Is it safe to run 12v DC LED from 8v AC bell transformer?

[Mikefromlondon]

The 78Lxx regulators made by Texas Instruments have internal thermal protection

I know they have build in protection, who is denying it? But you do not read small print, those things will only work when the regulators are used properly with recommendations of hardware to dissipate some heat, why don't you try and put 35V maximum rated input voltage and short out the output, see if it splits up, or gets real hot, unable to even dissipate some heat and then all internal safety circuits also cook up and self destruct. Read about thermal runaway.

 

[Mikefromlondon]

So you guys will implement a voltage regulator (an active device that can fail any time without any given reason) to run an LED light, then God help you in your carrier as experts.

 

[EFLImpudence]

I haven't read all the thread but this caught my eye.

free flow of air around the device, but also at the same time avoiding in supply of fresh oxygenated air, hence device enclosed in box big enough to circulate internal air, yet stop more oxygen entering the box if should the device burst into flames,

May I ask how that is achieved and what proportion of Nitrogen would be best?

 

[JohnW2]

I know they have build in protection, who is denying it? But you do not read small print, those things will only work when the regulators are used properly with recommendations of hardware to dissipate some heat

I think it may be you who needs to read the 'fine print'....

If internal power dissipation becomes too high for the heat sinking provided, the thermal shutdown circuit takes over preventing the IC from overheating.

Thermal protection is thermal protection, and serves to prevent dangerous overheating regardless of how well or how badly the device is heat-sinked.

Kind Regards, John

 

[endecotp]

Thanks for posting the follow-ups John.
I think posts like the one you've replied to confirm why I'm ignorong this guy; I don't have the required temperament for constantly writing polite but convincing replies to crazy ideas like "voltage regulators are dangerous they could catch fire but a resistor is safe". You seem able to do that without going mad; congratulations.

 

[Mikefromlondon]

No John, thermal protection is intended protection, but when it fails, you have no protection against overheated regulator, any way suit your self, you are free agent, use regulators at your risk, I swear on my life, when i once saw a regulator made by Toshiba, 7815, it actually burst in flames, ever since then I have stopped using any regulators made by Toshiba, you will find they are fully encapsulated and has plastic tabs, where you do not need isolating kit if you were mounting them on a heatsink which required isolation, I had a stock of 100 such regulators, already by the time this happened many were already out there in some of my applications and I prayed that none of those burst into flame if should something else fails on my circuit board, I purchased them from Anglia Components, this was about 1992, since then I have stuck to more reliable regulators with metal tab, manufactured by National Semiconductor.

You said you were not going to debate and now you have gone full Trump into this debate, you stick to your regulators and i will stick to resistors with correct rating for all eventualities, so in your example you used maximum LED current of 50mA, when all the while I have been saying modern LED are much higher efficiency and use moderate 20mA and the maximum voltage we are going to encounter os 16v x 1.414 = 22.6V, so that gives us 1130Ohms, at under 1/2 watt, so no worries, I am not going to bang my head with any of you, I have personally experienced regulators overheating, burning even tracks and pcb, often regulators failing and destroying sensitive circuits.

My side of the debate is now closed, I will consider safety as paramount rather than being lazy and using a small TO92 plastic regulator.

You are free agent, there are no regulations on what you can and what you cannot use, if you are an OEM, you are answerable to your equipment failing and catching fire, and further more all electrical equipment still has to meet stringent EEC safety requirement regardless of Brexit.

 

[Mikefromlondon]

Thanks for posting the follow-ups John.
I think posts like the one you've replied to confirm why I'm ignorong this guy; I don't have the required temperament for constantly writing polite but convincing replies to crazy ideas like "voltage regulators are dangerous they could catch fire but a resistor is safe". You seem able to do that without going mad; congratulations.

You are being very stupid now so I am putting you on ignore too,
so ignored you are and don't need to hear your crap from you.

BTW, I was being polite too, but now I can say, what a stupid idea, and a laughable one too, never ever had anyone use a regulator for an LED, and that is a fact.

 

[Mikefromlondon]

I haven't read all the thread but this caught my eye.



May I ask how that is achieved and what proportion of Nitrogen would be best?

If you light up a candle and place an inverted jar over it, the flame would starve of any oxygen and go out, if air frem outside entered the jar, the flame would continue to burn.
The same amount of nitrogen that is present in our normal atmosphere.

 

[JohnW2]

Thanks for posting the follow-ups John. I think posts like the one you've replied to confirm why I'm ignorong this guy; I don't have the required temperament for constantly writing polite but convincing replies to crazy ideas like "voltage regulators are dangerous they could catch fire but a resistor is safe". You seem able to do that without going mad; congratulations.

Thanks, but (although you won't have seen) it's 'getting worse', so I have also now had enough of it!

Kind Regards, John

 

[bernardgreen]

I have personally experienced regulators overheating, burning even tracks and pcb, often regulators failing and destroying sensitive circuits.

So have I. Any component can fail for no apparent reason while still operating within it's safe operating area ( on the voltage current graph )

A sudden rapid increase in the load on a regulator may result in damage to the regulator due to the delay in the heat reaching the temperature sensing element in the thermal protection circuit allowing the output device(s) to be overloaded until the shut down occurs.

I have also seen holes burnt in PCBs by over heated resistors.

 

[deadshort]

Well, this has turned into a bit of a DING -DONG !

DS

 

[EFLImpudence]

I'm still trying to work out how to get the "air" from upturned candle jars to circulate freely around devices.

 

[Mikefromlondon]

Well, this has turned into a bit of a DING -DONG !

DS

It won't ding dong much when you think about what would happen if you use a small TO92 style packaged voltage regulator, of course it has thermal regulation, which when working stops the device getting very hot, so what does it do........precisely, it shuts down, so that means what would happen to your Ding Dong Light, it would start to fade away and then as it cools it comes back on again, so you end up getting a flashing ding dong bell light.

 

[cjard]

. The supplier's website claimed it was a Bulgin part but when I sent my photos to Bulgin for confirmation they told me it was not one of theirs.

View attachment 108004

View attachment 108003

Looks like the push buttons I'm ordering dozens of so I can make my own light switches they are compatible with home automation dimmer modules. Search eBay for "momentary 16mm" or "momentary 18mm" and you'll turn up scores of similar and same looking things. Probably chinese

 

[Mikefromlondon]

I'm still trying to work out how to get the "air" from upturned candle jars to circulate freely around devices.

The entire world was taken by surprise with Donald Trump winning US Presidential elections, if he can, why can't the air circulate in a jar? you need to think hard mate. .......in other words Everything is possible.