Where to earth homemade led cob light?

[Stonederer]

Good evening uk420 community. Its been a while.

 

I have a heatsink with 4 smart integrated driver cob leds. I have them wired in series.

Now to earth/ground it.. but do I just earth the heatsink or do I earth each of the 4 cobs individually and if so where on the cob? (There are no solder points for earth)

[Stonederer]

Set up similar to this:

 

And cobs similar to this:

[Stonederer]

Anybody?!

 

I know now that should I need to earth each cob I would hook earth wire round a screw holding the cob to heatsink.

 

I still don't know if that is necessary though, or if one ground in the heatsink would do?

 

[This is an experimental project that should be upgradable cob-wise when mastered. 300w (2x 50w full spectrums, 1x 100w cool, 1x 100warm). Checking out the integ driver cob types but will change to branded cobs with separate driver in future once tested. Want to do a comparison with my current led setup.]

Edited January 9, 2018 by Stonederer

[Stonederer]

Bump

[Davey Jones]

Quote

I know now that should I need to earth each cob

 

No you dont mate, LED drivers are isolated, check that yours is as theres like a 0.1% chance some idiot designed a none isolated driver but its into the realms of I would post a picture of my arse if its not isolated

 

Not isolated means its not earth referenced i.e. the output doesnt form a circuit with the earth and shorting it wont do anything

 

You should just earth the metal plate at one point and that will cover you for the input supply and noise/spikes. Its probably exactly what you wanna hear as earthing each and every LED is a bit of a fuk around and it wouldnt look very nice at all

 

[Stonederer]

On 18/01/2018 at 7:23 AM, Davey Jones said:

 

No you dont mate, LED drivers are isolated, check that yours is as theres like a 0.1% chance some idiot designed a none isolated driver but its into the realms of I would post a picture of my arse if its not isolated

 

Not isolated means its not earth referenced i.e. the output doesnt form a circuit with the earth and shorting it wont do anything

 

You should just earth the metal plate at one point and that will cover you for the input supply and noise/spikes. Its probably exactly what you wanna hear as earthing each and every LED is a bit of a fuk around and it wouldnt look very nice at all

 

At last! 

Yes that's what I wanted to hear!

Thanks DJ

[Guest Buckfacked]

On 18/01/2018 at 8:23 AM, Davey Jones said:

 

No you dont mate, LED drivers are isolated, check that yours is as theres like a 0.1% chance some idiot designed a none isolated driver but its into the realms of I would post a picture of my arse if its not isolated

 

Not isolated means its not earth referenced i.e. the output doesnt form a circuit with the earth and shorting it wont do anything

 

You should just earth the metal plate at one point and that will cover you for the input supply and noise/spikes. Its probably exactly what you wanna hear as earthing each and every LED is a bit of a fuk around and it wouldnt look very nice at all

 

 

They're also all electronic so, by nature, they are "isolated". It's not a transformer that drops 240vac to 110vac, or a shaver socket which is an isolating transformer for obvious, wet, reasons, but a load of electronics which does the dirty after the voltage has been stepped down on entry into the driver. Everything from that moment on is at a lower voltage and protections will fry first IF things go wrong, all under UK, EU, US, ISO, pick a country that isn't a third world craphole, etc, regulations, so thankfully we won't be getting to see your spotty, hairy, dangleberried rusty sheriff's badge. I hope, anyway...

 

Also depends on the output voltage, if it counts as "SELV" or "PELV" (does the driver have an earth on the input or not? No? That's SELV as everything is double insulated. PELV is not, that's, as an example, my driver which is a metal cased, active cooled, driver) where the output voltage is under 50vac or 120vdc. The driver puts out under 120vdc, no earth to the heatsink is actually necessary, except for "noise reduction" as you say.

[Davey Jones]

7 hours ago, Buckfacked said:

 

They're also all electronic so, by nature, they are "isolated". It's not a transformer that drops 240vac to 110vac, or a shaver socket which is an isolating transformer for obvious, wet, reasons, but a load of electronics which does the dirty after the voltage has been stepped down on entry into the driver. Everything from that moment on is at a lower voltage and protections will fry first IF things go wrong, all under UK, EU, US, ISO, pick a country that isn't a third world craphole, etc, regulations, so thankfully we won't be getting to see your spotty, hairy, dangleberried rusty sheriff's badge. I hope, anyway...

 

Also depends on the output voltage, if it counts as "SELV" or "PELV" (does the driver have an earth on the input or not? No? That's SELV as everything is double insulated. PELV is not, that's, as an example, my driver which is a metal cased, active cooled, driver) where the output voltage is under 50vac or 120vdc. The driver puts out under 120vdc, no earth to the heatsink is actually necessary, except for "noise reduction" as you say.

 

 

Electronic doesnt mean isolated, there are very few ways to isolate circuits from each other. Off the top of my head I can think of a few ways one way is a transformer and another is an analogue opto coupler.

 

I have used one of these in a commercial design to isolate some analogue electronics that was used to sense temperatures in the outside world which was a harsh environment

 

https://www.vishay.com/docs/83622/il300.pdf

 

A circuit is included in the datasheet and its very smart, theres two outputs matched so you use one to go to the outside world and the other tells the microprocessor whats happenng, you can buy digital isolators but they are more expensive than rolling your own like I did with the IL300. An analogue opto coupler can only output approximately 20mA so it cant process the power to isolate for a power supply and your only option is a transformer

 

I am a power electronics engineer and I am currently working on a very large power supply (100kW) we are using a transformer to isolate the input from the output its a high frequency transformer which is used so that the size is decreased the faster the switching frequency the smaller the transformer. In fact its unbelievable the difference in size and weight between a 50Hz transformer and a 20kHz transformer because
 

Quote

 

Each AC cycle electric energy is converted to magnetic, and back again. The amount of magnetic energy that a transformer can 'store' is more or less linear in its mass. At a higher frequency, more of these cycles occur, hence the same transformer would transform more power, or the same power can be transferred by a smaller transformer.

 

 

https://electronics.stackexchange.com/questions/144329/transformer-size-vs-frequency

 

If you open up some power electronic converter like a ballast or LED driver whatever you will see they use a HF transformer and if you got the scope out you might be surprised to see they are driven with square waves (to reduce switching losses) and the currents are actually triangular shaped, its common to see a 1:1 ratio but step up is also common this is solely to isolate the input from the output to alter the magnitude of the output you use a switching converter for DC that would be a buck or boost depending on your requirements but its stepped up/down after the transformer its the only way to achieve the 98/99% efficiency which is an unbelievable efficiency but thats how good they are

 

SELV and PELV is from electrical installation regulations, I used to be an electrician a number of years ago now they normally use standard 50Hz transformers to achieve that but there is a whole universe which exists outside of electrical installation and those regs/standards dont apply they have their own specific requirements depending on the industry you are working in, BS EN 50155 is for rolling stock for example IEC 62196 is for electric vehicle chargers

 

https://en.wikipedia.org/wiki/IEC_62196

 

See the wiring regs only apply to the wiring in your installation thats fixed anything plugged into a socket outlet is not under the remit of the wiring regulations and there are an immense amout of different standards for different areas its a very boring subject indeed

 

Now if the output is isolated you are forgiven for thinking whats the point of the earth after all it wont do anything to protect against short circuits but the real world is complicated, there are parasitic capacitances all over the place and with high switching frequencies these can drive spikes of voltage straight through the transformer and give operators little zaps hence you still need an earth to protect against these

 

 

 

Edited February 17, 2018 by Davey Jones

[Guest Buckfacked]

3 minutes ago, Davey Jones said:

 

 

Electronic doesnt mean isolated, there are very few ways to isolate circuits from each other. Off the top of my head I can think of a few ways one way is a transformer and another is an analogue opto coupler.

 

I have used one of these in a commercial design to isolate some analogue electronics that was used to sense temperatures in the outside world which was a harsh environment

 

https://www.vishay.com/docs/83622/il300.pdf

 

A circuit is included in the datasheet and its very smart, theres two outputs matched so you use one to go to the outside world and the other tells the microprocessor whats happenng, you can buy digital isolators but they are more expensive than rolling your own like I did with the IL300. An analogue opto coupler can only output approximately 20mA so it cant process the power to isolate for a power supply and your only option is a transformer

 

I am a power electronics engineer and I am currently working on a very large power supply (100kW) we are using a transformer to isolate the input from the output its a high frequency transformer which is used so that the size is decreased the faster the switching frequency the smaller the transformer. In fact its unbelievable the difference in size and weight between a 50Hz transformer and a 20kHz transformer because
 

 

https://electronics.stackexchange.com/questions/144329/transformer-size-vs-frequency

 

If you open up some power electronic converter like a ballast or LED driver whatever you will see they use a HF transformer and if you got the scope out you might be surprised to see they are driven with square waves (to reduce switching losses) and the currents are actually triangular shaped, its common to see a 1:1 ratio but step up is also common this is solely to isolate the input from the output to alter the magnitude of the output you use a switching converter for DC that would be a buck or boost depending on your requirements but its stepped up/down after the transformer its the only way to achieve the 98/99% efficiency which is an unbelievable efficiency but thats how good they are

 

SELV and PELV is from electrical installation regulations, I used to be an electrician a number of years ago now they normally use standard 50Hz transformers to achieve that but there is a whole universe which exists outside of electrical installation and those regs/standards dont apply they have their own specific requirements depending on the industry you are working in, BS EN 50155 is for rolling stock for example IEC 62196 is for electric vehicle chargers

 

https://en.wikipedia.org/wiki/IEC_62196

 

See the wiring regs only apply to the wiring in your installation thats fixed anything plugged into a socket outlet is not under the remit of the wiring regulations and there are an immense amout of different standards for different areas its a very boring subject indeed

 

Now if the output is isolated you are forgiven for thinking whats the point of the earth after all it wont do anything to protect against short circuits but the real world is complicated, there are parasitic capacitances all over the place and with high switching frequencies these can drive spikes of voltage straight through the transformer and give operators little zaps hence you still need an earth to protect against these

 

 

 

 

Apart from anything else, I used to make some VERY expensive lights for a firm over here, and that's where I learned more about LED than most know, carved a few transformers/drivers apart to look at how they were made, even tested some with a very hot burner to see if they did self-extinguish (they did). Bottom line on installation is that it can and should include everything all the way up to the end of the chain, and if SELV then it should be impossible for an overvoltage to be applied to any extraneous metalwork irrespective of whether it's portable or not. You're doing a diy install, then that's under the same regs as "installation" as it will be something more permanent in use. So the same applies, it is only where there is a DC output voltage of under 120v, or AC at 50v, that an earth is ABSOLUTELY necessary. Advisable, yes, but not "mandatory".

[Davey Jones]

The world is so much bigger than BS7671 and SELV/PELV etc

 

The requirements for an earth is a much more complex decision than is the output below a certain value the wiring regs arenbt covering you in this department and you could be taken to court, light fittings are generally fixed equipment so the wiring regs go a long way. Power electronic converters are much more complex both in operation and the places they are used, you would be mental and wouldnt have much experience of the real world  not to earth metalwork on the output of a power electronic converter, those spikes hurt a lot. You can have an RMS output below SELV/PELV but its a switching converter the actual peak can be way way higher than that its just the switching that decreases the average output