33
votes
I keep blowing up irrigation solenoids
Let me guess: the solenoids that keep burning out are the ones furthest from the controller out of all the others?
It's not voltage spikes, or lightning, or inductance on the lines, or anything like ...
- 29.9k
17
votes
Any idea why circuit D would not be recommended for energizing the relay coil?
Everything that @Hearth says is true. But the reason that Omron recommends not using the diode is because if the turn off is slow, then that means there is more arcing on the contacts as they slowly ...
- 9,173
14
votes
Any idea why circuit D would not be recommended for energizing the relay coil?
It slows turn-off.
The coil is an inductor--that's the whole reason it creates that spike in the first place--and it takes voltage to discharge an inductor. With a diode on its own, you only get about ...
- 46k
12
votes
Accepted
Intuitive way of "visualizing" how the energy is stored in an inductor?
I'm going to start by discussing capacitors then move to inductors. I'll avoid complex equations (to save myself as well as this discussion.) I may even discuss duals between capacitance and ...
- 79.7k
10
votes
Would a room-sized coil used for inductive coupling and wireless energy transfer be feasible?
Having a room sized coil to transmit to a small receiver coil (within the room) is entirely feasible and, was used (and maybe still is) for museums and galleries for several decades. It's simple, ...
- 501k
9
votes
Accepted
Would a room-sized coil used for inductive coupling and wireless energy transfer be feasible?
The main limitation is, the coupling factor is roughly the ratio of cross-sectional areas of the two coils in question (whole-room transmitter and some local receiver). If the resonant Q factor is as ...
- 53.1k
8
votes
Would a room-sized coil used for inductive coupling and wireless energy transfer be feasible?
You'll get more power than you bargained for!
By turning the entire room into the core of a transformer, you will induce eddy current heating into any metallic object in the room.
7
votes
Accepted
Can every voltage source accept fly-back diode's current?
simulate this circuit – Schematic created using CircuitLab
Figure 1. OP's schematic redrawn with switch replacing the transistor and normal current flow from top to bottom (as is standard in ...
- 188k
7
votes
Accepted
P-MOSFET failing
The answer is simple, you need a diode across the output wire to the relay.
When you turn the current to the relay OFF you will get a large negative back EMF spike on the drain of the FET (IRFR5305). ...
- 22.3k
6
votes
Why inductive load heats up on modified sine wave inverter?
Modified sinewave inverters do not necessarily produce a pure sine wave: -
Image from here.
Because of the harmonics of the "modified sinewave", eddy current losses are increased (due to ...
- 501k
6
votes
Accepted
How does balancing currents within a cable or conduit cancel its magnetic fields?
To start, currents are not the same as bar magnets (i.e. permanent magnetic dipoles).
Consider a pair of conductors carrying equal-but-opposite conventional currents (red):
By the right hand rule, we ...
- 21.4k
6
votes
DC motor voltage kickback when turning off
The fast spike is the effect of the inductance of the motor windings,
The slow decline is the effect of the spinning motor acting as a generator as it slows to a stop.
- 40.4k
6
votes
Simplest way to isolate MOSFET from MCU
The relay provides isolation; all you need to worry about on the coil side is the inductive kickback, which D1 is managing. The R45/C12 combination is probably going to blow up Q1 though.
- 28.1k
6
votes
Are flyback diodes (D1 and D2) necessary in this H-bridge relay circuit?
The diodes are necessary.
The moment the contact disconnects from supply, that terminal of the inductor would otherwise be floating before it flies over and reconnects with ground.
Without diode, as ...
- 196k
5
votes
Npn transistor failed to work
Switching an inductive load, even with the flyback diode, is hard on the transistor, and you may be seeing an SOA (Safe Operating Area) issue that is causing the transistor to fail. When the ...
5
votes
Intuitive way of "visualizing" how the energy is stored in an inductor?
It seems to me that if you can "visualize" electric charges being separated in a capacitor as energy storage you should be able to do a similar thing with an inductor.
The energy in an ...
- 8,037
5
votes
Can wireless charging become more energy efficient?
Wireless chargers involve large circulating currents in coils, running at relatively high frequency, and that is always going to be lossy.
Between skin effect, relatively low mutual coupling and the ...
- 18k
5
votes
Accepted
Is there an equation to calculate the voltage spike caused by an inductor in the absence of a freewheeling diode?
The voltage at the drain when the MOSFET turns off depends on the peak current \$I_p\$ and the capacitance lumped at that node. Provided the breakdown voltage is high enough, the voltage will peak to ...
- 26k
5
votes
Any idea why circuit D would not be recommended for energizing the relay coil?
To see what is "better" ... you can simulate it across an inductance.
Here is the simulation made with microcap v12
Now, you can compare and see what is the "better" circuit (...
- 19.7k
4
votes
Accepted
Can I add flyback diodes to my car window motors?
simulate this circuit – Schematic created using CircuitLab
Figure 1. (a) Snubber with four diodes. (b) Snubber with bridge rectifier. Note that the two solutions are electrically identical.
...
- 188k
4
votes
Accepted
Transistor as a switch, what does the inductor do?
The inductor isn't something you want to have in the circuit.
But if your load is a motor or a relay coil, for example, it will behave like an inductor, and you'll have to design your control circuit ...
- 135k
4
votes
Accepted
How do inductive chargers detect a load?
Have you read this article ?
The transmitter transmits bursts and detects the resulting current flow in the transmit coil. Depending on the value/shape of that current the transmitter can detect if ...
- 81.9k
4
votes
Npn transistor failed to work
I guess the problem starts with the lack of base current. A 30 volt supply via a 10 k resistor can provide 3 mA into the base of the BD679 darlington. However, if you look at the Collector-emitter ...
- 501k
4
votes
Can every voltage source accept fly-back diode's current?
It's not going into the voltage source. The current circulates through the diode and motor coil resistance until the energy stored in the inductance is dissipated.
4
votes
What's causing the audible 7/8th rhythm in Qi chargers?
To keep the received voltage where the receiver wants it, the receiver sends data packets back to the transmitter. When the voltage is close, the packets are sent about every 250ms. When the voltage ...
- 894
4
votes
Accepted
What's the role of the capacitors in this AC circuit?
To analyze the circuit we can break it down to two parts:
1.RFI suppression LC Filter
A triac can be used to give variable AC power control by using a 'phase-delayed switching' technique, in which ...
- 173
4
votes
Transistor Limit Current
A transistor does nothing on its own. However, that is not strictly a transistor. It's an IC with a power transistor and other stuff in it.
Also motors do not drive current, they draw current. But I ...
- 58.1k
4
votes
Why does the quality factor include 2*pi?
There is no fundamental reason -- it's a convention, and happens to be convenient. 'Q' could have been defined to not use the 2π term, but then many calculations using it would require a 2π factor ...
- 20.7k
4
votes
Accepted
Inductive or capacitive load?
Is there a way to know whether this circuit is an inductive or a capacitive load?
Yes. The circuit will have inductive reactance when the driving frequency is above the resonant frequency, and it ...
- 34.5k
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