Domestic consumer unit used for 12V

[ajlelectronics]

just been down to an urgent call at His Honour's narrowboat. "My fusebox has melted"...

I arrived to find a domestic consumer unit in use for the 12V distribution. The incomer had melted at the busbar connection and the switch had welded itself in the open position somehow. I bypassed it to give him some power back and started to tell him that it was totally the wrong thing to use on DC low Voltage. However, I got to thinking about it and wondered if I am just being pedantic.

The incomer switch is rated at 100A AC but not sure how that derates for DC.

I will be looking for something more suitable but comments would be welcome.

 

[Terminutter]

As a narrowboat engineer (jims Mobile Marine Services) I can say that ive seen a lot of mains consumer unit used this way with no problem, its how it used to be done, ive changed many to a switched dc panel with resetable fuses , usually without difficulty, and its how it ought to be done, the only drawback is cost with dc panel ready made from £50 upward and into the £100's

 

[ajlelectronics]

That is what I thought. Can you point me at a suitable unit please? He has 7 circuits, which I could make six. Incoming supply could be an issue, the cables are at least 10mm so would need to terminate them safely. Not sure if the inverter is powered from it, I would doubt it as it would be pulling more than the MCBs in there are rated for.

Ideally it should be boxed rather than flat panel mount as it is on the cabin wall. Be interested in what you have or could recommend.

 

[Terminutter]

http://www.midlandchandlers.co.uk/C...elItemID=dc5393f6-0c6d-4497-8295-06d8220d923f

 

[Terminutter]

Ive normally taken a panel like that and mounted it on a electric wholsale plastic box or made a wood box

 

[ajlelectronics]

How jolly splendid! Many thanks for that, we can soon make a housing of some sort of course.

Next issue is the waste tank sender. It needs replacing as it is stuck on full. It is almost identical to the Hendersons sender, except that it is just pushed into a grommet, rather than the BSP coupling. Looks like that could be slid off though.

http://www.hendersons.co.uk/boattank/tank-level-indicator.html

 

[Terminutter]

How jolly splendid! Many thanks for that, we can soon make a housing of some sort of course.

Next issue is the waste tank sender. It needs replacing as it is stuck on full. It is almost identical to the Hendersons sender, except that it is just pushed into a grommet, rather than the BSP coupling. Looks like that could be slid off though.

http://www.hendersons.co.uk/boattank/tank-level-indicator.html

 

[Terminutter]

I've just posted them back for repair , I've seen others like that but come from someone called something like MTC ??

 

[colnerov]

Hi, the issue with the switch melting is that the switch is rated for AC which means that the voltage across the air gap falls to zero as it cycles and so extinguishes any arc. DC switches have a bigger air gap for this purpose because there is no fall off of voltage. So don't use the main switch to switch off 'on load', better still have a DC rated isolator switch before the CU.

Colin

 

[ajlelectronics]

Thanks for that confirmation. Is there a standard amount for DC derating? Not that it will be replaced, he is getting a proper panel if he wants me to sort it out.

 

[rtbcomp]

Consumer units shouldn't be used for switching under load AC or DC, they're isolators.

 

[Robotstar5]

Consumer units shouldn't be used for switching under load AC or DC, they're isolators.

Look for switch disconnectors instead.

 

[ajlelectronics]

Job completed...

 

[ajlelectronics]

As there have been no comments, I believe that it has the forumite's approval? ;-) Took 3 hours to install it.

One tweak of the software I had to do was to slow down the voltage reading. Probably because of noise from the chargers etc, it was all over the place. Ideally it should have had a n averaging function written, but as I was out of brain power at that point, I just stuck a delay in. So, this will win no prizes for structure or neatness, but here it is in case anyone else finds it useful. Feel free to use it, tidy and modify it (I mean improve it!) as required.



/*-----( Import needed libraries )-----*/

#include <Wire.h> // Comes with Arduino IDE
#include <LiquidCrystal_I2C.h>


int redButton = 9; // select the pin for the push button 1
int greenButton =11; // select the pin for the push button 2

int redLED = 13; // select the pin for the red LED
int buzzPin = 6; // select the pin for the buzzer
int greenLED = 10; // select the pin for the green LED
int voltaget; // variable to hold temperature sensor reading
int voltagel; // variable to hold leisure battery voltage
int voltages; // variable to hold starter battery voltage
int tempValue;


int spareAnalogue = A3; // Spare analogue line available for future use
// available on terminal 4 of choc block. No
// divider resistor pack installed.

int sensor1Value;
int sensorValue;
int sensor2Value;

int greenSwitch = 0; // front panel switch
int redSwitch = 0; // front panel switch

LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE); // Setup I2C parameters for LCD

void setup() {

pinMode(redLED, OUTPUT); // declare the pin for the red LED as an output
pinMode(8, OUTPUT); // declare a spare pin as an output
pinMode(greenLED, OUTPUT);// declare the pin for the green LED as an output
pinMode(12, OUTPUT); // declare a spare pin as an output
pinMode(greenButton, INPUT_PULLUP); // Setup the button 2 and enable 20K pullup resistor
pinMode(redButton, INPUT_PULLUP); // Setup the button 1 and enable 20K pullup resistor

Serial.begin(9600); // Initialise the serial monitor test function

lcd.begin(20,4); // initialize the lcd with 20 chars per line and four lines
}
void loop() { // start main program
tempCheck(); // jump to that function
normalDisplay(); // jump to that function

delay(2000); // Quick bodge to stabilise the voltage readings. Would be better as average over
// 10 readings or so.


// Do something with the push buttons. Currently it will make the sounder beep if either is pressed.
// No real purpose other than that. For future use...

redSwitch = digitalRead(redButton);
greenSwitch = digitalRead(greenButton);
if (greenSwitch == HIGH && redSwitch == HIGH) {
digitalWrite(buzzPin, LOW);
}
else
{
digitalWrite(buzzPin, HIGH);
delay(200);
}

}


// End of main program. Functions below

void tempCheck() {

int sensor1Value = analogRead(A1); // variable to store the value coming from the temperature sensor
float voltaget = sensor1Value * (5.035 / 1023.0); // Calculate the voltage at the Aurduino pin.
tempValue = map(sensor1Value, 278, 603, 175, 68);
int sensorValue = analogRead(A0); // variable to store the value coming from the starter battery
float voltages = sensorValue * (5.035 / 1023.0);



if (tempValue >180 && voltages > 3) { soundAlarm(); }
else { normalDisplay(); }
}
void normalDisplay() {
digitalWrite(greenLED, HIGH);
digitalWrite(redLED, LOW);
digitalWrite(buzzPin, LOW);
lcd.setCursor(0,0);
lcd.print("Molly's health is OK"); // Write the text to the LCD
lcd.setCursor(0,1);
lcd.print("Engine temp. F"); // Write the text to the LCD
int sensorValue = analogRead(A0); // variable to store the value coming from the starter battery
float voltages = sensorValue * (5.035 / 1023.0); // calculate the actual voltage
if (voltages <1) {tempValue = 0; } // zero the temperature reading if ignition is off
lcd.setCursor(16,1);
lcd.print(tempValue); // send the temperature reading to the display
int sensor2Value = analogRead(A2); // variable to store the value coming from the leisure battery
float voltagel = sensor2Value * (5.035 / 1023.0); // calculate the actual voltage
lcd.setCursor(0,2);
lcd.print("Leisure batt. V"); // Write the text to the LCD
lcd.setCursor(15,2);
lcd.print(voltagel*3);
lcd.setCursor(0,3);
lcd.print("Starter batt. V"); // Write the text to the LCD


lcd.setCursor(15,3);
lcd.print(voltages*3);
}

void soundAlarm() {

int sensorValue = analogRead(A0); // variable to store the value coming from the starter battery
float voltages = sensorValue * (5.035 / 1023.0);

// Serial.println(voltages); // check to see what the variable holds at this point (test)

while (tempValue >179 && voltages >3) // Conditional branch to only enable alarm if the ignition is on
{
digitalWrite(redLED, HIGH);
digitalWrite(buzzPin, HIGH);
delay(300);
digitalWrite(buzzPin, LOW);
digitalWrite(redLED, LOW);

digitalWrite(greenLED, LOW);
lcd.setCursor(0,0);
lcd.print(" WARNING! "); // Write the text to the LCD
lcd.setCursor(0,1);
lcd.print("*Engine temperature*"); // Write the text to the LCD
lcd.setCursor(0,2);
lcd.print("Too high, now: F"); // Write the text to the LCD

int sensor1Value = analogRead(A1); // variable to store the value coming from the temperature sensor
tempValue = map(sensor1Value, 278, 603, 175, 68);

lcd.setCursor(15,2);

if (voltages <1) {tempValue = 0; } // If ignition is off, zero temperature display

lcd.print(tempValue);

lcd.setCursor(0,3);
lcd.print("TURN OFF ENGINE NOW!"); // Write the text to the LCD

}
}


/*

Voltage range for sensor is 2.72V hot to 5.9V cold.
Divided by 2 gives 1.36 to 2.95
Arduino count is 278 to 603
Inverse mapping for 68-175F range

Normal running temp is 175


*/

 

[zx9]

Interesting, thank you for posting the code, it looks similar to that in the AMX boxes we use to control lecture theatre and meeting room systems.

 

[Terminutter]

very nice and neat