High Power LED's

[Jeremy Germita]

Attached, is our schematic for our custom LED driver board circuit.
The relevant part is the capacitor stage.
Depending on your robot and light, anywhere above 4000 microfarads would suffice. Unless you put a diode into the circuit, the rest of the robot will also draw power from the capacitor bank, nearly defeating the entire purpose of the bank.
Since you are powering this via a spike, you can turn it into a custom circuit and still be legal.

[Thad House]

Originally Posted by jeremypg399

Attached, is our schematic for our custom LED driver board circuit.
The relevant part is the capacitor stage.
Depending on your robot and light, anywhere above 4000 microfarads would suffice. Unless you put a diode into the circuit, the rest of the robot will also draw power from the capacitor bank, nearly defeating the entire purpose of the bank.
Since you are powering this via a spike, you can turn it into a custom circuit and still be legal.

Thank you very much. we might have to do something like this. I didnt know you could do stuff like this between a spike. but we will have both systems ready for competition just in case.

[Al Skierkiewicz]

Guys,
Generally caps are not going to fill in the current needed for the length of time that the battery browns out. You can very easily use a LM317 three terminal regulator as a custom circuit set for 5 or 6 volts with just two resistors. If you connect the reference terminal to a digital output, you can turn the supply on or off. Then it is a simple matter of wiring your LED string for the voltage you have chosen. Please remember to isolate and insulate your custom circuit.

[Thad House]

Ok. We were wanting to have 12 volts because our led's are currently wired for 12 volts. also would it be allowable to put a voltage regulation circuit between a spike and the led's or would that be disallowed?

[rthinman]

You can get a quick estimate of whether those 4000 uF and diode will be sufficient or a waste of time. Assume:
The LEDs draw constant current I (they won't, that's why they dim)
The battery drops out for a time deltaT, perhaps 2 seconds, while the shooter spins up. For that entire time, it is lower than the capacitor voltage so the diode is off.
We can only tolerate a certain amount of drop deltaV in the LED supply voltage before our constant current assumption is now longer good, or that the LEDs are too dim. Maybe use 1 Volt for deltaV.
Now since we've made assumptions of constant current, we ignore the calculus and estimate:

I = C * deltaV/deltaT ==> C = I * deltaT/deltaV

With the above assumptions and I = 200 mA, we get C = 0.4 F = 400,000 uF.
You will probably want C much bigger than that to cover our assumptions.

So Al is right, ordinary capacitors generally won't cut it. Super capacitors (also known as ultracapacitors and "gold" capacitors) would be a possibility, but they come with other problems. You will want to put a small-value resistor of sufficient wattage rating in series with the diode to temper the inrush current when you turn on the Spike.

Rod

[Al Skierkiewicz]

You can use a Spike to supply power to a constant voltage (boost/buck) supply to run 12 volts to your LEDs. Check out the power supply in the PD. You may also find these types of supplies in the Digikey catalog. Not cheap but exactly what you want.

[Thad House]

Originally Posted by Al Skierkiewicz

You can use a Spike to supply power to a constant voltage (boost/buck) supply to run 12 volts to your LEDs. Check out the power supply in the PD. You may also find these types of supplies in the Digikey catalog. Not cheap but exactly what you want.

Thanks for the rules clarification because this will make it alot easier.

[Jay Meldrum]

We are currently using the Angel Eye Headlight Accent Lights 60mm Blue and they worked great for us for vision tracking at our latest competition.

http://www.superbrightleds.com/cgi-bin/store/index.cgi?action=DispPage&Page2Disp=%2Fmini_tubes. htm

We just placed it right over the camera (M1011). We do get a dimming effect when we start up our cannon motors, however this has not yet affected our camera tracking.

[Mike9966]

Hi all,
The best way I can think of is to make a circuit for constant current. They make driver chips for just that purpose. You could also use the LM317 in a constant current mode.
Just google constant current LED driver and you will get a ton of hits.
You can probably only put 3 LEDs in a string as 4 might be too much of a voltage drop.

Good luck, and have fun,

Mike