XHP question for modders.

Flashlight Modding and DIY Parts
1

Hey guys, has anyone tried running a FET driver with 5 batteries into 2 XHP50 in Series? How about with 5 3.2volt batteries with 2xXHP50 in series?

I’ve got a light that uses 5x32650 and was thinking about Stacking it with XHP-50’s. It’s an 18xXML light but I would go 15xXHP-50 just to see exactly how crazy it would be.

I’m thinking maybe these batteries would be best to try it with.

https://www.aliexpress.com/item/6pcs-lot-Original-32650-3-2V-5000mah-rechargeable-Li-ion-battery-32650-LiFePO4-5C-discharge-battery/32807198241.html?spm=2114.01010208.3.156.Ox9sjP&ws_ab_test=searchweb0_0,searchweb201602_3_10152_10065_10151_10068_10130_10136_10137_10060_10138_10155_10062_10156_10154_10056_10055_10054_10059_10099_10103_10102_10096_10148_10147_10052_10053_10142_10107_10050_10051_10084_10083_10080_10082_10081_10178_10110_10111_10112_10113_10114_10181_10037_10182_10032_10078_10079_10077_10073_10070_10123_10124,searchweb201603_1,ppcSwitch_5&btsid=0db9a8f1-2e38-4582-a721-c700d1592236&algo_expid=ba3f3080-f336-4797-98ba-e2c32d5a22c5-21&algo_pvid=ba3f3080-f336-4797-98ba-e2c32d5a22c5

2

Got to admit I thought bout it trying to use that big monster for modding, but no, never took the big step.

3

I can’t help but reading this did made me do this. :slight_smile:

4

5s LiFePO4 cells with 2s 6V XHP50 might work.

I put together a tool for predicting current in different direct drive situations that might help you here. Basically you graph the supply voltage as a function of current which includes the voltage drop from all the different resistances in the circuit. Then you graph the forward voltage of the emitter. The point where the two curves intersect is the current that will result in a direct drive situation. I explain it more here: Tool/method to predict current in direct drive setups

Put this in google: graph 3.27*5-x**(.015*5.01.01) and 2**(.136*(x/1)+6.236)

x in these functions is the current in amps. The 3.27V is approximately the resting voltage of LiFePO4 cells, multiplied by 5. The next term is the voltage drop from all the circuit resistances. I approximate the IR of a cell as 0.015 ohms, times 5 for the 5 cells in series. Then the .01 + .01 are other resistances like FET and tailcap and wires, etc.

The other function is the forward voltage of the XHP50, which I approximated as a line from data from djozz’s measurements. The factor of 2 at the front is for two 6V XHP50s in series. The (x/1) means there is one parallel string, if you had 7 XHP50s in parallel you would put in (x/7) here.

You can get a good idea of what setups will work with this tool. To use Li ion instead of LiFePO4, put in 4.2V (or the voltage at whatever state of charge you want) and a suitable cell IR.

Hope this helps and please ask any questions if you have them.

5

Thanks,

How do I find the tool, I don’t see a link and copy and paste doesn’t get me anywhere from that one.

6

The rate at which lithium batteries drop voltage will make it run extremely hot and bright for a few seconds and then drop to mediocre levels.
If you have the ability of using that many batteries then just get a constant current driver like this one:

7

Thanks for the suggestion. Is there a driver like that in a 30mm size though?

8

Not that I know of.
If you know how to stack 7135s then you could get a smaller mountain electronics driver and add the chips to get the current you want.

9

If you type in google “graph 3.27*5-x**(.015*5.01.01) and 2**(.136*(x/1)+6.236)” (without the quotations) it will graph the functions. Then find the point where the two curves intersect.

10

Using 7135 chips is not really a solution here, IMO. The supply voltage and emitter voltages would still have to be matched fairly closely. If they aren’t matched the chips could burn up. If they are matched well then you just end up with “mediocre” output all the time.

Modding with direct drive setups has advantages. It is fun to plan, like the unusual setups proposed in this thread, it is electrically simple with fewer things to break, and it usually results in the highest performance.

11

OK, I got it now, Thanks.

And yeah I don’t think the other driver pointed out will work. I tried to build a 4xMT-G2 using that type of driver once and I don’t think it worked out right. Plus any way you go the massive heat is going to quickly reduce lumens no matter what you do. The point would be to have something that can blast out massive lumens if even just for a short while. It’s not like this is a “practical” light anyway. LOL Just horsing around to see how far I can take it.

The other option I was thinking of was a large 12x with 4x26650’s I know the wiring on that would work out fine, but I would have to buy that light and I already have this 5x32650. Right now it’s set up with XM-L2’s using 15 emitters and a FET driver. It’s pretty darn bright already. But it would be fun to see what it would do with 15xXHP-50’s. It’s a side switch light with no tailcap switch and I could get rid of the spring on the driver too. I’ve melted a few springs in my day making these crazy lights.

12

So you have 18 spots for XHP50s? A 5s Li ion with 2s9p 6v XHP50 would result in 47A from the cells, or 5.2A per XHP50. That current is doable for short times from the best 26650 cells. This will pretty much pull as much as the cells are willing to give, without overdriving the emitters. Or you could make it 2s8p or 2s7p XHP50s.

graph 4.2*5-x**(.026*5.01.01) and 2**(.136*(x/9)+6.236)

Tom E, I want to link to your 16x XHP50 mod because its the biggest one I’ve seen yet: What did you mod today? - #2517 by Tom_E

I think this has a 2s3p 18650 power source and 16p 6V XHP50 emitters. My tool predicts 47A will flow from the power source, or 2.9A per XHP50, which is consistent with the measured ~34,000 lumens.

graph 4.2*2-x**(.026*2/3.01.01) and 1**(.136*(x/16)+6.236)

13

No, the driver works with 2S and will run a 6v LED just fine.
Max output for most of the battery life.
Buck driver is also an option.

14

Ok, but we are talking about 5s here…

15

Yeah it’s 18x; 2s9p would be crazy and it looks like it would work. I kind of thought it would with that many emitters. There would almost have to be enough battery sag that it wouldn’t fry them. There is no way to run it long without something melting down but for short bursts it would be amazing.

Thanks for the help, that’s a cool tool.

16

Wow, that's cool! But how does it model the wiring? I would think the LED wiring is very critical, not to mention the FET, cell resistance, etc.

I'm expecting to break 40K though with VTC5A's and a UCLp lens .

17

True, I would go with a buck driver in this case…

18

The wire, FET, and cell resistances are in the first function (like .026.01.01). Of course, the numbers I have in there are estimates. The real value of the tool is being able to estimate how much of an increase you will get by changing things. For example if you change to VTC5As, which have, say, .02 instead of the 30Q’s .026 ohms, the total current will increase to about 52A from 47A.

19

I’m all for buck drivers, but it would need to pass 700+ watts to compete with the FET setup.

20

The problem with 7135’s(or any linear driver really) and series cells is the voltage change from charged to discharged is much too great for them to regulate well. With 3S cells the differential is 12.6V down to ~9V. If you pick LEDs with a maximum Vf sum of ~1V less than the max to protect the 7135’s then driver will be out of regulation from 11.6V down to ~9V. For series LEDs it seems to me that either boost or buck is the way to go.