LI-ION battery and maxflex2 settings question.

[trout]

Hi
I have a question and have tried searching and not found what I need

I am using the maxflex2 for the first time . it is driving 6 cree R2 leds from a 4 cell 15 v li ion 2400 mah battery pack
the maxflex can give warnings for
medium voltage
low voltage
and also cut off at very low voltage

I know my pack is protected from over charge and discharge

I just wanted to find out what voltages to set the maxflex to
for the 2 warnings and the cutoff setting .

Cheers Trout

 

[SilverFox]

Hello Trout,

The voltage under load is going to vary depending on the load. Do you happen to know the current draw of your set up?

If, for example, you are drawing 2 amps, a medium voltage that corresponded to about 50% of the capacity of the cell would be about 3.5 volts per cell. If you set the low voltage to trigger when you have around 25% left, you would use around 3.4 volts per cell for that setting. An ideal cut off voltage would be 3.2 volts per cell, but you could probably run it all the way down to 3.0 volts per cell and still get decent life from your battery pack.

You should also figure out a way to balance the cells in your pack. The protection in the cells will keep them from blowing up, but they will get out of balance and then you will suffer from poor performance.

Tom

 

[trout]

Thanks silver fox.
I am not sure how to know the current draw . and cannot get inside the light easliy to measure anything.

I will also be using the dimming settings of the maxflex so would this
have an effect on the current draw .

would I be ok using your figures as a good baseline for my settings.

cheers chris

 

[SilverFox]

Hello Chris,

That's easy to figure out. Set your light up on the test bench and do a runtime test. If you have 2000 mAh cells and your light runs for 1 hour, it is drawing 2 amps.

The numbers I gave you will work very well for a 2 amp draw on LG 2400 mAh cells. Different cells may show different voltages under load, but the numbers should still be in the "ball park." Different loads are where you run into issues.

At higher loads, the voltage drops more, and you can safely go to a lower voltage cut off. Under light loads the voltage stays higher and discharging to the safe high load voltage may over discharge the cell under light loads.

The ideal method would be to have the voltage set points adjusted to the current draw the light is using. If you had 3 settings, you would adjust the set points according to which setting you are currently using. This would require some programing, so it is probably not feasible.

Next, you will have to decide how the light is going to be mostly used. If you set the voltage points for high current draw, you run a risk of reducing the cycle life of your batteries. If you set the voltage points for low current draw, you will end up with reduced run time at higher settings. You will have to decide what is more important to you.

Tom

 

[trout]

Please forgive me for what may seem like dumb questions .

does the current draw equate to the settings of the maxflex driver .

because I will be mostly using the 1000ma setting which has a hi and low sub setting where hi is 1000ma and not sure what low is .

or if longer runtimes are needed then I will use 500ma or 750 ma

cheers chris

 

[SilverFox]

Hello Chris,

I believe it is a little higher. The settings are for the output of the driver. The driver itself will use a little power.

Tom

 

[ifor powell]

Hi Chris,

I measured this just now from a similar setup 6 q5's in may case but also a maxflex 2. Battery was half way empty initaly (15.45v) and is twice what you have size wise being 2*4 18650. Just a cheap meter. The led curent reading were from before when I initaly got the maxflex2.

Here are the diferent levels and the voltage close to the battery and the batery curent and led curent. I did the 1200 first then 1000 you will see that the inital voltage has broped a bit in between..

1200ma max
L1 15.40, 0.06, 0.04
L2 15.28, 0.33, 0.19
L3 15.13, 0.64, 0.41
L4 14.85, 1.18, 0.73
L5 14.24, 2.00, 1.15

1000ma max

L1 15.35, 0.06, 0.04
L2 15.24, 0.31, 0.19
L3 15.12, 0.55, 0.34
L4 14.94, 0.95, 0.57
L5 14.57, 1.68, 1.01

I have not bothered with the intermediate levels yet just the cutoff which I set to 13v eg 3.25 per cell. In practice the cell's will be lower because the maxflex measures it's input and you will be loosing on the cabeling.

With the borrowed usb cabeling you have on your setup this loss may be quite big if the cable run is any length. You should try and measure it...

If I was going to use the intermediate levels I would just try 14v and 15v initaly, then give it a test run on the bench and see where the warnings and the cutoff happen.

Ifor

 

[trout]

Ta ifor
I will try those settings and see how long I get

trout