Renogy Charge Controller 40A blank screen

Welcome to the forum Lotus18,

Until you get the controller to boot (LCD displays some sort of status), disconnect the solar panels (this can "confuse" the charge controller, or even, in some cases, damage the controller if you have solar power, but no battery connection).

If you have a simple voltmeter or 12 volt test light, touch the terminal screws on the Vbatt terminals. Do you have 12 volts there? Is it the correct polarity (with test light, touch ground (negative) on battery and + on Vbatt for controller--Light should light).

Also, check the +12 volts on your battery too... If the battery is around 12.5 to 13.2 volts, it reasonably charged. If the battery voltage is below 10.5 volts, it is "dead" (not good) and the charge controller may not "boot" or charge the "dead" battery bank.

If you do not have +12 volts on Vbatt+ and ground on Vbatt-, then trace back wiring (and through fuse/circuit breaker/switch on + battery lead) back to the battery.

If you have +12 volts on the Vbatt of the controller (and correct polarity)--Then it sounds like the controller needs to be replaced.

Lead Acid batteries shoudl be aroiund 75% to 100% State of charge (below 75%, they need to be recharged "soon").

If you have Li Ion batteries--There is usually a BMS--Battery Management System--That is there to protect your "expensive" Li Ion batteries. It is possible for the BMS to shut down the battery terminals if there are problems (battery voltage too low, battery voltage too high, too high of discharge or charge current, battery too cold (or too hot)).... If your battery voltage is zero volts--You need to check the BMS and follow its debugging chart.

-Bill