Driver/sandwich question

[Firecop]

I'm not terribly thrilled about direct driving a tri-Cree since I burned one up digging a freakin' hot basement fire, so I'm looking at using three AMC 7135 1050a chips to drive the leds in parallel.

Heat dissipation is my concern: can I wire up the boards to their respective led then AA epoxy the stack together? If I plop that stack on a sharksink against the side of the M@G, will they work okay?

 

[Firecop]

Anyone? Bueller?

 

[DaFABRICATA]

Maybe AA each driver to a dedicated sharksink if there is room. If not, get creative...

By sandwiching them together, you may need to run the light for shorter periods allowing things to cool if there is not good heat transfer from the drivers to the body/heatsink

 

[DaFABRICATA]

Anyone? Bueller?

Nice!:laughing: :twothumbs

 

[StefanFS]

If you keep Vin below 5.5 Volt you're ok with no heatsinking at all. It might work well with 3 D-size NiMH of high capacity.

You might want to consider a lower drive level, eg. 700 mA for longevity.

Realistically you would get a simpler, more robust and more economical solution using an SSC P7 C***I bin led in your Maglite with one of the driver solutions out there. Output is in the same general area as an 3CREE Mag.

 

[Firecop]

Thanks for the thoughts...I may have to switch people over to the P7s.

 

[LED Zeppelin]

FC, what cells are you using in what type of Mag?

 

[Firecop]

Well, most of the M@gs I've been making for people have been using 9AA to drive 3 Cree Q5s. They're not flashaholics and don't have the inclination to use any rechargeables beyond easily obtained AAs. I wouldn't expect or suggest to them to use Lions, so I tend to work around their limitations.

 

[TorchBoy]

Well, most of the M@gs I've been making for people have been using 9AA to drive 3 Cree Q5s.

Would those AAs be 9 in series or 3 series x 3 parallel?

 

[nein166]

I was able to teach my mom how to use a hobby charger for a Tri-Seoul Mag running on 8 eneloops, she hates wasting AA cells. Mdocod's battery holders make it easy.

 

[Firecop]

Torchboy-so far I've been running 9AA in series to 3xCrees in series. The tailcap MM amp readings have been around 1.1 with rested Eneloops.

 

[TorchBoy]

Torchboy-so far I've been running 9AA in series to 3xCrees in series. The tailcap MM amp readings have been around 1.1 with rested Eneloops.

That implies the Vf of the LEDs is quite high, so it sounds like using just one 3xAMC7135 board to drive all three LEDs in series might be appropriate. That arrangement has the advantage of having just one regulation voltage drop for the three LEDs instead of one voltage drop per LED. (Theoretically an extra 0.24 V.) The AMC7135 board drives just one LED, as per usual, but the other two LEDs are put in series with that setup to drop the extra volts, the same as you might do with a power/signal diode or two to drop multiples of 0.6-0.65 V. As the set current of the board is only a few microamps all three LEDs get very nearly identical current.

One of the problems with doing this is the variability of the battery voltage. Each NiMH cell has a working voltage range as it flattens which will be three times as much for nine cells in series (driving three LEDs) as for three cells (driving a single LED). However, with the right setup of LED Vf and maybe signal diodes it can provide good protection against over-voltage with fresh cells and come very close to direct drive as they flatten.

Perhaps you could crunch some numbers on it. Do your friends like to use primary batteries instead of Eneloops? What is the combined Vf of the three LEDs in series?