ToM Transistor based Extruder “Relay Fixâ€
by M_G, published
Description
Which is itself a derivative of ToM Extruder Relay Fix thingiverse.com/thing:5569 by MakeALot thingiverse.com/MakeALot
This uses transistors instead of Relays. Perhaps some will find this useful if they don’t have access to relays. A variant of the ToM Extruder Relay Fix for dying extruder motors that operates in the forward and reverse directions. This thing uses 4x NPN Transistors, 2x resistors and 4x 1N400X series diodes.
I have not yet built this myself though!
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They damp back emf from the motor. Basically, the motor has an electromagnet inside - this electromagnetic coil means it has a certain inductance. Switch power in and out of the coil doesn't happen instantaneously - so when you turn off the transistor, the coil momentarily oscillates as the power stored in the coil dissipates. This can create a large reverse voltage across the transistor when this occurs - the diode allows that power to dissipate to ground before it rings and protects the motor and the transistor, as well as other nearby electronics.
What are the diodes for? Have not done a huge amount of electronics but I have not seen them on an H bridge before.
nevermind, I'm an idiot
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Instructions
- 2x Resistors (somewhere between 100 to 1kohm)
- 4x NPN Transistors (2N3055 or TIP31 Recommended)
- 4x 1N400X series diodes (1N4001 would be fine)
- wires
- breadboard
- dying ToM
2. Assemble according to Circuit Diagram
3. Breath life back into your ToM DC extruder motor until you can source replacement parts
4. Thank Eoin for sketching the circuit diagram and recommending parts
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With my old motor (now use stepper and very happy), I found the instantanioius current was quite high. Dodgy brushes perhaps? Anyhow, once it got going, the average current was OK, all be it a bit noisy. Sticking a cap across it and a random inductor in series smoothed it all out. Didn't have any more problems. Both the capacitor and inductor could be found in an old PSU. Important to use an AC cap - not an electrolitic. It's to get rid of the noise rather than store energy.
that won't work, the low side transistor's b-e junction will prevent the high side transistor turning on.
each transistor needs its own resistor like http://static.electro-tech-onl...
alternatively, use a buffer transistor like http://www.eleccircuit.com/wp-... which is required if the input signals are less than Vmotor.
google knows of heaps of working h-bridge designs, no need to reinvent the wheel ;)
What are the diodes for? Have not done a huge amount of electronics but I have not seen them on an H bridge before.
I just want to point out; this design uses 2 more diodes than necessary. I'm working on a PCB out of this and it became obvious my ratsnest was odd...
nevermind, I'm an idiot