In a Maglite build with 5~7A of tailcap current. How does having a Fet Driver alleviate the load off the switch?

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Bigchelis
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In a Maglite build with 5~7A of tailcap current. How does having a Fet Driver alleviate the load off the switch?

Hi all,
Newbie type question here. I have several Maglites running MTG2’s. Some have Fet DD Drivers and work great.

I just want to understand why or how does having a Driver allow the Maglite stock switch to survive a bit longer with my high current builds.

BTW: Big thanks to MTNelectronics for the FET Drivers and MTG2’s and of course all of you for helping me as I figure things out. OldLumens especially you!

RMM
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The FET driver should increase the load on the stock switch when compared to most 7135 drivers.  What decreases it is to go to a momentary firmware, where the FET acts as the only switch and the power remains connected to the driver (stock power switch is eliminated).  The stock switch is replaced by a small momentary switch which tells the driver to turn on.  

Mountain Electronics : batteries, Noctigon, and much more! What's new? 

Bigchelis
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RMM wrote:

The FET driver should increase the load on the stock switch when compared to most 7135 drivers.  What decreases it is to go to a momentary firmware, where the FET acts as the only switch and the power remains connected to the driver (stock power switch is eliminated).  The stock switch is replaced by a small momentary switch which tells the driver to turn on.  

That explains it very well. Thank you.

Do you know how well the Fet Drivers need to be heatsinked? My heatsinks don’t have provisions to mount them flush on bottom of heatsink and loosely placed between switch and heatsink.

I saw thermal foam pads on some builds, but where to buy that?

Thank you,
bigC

RMM
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Bigchelis wrote:
RMM wrote:

The FET driver should increase the load on the stock switch when compared to most 7135 drivers.  What decreases it is to go to a momentary firmware, where the FET acts as the only switch and the power remains connected to the driver (stock power switch is eliminated).  The stock switch is replaced by a small momentary switch which tells the driver to turn on.  

That explains it very well. Thank you. Do you know how well the Fet Drivers need to be heatsinked? My heatsinks don't have provisions to mount them flush on bottom of heatsink and loosely placed between switch and heatsink. I saw thermal foam pads on some builds, but where to buy that? Thank you, bigC

They don't need much, if any, heatsinking.  The FET resistance is so low that very little heat is generated in the driver.  Our typical ~6 milliohm FET, even if driven with hot cells and an MT-G2 at 10A, only generates around 0.5 watts worth of heat in the driver, which isn't enough to cause any problems since the rest of the light will overheat with an MT-G2 at 10A long before the driver does.  

Mountain Electronics : batteries, Noctigon, and much more! What's new? 

kyfishguy
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Bigchelis,

  There is no reason to send all that current through your mag switch when using either nanjg or the BLFDD FET based drivers.  Just drill a hole from front to back through the mag switch body (avoiding all the mechanical bits) and connect a wire from the positive battery contact of the switch, through the hole you just drilled, and then to LED positive.  Then wire the rest of the switch and driver as you have been doing minus the wire from driver positive to the LED positive.  The emitter now gets it's positive directly from the battery and the only current through the switch is what the driver needs to play its part as a switching and regulating mechanism.  It's really just a way of doing what Richard said while using the stock switch.  Sort of.

Just my 2 cents,

Brian

Bigchelis
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Brian,
That is a simple yet efficient idea and one that I will explore on 100% direct drive builds. With the FET Switch it seems like the driver is great even at 10A.

Love this Fet DD driver and the last one I had many years ago was the exact same FET DD driver but just a single mode that Mr. Lamdalights built for me. That particular SST-90 Tripple was pulling north of 35A at the tailcap…..crazy to think I was pushing those NiMH D cells that hard yet they perform like champs.

bigC

wight
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Bigchelis wrote:
Brian,
That is a simple yet efficient idea and one that I will explore on 100% direct drive builds. With the FET Switch it seems like the driver is great even at 10A.

Love this Fet DD driver and the last one I had many years ago was the exact same FET DD driver but just a single mode that Mr. Lamdalights built for me. That particular SST-90 Tripple was pulling north of 35A at the tailcap…..crazy to think I was pushing those NiMH D cells that hard yet they perform like champs.

bigC

I’m pretty confused by the things you say here. Like RMM said above, just installing an FET driver without bypassing the switch for LED+ (like kyfishguy suggested) should be hard on the stock Maglite switch.

Still fine, still on a break. One day I’ll catch up with you folks! previous wight catchup Wink
list of my drivers & variants (A17DD, FET+1 stuff, WIP stuff, etc)