It's not in the original post but shows up here ...

https://forum.dronebotworkshop.com/postid/37469/

Working on a DIY project to charge Multiple battery's Lawnmower, Motorcycle etc...  The problem I am Having is the Serial.print only refreshes after relays run through it's loop. board  UNO Rev3 looking it my code Serial.print should refresh "printDelay = 50; the relays are batteryDetectTime = 300; my concept: in a if Control Structure the UNO Rev3 will set relay HIGH a acs712 sensor will detect if battery is connected if "true" it will charge battery if "false" it will go to next relay and I want to print status to a screen (type unknown at this time) I can't have screen refreshing every four min if four battery's are connected

Can  someone point me in the right direction?

He did state that the setup was essentially to replace manually using the charger one at a time for his four batteries. It would make sense to read up about charging lead acid batteries to work out the correct protocol even if it was being done manually using that particular charger.

The modern type of batteries used in hand tools and electric scooters and so on all use electronics to prevent damage or fires unless cheap rubbish is purchased as they have caught alight when left on a charger often resulting in burning down a house if left inside! With my hand drill the electronics is in the battery itself to prevent the voltage dropping too far during use and when plugged into the wall for charging.

The best solution would be to 'read' the state of charge then you could use that to know when to turn a charger off. 

If there is a light that indicates FULL, mounting a detector above it would be one crude solution, better would be to tap into the circuit that drives the light. I would still build in some sort of delay, say 2 weeks to a month between connecting the charger.

Since you will be connecting and disconnecting DC leads possibly under heavy load, consider using Solid State Relays or MOSFET's rather than mechanical relays as arcing may be a problem.

Good luck.

Hope you don't mind but I can't help dabbling in the problem :)

Here is how I turn each relay (actually a LED in my setup test) one at a time.

My LEDs are actually connected to a Mega so the pin numbers are not the ones you are using.

int relay = {34, 35, 36, 37};  // LED PINS


unsigned long previousTime;
unsigned long currentTime;


int currentRelay = 0;


void setup() {
  Serial.begin(115200);
  // initialize pin numbers
  for (int i = 0; i<4; i++){
    pinMode(relay,OUTPUT);
  }

  previousTime = millis();
  digitalWrite(currentRelay,HIGH);  // turn on first relay

}


void loop() {

  unsigned long currentTime = millis();


  if (currentTime - previousTime > 3000) {

    previousTime = millis();
    digitalWrite(relay, LOW);  // turn off current LED
    currentRelay = currentRelay + 1;  // next relay
    if (currentRelay > 3){
      currentRelay = 0;               // reset to zero
    }

    digitalWrite(relay,HIGH);  // turn on next LED

  }
  
}

I'm currently rewriting the sketch trying to solve one problem at a time.

robotBuilder  has a diagram of my project