Problem Description:

When charging low-cost lithium batteries, the IC shuts down and indicates Over Voltage Protection (OVP) error.

Background:

The IC2000 and IC3000 inverter chargers use low-frequency electronics to convert the DC power stored within a battery (direct current, 12V) into AC power (alternating current, 110-120V) that can be used to run your AC powered equipment. They also convert AC power (when available) to DC power to charge the batteries back up again.

Low-frequency inverters hold two important advantages over high-frequency inverters: peak power capacity and reliability. The IC2000 and IC3000 can output more than their rated power level for several seconds while high frequency inverters can do the same for a small fraction of a second. This is useful when starting up loads that require an initial surge of power (like air conditioners). The IC2000 and IC3000 operate using powerful transformers which are sturdier and thus more reliable than a high-frequency inverters’ transistors which use electronic switching and are more vulnerable to damage, especially at high power levels.

Even though there are distinct advantages to low frequency inverters, they have one characteristic that can cause problems with some lower cost lithium batteries: they have a significant ripple voltage riding on the DC output when charging.

The waveform below is a typical 110V AC waveform that the IC would see on its input from shore power or a generator. The red portion of the waveform has a positive voltage and then it swings down to the blue portion of the waveform that is negative.



This waveform is then rectified, which moves the negative blue portion of the waveform to the positive side as shown in the graph below.



Finally, the rectified waveform is filtered using large capacitors to create a DC voltage that charges the battery as shown below. However, the capacitors don’t completely remove all of AC component of the waveform so there is still some “ripple” voltage as shown in the image. The size of the capacitor determines the amplitude of the ripple voltage.


The IC was designed to work with lead acid-based batteries, and it works great for them. It works great with many brands of lithium batteries, too, but not all of them. The reason is lithium batteries have a battery management system (BMS) built in to protect the battery and make it safe. The BMS uses transistors to disconnect the batteries’ terminals during fault conditions to protect the battery and prevent it from exploding. If the transistors are high quality and the BMS has been designed to be robust, there shouldn’t be any problems using it with the IC2000 or IC3000. However, some low-cost lithium batteries use low cost components that can’t handle the brief higher voltages that the ripple presents. As a result, these low-cost batteries will disconnect the batteries terminals to prevent damage to the transistors that are needed to keep the battery safe.

Disconnecting the battery while the charger is charging creates a problem. Since there is nowhere for current to go anymore the large capacitors used to filter the output charge up really fast and this results in a voltage spike. The inverter has a built-in protection mechanism to prevent large voltages from damaging it, so it protects itself and indicates an over voltage protection error (OVP).

Resolution:

There is a way to change the hardware of the IC to smooth out the ripple voltage, but this will increase the cost and size of the unit significantly. The best resolution is to return your batteries and purchase higher quality batteries that can handle the ripple voltage. Our GP-LIFEPO4-100 and GP-LIFEPO4-250 batteries are a quality product and they have been designed to be 100% compatible with our 2000-watt and 3000-watt inverter chargers.