Do not use PWM solar charge controller to your Lithium Battery

2021-04-15

More and more camper vans are installed with the Lithium battery in nowadays. This battery has a good performance of charge retention, life cycle and large depth of discharge. With the light weight and large capacity, the appliances are all greatly powered by the high power.

Most lithium batteries have the BMS to prevent them from being overcharged, low voltage, over current or over temperature, etc. Therefore selecting a correct charge kit is important for the whole mobile power system.

Here is our point: PWM SOLAR CHARGER IS NOT A GOOD OPTION FOR LITHIUM BATTERY. 

PWM solar charge controller cannot provide the charge to the lithium battery? No actually they can. And even charge the battery to be full. But the problem is the “fully charged”. Lithium battery BMS will cut out the charge circuit to stop the redundant power input. At this moment, for the PWM charge controller there only PV module is connected. Without the battery being connected the PWM charge controller will be easily burnt, all the inside MOSFET will be impacted by the PV power input without any protection. That is the reason why the PWM controller dealer will tell you “Connect the battery first then wire the PV into it.” Without battery working as the buffer, PWM cannot take over the power from the solar panels.

Even the PWM charge controller will not get burnt, when you have a test of the DC output voltage on the controller, you will find the output voltage is much higher than it should give and very close to the PV input voltage. If the PV input voltage is 26.0V, when the 12V lithium battery is fully charged and cut out the charge input circuit, the PWM output voltage will go up rapidly to be around 23~25VDC. This voltage will kill your some 12V loads like the LED, or freezer, and the power inverter.

Watch this video:

MPPT charge controllers has the different circuit and different control technology. Therefore it will limit the output voltage at a reasonable level when the lithium battery is disconnected. Watch this video:

Some cheap MPPT controllers are also able to make the control of the output voltage, but the voltage will go up quickly and drop back to the correct voltage level within around 10 secs. 10secs is too long for some working loads and the inverters. 

The good MPPT should act immediately when it recognize the disconnection with battery and rapidly limit the output voltage under 14.4V(for 12V system). Popsail MPPT technology will fast(within 1sec) act to limit the output voltage when it lose connection with lithium battery. 

We charge your battery, and protect them.