01821 Workbench 101 #2 How does a Dim Bulb Current Limiter Work
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- čas přidán 9. 07. 2024
- In the first part of the video I go over how a dim bulb current limiter works and why you do not want to make one out of resistors. In the second part I do some practical demos of how a dim bulb works, the amperage differing wattage of bulbs let in, the difference between dim bulbs in parallel vs series and how it acts as a limited surge suppressor.
My multi-dim bulb build
• 01621 Make or Mend Mon...
Here is Uncle Doug's
• Build Your Own Current...
Though I would not test the way he does ;)
and here is Mr Carlson's version
• Big Dim Bulb Tester wi...
and here is the Granddaddy of all of them
• The National Radio Ins...
There are so many of them out there you would think making a dim bulb current limiter is a sort of 'Right of Passage' of all aspiring electronics youtubers
As an add in I think this link
www.electricalvolt.com/2019/0...
Which explains what a 'Non Ohmic' conductor is. - Věda a technologie
Enjoying your videos. Thank you. Cheers ...
Thanks that meas a lot to me.
Hiya, thanks for your time to make this video. Yes I agree that the in series dim bulb must be able to supply the required load current if you run the DUT loaded. However, the bulb is supposed to limit the current specifically so you can determine if the DUT has a short. In your example the objective was to protect the DUT (the light bulb used as the example load) hence the DUT should glow dimly. Putting a large bulb reduces that protection as it allows larger, potentially damaging currents to flow in the DUT.
On that basis I’d suggest the first test of the DUT should be with a single or series bulbs and later tests with load on the DUT (I’m thinking say the DUT is a Switch mode PSU) could be with a single bulb or bulbs in parallel.
Just for clarity for those who might not know... DUT means “device under test”
Thanks, yep that is an idea. This is more a 'How Does' video vs 'How To'.
This is the DBCL I created
czcams.com/video/7ME1iPrkhOU/video.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.
That type of dim bulb tester was what we called a " lamp bank" a couple jobs ago.....
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 czcams.com/video/7ME1iPrkhOU/video.html
Liked the demo of the transient at startup you showed at the end. Good vid. These are useful dim bulbs, not like the other dim bulbs I run into from time to time.
Glad it was helpful!
@ByteRock
Instead of expensive resistors, good electric cooker, iron, heater, kettle etc can be used to replace dim bulb when high amperage is needed. Some of them can handle 20 Amps and are available at homes
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.
Great video. I had the same question as your friend. Thanks for taking the time to create all the diagrams as they really help. Also good to know that the higher wattage bulb lets through more current than a lower wattage bulb. I was worried about using 60W bulbs but I think they will be safer now.
Thanks glad you like it. don't forget to asks you friends to subscribe as well. ;)
Interesting video. Thanks
Thanks good to hear more builds very soon. Don't forget to subscribe ;)
Excellent
Thank you. Nice to see people enjoying the effort. Don't forget to subscribe to see more ;)
Good vid, good info, thanks.
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 ;)
👍👍
Thanks Mike
What is the formula to calculate the bulb wattage needed related to the device?
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
czcams.com/video/MIWz8RlloLU/video.html
at about the 10min point I use bigger and bigger bulbs to load an old HP Nixi Counter
🙂
Check the cold resistance of the 100W bulb, it's worryingly low, even at typical indoor room temps, cold weather drags it even lower. Less than 10 Ohms. Inrush can be huge if you happen to turn it on just as the AC reaches its ~170V peak.
120V RMS is kinda misleading to the average person, we're really dealing with 170V peak potential between the outlet prongs. A cold 100W bulb can easily have an inrush current more than 20 Amps.
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.
Hi,
I got a power mixer 110V 700W power consumption, powering it through a dim bulb 100W bulb, press power, the bulb start flashing on and off.
And the mixer led light flashes too.
You think the bulb is limiting current to the mixer?
This video is a decent attempt. But I feel it would be more valuable with more explanation of the principles (theory) involved. Especially why and how the bulbs help limit the current. More explanation of ohm's law, and more explanation of how the voltage is distributed at the moment of switch closing, and how and why the voltage distributed at quiescent status. Also, explain WHY we use dim bulb testers (excessive current flow into DUT, due to internal shorts, shorted capacitors, damaged cords, etc. Also, I may have missed it, but a graph showing initial inrush current leveling off to quiescent current would help, if it is not already shown. Otherwise, good job.
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
R Thevenin. (Thay-Ven-In or Tay-Vin-In) & Kirchoff's 2nd Law.
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.
Looks like a Frankenstein science project. Its a gimmick!
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 czcams.com/video/7ME1iPrkhOU/video.html