# Thread: boost driver runtime calculation?

1. ## boost driver runtime calculation?

I'm having a total brainfart this afternoon, and can't remember how to calculate runtime for a boost driver situation.

Can someone show me the math?

If you want to use my numbers:

6 XP-G2 in series - vf= 19.2v
driver running 1.5A

assume for now battery is 11.1v, 2200mah.

I'm seeing output power as 28.8watts, (19.2vf*1.5A=28.8W)

Input power is Output/efficiency - we'll assume 90%, so 28.8/.90=32W.

this is where I get stuck, and don't know the next step to convert it into a runtime guesstimate.

any help is appreciated.

2. Do I take my 32W of input, divide it by my 11.1v battery to give the amp draw from the driver?

32/11.1=2.88A

I have a 2.2A battery, so 2.2Ah/2.88A=.76h 60min/.76= 45.6min?

3. Your battery has if I am working it out right
11.1 v * 2.4 ah = 24.42 watts of energy

your using 32 watts so less than an hour runtime

4. Yeah - I just realized that the LED_PRO calculator does all the math properly for this too. for some reason I just thought Boost drivers included some technical majik that made the normal runtime calcs not predict it properly.

5. Keep in mind, that discharge curve is not flat and linear. Once the voltage starts dropping, the current rises and batteries drain rapidly. So expect even less run time than that calculator says.

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