P7 Direct Drive with A123

[Fulgeo]

I am contemplating setting up a SSC P7 Direct Drive A123 light and wanted to try and glean some information before the build. On my other P7 builds I have always used the 8 x 7135 linear driver solutions and been satisfied with the results. I have searched the CPF and found treads on DDing the P7 on single Emoli and 3 to 4 NiMH battery sources but nothing specific on driving the P7 on a single 3.3 volt A123 cell. Anyone ever try this? Would a P7 with a lower Vf be desirable? For example would a DSWOI be better than a DSWOJ because of the lower voltage of the A123 cell? The goal would be to run the P7 at up to 2.8 amps to maximize output and minimize heat yet still have the inherently safe chemistry of the LiFePO4 cell.:candle:

 

[A380]

Hellow Fulgeo.
I did try once to direct drive a Q5 with a spare A123 cell I had from my rc planes and I was very disapointed with the result of it. It didn't have a high output because of its lower voltage.
Mayby with a low Vf it could work, but you should think about the minimum voltage an A123 give (2v). At this voltage I'm not sure if the led it would work, so you'll have to charge it again before it's completly empty.
I hope I've help you.

 

[jar3ds]

under load i'd be suprised that cell would get that much current to the P7...

 

[Fulgeo]

under load i'd be suprised that cell would get that much current to the P7...

The cells in question are from a Dewalt battery pack. The A123 M1 cells are 3.3 volt 2300 mah capacity cells. I remember reading that they can handle a 70A continuous discharge and 120A 10 sec pulse discharge. They are a very robust cell. Now under load the 3.3 volts might be a limiting factor to getting the desired approximate 2.8 amps to the P7 which is what I think you were getting at. My novice understanding of electric theory is that voltage is the water pressure, the resistance is the pipe size and the current is the flow rate and/or reservoir size. In this case not enough pressure. Ignoring thermal runaway I was hoping to rattle the cage of an electric engineer and get a better understanding of the set up.

 

[old4570]

You will need to test ..

Put the ssc P7 on a heat sink .. Hook up some wires and use a multimeter to measure amps ...

Ive driven RCR123A Li-ions to 2A but thats seems to be about it ...

 

[Justin Case]

Here's the problem with using A123-based nanophosphate cells. Their voltage is low. Resting, you are looking at around 3.2V-3.3V. Even if we assume no voltage drop under load, direct drive at 3.2V-3.3V means that's going to be your Vf. Each LED has its own unique Vf-If curve. But at that low of a Vf, the corresponding If is probably going to be in the range of 300mA-350mA per core for an I voltage bin P7. That drive current means you will be underdriving the P7. For a D flux bin P7, you'll still get plenty of lumens (perhaps up to 400 OTF if the A123s can really deliver 3.3V under load), but you aren't going to get the max.