TOPIC: Lit while Charging

Correct me if I'm wrong, but when I first started investigating sabers, 'round November last year, SF had an option for certain tiers that allowed hilts to be lit up while charging. That was a real thing, right, I didn't imagine it?

Does anyone know of/own hilts that do this? Anyone know how to wire up a saber to do that, on a Spark 2, specifically?

On Champion tier, never. I remembered I asked this question too.

I am planning to install Spark 2 on my ASP, let me see what I can find out.

Ah, must've been on Hero tier's then. I look forward to what you find out; I'll keep doing some digging on my own.

Edit: It's been brought to my attention that was just on warrior tiers, which makes sense. Makes things a bit more interesting.

I messaged Naigon about it, and he said that it's generally a bad idea to have things running while charging, and said that it could be wired to be lit while plugged in, but it wouldn't charge while doing so.

I think you're thinking of the Nightlite configuration:

My first thoughts are:

1) You'd need a charger that provides more current than the LED's using. So the SF 3A charger might work fine with a 6W LED, but you'd need something capable of 5-6A to charge a battery while your 12W is running (or even just to run the 12W without a battery).

2) Assuming you can get a capable-amperage charger, it *should* be as simple as bridging the negative contacts on a charge port. This prevents any kill-key functionality, however.

On top of that, I remember researching diodes a while back when I was trying out different voltages for boards and LEDs. A bit of creative wiring and the diode acts as a simple switch, switching the saber to outlet-power when plugged in, and switching back to the battery when separated. The diode itself consumes a bit of power, though, so it would probably need to be something like a 5V charger rather than the usual 4.2v.

Kouri wrote:
Hey Kouri, can you elaborate on this? It sounds really interesting but I can't quite wrap my head around how you could do this with a diode. Might just me being slow due to my lack of morning coffee though.

I was actually mis-remembering, Would work for using the outlet as a primary power source with battery backup, but the basic circuit wouldn't actually charge the battery - not sure if it could be modified for both.

Anyway, diodes only allow current one-way (this is why LEDs only light up when wired properly. On top of that, rectifier diodes won't allow any electricity to pass if the voltage in front of them is higher than what's behind - the idea being a 4.2v charger could prevent a 2.5-4.1v battery from powering the device. Then as soon as you unplug, saber goes back to running on battery power.



The black triangles represent the rectifier diodes.

Trouble with this setup is you can't really use it with high-voltage LEDs like Blue and Green since the diodes eat a bit of voltage. I never really got serious about this sort of setup, since I only use rectifier diodes for bumping up the voltage requirements on Red LEDs when I'm color-mixing with an LED driver.

You could probably accomplish this kind of charging using a N-type mosfet.





There are still issues with this, however. Like in the circuit you discussed, your voltage output is greatly limited (assuming at typical diode voltage drop of 0.7V, you'll have 3.5V available on adapter power.

In terms of battery power, the best FET I could find might be the Vishay SUB85N02-03. Accounting only for the threshold voltage you would be limited to a charge of 3.75V, but because of the source-drain voltage drop you'll be limited to a charge of 3V maximum. With the diode taken into account that's 2.3V available for running LEDs at a level where the charge will probably last only a short period of time. Not exactly worth the effort.

Edit: Rerunning numbers now, may have made a mistake:

We know there is a forward voltage drop of 1.2V minimum across the MOSFET. The drain-to-source voltage should be roughly equal to the charger voltage minus the forward voltage minus the battery voltage, and in the orientation this is wired the gate-to-source voltage should be roughly the same. The MOSFET will act as an open switch around the time the gate-to-source voltage equals the threshold voltage, or 0.45V. Knowing this, the maximum battery voltage you can achieve is 2.55V. After the diode you are left with 1.85V left for running your LEDs, and since the lowest forward voltage for a Cree is 2.2V you're kinda screwed in that regard. So in-hilt light up and charge doesn't seem feasible to me.