Fatman Help!

I trying to wire a fatman with a potentimeter to power a lux V, from 3D alkaline batteries in my maglite.

Initially, I directly wired the Fatman to the luxeon to test. It was pulling 2amps from the batteries at 3.1 volts. 2A x 3.1V x 90% efficiency would be about 5.58 watts, so I was only slightly-overdriving, and since i have adquate heat-sinking, everything was good.

However, today, I wired up the potentimeter (also purchased from taskled), and put an connector in-line between the emitter and the driver. Dimming functions worked fine but I noticed that the output was noticably dimmer. So I make sure that the potentenmeter is set so that the output is the brightest, and dialed the trimpot on the fatman all the way clockwise to increase output...still dimmer than before. I measured the current going to the emitter...only about 500ma. I thought that was strange, so I added a temp 4th battery (thinking that my half-depleted alkaline batteries couldn't supply enough power)...still only 500ma going through the emitter.

Can you guys help me out with my first mod? Is it a problem with the batteries not being able to supply enough current? Or would the in-line connector to the emitter be adding resistance? Is it a problem with the Potentimeter? Or is it a problem with the fatman board? or anything else?

Please...:help:

The new external pot is connected in parallel with the onboard pot.

Normally george keep the onboard pot @ 9.37 KOhms for 700mA output when shipped. Now you added 50K (assumed) external pot to the system without adjust the onboard will reduce the overall resistance of the system.

The effective resistance of the two pot is 7.89 KOhms so your max output will be 592mA.

1/Rt = 1/R1 + 1/R2
Resistance_in_ohms = ( 13.87 * Current_in_mA ) - 322.7

You need to increase the resistance of the onbard pot.
For 700mA output change the onboard to 13 KOhms.
For 1000mA output change the onboard to 18.5 KOhms.

Try the other side of the external potentiometer. One wire to the side, one to the wiper. It sounds like the resistance is too high through the external pot.

You can check by removing the external pot and checking it on a meter. Max resistance should be 50K ohms minimum should be < 1 ohm.

Don't adjust the onboard pot too may times. It has a useful life of about 20 sweeps.

Also, be very careful not to lose a connection to the LED with the Fatman powered up.

Edit: Thinking about it now, it sounds like you're adjusting the onboard pot the wrong way. Set the onboard pot to about 10K ohms with the external pot set to MAXIMUM resistance (should be about 50K ohms). Now all the current is flowing through the onboard pot. Now when you reduce the resistance on the external pot, some current will begin to bypass the onboard pot and flow through the external pot.

The exact directions to hook up the pot areon the fatman tech page at http://taskled.com

Sounds like you made the simple mistake of putting on the external resistor after already setting the onboard pot.. you need to have the external pot attached when setting the resistor onboard .. also make sure you have the external pot wired the right way so that resistance increases exponentially as you turn the pot or you won't get the proper scaling of brightness.

-awr

I think that is the problem. I had already realized that, but the problem to me seems that the onboard trimpot on the fatman board is stuck. I can't seem to rotate it past a certain point. Any ideas?

A great idea is to email George at TaskLED. He is incredibly helpful, knowledgeable, friendly, and responds quickly (usually within hours) to technical issues regarding his products. His customer service is outstanding.