Hi All
I am looking at using the following Circuit Breaker on my 3D printer, on the 2 heater lines ( both 12VDC )
The contacts are marked : Line / Load / WS
So the 12V feed goes to Line, Load goes to the heater element. What is the WS for ?
Regards
Dave
I'd guess it's for the light. What happens when you disconnect it? The strange thing is, it says neon which wouldn't light-up with 12V.
Yeah, probably the ground for the lamp inside. Note that the products page says 220 250 volts, so it's a common mains switch with a neon bulb inside.
The description says : AC / DC P/M MINIATURE ROCKER 220V-NEON ILLUMINATED CIRCUIT BREAKER. 250VAC / 50VDC MAX.
The spec sheet also says : Double Usage of DC and AC
Am I incorrect to think that this can be used on a DC line to protect the Arduino ( & Ramps board ) from a failure / short in one of the heaters ?
Although I will only get the switches to test tomorrow, is it possible that the 'Line' is diverted from 'Load' to 'SW' when the breaker trips ?
Looking at the position of the contacts in relation to the rocker type switch, this looks to be the most likely case.
If so, this could then be used to trigger a separate input on an Arduino.
Am I incorrect to think that this can be used on a DC line to protect the Arduino ( & Ramps board ) from a failure / short in one of the heaters ?
Yes, you are incorrect. It is a 10A breaker and you would need a 100 arduinos and ramps boards to get anything close to that.
Just use and inline fuse. They don't make circuit breakers for 100mA load. Just use an inline fuse and a 0.1A or 0.2 or 0.3A 5x20mm fuse.
Or you can get one of these and put it between you combined load and the GND of the power source. Then you can
use an analog input to measure the voltage drop across the current sense resistor.
V = IR
P = Iv
let I = 3.15A
V = 3.15A0.1 ohms = 0.315V
P = 3.15A0.315V = 0.99225W
So you could measure up to 3.15A without exceeding the 1W rating of the current sense resistor.
If you are going to use this approach you need to establish your design criteria by calculating the
maximum load your circuit would draw if there were no problems and then add 20% to that and
write your code to disconnect the load if it exceeds that.
If you have a relay that has the power source connected to the COM and the circuit load is connected
to the N.O. contact, and your setup code energizes the relay , all you need is a push button start
button that connects the relay code directly to the relay power, energizing the arduino. You only
have to press the button long enough for the startup code to run which would probably be 100mS,
then you can release it because the arduino is already energized by the relay. Then, when your
analog pin detects a voltage drop on the current sense resistor above your circuit maximum, the
code turns off the relay , disconnecting the entire circuit t from the power. This is a software latching
relay circuit. (as opposed to a hardware latching relay circuit where the relay energizes a contactor
that has a switch activated relay use for the latching relay circuit. When the contactor engages
the switch pushes the microswitch on the latching relay which holds the contactor on until
you push the OFF button which opens up the coil circuit causing the contactor
to drop out of latch.)
raschemmel:
Yes, you are incorrect. It is a 10A breaker and you would need a 100 arduinos and ramps boards to get anything close to that.
My intention is to place the breaker ( or fuse ) on the 12VDC line that goes to the 3D Printer bed heater ( 12V 120W 10A ) - not for the power going to the Arduino.
The Arduino controls the Ramps board, Ramps controls an external Mosfet board, and the Mosfet controls current to the heaters.
I have, once in the past and probably caused by the constant movement of the printer axis, had a heater short. My intention is adding the breaker / fuse to protect the rest of the electronics back down the line.
The circuit breaker page says "AC/DC" so it should work.
JUST FYI - A fuse or circuit breaker RARELY protects the electronics. There's an old joke, "The transistor blew to protect the fuse".
The fuse/breaker is normally there to prevent a fire or "further damage" AFTER something has burned-up. It won't hurt anything but it probably won't protect your MOSFET board. 
Is the printer bed heater an electronic circuit?
raschemmel:
Is the printer bed heater an electronic circuit?
the bed heater is a Kapton heater - Element Type - Etched Foil, Insulation - Polyimide Film (Kapton Tape)
The hot-end heater is a 12V 40W cartridge
In that case I believe the circuit breaker should work , howver, 40W/12V is only 3.33A, not 10A.
How did you come up with 10A ?
raschemmel:
In that case I believe the circuit breaker should work , howver, 40W/12V is only 3.33A, not 10A.
How did you come up with 10A ?
there are 2 heaters in most 3D printers. Bed and Hotend
In my printer, the bed heater is 12V 120W 10A
In my printer, the bed heater is 12V 120W 10A
Do you have any link for these heaters that gives their electrical specs ?
If neither of them are electronic circuits the circuit breaker will probably work.
It is possible to make a current monitoring auto shutdown circuit using a shunt , a microcontroller and
a fast power switching device that might be faster than a fuse but I don't have any data on that so I
don't know what the turn off time is compared to a fuse, but I'm pretty sure it's much less than a second.
The turn off delay time for this one is 40nS.
Fuse response times are in seconds.