Trakmate IR diode Voltage

[keven]

I bought an IR diode kit from TrackMate a while ago.
it came with four IR diodes and a Resistor (100 ohm).
I may have had a schematic on how it was to be wired, but I must have misplaced it?
I'm pretty sure it was to be wired with the provided resistor in series with the four IR diodes.
Just not sure what DC voltage this was to work at?

[keven]

Got an answer from Trackmate:

12-volts

[jmacartney]

I admit to "borrowing" this image from Steve Medanic's Siberia Racing tech pages.

IR schematic.jpg

[keven]

In the case of the trackmate DIY kit components, the current draw is 120 ma…
resistor is 100 ohms and dc voltage of 12 volts.

[Maddman]

A current draw of 120ma indicates to me that the LEDs are wired in parallel and not in series as shown in Jmacrtney's post.

[Axle]

In the case of the trackmate DIY kit components, the current draw is 120 ma…
resistor is 100 ohms and dc voltage of 12 volts.

Where did you get 120mA from? If you had only a 100 ohm resistor (no LEDs) connected to a 12V supply, that would pass 120 mA (12V / 100 ohm = 0.120A)

But 120mA through a single 100 ohm resistor would burn 1.44 W in the resistor. That seems excessive. How big is the resistor?

The diagram posted by jmacartney seems like the correct way to wire the LEDs if you were only provided a single resistor with the kit.

With all the devices wired in series (4 LED + resistor), and assuming roughly 1.5V drop per LED, the overall current would be around 60mA at 12V. The LEDs might be ok with that.

Also, 60mA through the 100 ohm resistor would be 0.36W for the resistor, so a common 1/2W resistor would be ok here.

If the LEDs were wired in parallel, it would be best to include an individual resistor with each LED, since LEDs wired directly in parallel do not share current evenly.