# question

## How to calculate low-power settings

Can someone share the math for calculating these settings:

• DC input low-shutdown (volts):
• DC input low restart (volts):
• DC input low-alarm (volts):

Thanks

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Murray van Graan answered ·

Hi @tlandfried. Those values are determined by your battery, so you’ll need the battery spec sheet for this. For example, let’s say you’re using a Lifepo4 battery. In a 48V setup it would have 16 x 3,2V cells, to make a battery with nominal voltage of 51,2V. (Some manufacturers use 15 cells but that’s besides the point here) The DC input low shutdown is to protect the battery from damage when discharging, for this example you don’t want to discharge a lifepo4 below minimum 3V really, so that makes the low shut down 48V. Your input low restart value, is the voltage that the inverter would turn back on after shutting down due to low battery voltage. This is generally a little above the nominal voltage, to ensure the battery has a higher SOC than when it shut down. In this case, around 3,3V per cell would suffice, 52,8V.

The dc input low alarm is when the inverter would start warning you about a low battery situation, and it is before you reach the low shut down voltage. In this case I would make it a little higher than the shut off voltage, say between 50 and 51 volts.

This is just a theoretical example, and your battery data sheet should contain all the information to determine the correct values for your battery bank

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