Mag Charger with 2x32650 LiFePO4 and MT-G2 Possible...?

Hi, all! I am wondering if this build is possible:

Parts List:

-Mag Charger
-Mag Charger charging base
-Cree MT-G2 6.0v
-heatsink
-LED driver
-2S LiFePO4 BMS
-2x32650 LiFePO4 cells
-reflector
-power supply to charge with
-willing modder (already emailed a modder)

Thoughts:

1) LiFePO4 can be fast charged and have very long lifespan.
2) MT-G2 at 6.0v should draw about 2000mA and put out ?????? lumens.
3) Would use stock Mag Charger charging base with high current power supply for fast charging.
4) BMS for two series 32650 cells would take care of charging cutoff, and overdischarge protection.

Is this build possible? How hard would it be?

I've seen some buck circuits at intl-outdoor that can output 3 or 3.5A that can be used on a MT-G2. The only thing that I can see missing from your list is a heatsink.

Three to 3.5 amps isn't objectively bad, but it will drain the batteries faster than I would like. I figured two amps would be a good value.

How many lumens would I see at two amps drive current?

Heatsink added to list.

I forgot to mention the drivers are multimode (H-M(30%)-L(5%)) via PWM. As for a lumens estimate take a look at the MT-G2 datasheet on crees website.

Reading the Cree MT-G2 PDF from Cree's datasheet is how I pulled the forward voltage and drive current spec.

Being uncertain as to what the lumens were at 2000mA drive current even after reading the PDF datasheet is why I posed the question.

First determine what bin emitter you are going to use and find its corresponding minimum luminous flux on page 3 of the data sheet. Go to page 8 and find the Relative Luminous Flux vs Current graph. On the graph locate the desired current on the x-axis of the graph as a reference point. Look up to where the curved line intersects the desired current. At that point look over to the y-axis to find the relative luminous flux (%). Take the minimum luminous flux number from page 3 and multiply it by the percentage you determined from the graph on page 8. This number is lumens at the emitter (not OTF).

This concludes "learning how to determine luminous flux at drive currents 101". Class dismissed:wave:

Oh, boy.

I'll give it a shot. Wish me luck.

Okay, please let me know if I am close:

I find 750 lm/1100 mA.

I want to run it at 2000mA.

So, 100% = 1100mA.

The curve looks like 2000mA is about 170%.

So, 750 lumens * 170% = 1275 lumens.

Is that about right?

Congrats you have passed your first exam:thumbsup:

Just a FYI in the past luminous flux was commonly rated at a temperature of 25C. Recently Cree has started to rate luminous flux at 85C which is more realistic scenario during use. As heat rises luminous flux decreases as seen on the graph on page 6 of the datasheet. If you wanted to compare two different LED's such as a SST-90 vs a MT-G2 it would be more proper and correct to compare both at a temperature of 25C.

Noted.

I just want to make sure I understand one key point:

I can use any dumb power supply to charge with, correct?

As long as the protection circuit/BMS treats each cell individually and takes into account overcharge, overdischarge, etc.
then the only concerns are:

1) Finding a 2S circuit which can physically fit into the Mag Charger body
2) Figuring out how to get the wires from the circuit to each individual cell

I am thinking there should be a way to adapt the Mag Charger wiring to fit the two 32650 LiFePO4 cells,
connect the 2S circuit to the metal charging contacts, and connect the circuit to the cells...

I'm not too familiar with the inner workings of the mag charger or that BMS circuit. Perhaps someone more familiar can jump in and help here?

That would be great.

One of the key questions still requiring an answer is whether or not the Mag Charger system:

1) Contains electronics for charging in the power supply, or, whether it is simply a plain AC --> DC adapter
2) Contains electronics for charging in the charging base, or, whether it is simply a mechanical point of contact to transmit electrons
3) Contains electronics for charging in the flashlight body, or, whether it is simply a housing
4) Contains electronics for charging in the battery pack, or, whether it is simply a string of NiMh cells in series

The answer to this question plays a large role in determining how the rest plays out...

Ongoing research indicates a Mag Charger body is essentially equivalent to a 3D body.

The same research also indicates that while two 32650 will definitely fit in a 3D body, three 32650 cells will be too long. :-(

So we can either use just two 32650 cells in the stock Mag Charger body, or, use a D cell Maglite extension, assuming the threads are compatible.

I am leaning towards the extension for the extra runtime.

That leaves the issue of charging each 3.2v LiFePO4 cell individually.

After scouring the net, I found the maximum "safe" internal diameter of the Maglite to be about 34mm.

I found a PCB with dimensions 32.6mm by 13mm.

1) What do you think of this charger?

Google: " Tenergy 9.6V (3-Cell) Intelligent 2A LiFePO4 Battery Pack Charger "

2) What do you think of this PCB?

32.6mm by 13mm

Google: " Protection Circuit Module (PCB) for 4S LiFePO4 Battery Pack (5/12A) "

3) Are Maglite "D" cell tubes and tailcaps thread compatible with Mag Charger tubes and tailcaps?

Since direct links to merchant websites are not permitted,
please copy and paste the following block of text directly to Google to view the specific LED I would like to use:

(omit the quotes when pasting):

" CREE MT-G2 P0 on Noctigon MT-G20 MCPCB 6V Version Approximated light output: 920lumens @ 1100mA 25°C Maximum drive current: 3000mA Color temperature: 5000K (2Step MacAdam) 20.6mm x 1.55mm direct thermal path copper base "

Here is a link to testing of the MT-G2 I would like to use!

A regulated 2000mA drive current should provide just over 1500 emitter lumens.

Multiplying by 0.8 to get a rough estimate of OTF lumens puts us at about 1200 lumens.

Nice!

Link

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