BU-406: Battery as a Buffer

Find out how to combine the battery and power supply to meet peak requirements.

The main purpose of a stationary battery is to provide power during power outage. Battery banks are also designed to provide extra power during high-traffic periods when the AC power supply does not have sufficient capacity to feed the system. In this case, the battery acts as a buffer similar to the battery in a hybrid car that assists in acceleration.

Cellular repeater towers are an example where the backup battery serves as a buffer. The batteries get fully charged during off-peak periods and go into discharge mode to assist the AC power supply during the peak times.

When relying on the battery as buffer, make certain that the battery has enough time to charge between peak periods. The net charge must always be greater than what was drawn from the battery. Avoid deep discharges as this would wear down the battery prematurely. Note that stationary and starter batteries are not made for deep cycling. If periodic cycling is needed, choose a deep-cycle battery. 

Last updated 2016-02-23


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Comments

On May 30, 2011 at 10:03am
Alessio Sangalli wrote:

Hi! I would need exactly this for my hobby. If I use a 60Ah 12V SLA battery, are you suggesting I could simply put the power supply, the battery and the load in parallel? What voltage for the PSU? Should I compensate the voltage for the temperature (ambient T will vary between 5 and 25C) and/or do some sort of current limitation? I will implement an under-voltage cut-off circuit.

On May 30, 2012 at 12:05am
Hassan wrote:

I am doing a DC back-up system where the battery has been dropped in // to the load for standby application.
Question:
  What stops the batteries from absorbing all the available current from the AC/DC power supply after an extended power outage.

On December 4, 2015 at 11:41pm
dave wrote:

Quote: “A starter battery in a vehicle works in a similar way. While the motor is on idle at a traffic light, the battery complements the power to run the lights, windshield wipers and other accessories. Driving at highway speed replenishes the borrowed power.”

While this “seems” like a sensible thing to state, it’s not true.  Alternators and their pulley ratios (for a sweet spot on the climbing RPM vs current curve) are selected such that you could park your car with the lights, wipers and such on, and it would run that way till it was out of gas. 

This is done for practical reasons, for example if you were stuck in traffic for hours on a cold snowy day, you’d *need* your lights, wipers, heater blower, defrosters, etc to keep working.  A vehicle that couldn’t do that would be deemed a lemon by design.