Lightsaber project, can I power it like this?

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Jinxvar

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Hi all, I am doing a custom lightsaber together with my son. We already have it working from the computer.
Setup is as following:
- Teensy 3.2
- Teensy Prop shield
- 4 ohm (2W I think) small speaker
- 2x addressable LED strip (https://www.antratek.nl/apa102?gclid=EAIaIQobChMI3bSc3ena2gIVE5IYCh33Fw1sEAQYAiABEgIcBfD_BwE)

When on USB I can not fully turn on LEDs because of too little power.
I am a complete noob when it comes to calculating how much volts, amps, etc.
What I would like is to use this to power it:
- LiPo battery charger (https://www.tindie.com/products/onehorse/stbc08-high-current-lipo-battery-charger/#specs)
- LiPo battery itself (https://hobbyking.com/en_us/turnigy...-15-25c-lipo-airsoft-pack.html?___store=en_us)

Am I thinking too complex here? Is this at all possible with this battery setup or will I fry my Teensy?

Kind regards,
Jinx
 
You don't want that battery. It puts out a nominal 7.4 volts. You will fry the LiPO battery charger, the LEDs, and possibly the Teensy/Prop shield if you use that.

Two strips of the LEDs is 120 LEDs. That probably means you will need something like 2.4 amps at 5 volts (10 watts) if you turn every light on to its full power. If your computer is providing the USB power, it will likely only provide 100mA (0.1 amp) and maybe 500mA (0.5 amp if you are lucky). You can get USB charger batteries that can provide 2 amps or so, and power the saber with that. Note, that many USB power supplies will only give out 500 mA unless your USB device asks properly for high power (and the Teensy doesn't). There are USB power supplies that give you the full 2-3 amps or so, but it can be frustrating looking at the specs.

However at full power, I suspect you will also temporarily blind the poor jedi wielding the saber and the people nearby if you turn on all LEDs to their maximum. So you likely will need to use less that full power to the LEDs. This means your power budget will be less, depending on how many LEDs you have lit at a time, and at what power level.

If you can keep it to 1/2 power or under, you might want to look at this battery from Adafruit, which is essentially a 18650 battery with a protection circuit and a JST plug (that is provided with the charger). Being a cylinder, it might fit better in the light saber handle than some of the other lipo batteries that are more square.

This battery provides double the power, but it might get to being too wide:
 
Last edited:
USB 3.0 power

tonton81 said:
USB3 (blue port) provides 1.5A
Click to expand...

According to: https://en.wikipedia.org/wiki/USB_3.0, the typical amount of power available is 900mA, which is a step up from the 100-500mA available on USB 1/2, but still if the OP needs 2 amps it still may be a problem. If the USB device indicates it needs different power profiles, it can get more, but the Teensy USB 2.0 connection doesn't set those:

As with earlier versions of USB, USB 3.0 provides power at 5 volts nominal. The available current for low-power (one unit load) SuperSpeed devices is 150 mA, an increase from the 100 mA defined in USB 2.0. For high-power SuperSpeed devices, the limit is six unit loads or 900 mA (4.5 W), almost twice USB 2.0's 500 mA.[10]:section 9.2.5.1 Power Budgeting

The term "available current" can be misunderstood. It implies that if a low power device or a USB2 device is connected to a USB3 port it can only draw 150 mA or 500 mA from that port. However, the available current for any USB device plugged into a USB3 port is 900 mA (unless it is charging port compliant) as defined by the USB3 spec. The actual current draw is determined by the device capability. The Vbus, pin 1, and Ground, pin 4, are the same for USB 1, 2, or 3. A USB2 HDD with 2 USB2 connectors needing a total of 800 mA will draw full power from a single USB3 port. A USB2 phone will probably charge faster since 900 mA is "available" to it.​

One thing the OP can do for debugging is program the Teensy, and then use a wall wart to power the Teensy that can give more power. It may make sense to get one of the cheap USB power meters, and plug the unit into a wall wart (which can typically give 1-2 amps, depending on the unit), and see how many amps are needed for the use (rather than trying to calculate it ahead of time), and then look for a battery that matches those specs.

Looking at other saber projects:

 
that may be true per spec, but different components can have higher ratings, specifically if they specify it, they can not lie, or else they’d be facing issues legally. if motherboard manufacturers specify their ports to be 1.5A, they have to honour that based on the layout design of their power source.

i was able to power 2 5v displays and one teensy off my usb3 port with an ESP8266, i doubt “900mA” would have been efficient enough..

the output should be tailored per device spec, not whats written originally in stone.

just because the speed limit is 100km/hr doesnt mean people maintain it.
 
If you are wanting this for anything more than a one off event where you hand tweak things, you will need some form of power management hardware. The above batteries are only 3.7 on average so will go from 4ish volts down to somewhere under 3 as you discharge. Simple solution is a boost controller, better is some research on your chosen battery chemistry will find better boards to both boost up to your required drive voltage (you will probably need 5V for the LEDs) and protection from trying to run batteries too flat. Some batteries types just loose a bit of capacity being run down too much or too hard, others start doing exciting stuff like catching fire so a topic worth some study. Good battery managment involves monitoring cell temperature and controlling charge/discharge rates - which may be overkill for this design but nice ideal.

Do not get too fixated on the nominal output voltage, since you can convert any voltage to any other voltage, more important is iff you can fit the required power (currant capacity*voltage) into the size and space you want (not all batteries come in all shapes) at a price you want.

If you just want to make this and move on, buy a USB power bank of sufficient capacity in charge and peak current and either use as is into the USB jack or use the parts in a handle of your design.

Whatever you do in your design make sure you have a method to safely isolate the batteries (first step on opening, last step on buttoning back up) while working on the thing or the first loose wire will turn into a spot welding lesson.
 
Ok, will finish up the setup first and hook it up to an amp USB meter to check required amps, etc.
Good tips, thx all!
Will post back with the finished item! (or another question, lol)

Much appreciated!
 
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