Prizm 5.1 with 7.4 18650 trident setup

[jaylakejr]

Hey guys, I am a newbie here and am looking for a little help.

I am setting up a saber with a Prizm 5.1 and a Lion 7.4v battery pack. I am a little lost with the resistors I will need.

I have 1 tri cree RRW that has Forward Voltage @1000mA = 2.65v on the red and Forward Voltage @1000mA = 3.15v on the white

The tridents are Cree XP e2 both are Red Forward Voltage @1000mA = 2.65v

Can anyone help me with what resistors I will need?

Thank you so much.

[Jay-gon Jinn]

FYI, you'll destroy that prizm if you hook it up to a 7.4v pack. It is designed to run on a 3.7v battery.

[jaylakejr]

FYI, you'll destroy that prizm if you hook it up to a 7.4v pack. It is designed to run on a 3.7v battery.


Glad I asked. OK, so if we use the 3.7 what resistors am I going to need?


I am thinking a 1.2 ohm resistor on all red and 1 ohm on the white.

Thoughts?

[Jay-gon Jinn]

I would recommend using this topic to figure it out: http://forums.thecustomsabershop.com/showthread.php?17109-Tutorial-FJK-s-quot-Down-and-Dirty-quot-guide-to-Ohm-s-Law I will tell you that I usually use a 1.5ohm, 1/2 or 1 watt resistor on the cree reds with a 3.7v battery source. My math comes out to a 1.1 ohm, but I happen to have a bunch of the 1.5ohm carbon films already, and the red lights up just fine using those. The 1ohm on the white should be fine.

[Darth Nurse]

I will go a step further. If possible actually measure the forward voltage of your LEDs (there are videos online). This will give you the true numbers to calculate from for your resistors. You will be surprised how different the forward voltage may be from the spec sheet.

Also, I cannot emphasize this enough. Read the Prizm manual. Then, read it again. And have a hard copy with you when you wire the board. The 7.4v question would not have come up with a read of the manual. Also, the formulas for calculating the resistors are in the manual.