Schematic approval

[mikeclem]

Back to the 'saber scene' due to my son now being of age to want/have one. Things have moved on since my humble 3W Luxeon days. He's getting the 3W but I'm after something a bit more meaty. Nice to see TCSS still going strong and I'm sure that will only continue as 2015 draws nearer....

So, I'd welcome reasons for why this schematic for electronics would not work (or vice versa):
Let me head off some questions at the pass:
1) before everyone freaks out about using a LiPo as a power source: I'm happy with it and confident with using them - and bear in mind it's for me (38 yrs old) and not my son.
2) the NB board gives me everything I need in terms of requirements (and a bit more) and I am not aware of any boards that will support a voltage of 14.8v (so, recommendation of 7.4v board such as a CF or PC irrelevant)

I'm really just sense checking this design from those with more experience than me and would welcome perhaps previous insight.



Ta,
Mike

[Silver Serpent]

You're obviously aware of the risks involved with LiPo, so I'll leave that one alone.

The voltage regulator is going to get rather hot from dropping down 14.8v to 5v. Be sure you heatsink your regulator properly.

I'm not sure if the Power Extender in the shop will handle your LiPo pack. From the store page http://www.thecustomsabershop.com/Po...r-20-P652.aspx it states that the output power limit is only 12v 1.5A.

A 10W GGGG LEDEngin wired all in series can (depending on bin) go upwards of 20v to power properly at 1000mA. You can halve the voltage requirement by wiring it in a "seriallel" setup (two dice in series, plus the other two dice in series, and the two sets wired parallel to each other), but you will need twice the current (about 2000mA) to fully power the LED. You could get a 2000mA LED driver or you could use two 1000mA drivers, and use one on each series pair.

LEDEngins are power hungry, especially the greens. Powering one to it's full potential is always a fun challenge.

Best of luck to you with your build!

[mikeclem]

Thanks,

Heat sink advice noted and aware.

I did notice the power limitations of the Power Xtender but left it in the schematic on purpose to see if anyone had tried overdriving it. The other option would be to use a MOSFET (which I suspect is what the Power Xtender is) with a higher voltage rating. What I was unsure about in using a MOSFET is whether ramp up/down effects would be maintained (I believe flicker effects would be unaffected).

Do you know if using a MOSFET would maintain ramp up/down effects from NB?

I got the forward voltage figures from the LEDEngin data sheet and while I see what you mean regarding the Vf range for a GGGG 10W (13.0-19.0), I was basing my voltage requirements on the following (bottom of page 4):



I thought 14.8 (nominal) would be close enough to the typical value of 15.0V with a 1000mA current. What do you think - close enough, or push it further (I could use 11.1v instead in dual series as you suggest)?

[Silver Serpent]

The PEX is either a MOSFET, or something equivalent. I know enough to hook it up, and what it does, but not enough to build my own.

I'm uncertain about the ramping effects. I'm sure one of the other sabersmiths here will have some insight on that.

The values for the LEDEngin are "typical" values. If you get one of the low voltage binned LEDs, you'll do just fine. If you get a higher voltage binned one, it won't be driven quite as well. Sadly, you can't choose your binning unless you're ordering in the 1000x quantities. That being said: it'll still be VERY bright. Four dice of a LEDEngin green are painfully bright to the eyes, even underdriven. I have a saber running GGGG myself, and it's uncomfortably bright in a dark room.

Give it a shot with your setup, and see how it works. It may be bright enough for you. Tweak the setup if it isn't. And if you still want even MORE brightness, then you might consider looking into a string blade setup. It's a lot more work, but string blades have the potential to make the brightest blades.

[mikeclem]

Thanks SS,

Putting together a switching (N-channel, I believe) MOSFET is not that difficult - it is essentially a transistor package (like the 7805 voltage regulator) with the addition of a resistor.

It would be great if someone else could comment (please) on whether ramp up/down would be preserved with a MOSFET.

Like you say I think I'll give it a go with the 14.8v in series. While this is the nominal voltage for a 4 cell LiPo when fully charged each cell puts out 4.2V (4.2 X 4 = 16.8v) which I guess is middle of where we need to be with the Vf.

I might give a string blade a try at some point but this particular saber will be used for duelling with my son - so a string not ideal for this.

Many thanks for your advice. May put up a separate thread in a day or two if nobody answers the MOSFET question from this thread.

BW
Mike

[hedgehog1]

Here is an option using two buck pucks and two Li-Ions that means no heat sink Required:

[hedgehog1]

Or an even simpler one with resistors instead of buck pucks:



Either way, two of each die a paralell giving you about 2000ma of power.

[mikeclem]

Thanks HH,

I did consider this type of setup but discounted it for the following reasons (please let me know if you think reasonable):
1) reduced run time by using 7.4V
2) I have a complete LiPo setup already - charger, leads etc... (excluding the battery I would need for this project)
3) If using LiPo a requirement, then no way to (easily) split output from one cell.

Any idea whether using a MOSFET would allow ramp up/down effects?

BW,
Mike

[Ari-Jaq Xulden]

The real question then is, what is the current output of your LiPo and how do you plan to mount it ? I am not trying to shoot down your idea, but most of the LiPo packs I have seen will not even fit inside a hilt. Nor do their outputs match that of a comparable cell size, even burning through the current at twice the rate. As is much within our hobby, test it out, and if you figure out a better way, let us know.

[PhoenixReborn]

I would do this a little bit differently. Tri-Rebel Greens tend to have a lower vF per die than the LedEngins. I would go Tri-Green with a single 18650 3.7v, using power extenders to allow each die to be driven at 700mA to 1A. Less batteries, less parts, easier to do.