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DIY Lightbulb Limiter, how to ground the 2 elements in the most robust way?

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  • DIY Lightbulb Limiter, how to ground the 2 elements in the most robust way?

    Hi all

    So, fairly simple question but not sure which would be considered the most robust...

    I'm making a DIY lightbulb limiter, a wooden box with plug socket and bulb socket on it. I need the earth on the plug socket, of course, but the bulb socket is also metal and requires safety earthing. Given that pig tailing with a screw on wirenut is not an accredited method here in the uk I wanted to pick brains on my other options -

    1 - strip back the ground wire sleeve a few inches from the end, AND at the end, fold the exposed area in the middle of the sleeve and use that for the lightbulb. It's stranded core, I feel like this would probably be ok but I'm worried it might be considered bad practice...

    2 - Install a chassis ground point like on a metal amp, wall earth to that, 2 wires off to the plug socket and bulb socket. I am kind of comfortable with this form but means the earth wire from the wall now has a non-continuos route to the ground pin of the plug socket... and I know that's frowned upon and, well, I don't want to cut corners on the safety earth of the DUT. Maybe it's not a problem if I follow the usual standards for a really secure safety ground... EDIT, less into this ATM, 3 mains earth connections on one terminal? Thinking more of making a ground strip with 3 terminals...

    3 - Buy something like a terminal block with gangs to allow safe connection of more than 2 wires, comfortable wit this too but has the same problem as no. 2...

    4 - Ground the bulb socket, with a separate wire, on the back-chassis of the plug socket by screwing it down to the mounting bolts on the inside side

    It's a somewhat small thing technically but as it's such a hugely important thing, safety wise, I wanted to run ideas here too. I will probably ask the electrician at my work too when he's next in, before I build anything. As ever, I know the risks and am solely responsible for my final decision on how to connect it!

  • #2
    Actually, I'll probably just use a wago 222 splicer lever block thing...

    Comment


    • #3
      Dunno what that is?
      Whatever, use of some terminal block/s to suitably bond the earth wire terminations together would be fine.
      Get a handful of incandescent bulbs in (of various wattages) before they get even harder to find.
      My band:- http://www.youtube.com/user/RedwingBand

      Comment


      • #4
        Originally posted by pdf64 View Post
        Dunno what that is?
        Whatever, use of some terminal block/s to suitably bond the earth wire terminations together would be fine.
        Get a handful of incandescent bulbs in (of various wattages) before they get even harder to find.
        Yeah I've stocked up on bulbs!!

        They are basically snap on terminal blocks that seem to have a good rep with installation electricians -

        https://www.rapidonline.com/WAGO-222...-%20New%20feed

        Cheers!

        Comment


        • #5
          I just built this one tonight:

          Click image for larger version

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          Click image for larger version

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          After building my first one, it had an attached power cord and worked fine. But after some time using it on the bench at home and at work, it was kind of clunky and I'd have to shuffle it around the bench dealing with the attached cord, as well as the equipment cord being tested. Plus, there was the added step of plugging in the equipment for current limiting, and unplugging it from the junction box when I needed to run further testing.
          I've been wanting to build another, and incorporate some changes which would make this tool work better for my needs. So, I installed a Schurter IEC inlet, a toggle switch to bypass the current limiter, and pilot lamp to indicate that the current limiting is engaged.
          I bought the junction box, and Leviton light bulb socket and power outlet at Home Depot. It's nice and compact, easy to manage, and efficient. Plus, to your initial question, there is raised inset located in the bottom of the box making it easy to terminate all your earthed conductors to a common point.
          If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

          Comment


          • #6
            That looks convenient. I decided they didn't all have to be in one spot. SO I had a special outlet on my bench riser, and a handy wall switch - same Leviton switch I might use on the bedroom wall - mounted in a box hung under the benchtop. Bulb socket was visible but out of the way.. Wiring was like the rest of my bench mains wiring, unseen. I didn't add a bypass switch, though that would have been handy. I just move the mains cord into one of the many regular mains outlets on strips on, over, or under the bench.


            Speaking of those square boxes, something I have kept around my shops for decades: plain old outlet drop boxes. One of your boxes with a four-banger outlet panel on top. A pair of duplex outlets. I then run a long mains cord from the box. basically it is a heavy extension cord with four outlets. Not for the bench, but real handy in the warehouse area. You go to check out a basic PA system, and you need to plug in the mixer, the amp, the god-knows-what-else. SO one sturdy box with long cord and four outlets.
            Education is what you're left with after you have forgotten what you have learned.

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            • #7
              Great design SoulFetish! I love the idea of a bypass switch, and an IEC socket rather than permanently wired... And something like you are talking about Enzo is what I want to do when I'm in a more permanent space, have it all 'in the walls' and out of the way so I can go through it straight away if necessary and not have to have a bulb box on my desk...

              As it was I was keen to get it working as I have an amp that needed it to be tested for big faults, so I just made do with whatever wood I had lying around and came up with this -

              Click image for larger version

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              I probably spent a bit too much time with the woodwork, making sure it was all flush, and making the insides bomb-proof rather than looking at flexibility but, hey, it's my first one so I'll use it and let it annoy me and work from there later

              Comment


              • #8
                Originally posted by OwenM View Post
                Great design SoulFetish! I love the idea of a bypass switch, and an IEC socket rather than permanently wired... And something like you are talking about Enzo is what I want to do when I'm in a more permanent space, have it all 'in the walls' and out of the way so I can go through it straight away if necessary and not have to have a bulb box on my desk...

                As it was I was keen to get it working as I have an amp that needed it to be tested for big faults, so I just made do with whatever wood I had lying around and came up with this -

                [ATTACH=CONFIG]56789[/ATTACH]

                I probably spent a bit too much time with the woodwork, making sure it was all flush, and making the insides bomb-proof rather than looking at flexibility but, hey, it's my first one so I'll use it and let it annoy me and work from there later
                nice woodwork! Mahogany?
                If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

                Comment


                • #9
                  This might be getting a little off-topic but I've never used a light bulb for limiting. What always bothered me is that I would like to know how much
                  current I'm allowing. With the non-linear resistance of a light bulb I'm not sure. To be fair I haven't done any measurements, maybe I should.

                  I will temporarily connect a DC power supply, current limited at 300mA to make sure a newly repaired SS amp won't smoke when I apply AC power.

                  For an AC circuit like an offline switching power supply I built this AC current limiter. The pot can be set for 100mA to 1A at full CW
                  If the DUT is drawing too much current the output voltage won't reach 120V.
                  https://music-electronics-forum.com/...1&d=1580177463
                  Attached Files

                  Comment


                  • #10
                    Well, the bulb is in series with the load, so if we have a 60 watt lamp in it, a dead short on the DUT means half an amp flows through it. Half an amp ought not stress the primary winding. But remember that is only current through the winding, the voltage across it can approach zero. If the bulb shines bright, then the majority of the 120v is across it, not the DUT. If the bulb is dim, then most of the voltage is across the DUT, but at low current. If the DUT has a shorted primary, then this is as far as it goes. That half amp max won't hurt anything further.

                    Let's say the transformer is OK but we have shorted output transistors. They make a huge load on the power supply, or try to. And that will try to draw a lot of current from the primary, well through it. But the bulb is there to limit it to half an amp. And that means the voltage across the DUT primary will remain very low - most of it is across the lamp - and so the secondary voltages will also remain very low

                    if you are timid you can start with a 25 or 40 watt bulb. And remember a 200 or 300 watt bulb will offer little protection.


                    I use a variac and a current meter in similar fashion, but someone with neither can whip together a bulb limiter in a few minutes and cheaply, without having to buy a variac and meter.
                    Education is what you're left with after you have forgotten what you have learned.

                    Comment


                    • #11
                      Originally posted by SoulFetish View Post
                      nice woodwork! Mahogany?
                      Thanks! It's actually Sapele, so not genuine mahogany but it looks real similar and still has some of the tough-qualities of genuine!

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                      • #12
                        Light Bulb Current Limiter

                        https://ampgarage.com/forum/download/file.php?id=39748
                        It's All Over Now

                        Comment


                        • #13
                          Originally posted by vintagekiki View Post
                          That's members only. Can you upload it here?
                          Originally posted by Enzo
                          I have a sign in my shop that says, "Never think up reasons not to check something."


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                          • #14
                            https://ampgarage.com/forum/viewtopic.php?f=6&t=20341
                            You must log in or sign up

                            tag_light_bulb_limiter_r1_102.pdf
                            Attached Files
                            It's All Over Now

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