how many 10v leds for 230AC and a few other questions.

[gamernixin]

Hey all. I didn't know where to post this question so i thought i would post it here.

Well my question is as follows. I have a 230v AC outlet, how many 10v (or perhaps they're 12v i'm not sure tbh.) do i have to use to make sure that they don't blow up? And will i have to set them all in a parallel or serial connection?

And while i'm at it.

I have some old electronics laying around, can i unsolder the resistors, capasitors etc. and use them for my future projects?
Oh, and, just came to my thoughts. There is alot of guides how to make 12v to 24v or so. does anyone have guides for the opposite? Making 230v to say.. 12v?  ::)


If i explained my problem poorly, please tell me and i'll try to rephrase it.
Thanks in advance.

[Hero999]

It depends, LEDs are normally constant current devices unless they already have a built-in current limiter.

How much current do the LEDs need?

For 12V just buy a wall adaptor.

[audioguru]

A red LED is 1.8V to 2.2V. A blue or white LED is 3.3V to 3.6V.
I have never seen a 10V or 12V LED so maybe it has a current-limiting resistor inside.

If you connect AC to an LED then the reverse voltage of more that 5V will destroy it since LEDs operate on DC, not AC. To use AC then you must rectify it into DC.

If you connect a 12V LED to 230V then it will blow up.
Use a transformer to safely isolate and reduce the voltage to about 12VAC then rectify and filter it into 16VDC. Connect a suitable current-limiting resistor in series with the LED.

[Hero999]

A red LED is 1.8V to 2.2V. A blue or white LED is 3.3V to 3.6V.
I have never seen a 10V or 12V LED so maybe it has a current-limiting resistor inside.

Some power LEDs consist of many LEDs internally connected in series giving a higher overall forward voltage.

http://www.rapidonline.com/netalogue/specs/56-0196.pdf

[gamernixin]

Hey again. Thanks for your replies, they're helpfull.

Well all i know about those LEDs are that they are used for making a light testing thing for cars to check if the trailer lights works or if its the cars wiring. and the cars are using 12v batteries.

But yes of course, i didn't even thought of the AC and DC :) .

I have both green, red, and yellow LEDs.

I just thought of using those leds for making a, well.. Really bright lamp and i tend to use my old cell phone charges for the power source but i ran out of those. So i thought of making a ''real lamp'' which would be plugged in to the outlet.

are there any way of checking if the LED have internal resistors?

[Hero999]

If you can connect the LEDs directly to 12V without blowing up then they have built-in resistors. ;D

To test this non-destructively I'd connect the LED to 12V in series with a 1k resistor and measure the LED's voltage, if it's about 2V then there's no series resistor, if it's much higher, about 7V, and the LED is dim, then there is an internal series resistor.

It's possible to build your own 12VDC power supply but it's cheaper just to buy a 12V wall plug.

http://www.rapidonline.com/Electrical-Power/Power-Supplies/Plug-In-PSUs/AC-AC-and-AC-DC-plugtop-linear-PSU/71060
http://maplin.co.uk/Module.aspx?ModuleNo=13453

[gamernixin]

Oh i'm so stupid.. i just came to think of it..

We soldered resistors on every LED before mounting them in the case for testing. i cant remember which ones tho, but i can calculate the resistance with a formula i found..

Say if i had 1k resistors and i needed 10k resistors.. could i then connect them in series and make up 10k or would they simply count as 10 1k's  and blow up?

[Hero999]

Yes, if you needed 10k and you used 1k then you could solder 10k or 9k1 in series but as 1k is a reasonable value, you don't need to.

[gamernixin]

Okay thanks alot for your fast and helpfull replies :D
The resistor value were a theoretical question.

All my problems (so far) have been solved :)

Thanks for the help :D


Im starting an electrician education soon, and i think you guys will be able to help me alot if i encounter any problems, and i hope i will be able to help other beginners like me eventually.

[audioguru]

Im starting an electrician education soon ....

We do electronics where we design and build complicated electronic circuits.
Electricians install conduit and pull wires into the conduits. Then they connect simple lights and switches. Most electricians do not know anything about electronics.

[Alex Tsekenis]

I classify them as (there are always exceptions):

Electricians that install wiring and electrics in buildings from tables they have memorised.

Electronics repair technicians that repair your TV using using memorised tables and a fair amount of original thinking. These could install their own electrics so that they merely function and are not eager to expand their knowledge.

Electrical engineers. These can wire a city if you give them enough time. They will analyse the problem, devise a plan, perform research and evaluate the performance of the solution. They are mostly concerned with high power/high voltage electrical systems such as generators, transmission lines, distribution transformers, circuit breakers, motors etc.

Electronic engineers. These can repair TVs or build a computer from scratch if you give them enough time. Once again, they will follow a scientific approach to the task in hand. They are mostly concerned with lower power miniature electronics such as microprocessors, op-amps, process controllers etc.

Very often, if not always, electronic and electrical mix in complex modern systems. Electrical and Electronic Engineering degrees address this.

One can say that Electronic and Electrical Engineering is perhaps a victim of its own success. Technology has penetrated into our lives so deeply that we take it for granted. The average person does not realise how complex systems and devices are and that is bad news for engineers.

Having said all of these things, engineers possess a mindset that allows them to tackle problems from different disciplines, not just electronics or electrical. This is why e&e engineers are easily absorbed by the job market and why you find many of them in senior management positions or in research into new technologies.

I will dare say that pure engineers are born like this, not made into.

These professions, although sciences in their own right, bring in different fundamental physical sciences like chemistry, physics and maths.

I don't know your circumstances but if you are 18-30 say and have enough drive, then why not study Electrical and Electronic Engineering at a university? Very often undergraduates get job offers long before graduation. You can even go and work at a company for 1 year and gain industrial experience. Apprenticeships in companies is another good way to learn and become professional. It is my belief that you will need to study more theory on your own this way, but this applies for university to some extent.

Good luck!

[gamernixin]

Electronic engineer
then i suppose that it's that i'm going to "be".

The base education for this is the SSI (Str