Resistor for led

[ians]

A quick question :

Low voltage LED - 1.8 - 3.3 VDC

Power supply - 12 -13.8 VDC

If I want to install a single LED indictor for alarm status ... can I fit 1 x resistor at the 12VDC source and fit a bunch of those little LEDS located around the building ... or do I have to install a resistor at each LED

My concern is volt drop ... 12 VDC is already low voltage ... now installing a resistor at the source and then still running 20 meters of thin wire at a super low voltage that kind of distance ... just seems crazy.

I know I am being lazy ... but there are lots of smart people here ... maybe I am missing something ... maybe the power required for a single LED (1.8 - 3.3 VDC) is so low it wouldnt matter.

[Dylboy]

I don't know much about alarm stuff but could you perhaps do a restistor at each LED to get the required voltage. So keep 12V at source then parallel each LED with its resistor?

I am having a few early Friday beers in celebration of a great achievement so may not be thinking to clear either


Side note I feel I am on here too often when having a beer hahah.

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Edit, I now took notice of you saying shoudl I do a resistor at each LED so ignore all this...

[adrianh]

...more scary stuff....and I'm not even an electrician...

I mean come on guys ....parallel/series ...resistance | voltage drop etc....

[Justloadit]

The first question to ask, is what is the current rating of the LED?
Now that you know the current, you can calculate the resistor value for the specific LED, by using Ohms law.
R = Volts / Current Note the Volts value here will be Supply Voltage - LED Voltage. The Resistor value does not have to be exact, but can be to the next higher standard value.

You do not have to run the LED at its rated current, as this will reduce the LED lifespan, or it may be too bright for the application, especially when it is dark and you want to sleep, that damn things seems to light up the whole room.
My recommendation is that you place a resistor on each LED. Trying to place one resistor for all the LEDs in parallel will cause so many issues, and if something goes wrong, then all the LEDs will be damaged simultaneously. I ususally devide the rated current in half and go from there.

[ians]

I normally just put a resistor at each LED ... buy the LED complete with a wire to connect to 12 VDC ... however I am busy with a job and the technician has installed the resistor at the panel and run wires to directly to the led ... it seemed a bit strange.

Like the diodes on the relay outputs ... I can understand using a diode if the load is high ... but feeding another relay coil ... I am not a low current person so hence the queries.

Some strange things I see everyday ... another project ... there is a ratchet relay ... a siren and a resistor across the siren +/- output terminals ... so what happens when the alarm is activated ... the lights switch on but you cant switch the lights off until you re activate the siren ... which also creates a flashing light on the keypad ... indicating there is a problem with the alarm ... when you press and hold 7 it should siren trouble ... think what he did was just copy the old panel wiring.

This is one of the reason I am seriously considering going down the consultant route ... you call me I review the quotes submitted by contractors ... ensure that they have quoted correctly and not under quoted ... which generally results in some for mod short cut ... or site hopping to try keep the projects alive with limited funds.

I visit the site and check progress ... then verify the installation is complete ... so you dont get half new stuff and the other half left because it still works but the customer wouldn't know the difference.

Another big issue I find on a daily basis ... people not removing the old piping geysers wiring etc ... the roof space turns into the local dump ... you end up with all these cut ends which dont go anywhere ... which creates a fault finding nightmare.

[Dylboy]

Ians I personally would happily pay you for information on projects or jobs.. so if that helps then do the consultancy. Also if there is no hook on the line you can't catch a fish so throw the hook.


If inhad the bucks and no family I would pay you right now to teach me all you know and spend another bunch of years of "apprentice"

Feather in your cap.

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[ians]

Its a pity you live in JHB.

I was hoping my son was going to take over the business ... he worked with me for a while ...but it didnt work ... he works in a different field and is really good at what he does ... the attention to detail is what seperates him form the rest ... I have employed many youngsters ... but none who had an interesting the electrical industry .. they just needed a job to pay the bills ...

I had a person contact me ... he wanted his son to work with me to gain experience ... he was going to pay his son ... but it never materialised I tried that once before but when the youngster doesnt want to do it ... its a waste of time.

[ians]

When it comes to employing staff ... that say everyone is replaceable ... not true ... I had a guy work with me when I started this business ... he was an asset to this business ... we worked together for many years ... we had a disagreement over a vehicle ... I offered to sell him the vehicle and buy him a new company vehicle ... anyway cut a long story short ... he dropped off the vehicle ... I never saw him for about 8 years ... then he came back .. .but it just wasnt the same ... he eventually left again ... after he left the first time I sort of lost interest in growing the business ... I just continued on my own at my own pace ... I did try employ other more skilled staff ... got conned with a pile of false certificates ... since then been doing it on my own and just doing enough to pay the bills .. .then covid arrived ... had my best start to a year in 2020 ... lock down sucked the life out of me again ... here we sit just doing the daily routine to pay the bills ... talking shyte on the pub (forum)

[Dylboy]

I am hoping to head your way middle of next year, my sister is a private facility manger of sorts and they need some second verification done of someone verification. Basically 2 inspection and reports to then compare. But If if bears fruit or I can head that way and meet you would love it. Education is one thing and knowledge is another but learning from you would be inspirational.

I am young still in this industry, I am here now when light ballasts went from choks to drivers now to straight LEDs and all I cought was a quick glimpse of how it was before.




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[adrianh]

When it comes to employing staff ... that say everyone is replaceable ... not true ... I had a guy work with me when I started this business ... he was an asset to this business ... we worked together for many years ... we had a disagreement over a vehicle ... I offered to sell him the vehicle and buy him a new company vehicle ... anyway cut a long story short ... he dropped off the vehicle ... I never saw him for about 8 years ... then he came back .. .but it just wasnt the same ... he eventually left again ... after he left the first time I sort of lost interest in growing the business ... I just continued on my own at my own pace ... I did try employ other more skilled staff ... got conned with a pile of false certificates ... since then been doing it on my own and just doing enough to pay the bills .. .then covid arrived ... had my best start to a year in 2020 ... lock down sucked the life out of me again ... here we sit just doing the daily routine to pay the bills ... talking shyte on the pub (forum)

What has you giving up on your own business got to do with people not being replaceable - EVERYONE IS REPLACEABLE - Choosing not to replace them is a choice you made!

More often than not it is THE BOSS that should be replaced!