Re: Light / LED Voltage Recommendations?

[warpig2011]

As long as the topic of flashing lights is being batted around, I figure this would be a good question to toss out there:


What would the best bulb (or LED) voltage be if creating a flasher circuit (from scratch or using EZ-B, Arduino, etc.)? I plan to power my B9 with two storage batteries, 24v DC in the legs for the drive with a step-down to 12v DC for torso components. I was planning on using both incandescent and LED bulbs (in different places). I'm not going to mix voltages (or types) in sub-assemblies, but if I'm running 12v incandescent flashers in the finger lights, and I want to use a microcontroller and LEDs in the belly lights, what would my best voltage option be for the LED bulbs? 

I guess what I'm driving at is how can I "standardize" my approach to power so I don't end up frying stuff? 

[Bob Darlington]

If you have 12 volts available, you should definitely use it vs stepping down 24 volts.
LEDs have a forward working voltage. Say 2.2 volts. Running them on anything higher than that is fine, but you'll be burning up that voltage difference as heat across a resistor. That's throwing out electricity. When you're plugged in, that's just fine. You can easily run a 2.2 volt LED on 120 volts if you can burn up that 117.8 volt drop across a 5 watt resistor. It'll be about 2.5 watts of power thrown out just to run one LED at that voltage, so let's not run that high.
About the best you can do, efficiency wise, to get the voltages you need is to use a DC-DC converter. 5 volt modules that will take a wide range of voltages as an input (say, 12 to 22 volts) will happily run most microcontrollers. I use these modules here and there, and they're about $4.00 delivered.
http://www.ebay.com/itm/DC-DC-Converter-12V-Step-down-to-5V-3A-15W-Power-Supply-Module-New/191686310605

Here's another with 3.3 volts out for other microcontrollers:
http://www.ebay.com/itm/DC-DC-Converter-12V-to-3-3V-3A-Step-Down-Car-Power-Supply-Module-Waterproof/361068442037

Many ready to go LED bulbs have a resistor built in and are designed to work at a particular voltage above the forward working voltage, such as 12 volts (13.8V for automotive use most likely), or 6 volts as drop in replacements for 6 volt bulbs. Running them on higher voltages will require yet another resistor in line with them. They probably won't work very well at all at lower voltages. You may be able to swap out the resistor if you're willing to open them up and do the work.
-Bob

On Sat, Nov 28, 2015 at 4:51 PM, warpig@cyberpigstudio.com [B9Builders] wrote:


As long as the topic of flashing lights is being batted around, I figure this would be a good question to toss out there:


What would the best bulb (or LED) voltage be if creating a flasher circuit (from scratch or using EZ-B, Arduino, etc.)? I plan to power my B9 with two storage batteries, 24v DC in the legs for the drive with a step-down to 12v DC for torso components. I was planning on using both incandescent and LED bulbs (in different places). I'm not going to mix voltages (or types) in sub-assemblies, but if I'm running 12v incandescent flashers in the finger lights, and I want to use a microcontroller and LEDs in the belly lights, what would my best voltage option be for the LED bulbs?

I guess what I'm driving at is how can I "standardize" my approach to power so I don't end up frying stuff?

[warpig2011]

Bob,

Thanks! That makes a lot of sense. I will probably step down the 24v, as the source will be two 12v batteries in series (to power the treads). I remember reading a post saying *not* to tap off a single battery, so once through the slip ring it will go to a 12v step-down to power the higher voltage systems, and to step-downs like you recommended for the microcontrollers and "raw" LEDs.

Am I correct in my thinking to keep 24 volts as the "working" voltage in the torso and step-downs as needed, so that in any given circuit there is only one step-down?

As a side note: all preliminary wiring will be done and tested using circuit-breaker protected power supplies. Having done my own automotive wrench work for many years, I know what a nice arc a storage battery can produce, and I'd prefer to leave my electroBOOM days behind me.

[Bob Darlington]

I don't think you read my post! I'm saying stepping down from 24 volts is a bad idea if you need something below the 12 volts you have (in spades with 2 batteries). Doubly so if you're going to do it on the other side of a low power slip ring. You're going to put a lot more current through the slip ring than you're actually going to need, just in the process of bringing your voltage down to what you need. To me, that's crazy. Presumably if you're running on batteries you're planning on running it for as long as you can. You can either load in 100 more pounds of batteries or use the power you have more efficiently.
What are you running on 24 volts? Is there anything in the torso that needs it? Does that stuff need to rotate?
-Bob

On Mon, Nov 30, 2015 at 9:39 PM, warpig@cyberpigstudio.com [B9Builders] wrote:

Bob,

Thanks! That makes a lot of sense. I will probably step down the 24v, as the source will be two 12v batteries in series (to power the treads). I remember reading a post saying *not* to tap off a single battery, so once through the slip ring it will go to a 12v step-down to power the higher voltage systems, and to step-downs like you recommended for the microcontrollers and "raw" LEDs.

Am I correct in my thinking to keep 24 volts as the "working" voltage in the torso and step-downs as needed, so that in any given circuit there is only one step-down?

As a side note: all preliminary wiring will be done and tested using circuit-breaker protected power supplies. Having done my own automotive wrench work for many years, I know what a nice arc a storage battery can produce, and I'd prefer to leave my electroBOOM days behind me.

[warpig2011]

My robot is going to be mobile. The tread drives (wheelchair motors) are 24v. My slipring is a Mercotac 830 which has 2 conductors at 4A and six conductors at 30A. Probably overkill, but I got a good deal on it.

The plan is to have him able to spin 360 degrees. There won't be anything in the torso over 12v.