01821 Workbench 101 #2 How does a Dim Bulb Current Limiter Work 

Thanks that meas a lot to me.

Glad it was helpful!

Thanks, yep that is an idea. This is more a 'How Does' video vs 'How To'. This is the DBCL I created ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-7ME1iPrkhOU.html How it is employed is based on what I am testing. Lots of bulbs for a 5 amp CRO one 40w bulb for an old 100ma AA5 portable. With the Dim Bulb it always best to start low and add more. Unlike say an old analog volt/amp meter measurement where you start with a high voltage/amperage and then scale down.

: The in-series DIM BULB must be able to supply the required load current - when running the DUT loaded. The bulb is intended to limit the current - so one can determine if the DUT is presenting a Short Circuit. In the example shown - the objective is to protect the DUT. The light bulb used as the example load - hence the light bulb should glow dimly. Using a higher Wattage bulb reduces the protection - since it allows larger and a potentially damaging current to flow in the DUT. : Higher wattage bulb lets through more current than a lower wattage bulb so a 60W bulb is generally enough Also DUT means “Device Under Test” not DUT means “device under test” Pay attention that the first letter is in ALL CAPS Learn also that all CORPORATE {Legal NAMES} are always in ALL CAPS ** There are writing rules that you do not yet understand and have not mastered. Undertake an extensive reading program to better educate yourself. Also study the Chicago Style Manual. Writing is an art form that you should master - and you can ONLY do that by reading and studying manuals. I have authored /co-authored eight for the USAF and a number of manuals for the purpose of obtaining ISO 900/9001 Certification. These manuals were in excess 1200 pages Understand that such Manuals have to be a very high standard of detail - clarity and grammar.

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Yep I would guess they would do though there is no easy way to tell if you have a short until they start to glow red. I have seen them used in RF dummy loads for HAM work but they one I saw was also in a sealed oil bath to disperse the heat more quickly.

Yep it is an old style apparatus, we had one in our high school to show the difference between parallel and series resistance, Good old days before they where safety standards, lawn darts, BB-Guns,Vac-U-form I do not how any of us survived to now. Any way I did build one with a load of bulbs here ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-7ME1iPrkhOU.html

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Thanks, The key for me is we are always told to use one but no-one really explains how it works at least from the serial vs parallel point of view. Thanks again and don't forget to subscribe ;)

If you look at about the 8min point I explain the formula P(w)=VI, so for 40w it would be 40=120/X so .333 of an amp for a 40w bulb. (varies by the bulb and the state of the mains voltage) Normally most items have either a working wattage or amperage listed so I just select bulbs for about that working amperage /wattage If I do not know the working amperage /wattage then follow the 'old' rule of analog meters but in reverse. I start with the lowest bulb and then add in as I go. If you have a look at this video ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-MIWz8RlloLU.html at about the 10min point I use bigger and bigger bulbs to load an old HP Nixi Counter 🙂

Thanks Mike

It we are talking about a Mixer for Audio like an MG-12 it more than likely does does not have a power transformer but a SMPS. My guess what you are seeing the SMPS starting and stopping (shuttering) and what you are seeing is SMPS turning on giving the correct power so LEDs come on and then shorting out causing the DIM Bulb will flash and then turning itself off. I usually a never use a Dim Bulb on an SMPS device as there is no transformer to burn out. I think 700w might be the Audio output and not the input power requirement that should be between 35~100w. My guess it is limited the current but the SMPS is resetting by itself so the dim bulb is not doing much.

@@byterock hello Sir, thank you for replying to my comment. The power mixer is 400W per channel. 700W power consumption. Labelled back panel. I took the chance and plug it in directly to the wall plug. Works fine. Yes the dim was limiting the current. It has a 6.3A fuse as well.

And yes it a big SMPS power supple.

@@anoushan Wow 700w power consumption. and a 6+ amp fuse. You would need like a 1500+ watt bulb. But that makes sense the Dim bulb would limit the current and the SMPS would detect that and then turn off suspecting that there is some fault with the power coming in. If it was designed to that sometimes low current can cause as much damage as high current 😆

Isn't that the whole point of the dim-bulb current limiter ;). Take a big wack of current to start vs the DUT. But I see your point on the little graphs I created. A even bigger spike on the graph might of been better.

Sorry for the late reply, been away. Yeah I had a longer version but I wanted to keep it short a sweet. If I remember correctly my old teacher spend well over 4 classes on just the theory of series vs parallel light bulbs, but that was a long time ago ;)

@@byterock yeah, no problem. I didn't mean to sound too critical. Any effort that helps people is to be applauded. When I give feedback, it is with the best of intentions. I have a Rock solid understanding of ohm's law and have watched many vid's about Dim tester's. But I am still having trouble visualizing how the voltage drops are distributed across the bulb and the Device Under Test, in quiescent conditions, after the initial inrush surge (assuming there is nothing wrong with the device). I really need to sit down with a calculator and pencil and work it out. The variable resistance of the bulb from cold to hit is slightly tricky to figure in, especially when the voltage across it is less than rated voltage, so we can't rely on the wattage rating to mean much, except in limiting initial inrush current. I am hoping to build my own tester soon, ultimate deluxe version, with analog panel meters for voltage and current, and about 5 different load bulbs that can be switched in or out for different conditions. Thank You. -from Minneapolis

@@douglas2lee929 No problem Douglas I love feedback. It is a very tricky subject and there are whole physics and engineering books written about ''Non-Ohmic" conductors or resistors. The whole point of a 'Dim Bulb' is that is does not follow 'Ohms Law', maybe I should of pointed that out better in the video. I will change the description an add in a good link on 'Non-Ohmic' thingy. Yeah good old 'ohms' law goes only really good when dealing with DC wait until you get into 'Impedance' I am still trying to work that one out ;)

@@byterock Thanks. Yeah, my schooling included impedance and reactance. Sometimes I have to look up the formula's. Never did get totally comfortable with the phase shifts from the inductors and caps. 😥

Unfortunately mine didn't I only figured it out reading an old 'RCAF' 1950s training manual that had a good section on it. Used very practical examples vs the theory of waves 2d graphs one use to see. There are some good 3d animations out there as well that demo it TTFN

I am sure there is a Mock German pun in there some place but jsut for fun here is the original ACHTUNG! ALLES TURISTEN UND NONTEKNISCHEN LOOKENSPEEPERS! DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKEN. IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS. ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN.

No it is a design used way back in the day from high school physics to explain series and parallel circuits. You would not see it today as it is a little dangerous for today's standards. It is just a demonstration apparatus. Here is a good design of a Dim bulb CL ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-7ME1iPrkhOU.html