Portaflood Resistor values?

**Penfold** · 03-16-2010, 03:26 PM

As I understand it now I am supposed to use the lled value as my basis for what resistor I am supposed to be using for the leds on the portaflood. I bought a package deal from bestshophk2008 that gives me enough for three boards worth.

http://cgi.ebay.com/167-of-5mm-Red-G...item19baa91402

Looking at the specs provided in the auction am I safe to assume that the reverse current Vr-5v max is the lled talked about in the table of the construction manual?

Please let me know if I am on the right track here or did I totally get this wrong.

**Matt_Edwards** · 03-16-2010, 05:10 PM

NO! ( hope you can hear me from down under)
Vr is the Max voltage you can apply the "wrong way"
Use Vf or Forward voltage for the calculations.

**Penfold** · 03-16-2010, 05:49 PM

Thanks for letting me know Matt! (Even though it was barely a whisper by the time it reached the US).

If I am supposed to use the Voltage forward that happens to be the same for all three columns how do I know what resistor to use? The only difference that I see here is the lled number. How do I go about finding the lled number? Should I ask the vendor if that information is available? I am sorry for sounding so ignorant about this, but I just want to make sure I have all my ducks in a row before I mess up something that can be easily preventable.

What I originally thought was that these three column tables for leds corresponded to the segments of six leds. 1 set of six led segment would have been one value. Two segments of six leds would have been another resistor value for two segments and finally three segements that would make up a whole row would have been the value in the third column of values. Incidentally, I have also misread this.

**Matt_Edwards** · 03-16-2010, 06:25 PM

Table 2 of Construction manual give the resistor values for different Currents with 20mA the highest value.
In your case you want 25mA.
So Rgreen will be 180R
Rblue will be 180R
Rred will be 470R

BUT I would build one section of each colour first and fit measure the voltage across the Resistors. This will then give the real forward voltages and enable you to re-calculate the Resistors with more accuracy if needed.

**Penfold** · 03-16-2010, 06:33 PM

A breadboard is starting to look really inviting right about now.

Thanks Matt.

You have been very helpful and I appreciate it. I will go tinker with a breadboard first before I go full on with the PCBs. I will use your resistor values as a start and see what happens.

Thanks again.

**Matt_Edwards** · 03-16-2010, 07:02 PM

Forget the breadboard. just grab 6 LEDs, 1 resistor and solder the legs together.

**budude** · 03-16-2010, 08:14 PM

Originally Posted by Matt_Edwards

BUT I would build one section of each colour first and fit measure the voltage across the Resistors. This will then give the real forward voltages and enable you to re-calculate the Resistors with more accuracy if needed.

Here Here! - I suggest those building ANY LED fixtures do this and use the actual power supplies you are planning to use as well.

**rkhanso** · 03-16-2010, 10:54 PM

I posted a question some time back on a different thread about the restors needed for a portaflood...but got some different values. Though I bought my LEDs from the same eBay shop as Penfold, at the time I bought them, the chart on the LEDs said the current should be 20ma instead of 25ma (all other numbers were the same). Can I safely jump up to 25ma?

The resistor values I used were 240 Ohm for the green and blue. 604 Ohm for the Red.

I didn't realize that I should do a 'test' and fine-tune the resistors to the LEDs after it's all put together. It makes sense, but is it critical?

**Penfold** · 03-17-2010, 09:38 AM

I did a general search for an led calculator and tried a couple of sites and got the same values. I chose the leds in series calculator. For my voltage drop for red I entered 1.8, supply voltage I entered 24v, desired led current I put 25ma, and how many leds connected was 6. I get 560ohm resistor for red, Green I got 270ohm, and Blue I also got 270ohm.

This was the calculator I used:

http://www.hebeiltd.com.cn/?p=zz.led...tor.calculator

**rkhanso** · 03-17-2010, 10:21 AM

Originally Posted by Penfold

I did a general search for an led calculator and tried a couple of sites and got the same values. I chose the leds in series calculator. For my voltage drop for red I entered 1.8, supply voltage I entered 24v, desired led current I put 25ma, and how many leds connected was 6. I get 560ohm resistor for red, Green I got 270ohm, and Blue I also got 270ohm.

This was the calculator I used:

http://www.hebeiltd.com.cn/?p=zz.led...tor.calculator

I did the same thing, though maybe a different online calculator. Using the data that was on the ebay auction for the LEDs I bought, I used 20ma and 2v for the red. I used 20ma and 3.2v for the blue/green. Yes, I used the series calcualtor - to come up with the values I did....but I was wondering if I could safely jump to 25ma and maybe get a little more brightness out of the LEDs without shortening their life.

On second thought, it was a hassle to solder all those resistors on (I have 7 LED Portafloods total). Maybe I'll just leave 'em as-is.