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I have a LiPo 4S battery which the output should be 14.8v but it outputs, fully charged, 15.6v. The issue is that I have a voltage limit of 15v on a non-drone device that gathers data from sensors. So, my first thought would be to discharge it a bit until it drops below 15v. Does that make sense?

Also, I would like to know if that "over voltage" can be avoided?

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  • $\begingroup$ You may be interested in the term nominal voltage. Additionally, if the 15V is really the limit, you should take one of the below suggestions to regulate it, probably to the rated 12V or 9V. $\endgroup$ – chrylis -cautiouslyoptimistic- Aug 14 at 3:08
  • $\begingroup$ If you have to discharge a battery every time, that might be a bit too tedious. You should use a buck converter and stepdown the voltage. $\endgroup$ – DragonflyRobotics Aug 18 at 15:02
  • $\begingroup$ What about the noise of the dc-dc converter due to its high frequency? Can't that affect the digital circuits? $\endgroup$ – aripod Aug 19 at 7:13
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As others pointed out, 16.8 volt is what that battery should be reading (unless there is a specific chemical composition that makes that different).

Discharging a battery to use with your application is an anti-pattern, please avoid. Put a voltage regulator in there with the correct amp rating (draw) and you will be all set.

Pololu has some 1-2a 12v step-downs that cost $3-10. You can also go adjustable, here is a 9-30v 1 amp step up/down.

I know a few good ones on Amazon. Bottom line, this is a common part, easy to use, and I have had high reliability for nearly identical situations.

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A LiPo reaching a higher voltage than stated on the LiPo is quite normal and is not actually "over voltage." Generally, when talking about a LiPo battery cell, 3.7v is mentioned because that is the nominal voltage of the cells. However, when fully charged, a LiPo cell should reach 4.2v. So for a 4s LiPo, 14.8v would be considered the nominal voltage but when fully charged, a 4s LiPo can reach 16.8v.

Seeing as you have a 15v limit, there are a few options. Firstly, as you mentioned, you could discharge the 4S LiPo to 15v and this should work just fine, although you would be losing a significant part of the battery's capacity. Alternatively you could get a 3s LiPo (if that is sufficient voltage) because a 3s LiPo will not go above 15v. And lastly, if this is an option for your project, you could use a 15v power supply to deliver steady, consistent power.

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  • $\begingroup$ Thanks @Jacob B for the answer. A power supply would not be possible as it is to mount it on a drone while it flies. I thought of using an LDO like a 7812. However, that would dissipate a lot of power wasting energy from the battery, right? $\endgroup$ – aripod Aug 13 at 12:03
  • $\begingroup$ @aripod I wasn't sure if this was being mounted on a drone so I figured it was worth mentioning a power supply. I hadn't thought of an LDO. It is an interesting idea, but you could encounter problems with the voltage dropping too low. $\endgroup$ – Jacob B Aug 13 at 12:33
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It is probably easiest to charge the battery as normal, but reduce the voltage to your equipment.

You could just add a diode in line with the battery; this would introduce a voltage drop of about 0.7V, plus give you reverse-polarity protection. If you can't modify the sensor device, you could add it in the power cable. Just make sure the current rating is high enough for your device, and that you can remove it for charging!

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Another small, simple approach would be to add a 15V LDO (low drop out linear regulator) to your circuit. During the first part of operation, it would drop your voltage down to 15V at reduced efficiency, on the order of 88% to start out. Once your battery is discharged to 15V, it will drop the voltage only by its dropout voltage, so unlike a diode it won't be reducing your efficiency much during most of the discharge cycle. These are a few samples, but you can run your own search based on the exact voltage and current you want to use.

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