What's new
By:
Pinball info

Register a free account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members through your own private inbox!

LEDs - Voltage? And why. And How...

bluejonny

bluejonny

Site Supporter
10 Years
Joined
Jul 21, 2011
Messages
290
Location
Southampton, UK
hi all

A bit confused by this LED nonsense.

I though GI was AC powered, and LEDs were DC. So how come these new fangled LEDs just plug straight into existing sockets without a problem?

Also, the mods you can get on eBay like the snake one for IJ with LEDs - where do they plug in? They must be DC as well, but if they are AC I certainly don't fancy welding bits to connectors. Or boards. That's a sure sign of pinball catastrophe for me (if I am holding my soldering bat)...

Seems like witchcraft I tell thee.

Cheers
BJ
 
It depends what LEDs you buy but a lot of them have diodes and capacitors built in to them to rectify and smooth AC current so they can be used anywhere with a supply close to 6.3v.
 
An LED is a Light Emitting DIODE. A diode is a rectifier so it inherently converts AC to DC. So in AC they will work either way round, but in DC must be oriented correctly.

Now. Diodes have a stated maximum forward current in there spec. It's the current that's important not the voltage. Whatever current you pass through the LED will create a voltage drop across the LED of nominally 0.7v. (That's what you measure on a diode or transistor when testing).

So, plucking figured out of the air now. You have 12v supply, LED with max current 0.1amp, voltage drop 0.7v.

You need a resistor in series to set the current through the LED.

Resistance = Voltage/ Current
V=supply minus diode drop
V=12-0.7=11.3v which will be dropped by the resistance, also carrying 0.1amp as its in series.

So R=11.7/0.1 = 117 ohms.

In practice you'll set current below maximum so increase resistance somewhere above 120 ohms, accepting a drop in LED brightness.

Here endeth the lesson
 
Andy,

I am at a loss as to where the GI 50hz / 60hz freq comes in.

As I wanted to install the product GI OCD, but was told by the designer that it will not work our our 50hz, now I guess this is due to GI being AC, and this is why the LED OCD works on inserts (being DC).

What I am at a loss to understand is why GI OCD will not work on 50hz as to my basic understanding the freq is about timing which has nothing to do with GI unless that is the dimming effect will be screwed.

Can you shed any light on this subject (excuse the pun)!

http://ledocd.com/cart/index.php?main_page=index&zenid=prod1hn2p6241rjadcf4sserl6
 
Andy - wise words and thanks. So you couldn't take any old 6-12vac LED and wire it straight into the GI circuit without a resistor. Based on your maths above and the voltage is 6.3v to GI (non controlled),

6.3v - 0.7v = 5.6v accepting 0.1amp as in series

R=5.6/0.1 = 56ohms

However, as the voltage here is lower than the 12v you used, I assume the voltage drop would be lower too.

Oh, and @Spandangler - this is all new to me, so no - not basics at all. A different language. Sadly some of us do not have the luxury of this knowledge - so when human cloning arrives, you all need to form an orderly queue please. Hoohaaahaaa...

Yours

Einstein's Evil Twin
 
Off the shelf #44 and #555 LED replacements, have already had the hard work done for you, they will contain the necessary resistance to match the diode component used, for the application intended e.g. 6V.

When a modder builds a mod, they may choose to take the supply from a 6v or 12v supply, and calculate the required resistance that they must add into the circuit as per the above calculations.
 
You must log in or register to reply here.
Back
Top Bottom