SST-90 / LiFePo4 / 9amps?

[chelboed]

I'm considering another build already. I finished my P7 2.8amp hack job which turned out quite well for a first time bike light build.


I've been looking at the LiFeP04 "M-size" cell with maybe a Lumuinus SST-90. It'll do 50amp continuous, 100amp burst discharge. 10Ah will give me maybe a little over an hour runtime, right?

1. Will this LED really handle 9amps of current?
2. I can order some relatively inexpensive 1.4amp driver boards. I used 2x for my 2.8amp P7 build. Can I just use 6x for 8.4amps to the SST-90? Maybe do a 3x3 setup with the boards so I can have a 50% mode?
3. Heat sinking will be an issue, but if I use a big ol' chunk of aluminum and install a cooling fan...I think I'll be alright. Sound okay?


Any helpful input would be very welcome.

 

[The Dane]

LiFe technology dictates a max. cell Voltage of 3,6V and that will sag under use to 3,2-3,1V!
You need 3,6V when the cell(s) are delivering 9A so maybe 4 x 10000mA NiMh D cells are a better choice?

 

[chelboed]

Aaaaaaaaaahhhhh...ya see...this is why I come here. I wouldn't even consider that on my own.

What's the min voltage of the sst90?

Is there a better board that would take 3-4v input and 3.6v output?

I'm really liking this cell b/c it's small'ish for the performance...keeping it semi-compact in comparison to running 4x Dcells.

 

[luckybucket]

I don't know how much that cell will sag, but i get decent output from 3v with my sst-90. I use 3 C cells at the moment because I'm waiting on a high power regulator. When they are ready to purchase I'll use 3 d size lifepo4's.

About the best you can do right now is 3 NiMh cells. Several people have burned up led's with 4 and Li-on can't handle the current. IMR cells are a possibility also, but they drop voltage quickly so you will see dimming without a regulator.

 

[chelboed]

I don't know how much that cell will sag, but i get decent output from 3v with my sst-90. I use 3 C cells at the moment because I'm waiting on a high power regulator. When they are ready to purchase I'll use 3 d size lifepo4's.

About the best you can do right now is 3 NiMh cells. Several people have burned up led's with 4 and Li-on can't handle the current. IMR cells are a possibility also, but they drop voltage quickly so you will see dimming without a regulator.

So maybe I will be alright running a 3x3 board setup with the LiFePo4 and the SST? I don't think I'll be in danger of burning up the LED if it can handle 9amps.

 

[luckybucket]

I just stuck a A123 in my light and it was a bit brighter than with 3 NiMH. The starting voltage of the cell was 3.7v and ended up at 3.3 when I removed it. I couldn't check voltage with it installed because I didn't have enough arms. You should be fine running 3 leds from that battery. My unscientific evaluation is that LifePo4 batteries drop to around 3.2 volts instantly under load and stay around there. I did measure 2 of mine powering a 5761 that draws 5 amps of current and I ended up with 2.9v after an initial of 3.6v. I then found out charging two cells in series doesn't work very well. I get one battery with 3.7v and the other with 3.3, so I don't think they are getting charged correctly and that is why I get less than 3v under load. These are true A123 26650 and are rated for very high current draw and very little voltage sag.