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How do I reduce a Lithium Polymer battery voltage? Answered

I have a 7.4V lithium polymer battery (http://www.all-battery.com/74volt-6000mahli-polypackwithpcb31185.aspx) and an 8.4V smart charger (http://www.all-battery.com/universalsmartchargerforli-ionpolymerbatterypack37v-148v1-4cells.aspx).

The issue is that I need to power a device that needs 6V. If I put a voltage regulator in line with the battery leads I'm sure it'll work, but then how do I charge the battery with that charger, as the regulator will also reduce the 8.4V the battery needs for charging? Maybe by introducing some kind of "bare metal tap" upstream of the regulator, so when I plug in the charger it bypasses the regulator and wires straight to the battery? (see the attached illustration) Would this work? Or should I do something else?



3 years ago

Your schematic looks fine, just connect up or wire the charger to the battery as you would normally would, making sure polarity is correct. A Buck converter can be used to step down the voltage efficiently. Get one with a low dropout voltage so that you can utilize the most capacity of the battery. You can safely discharge a LiPo battery to 3V/cell, so for a 2S battery, thats 6V. Although a regulator is supposed to output 6V, the input voltage usually has to be a few volts higher.)

What's wrong with having 2 connectors? One for charging, and one for the 6V output. You may even want to include a 5V buck converter to output 5V to a USB plug to charge phones!

If you really want to use one plug to charge and discharge, I suppose you can make up some circuit using diodes, one directly on the output of the regulator with the cathode going towards the output, and another diode bridging between the positive of the battery and the positive output, and the cathode on that one will be on the positive output of the LiPo. I do not like that solution, although it means only one plug, you cannot charge and discharge the battery at the same time, and it is more parts, more room for failure.

As long as that charger is designed for that cell config/capacity , ie 2 para or 2 series etc, then it should be good.

That's right, you tap before the regulator