1200mAh lipoly battery Calculation

[lesliewong]

I was trying to calculate the recharge capacity of the Lithium ion polymer 3.7v, 2600mAh battery and was using the calculations in the MintyBoost user manual – choosing batteries page (http://www.ladyada.net/make/mintyboost/power.htm), as a guide. I wonder if there is an error in the output calculation line for the 1200 mAh lipoly battery in the “How many recharges will I get?” section.

If the capacity calculation is correct with:

MintyBoost mWh = 3.7V * 1200mAh * 100% = 4440 mWh input

The calculation for the milliAmp hours the mintyboost will output at 5V seems to use the battery capacity for two Sanyo AA NiMH 2700 mAh batteries:

Output mAh @ 5V = 5184mWh / 5 * 80% = 710 mAh output

Shouldn’t the calculation be:

Output mAh @ 5V = 4440mWh / 5 * 100% = 888 mAh output?

Thanks.

[adafruit_support_bill]

Shouldn’t the calculation be:

Output mAh @ 5V = 4440mWh / 5 * 100% = 888 mAh output?

No. The multiplier is 80% to approximate the conversion efficiency.

It looks like some of the terms were copied from the Sanyo AA calculation. But the results are correct.
It should read:

MintyBoost mWh = 3.7V * 1200mAh * 100% = 4440 mWh input
Output mAh @ 5V = 4440mWh / 5 * 80% = 710 mAh output
# of iPhone 3G recharges = 710 mAh / 1200 mAh = 0.60

Thanks for pointing it out. We'll correct the tutorial.