MOM is short for Miserable Old Man.
Would either of these boards work for driving an MT-G2 led? I am thinking of 8 Eneloop NiMH for power.
They look like the same board?
It would fit in a Maglite body. I thought about one of these and possibly some sort of Trim Pot? somehow??
Questions are from the guy who still says "What's an Ohm??"
How much current do you want?
I would say this will work but it is hard to say how well, order a module and report back your results…
The only thing which I am wondering about is that you will have a constant voltage and no constant current, so if the forward voltage changes the led current will change too…and of course how much current this small thing can provide…
I'm certainly no electronics guru, but I would concur with Werner regarding the desired current. Those drivers don't have any specs as to how much current they can deliver. They will be able to handle the voltatge, but if they only deliver 1A max, your not going to have an impressive output from the MT-G2.
Have you seen this post regarding MT-G2 driver test results? Some may be more than what you want to spend on a driver.
The 2nd one
you’ve posted will be better, it’s more efficient and has more lower voltage range to play with which might be good as the 8 eny is only giving 11.52v (1.44v each cell after a break in cycle)
Wow, those are small.
These are buck converters. Don’t need anything else, the pot is built in. Current ability WAS specified, it’s 2A continuous/ 3A burst.
Since you’re using 9.6V source, I presume you want to use a 6V MTG2? Then these will work, if you’re willing to limit your output to 2A. That’s 12W of power, about the same as slightly overdriven XM-L.
I do hope you give this a try though, just to see how it turns out.
Both are constant voltage regulators. You would need to set voltage to get current you want and this will change as LED heats up (your current will go up at the same voltage, LED will heat more, current will go up even more and you may blow a LED - this is thermal runaway).
You want constant current regulator.
Something like that
http://www.ebay.com/itm/DC-5A-0-8V-30V-Constant-Current-Voltage-LED-Driver-Step-Down-Power-Module-new-/121108371961?pt=LH_DefaultDomain_0&hash=item1c329f19f9
You would set voltage little above Vf of LED, for 6V MT-G2 let say 7V. It will be upper limit and regulator will not go above that. Then set current to required (3A) and you good. Note that both are limits so if LED requires more than set voltage to reach set current it will not get yhat current. You need to dial up a voltage little.
MTG2 won’t blow at 3A, and that’s the max current the converter will give. Supposedly, at least.
Yes, your linked item is the better choice, but it’s comparatively HUGE, remember this needs to go into a flashlight.
Yes MT-G2 will not blow at 3A. In that particular case converter probably will blow before LED.
But converter is rated 3A, it does not mean it will not try to go higher if forced (by LED Vf in this case, LED will still suck more and more current when heating up with set output voltage from converter).
LED may be used with constant voltage driver but there is a risk of thermal runaway and it has to be taken into account (e.g., ensure good heatsink and do not push too hard). My guess is just that one does not get MT-G2 to run it at half speed :-), may not be a case maybe OP is after high efficiency.
I linked it as an example not as solution in that particular case.
The MT-G2 in my K3 is pulling 5.79A with a Vf of 6.72. It’s getting this through 2 18650 cells that are providing 8.07V under load. The 5.79A is what the emitter is actually getting, tail amperage is 4.82A.
Output current in the second one lists 3A max. The other one states 3A if heat sinked. How would the voltage increase, if it's trim pot adjustable and if it really is 3A max? Would it not stay "close to 3A and 6V" until the batteries ran down enough to be too low on the input voltage?
Yes, the better drivers are too much for me. $15 up to $40 if you go with a taskled. I just want to find something cheap that I can use 8 NiMH in series with and get 3 amps or so. I don’t care to push the led with a lot of amps.
With LED Vf and current are related (as any diode for that matter) and one is forced by another.
With constant current driver you push set current to the LED. This forces particular voltage on LED. Let say for example 3A to MT-G2 results in 6.5V on LED. Now when LED heats up Vf (forward voltage at particular current) will go down, to let say 6.3V or whatever. It does not matter since you till have 3A because of constant current driver.
With constant voltage driver and the same LED you set 6.5V output, you will get 3A when LED is cool. It heats up and Vf goes down, but driver still suplies 6.5V. Now problem is that 6.5V to hot LED (because its lower Vf now) forces higher current, curve is expotential so it may be much higher, let say 4A. This causes LED to heat up even more and cycle repeats, current raises even further. At some point it will either stabilize or run away.
You don’t want second thing to happen.
So, to give a go one of drivers you listed try slow. Connect batteries and LED (on heatsink you intend to use or better already in light), start with low voltage, 6V or so, measure current thru the LED. *Give it a time to heat up *and see if current is where you want to be. If it is lower than you want dial voltage up a little. Go slow, remember about expotential relation between current and voltage.
I've used those LM2596 boards with LEDs, including MTG2, in desk lamps and bench testing. The boards will do a MAX of 3.5-3.6A with the voltage pot cranked to the max, that's the current limit of the components and isn't related to the 2A/3A mentioned in the sales data.
The onboard pots are fragile, they'll wear out if you use them regularly like a dimmer for a desk lamp. Replace the tiny onboard pot with a remote mounted normal dimmer/volume style pot. I think the original is 10k.
The Schottky diode on both boards listed by OL are a SS-34. There only rated at 3 amps. Even so I have pushed them a little further before but have no idea what the magic smoke release current is.
So what about only using the pot for setting the voltage and having an external pot that could use a knob, (A knob that would be on the outside of the body), as a dimmer. Would there be some type of dimmer available like that and what are the negatives of using it?
The variable brightness comes from turning the external pot (dimmer). Match a same value linear pot to the same pot on the board. Take off the small pot on the board that controls voltage and wire it to a external pot. When you turn the pot it varies the voltage with the vf of the led varies the current and controls brightness.
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I buy my small stuff at this place Linear - Rotary Potentiometer - Potentiometer / Variable Resistors
They have a US warehouse in Colorado. I have received my stuff in as little as 4-days from ordering. It could depend on what you order though, could come from the Bangkok, Thailand warehouse. 
Not affiliated, just thought I would share.
Slightly OT: Is there a guide for dummies that shows how to use either a fixed resistor or a second pot to limit the output from the main pot? I fought and cussed and pulled my hair out a while back trying to rig something to do that but never could get there.
For example on my desk/keyboard lamp, the external pot turned to full clockwise is too much current, 3.5A, I need the max to be around 2A. I thought it would be 'simple' (ha ha!) to use two pots in series, but no joy. Then tried using one of the pots in variable resistor mode inline with the center (output) pin of the main pot, no worky again. Got frustrated and gave up, using it now in 'just remember not to turn the knob too far' mode.
Digikey is also a good supplier those those types of parts (LEDs too). Reasonably priced, cheap and fast shipping.
I have also ordered a few hard to find things from digi-key. There service is A+.
Tayada doesn’t have the variety of digi-key but if your looking for common things like resistor and capacitors its hard to beat 10 cents for 10 resistors or capacitors, especially compared to radio shack. I usually place a big order of various components for $25 bucks or so. I still don’t know how they can make money with selling me so many things in a order that have to be individually pulled and packaged. For $25 bucks I end up with a whole box full of stuff, well over a hundred different items and close to two thousand individually items.
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Tayada was just a suggestion to where to find pots cheap. Didn’t intend to derail the thread into where to buy electronic parts. No flame intended Hill, My post was no different than yours. We need to try to get back on OL’s topic. Me :zipper_mouth_face:
