MagMod 4x P4 HELP

[Changchung]

Hi... I have a old magmod with 4 P4 running with 4 18650 and two Fatman from taskled, so, two of the leds turn blue when I turn the light on, so, maybe one of the fatman is give them a little of much current to the leds, so, I am thinking in change the drivers, maybe I can use a single driver for the 4 leds, I have a buck cenverter old version from Der Wichtel and some differents driver from dealextreme, what can you recomend me???

 

[ejot]

The Der Wichtel driver, or hipCC from taskLED, would be able to handle all four P7's in series, but you would probably want to use to a 5 cell solution to stay in regulation longer with those drivers.

 

[Der Wichtel]

I don't know how the fatman looks like but there should be a current sense resistor. You can try to change it to a higher value in order to get less current.

 

[MorePower]

The Fatman is a boost circuit. Running 2s2p 18650 cells is putting the circuit into direct drive, until the battery voltage drops below the forward voltage of your 2 series connected LEDs. That's why the LEDs are turning blue. The other pair of LEDs probably has a higher total forward voltage and therefore isn't being driven as hard as the pair that turns blue.

From the Fatman tech page: "Fatman is a Boost regulator (step up), so input voltage must be less than the output voltage to ensure Fatman remains in regulation. If the input voltage exceeds the output voltage (at the dialed in drive current), Fatman will no longer regulate and the input voltage will go through the series inductor and schottky diode directly to the load. This will cause the output current to a LED to rise rapidly since LEDs have a very steep Current vs Voltage curve (Vf)."

Depending on the current at which you're attempting to drive them, you may be able to simply run all 4 LEDs in series with one Fatman, using your existing 2s2p battery setup.

 

[Changchung]

The Fatman is a boost circuit. Running 2s2p 18650 cells is putting the circuit into direct drive, until the battery voltage drops below the forward voltage of your 2 series connected LEDs. That's why the LEDs are turning blue. The other pair of LEDs probably has a higher total forward voltage and therefore isn't being driven as hard as the pair that turns blue.

From the Fatman tech page: "Fatman is a Boost regulator (step up), so input voltage must be less than the output voltage to ensure Fatman remains in regulation. If the input voltage exceeds the output voltage (at the dialed in drive current), Fatman will no longer regulate and the input voltage will go through the series inductor and schottky diode directly to the load. This will cause the output current to a LED to rise rapidly since LEDs have a very steep Current vs Voltage curve (Vf)."

Depending on the current at which you're attempting to drive them, you may be able to simply run all 4 LEDs in series with one Fatman, using your existing 2s2p battery setup.

Hi Morepower, I just make what you recomend me, 4 Leds in serie, but dosent work, not even the Leds turn on a little... I try moving the pot in the fatman...

 

[ejot]

That combination should work, so it is strange that the LEDs did not light at all.

This driver isn't capable of pushing this many P7's very hard, though. Input current to the Fatman is spec'd at 2.2A max. To keep below this with the batteries fully depleted, you're limited to 2.2A*6.8V = ~15W input power. If you manage ~93% efficiency, you can deliver 14W to your LEDs. If your P7's are Vf~3.5V, the current to the LEDs is 14W/(4*3.5V)= 1000mA.

You probably need to heatsink the Fatman at that drive.

According to the specs, you would want to set the trimpot to 13500Ω if these numbers are about right.

Someone please correct me if my reasoning or calculations are incorrect.

 

[Changchung]

That combination should work, so it is strange that the LEDs did not light at all.

This driver isn't capable of pushing this many P7's very hard, though. Input current to the Fatman is spec'd at 2.2A max. To keep below this with the batteries fully depleted, you're limited to 2.2A*6.8V = ~15W input power. If you manage ~93% efficiency, you can deliver 14W to your LEDs. If your P7's are Vf~3.5V, the current to the LEDs is 14W/(4*3.5V)= 1000mA.

You probably need to heatsink the Fatman at that drive.

According to the specs, you would want to set the trimpot to 13500Ω if these numbers are about right.

Someone please correct me if my reasoning or calculations are incorrect.

Thanks a lot, let me try again...

 

[MorePower]

That combination should work, so it is strange that the LEDs did not light at all.

This driver isn't capable of pushing this many P7's very hard, though. Input current to the Fatman is spec'd at 2.2A max. To keep below this with the batteries fully depleted, you're limited to 2.2A*6.8V = ~15W input power. If you manage ~93% efficiency, you can deliver 14W to your LEDs. If your P7's are Vf~3.5V, the current to the LEDs is 14W/(4*3.5V)= 1000mA.

You probably need to heatsink the Fatman at that drive.

According to the specs, you would want to set the trimpot to 13500Ω if these numbers are about right.

Someone please correct me if my reasoning or calculations are incorrect.

@ejot
The only thing I see wrong in your post is that Changchung is using P4 LEDs, not P7s.

 

[ejot]

@ejot
The only thing I see wrong in your post is that Changchung is using P4 LEDs, not P7s.

It appears that you are 100% correct.
I've had multi-P7 mods on my mind lately and somehow I thought .... oh, I dunno what I was thinking....

Thanks a lot, let me try again...

Please ignore my comment about under driving, the driver is well suited for this application.

Check on the max current for your bin P4's. I recall that 1000mA may be about right, or may be a little too much. You probably want to run a little lower anyway to get the input current down around 2A or less, as recommended for best driver performance. Use the actual Vf of your particular LEDs for your calculations. The Fatman tech page at taskLED has everything you need to know to work it all out.
You would want to set the trimpot to a smaller resistance for less current, also detailed on the tech page.

 

[Changchung]

Ok, a make a bad connection before, now the 4 leds come on, but very low... :huh:

Let me read the pass post again... I think someone is confuse...

 

[Changchung]

Dont worry ejot, this things happen... Look, I try moving too the trimpod with no changes.. :thinking: what I am doing wrong??? Can I try with the Der driver???

Take it from the task page:

6V SLA or 7.2V 6 cell NiMH driving 3 series connected Lux3's or 2 series connected LuxV's


I think the fatman cant drive 4 Leds in serie...
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