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ArcticMyst Security by Avery

FMT Buck Driver testing

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Dec 27, 2011
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I am terribly behind on so many things right now, it is frankly embarrassing. This is one of those things. Tom has sent me several FMT drivers to test and I've had several problems on my end - finally I have one that I haven't killed and is ready to test... and I have finally gotten around to testing it today.

I'm open to suggestions from experts on oscilloscopes if there is anything I am doing wrong, but I have done a few of these now and this was very promising.

First, here is my setup... I have a custom built test load with some serious heat sinking with heat-sinked TO-220 8A diodes and a 60W 1% 1 ohm resistor + 80, -20ppm/°C resistor that is also highly heat-sinked.

I have selected three of the diodes for this test. I have a Tek TDS210 with a 82003 DMM attached to the output posts.

I have also attached at heat sink to the back side of the FMT driver for this test, although at ~500mA it never got warm.

I was using a mix of a cheapie trust/ultra/whatever-fire and a good AW IMR 14500 Li-Ion cell in series for 8.4V of output (edit: from the battery pack to the driver, or more commonly known as input) :p


Test Load by tsteele93, on Flickr

First the output, it seemed to be falling a bit as the batteries started to drain - these drivers seem to pull some serious current - I did not test that though.


Basic Output by tsteele93, on Flickr

Here is startup in DC mode - to show the startup spike - or lack thereof...


FMT startup by tsteele93, on Flickr

I set the baseline to the second line up from the bottom and the divisions are 100mV per line, so as to use as much of the screen as possible.

Virtually no spike on startup at all.

Next I took a picture of the the oscilloscope running with NO INPUT - just noise attached to the output pins of the test load with no input, in AC mode. So the DC is removed and we ignore any positive voltage. In this instance, there is NO voltage, so all we are seeing is the oscilloscope noise.


No Power - Oscilloscope Noise by tsteele93, on Flickr

Then I turned on the driver and waited for the scope to filter out the 500mV of positive voltage and just show the AC ripple... of which there is none. It looks just the same as when the driver is turned off. The only difference is that there is ~494mV of positive voltage which we aren't seeing here because of the AC setting on the scope.


FMT Driver turned on with 494mA current by tsteele93, on Flickr

These are for sale at cajunlasers.com (although I think the hurricane has things out of order for the time being and they seem like a very stable driver. You can contact Tom (aka FoulMist) here on the forums via PM for any questions you may have and there is a nice thread on his drivers in the forum as well.

I have no connection to these drivers, monetarily or otherwise, and I even paid for this driver that I tested - so full disclosure is that I have nothing to gain from any of this - just reporting my findings to the forum. And I would encourage anyone else with the resources to do the same.

I also would encourage anyone with any ideas of how I could do better, or anything I might have done wrong or other tests that you would like me to do - please let me know as I would like to be able to test any drivers I can test and report back to the forum.

Thanks for looking!
 
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Thanks Tom,

but I didn't understand the 8.4V output with the batteries??? Are you saying you put the driver's input to 8.4V o_O The max input should be 6V TOPS!
I hope you don't kill this one too :D

DTR is selling them at his shop too.
 
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My bad, I meant 8.4v of input. Just worded it poorly/wrong. Hmm, I am confused now. It does take two Li-ions as input, right? Otherwise it won't buck down to the proper voltage for the diode...

This seems to be working so far.

If I drive it with one Li-ion I won't have enough voltage to buck, correct? I better go read the manual again... :thinking:
 
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My bad, I meant 8.4v of input. Just worded it poorly/wrong. Hmm, I am confused now. It does take two Li-ions as input, right? Otherwise it won't buck down to the proper voltage for the diode...

This seems to be working so far.

If I drive it with one Li-ion I won't have enough voltage to buck, correct? I better go read the manual again... :thinking:

NO! what are you saying :D It is supposed to be run with only one battery! 2 batteries are going to kill it! I suspect your batteries are dropping the voltage to 6V somewhere or otherwise you would have instantly kill it!

1 Good li-ion 4.2V is working perfectly in buck mode for Reds whether LPC or Mitsibishi.
 
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Well heck, I assumed since this was a buck that it took two Li-ions.

Ok, so let me get this straight... This driver is meant for reds and it bucks from 4.2v?

What will and won't it drive? I've got to go back and re-read the thread on your driver. I assumed that with currents up to 1.9A that it was for blues too.

No wonder I keep killing them! :D

Ok, I just read the specs...

I was totally confused. I made the assumption that buck boost meant 2 Li-ions for buck, one for boost. I see now that I'm supposed to be running one Li-ion no matter what. I'll see if it is still alive tomorrow. I think it is...

If so, I'll go back and try it with one Li-ion and see what I get... Sorry for the confusion. That is what assuming does for me...
 
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Ok, looking over your instructions which I just skipped right over battery, thinking I already knew that part, I'll need to do a totally new thread tomorrow assuming I haven't killed it. This thread is useless and misleading now. I'm not sure if I'm just stupid or green (or hey, there's always both!), but I always think of buck as two Li-ions and boost as one Li-ion.

Clearly I've been quite confused! :(
 
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:D

yes you should try it again with 1li-ion.

look at it this way:

buck - higher to lower voltage
boost - lower to higher voltage

:D

It works for any diode in the 6V range but higher currents cannot be achieved at 6V output with 3.7V input you know :D there are some limitations. The max input current it can take is 4A. Even if you have the best batteries you won't get more than 4A draw. Depending on the input/output difference different currents are available.
 
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Mr.Steele you had me thinking that FM had a new driver, then after reading the thread and seeing all the hard work you did I wanted to reach out and grab ya and say NOOOoooo only one li-ion:crackup::beer:
 
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:D

yes you should try it again with 1li-ion.

look at it this way:

buck - higher to lower voltage
boost - lower to higher voltage

:D

It works for any diode in the 6V range but higher currents cannot be achieved at 6V output with 3.7V input you know :D there are some limitations. The max input current it can take is 4A. Even if you have the best batteries you won't get more than 4A draw. Depending on the input/output difference different currents are available.

I understand the basics of buck and boost, (I promise that I do, even if I seem slow sometimes!) I just assumed you were bucking from 8.4v down to whatever was needed from the diode.

That IS typical for many buck drivers, right?

I just overlooked that this was a one Li-ion ONLY driver.
 

Blord

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Bucking from higher voltage is sometimes a better idea. The current delivered by the batteries are much lower and the batteries don't have to struggle from high drain.

But it depends on the drivers sweetspot of operation.
 
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The IC limits are 6V input/output so you can't use 2 batteries in series unless they are 3V each when FULLY CHARGED.

that means ... you are better off to stick with one Li-Ion battery :D
 
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DTR

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The IC limits are 6V input/output so you can't use 2 batteries in series unless they are 3V each.

You also may want to qualify that statement as someone may think two 3V RCR123A's or similar will work not realizing the fully charged voltage is 3.6V each for a total of 7.2V fully charged.:beer:
 
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Are you saying you put the driver's input to 8.4V o_O

My bad, I meant 8.4v of input.

jiq3C.gif
 




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