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How to Correctly Use an External Low Voltage Alarm

Article by Hunter Wick

You may be wondering what a low voltage alarm (LVA for short) is. It is a small electronic device that measures the voltage of your RC's battery and emits a loud sound when the battery drops below a certain voltage. This is to let you know when it is time to stop running your LiPo down and it is time to charge it. This will prevent the cells from dropping too low and possibly becoming damaged. Sometimes, however, an external LVA is not needed.

Either (A) your RC's ESC may already have a built in LVC (low voltage cutoff) which will not allow the pack to be drained below a certain point or (B) you are simply not running LiPo batteries and have no need to monitor the pack's voltage. Regardless of whether you currently use LiPos or not, it's a good idea to learn how to use one of these little gadgets since LiPos are becoming more and more popular while many ESCs still don't come equipped with a LVA or LVC. The following will explain the basics of using an external LVA.

The first order of business is to decide the voltage that the alarm will sound at. Each LVA will vary slightly depending on the manufacturer, but most are very similar and exhibit options between 2.6v and 4v (of each cell). The voltage that you choose is the lowest voltage that the LVA will allow before sounding a loud buzzing noise, alerting you that the pack should not be drained any further. I recommend setting it at no lower than 3.3v or 3.4v per cell, as this will prevent the pack's voltage from dipping too far and damaging the cells. Keep in mind that the voltage level you are setting the LVA at is the voltage of each individual cell, not the entire pack. Programming the LVA will be dependent upon the manufacturer of your LVA. Most include directions so please refer to those.

Secondly, decide if you will be mounting the LVA on the car or if you will be simply using it to check the voltage of the pack periodically during the run. If you would like the LVA to be mounted on the car so it sounds when the pack is drained, you will want to mount it somewhere safe where it can also be plugged into the pack's balancing plug (as is in the picture). The other option is to keep it in your pocket and then stop the RC vehicle to test its battery during the run, by simply pulling the car over to the side and testing the voltage of the pack. If the alarm sounds once plugged in (make sure it's a continuous whine, not just a small beep when you plug it in) then you know that it's time to stop running that pack. If you do chose to go this route, then make sure you check the pack's voltage regularly (about every five to ten minutes).

battery low voltage alarm

Lastly, run the vehicle! I always like to give my LVA a nice test run with a voltage meter in hand so that I can assure myself that the new LVA is measuring voltage accurately. Note that the LVA can also be used as a small voltage meter when out at the field or track. To do this, simply turn off the alarm and read the voltage when it's plugged in. As you can see, a low voltage alarm can be an inexpensive tool, but also a very useful one. Just make sure that you use it properly and it will keep you and your expensive LiPo batteries safe.

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