks, and heatsink to the metal lamp casing also as they do run hot. I tuck the transformer away safe in the machine base with the other electrics. For heatsinks I have access to some dead computers and I go swipe a cpu heatsink to mount them onto directly with some compound.
              I have 4 seperate 10w chip style lights pointed at my motorcycle work bench to give additional lighting to improve the work area too, theyre great and not too bright so theyre probably fake 5w units :-) but they were just bought as 10w leds.
              When you said led corn cob type bulbs, I thought you meant the led corncob bulbs that fit the ex halogen floodlight fittings. They are good too, lots of light for significantly less power budget and a lot less hassle to fit, but theyre not quite as good as converting to the chip style ones and probably a shorter life as they dont have great heat transmission to the case unlike mounting a flat one right on the casting.

              Comment


              • #8
                Yes, I have recently used these for the job you describe, Mine did draw the 50watt so are true to claim. If you buy a new light that is what is in it.

                Longevity, I don't know yet but they work. They need flat metal contact and silver paste for the heat sink.

                This seller https://www.ebay.co.uk/sch/baoshengh...p2047675.l2562
                "...do you not think you have enough machines?"

                Comment


                • #9
                  I appreciate the additional input and the need to get rid of the heat. I fully intend to use thermal paste as I do have lots on hand. I'm thinking of machining the housing flat where I intend to mount the led as it will certainly aid in the heat transfer, I also have a number of cpu heat sinks so if necessary I'll try to utilize them as well. I'm hoping to keep the cooling process passive as adding fans will only complicate the installation and add noise as Darryl mentioned.

                  I should probably have clarified the term "cob" when referring to these as cob leds. It does not mean corn cob style lights but instead cob is simply an acronym for "chip on board". The technology on these types of products is progressing so fast these days that we don't always have time to catch up on all of it as it transpires. Only a few short years ago none of these terms would have been recognized by any of us.

                  I do have several led flood lights already as mentioned with an integrated power source mounted externally and I've been very impress with them, even the 10 watt units are very impressive given the power required to drive them.
                  Here's hoping that the cheapest chip on board type of light that I could find will be only half as good as it'e 50 watt claim says it it is. This is kind of an experiment to see how much light I can get out of a buck and a half and a bit of experimentation. Nothing ventured nothing gained.
                  Home, down in the valley behind the Red Angus
                  Bad Decisions Make Good Stories​

                  Comment


                  • #10
                    Check out this website to see if you have similar package

                    http://www.cob-led.com/COB-LED-array-standard-CRI.html

                    Most of these devices have 3*C per watt thermal resistance, and have to be de-rated above 80*C

                    Max voltage 60 @ 800mA

                    Comment


                    • #11
                      Willy wrote: I fully intend to use thermal paste as I do have lots on hand. I'm thinking of machining the housing flat where I intend to mount the led as it will certainly aid in the heat transfer,

                      You probably already know this, but I'll say it anyway. After machining you need to lap the housing to get it as flat as possible. Then use as little thermal paste as possible, just like with a CPU heat sink. That's the way to do it if you need to maximize the heat transfer.

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

                      Comment


                      • #12
                        Originally posted by danlb View Post
                        Willy wrote: I fully intend to use thermal paste as I do have lots on hand. I'm thinking of machining the housing flat where I intend to mount the led as it will certainly aid in the heat transfer,

                        You probably already know this, but I'll say it anyway. After machining you need to lap the housing to get it as flat as possible. Then use as little thermal paste as possible, just like with a CPU heat sink. That's the way to do it if you need to maximize the heat transfer.

                        Dan
                        In practice I found the COBs to be thin and flexible, not rigid like a CPU, so just piled the paste on.
                        "...do you not think you have enough machines?"

                        Comment


                        • #13
                          Originally posted by bob_s View Post
                          Check out this website to see if you have similar package

                          http://www.cob-led.com/COB-LED-array-standard-CRI.html

                          Most of these devices have 3*C per watt thermal resistance, and have to be de-rated above 80*C

                          Max voltage 60 @ 800mA
                          The ones I'm dealing with are like those shown in my first post and linked to. From what I've been able to gather most do seem to need derating beyond 80°C. Who knows if these ultra cheap units don't get close to the advertised 50 watts it may not be an issue.

                          Originally posted by danlb View Post
                          Willy wrote: I fully intend to use thermal paste as I do have lots on hand. I'm thinking of machining the housing flat where I intend to mount the led as it will certainly aid in the heat transfer,

                          You probably already know this, but I'll say it anyway. After machining you need to lap the housing to get it as flat as possible. Then use as little thermal paste as possible, just like with a CPU heat sink. That's the way to do it if you need to maximize the heat transfer.

                          Dan
                          Thanks Dan, yes well aware of the proper technique and for a more worthy component this is what I'd do also. However for as little as these things cost I'm not going to get too anal on their install. A milled seat and a good quality thermal paste is all they'll see.


                          Originally posted by Davidhcnc View Post
                          In practice I found the COBs to be thin and flexible, not rigid like a CPU, so just piled the paste on.
                          These have an aluminum backing plate. Not sure how thick or rigid but I suspect flexible is probably going to be an apt choice of terms. We'll see.
                          I will monitor temperatures though as well as current draw and a subjective appraisal of light quality/quantity. I have light meters but I don't need to turn the house upside down in order to find them.
                          Home, down in the valley behind the Red Angus
                          Bad Decisions Make Good Stories​

                          Comment


                          • #14
                            If you really need low thermal resistance, which you may not actually in this case, "thermal paste" is the WRONG material to use.

                            Actually, IMO, thermal paste is USUALLY the wrong stuff to use.

                            The best material is a "phase change" type material, which will wick in and fill tiny spaces once the part gets hot. The thermal resistance of the joint can go very low, as low as 0.02 C in^2/w.

                            https://www.digikey.com/products/en/...=0&pageSize=25

                            https://www.aavid.com/sites/default/...ultrastick.pdf
                            1601

                            Keep eye on ball.
                            Hashim Khan

                            Comment


                            • #15
                              Originally posted by J Tiers View Post
                              If you really need low thermal resistance, which you may not actually in this case, "thermal paste" is the WRONG material to use.

                              Actually, IMO, thermal paste is USUALLY the wrong stuff to use.

                              The best material is a "phase change" type material, which will wick in and fill tiny spaces once the part gets hot. The thermal resistance of the joint can go very low, as low as 0.02 C in^2/w.

                              https://www.digikey.com/products/en/...=0&pageSize=25

                              https://www.aavid.com/sites/default/...ultrastick.pdf
                              Good info. Perhaps the use of the term thermal paste is the wrong wording on my part.

                              I was of the understanding that this is exactly what the role of a thermally conductive paste/compound was, although I do realize that there are good products and then there are the rest.

                              I have seen some that bleed and run when subjected to normal component operating temps while others have dried out to the point they are no longer able to function as intended.

                              In your opinion how does the Arctic Silver 5 that I'm now using compare to those you linked to?
                              Home, down in the valley behind the Red Angus
                              Bad Decisions Make Good Stories​

                              Comment

                              Working...
                              X