Hi .
I dont know how (where) to place a thermal fuse (240 C) to protect some thing from burning . Problem is that , there is an 8 A heat-bed or 3.35 A hot-end . I assume 8 A / 3.35 A cannot pass through the fuse's pins or will cause enough heat to shut everything down . Placing it before the PSU is also impossible , as it is 30 A .
So how should I place it to prevent fire or stop fire from increasing ?
thanks in advance .
The thermal fuse is specified for a certain current. The normal ones, used in household appliances, are often 15A. Even if they are small, they still can be used up to 15A.
The best position of the fuse is impossible to say. When for example a part is covered by something, then the heat will build up there. The fuse might be in an other location.
You could put 3 or 4 thermal fuses into it, and hope they will capture the heat.
When you measure the current and the voltage, you might be able to determine if all wires are still okay. Is the heating done with multi-core wires ? Are those core wires seperated from each other ?
For example a heated blanket for beds use multi-core wires that are seperated from each other. That means that if a single core wire breaks, it wil not create a hot spot. Some have an extra outer wire around the middle wire, to detect melting or burning of the isolation.
I assume that are other methods for safety. In Europe I think every heated blanket turns itself off after 90 minutes.
When I don't fully trust a heated blanket (the blanket or connector or something else), then I don't use it anymore and throw it away. That is perhaps the best safety measure.
I believe a "hot end" and "heat bed" are parts of a 3D printer.
Thus the connection with Arduino.
That's funny! since also heated blankets have sometime a warmer end. But you are right, a "heated bed" is for a 3D printer. I don't have an Arduino controlled heated blanket yet.
Or a 3D printer, apparently.
Yes it is for a 3dp , preventing burning (fire) .
By placing I meant like , cut the wire and connect the two ends with a fuse , or place a mosfet and control the gate with a fuse , or something like that ?
thanks .
If you use a NTC or thermocouple, then that is used for a mosfet or relay.
If you use such common thermo fuses, then it should be directly in the line to the heater.
Those common thermo fuses are fuses. They need to be replaced when they have been activated.
Peter_n:
If you use a NTC or thermocouple, then that is used for a mosfet or relay.
If you use such common thermo fuses, then it should be directly in the line to the heater.
Those common thermo fuses are fuses. They need to be replaced when they have been activated.
Which kind of common thermal fuses are you talking about?
I know that bulky, sort-of disk-shaped thermal cut-out switches are very common, and often rated for multiple amps. The disk-shaped thermal cutout switches are self-resetting (they use a bimetalic strip). That's what I think of when I think of "common thermal fuses". I don't think I've ever seen one-time-use thermal fuses.
I see one-time-thermal fuses all the time :o
Arman5592:
So how should I place it to prevent fire or stop fire from increasing ?
Most 3D printers I have seen use an RTD to monitor the temperature of the hot end - the heating element is PWM controlled (via a PID routine or similar) to ensure that the hot end stays at the proper temperature. If it goes above a certain temperature (or any other temperature error occurs - such as the temp abruptly going to min or max - indicating a problem with the sensor) - the machine (and hot end) shuts down.
Something similar can also be done with the heated bed.
Both provide a much finer level of control; if you already have this in place - and you have put into place proper continuous error checks (which include not just the hot parts, but other parts of the system itself - including the Arduino) - there shouldn't be a need for thermal fuses.
If you still feel that there needs to be a fuse, use one rated for the hottest temperature plus 10 degrees (or so) that you plan on using. Ideally, it should be reset-able - but not automatically.
Note that regardless of what you plan to implement, a 3D printer should never be left to run unattended.