Light Bulb Current Limiter (Dim Bulb Tester) FAILED

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Light Bulb Current Limiter (Dim Bulb Tester) FAILED

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3 жыл бұрын

Learn Electronics Repair #082
Light Bulb Current Limiter FAILED
One of the most useful devices you can have on your electronics work bench is a light bulb current limiter. This will prevent devices under test going BANG if there is a short circuit, and they are chap and easy to make.
In this video I explain what a light bulb limiter is, and how to make one and how to use it.
However there are situations where they will not help you, and in fact can hinder your repairs or cause you to waste time trying to diagnose a short circuit that isn't there. Watch this video to see one such example.
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Пікірлер: 37

@ianhuxstep211 2 жыл бұрын

I used to use a dim bulb tester but found a lot of PSUs I work on have PFC's and quite often I will land up blowing the primary stage because the PFC is overcompensating. This is particular in TDK/ Lambda/ Coutant Industrial power supplies. I now just check across any mains input of an unknown PSU with my Huntran tracker or (octopus circuit) and see if I get a good capacitor charge, this usually tells me the bridge and Switch mode is good. I then start the PSU up on a Variable transformer (variac) and monitor voltage and AC current, yes the I may get a high current pulse as the PFC comes in and charges the caps. I've been doing it like this for years as I repair PSU's every day.

@Herbsurburb Жыл бұрын

Thanks share valuable

@knightwar3 2 жыл бұрын

I just finished building my dim bulb current limiter with a 100w incandescent light bulb and tested it with a working psu the corsair cx600 and the light bulb does the same thing just flickering, glad that i've watched this video before otherwise I would have thought that is short thanks again

@LearnElectronicsRepair 2 жыл бұрын

Nice work!

@user-pz6cx8zf2y Жыл бұрын

For testing high power modern power supplies using active PFC circuit, one needs a test lamp power of at least the half of the nominal power of the psu. Otherwise problems like the shown one appear during testing. For example, a 750W psu needs lamp(s) of at least 300W of power for this test...

@davidrobertson1980 2 жыл бұрын

"If it goes bang, yeah.... hope you enjoy it" HAHAHAHA Richard you are a funny man :D

@tomluque Жыл бұрын

If you measure the input voltage at the PSU, you may find that it is below the minimum needed to run the PSU.

@faceboxtv4789 3 ай бұрын

What is the formula to calculate the bulb wattage needed related to the device?

@knightwar3 2 жыл бұрын

Useful information thank you

@LearnElectronicsRepair 2 жыл бұрын

Glad it was helpful!

@CXensation 2 жыл бұрын

I wonder if a capacitor acrost the limit/live switch would solve the problem ? Something like 100nF/400v. The idea is to compensate for inductance in the filaments.

@t1d100 Жыл бұрын

I do not mean this negatively; I just want to make sure that I understand. The DBT did not fail/break. It caused a phantom fault condition in the PSU? If so, I did not catch how the DBT could do that. I think that you did not explain it, but just said that it could occur. If I have all of this correctly, I would really like a video explaining the cause. My guess would be the PSU was starved for current, making it act oddly, but not shut off... Thank you for all that you do for us.

@surgingcircuits6955 Жыл бұрын

Good to know. I seemed that the longer you had it OFF, the better the chance it would act normal; as if ... a resistor was discharging the PFC cap ... which didn't have enough time if you did it On/Off quickly. Thx.

@byterock Жыл бұрын

Yeah a little Occam's razor going on here, one other problem that might effect using a Dim bulb is how hot the bulb is, it is a temperature coefficient resistor so even a few seconds at full resistance may stop it from working as expected. It is an old TV repair shop problem when looking for shorts, if you use you dim bulb too often in a row it will glow bright even without a short as long as there is sufficient amperage draw. Anyway the most likely reason is the one others have given you need a much bigger light bulb when working with a PFC. Dim bulb is really good for old linear PS and really old system such at a 5 valve radio.

@antoniosnikolaoy3754 2 жыл бұрын

Good evening from Greece, after I saw your video with the lamp I would like to ask you something, I have an amplifier in my house that burned out the output transistors, I changed them but when I open it the transistors heat up, I put the lamp in order and as soon as I turn it on the light comes on momentarily and then it stays on for a long time and then the transistors heat up but not so much, if you can please give me some idea why I did this, thank you from the bottom of my heart.

@user-pz6cx8zf2y Жыл бұрын

To έλυσες το πρόβλημα;

@Xorat 3 жыл бұрын

Really interesting. Would a light bulb with Higher Watts Help ? But that could also defeat the purpose at the end of actually limiting , what do you think Richard ?

@LearnElectronicsRepair 3 жыл бұрын

Hi Daniel I put a 160W limiter on to it and it still did the same. As you suggest, there is a pay off between the limiter and protection - for example, on a 1Kw lamp (like some old school Halogen outdoor floodlighting) the device you are trying to protect could still draw a good few amps and self destruct. I have only come across this issue with power supplies that have PFC and I think I described the problem pretty well (though I don't know the exact reason they act this way, there is a bit of supposition and guess work going on here) I also read that old audio amplifiers with JFETS can be destroyed by using this sort of limiter but I don't know from personal experience if that is true as I don't think I've ever worked on one

@alexluz7023 2 жыл бұрын

@@LearnElectronicsRepair hello nice enigma but i think you never used 160w because the bulbs are in parallel at least in schematic (making it as if it was around 40w total lol) one more hint, with 60w bulb the tester lights on and with both bulbs dosent even start.... it proves the current in were even less with both bulbs parallel and proves you are wrong in schematics and hardware! to work properly i think you should wire switch, bulb, bulb all in series keep the good work

@MrVeryCranky 2 жыл бұрын

I've been using a 300 watt light globe in this manner for around 40 years. The globes he's using are insufficient.

@user-pz6cx8zf2y 6 ай бұрын

@@MrVeryCrankyYes, I also use a 300W halogen lamp with such high power supplies. Lower wattage cannot start up these units under repair. It needs to be at least half the nominal power of the psu, ideally the same power with it...

@ohmware2020 3 жыл бұрын

mine, i use 50w incandescent bulb. it saves a lot of time, money, and effort in trounleshooting and diagnosing repairs, especially power supplies

@LearnElectronicsRepair 3 жыл бұрын

Hi mu no, Yes 100% I agree these are very useful devices to build - every electronics workbench that is repairing mains powered devices should have one. I even have two of them! On this video I just wanted to highlight a situation I have found specifically with PFC in power supplies that causes the light bulb to come on bright even though the PSU has no load - giving a kinda false indication that the PSU has a short circuit load when it starts up (for example short circuit rectifier diode one a secondary 12V, 5V 3.3V etc) Once you realize that a good working PFC circuit can behave like this then it also saves you time money and effort in your diagnosis.

@ohmware2020 3 жыл бұрын

@@LearnElectronicsRepair exactly,... thank you for the videos you shared... more to come!

@user-pz6cx8zf2y 6 ай бұрын

@@LearnElectronicsRepairYou need a lamp of much higher wattage for this purpose. Please see also my other comment above.

@cathound888 2 жыл бұрын

Will this work with led bulbs or do they have to be tungsten filament type?

@Aneesh.Asokan 2 жыл бұрын

No, only filament type! Now a days, it's hard to get hold of one!😢

@cathound888 2 жыл бұрын

@@Aneesh.Asokan thanks Aneesh, though that would be the case, I just found a couple in an old box of bulbs I have in my shed🙂

@ianhuxstep211 2 жыл бұрын

Must be a filament, tungsten may work but filament is better.

@engineering8903 Жыл бұрын

Phantom FauLt😁👍👍👍

@Moonlightshadow-lq4fr 6 ай бұрын

The dim bulb didn't fail, it did its job! Just because you determined there is a short or fault does not mean the safety protections cirguit failed. Bit of click bait there!

@MrVeryCranky 2 жыл бұрын

Your explanation of PFC is rediculous. This is acheived with chokes and capacitors. There is no such "boost" arrangement, the voltage on the capacitor will be around 340 volts, ie supply multiplied by aprox 1.4. Suggest you do some study before posting such claims.

@martinfairweather700 2 жыл бұрын

You are kind of correct but…..you’re talking about passive PFC. Active or boost PFC is more common than you may think.

@ianhuxstep211 2 жыл бұрын

Sorry I don't agree, most switch mode PSU's will start up from around 80v therefore the PFC will act as a buck converter to give the 300 plus volts on the Bus capacitor. I work on a lot of industrial power supplies

@user-pz6cx8zf2y Жыл бұрын

The PFC circuit (among other things) boosts the rectified (230V) mains voltage to around 385V and keeps this level stable on the terminals of the bulk capacitor for further processing...