Flexdrive Power Consumption?

[Meatball]

I figure that since the flexdrive is not a linear driver, it's power consumption will change over time considering the battery's voltage will drop as the driver tries to regulate a higher voltage and current. This stands in opposition to linear drivers which suck the same amount of current away from the batteries until the batteries cannot hold a sufficient voltage.

I have a BDR-205 12X BR build with a flexdrive feeding 305ma to the diode. I am powering the driver with a single 3.6V (4.2V at full charge) Trustfire RCR123 rated for 880mah.

So considering the all of this, along with the voltage drop across the diode... 5.5V?
And that the flexdrive will turn off at 2.5-2.6V..

How do I calculate battery life in this build? How much longer will a 1400mah 18650 power the flexdrive? Is there a function I can plug all of this into?

I think that a ma/hours graph of the flexdrive's current consumption would help a lot... would it be an exponential function?

Any thoughts or advice is much appreciated...

-Tyler

 

[jayrob]

You could easily test the current draw at full charge, and then test the current draw at different charge levels to get an idea of run time vs capacity.

But remember that stated capacity is not always very accurate.

As the battery drains, the driver will demand more and more current to continue boosting voltage that the diode is asking for. Using current to boost voltage.

But the FlexDrive will also efficiently use every bit of battery capacity available before it drops out of regulation. So it is the most efficient driver that we have at easy availability.

If your battery had 600mAh's capacity, it would be a fair guess that your 12X build at 305mA's would have at least an hour of run time before needing a recharge...

 

[Meatball]

I just placed a one ohm resistor in series between the battery-, and the negative case. I read the voltage going through, and it was about 630ma. This is what is changing over time as the battery drains... like you said. Right?

One curious thing happened though, the flexdrive made a high frequency whine when I had it connected with the one ohm resistor... weird.

I'd like to figure out how fast the current consumption will change, and how it will change... any ideas? Thanks for the help!

-Tyler

 

[jayrob]

I don't think you need the resistor, just set your meter to read mA's, and have the plug in the 10A input (not 400mA).

It will read the mA's directly...

First check the voltage of the battery. Because at full charge, the current draw will be the least. You will most likely see the reading going up. Because as the laser runs, the battery is draining. And the driver will be asking for more current to keep boosting voltage...

I just checked my 8X current draw with a slightly less than full charge RCR123 that read 4.03 volts.

It is set at 275mA's and draws 472mA's from the RCR123 charged at 4.03 volts.

One other thing. I would recommend an AW battery for high current demand builds. I found that doing test comparisons with AW vs Ultrafire in P7 flashlight mods, that there is a huge difference in available current, depending on battery brand. You can get AW's at lighthound.com

 

[Meatball]

Lets see... at 3.51V, it was pulling 580ma.

With a fresh battery at 4.19V, it's pulling 470ma.

I think that the batteries ran dry at about 3.4V... they must not have had much capacitance left at that voltage. I put my 3.5V cell back in... the one I just tested with. And it died about one minute of more use. There is no more voltage potential across the thing at all! Wow that drained quickly!

The current consumption of the flexdrive MUST be exponential then!
But by how much is the question?

Thanks for the recommendation! I'll keep those in mind, because I didn't know what to expect at from the ultrafires.. other than they were cheap. I've never heard of AW, but the prices at the website you linked me seem quite reasonable.. wow and their 18650s are rated at 2600mah! It looks like they have spacers as well! Darn it Jay, it looks like I'll be spending some more cash tonight! lol

Is Dr. Lava still active on LPF? He built the darned circuit, maybe he can help a bit..

 

[jayrob]

You can PM him, but it mostly is going to depend on the quality of the battery...

Read up on AW. Especially when it comes to something that has a high current demand. They are the best Li-Ion's...