using 555 and 4017 to cycle 7 LED's

DickCappels

Joined Aug 21, 2008
10,152
How do i measure the inductance of a copper coil?
If you can, measure it with an inductance meter. If it is a relay, measure it while holding the moving part in the energized position.

If you cannot measure it, describe it physically as best you can and someone here can come up with an estimate. Or better yet, post a manufacturer and part number or a photograph of it.
 

eetech00

Joined Jun 8, 2013
3,859
Would i connect the outputs of the 4017 to the ULN2004 or would i need a new circuit?
GopherT said:
You use the exact setup you have for the 555 and 4017, and the ULN2008 is a single chip that replaces all of the diodes (7) and mosfets (7) and resistors (7). Super easy.

Connect the chip to ground and positive power, feed your 7 signals from the 4017 into the ULN2004 and have power to drive relays out of the last 7 pins (internal diodes protects all transistors).
Its just like GopherT states. Connect the output of the 4017 to the ULN2004 like I show in post #46.
What is the part number of the relays you intend to use?
 

Thread Starter

Tony Spence

Joined Dec 20, 2013
64
If you can, measure it with an inductance meter. If it is a relay, measure it while holding the moving part in the energized position.

If you cannot measure it, describe it physically as best you can and someone here can come up with an estimate. Or better yet, post a manufacturer and part number or a photograph of it.
it a coil of 125 windings around a 10mm hole its just windings no core the copper wire is thin as its trom an old television unit
 

eetech00

Joined Jun 8, 2013
3,859
it a coil of 125 windings around a 10mm hole its just windings no core the copper wire is thin as its trom an old television unit
Ok....now I'm worried. :(

I thought you wanted to drive relays?
It sounds like your asking about an air core inductor(?)
To calculate the inductance (for a single layer winding) you need to know the length and diameter of the core, wire size, number or turns.

What are you planning to do with the circuit?
 

GopherT

Joined Nov 23, 2012
8,009
it a coil of 125 windings around a 10mm hole its just windings no core the copper wire is thin as its trom an old television unit
That makes about 3.1 cm per turn. 125 turns makes about 3.75 + .125 = 3.875 meters
Look for wire gauge on Wikipedia to get the resistance if the wire. Approximate diameter of your wire is 1% of your coil length if it is evenly wrapped.

From there, Google, inductor calculator to determine the inductance based on the diameter of your coil, the number of turns (125) and the length of your coil. Done.

I hope you have some very fine wire.
 

Thread Starter

Tony Spence

Joined Dec 20, 2013
64
Ok....now I'm worried. :(

I thought you wanted to drive relays?
It sounds like your asking about an air core inductor(?)
To calculate the inductance (for a single layer winding) you need to know the length and diameter of the core, wire size, number or turns.

What are you planning to do with the circuit?
I plan to produce a magnetic field from each coil, one after another and be able to control the speed in which they turn on
The coil needs to be strong enough to affect a neodymium magnet.
 

wayneh

Joined Sep 9, 2010
17,496
Until you know the current needed to drive your coils, you can't specify a transistor to switch them.

The current will depend on the DC resistance (length and gauge of the wire) at low frequency but as the switching frequency increases, the coil inductance will present an impedance and reduce the current. That why a wall wart transformer doesn't explode when you plug it in – there is a high impedance in the primary coil at 60Hz.

The Wheeler formula can be used to estimate the inductance of an air-core "pancake" coil. It's meant for solenoids and there may be a superior formula that does a better job for pancakes.
 

Bernard

Joined Aug 7, 2008
5,784
That will be a low inductance, maybe around 10 uH and probably low DC resistance which is your main
concern. Do you have a measurement ?
 

Thread Starter

Tony Spence

Joined Dec 20, 2013
64
If you can, measure it with an inductance meter. If it is a relay, measure it while holding the moving part in the energized position.

If you cannot measure it, describe it physically as best you can and someone here can come up with an estimate. Or better yet, post a manufacturer and part number or a photograph of it.

Sorry for the long replies I work away from home.

I have tried to measure the resistance of my coil by connecting a 10 ohm resistor and one of my coils in series and the max reading i get from my multimeter is 12.1 ohms. With the coil on its own i get a reading of 1.4 ohms hope this helps
 

Bernard

Joined Aug 7, 2008
5,784
That helps, @ 9 V,
I = 6.4 A, 5 V = 3.6 A. Might be best to use individual FET drivers as shown before.
Should have an effect on a magnet. Tell us that this isn't a miniature rail gun?
 

Thread Starter

Tony Spence

Joined Dec 20, 2013
64
That helps, @ 9 V,
I = 6.4 A, 5 V = 3.6 A. Might be best to use individual FET drivers as shown before.
Should have an effect on a magnet. Tell us that this isn't a miniature rail gun?
Its not a rail gun mate sorry. Using my circuit provided can anyone state how I can boost the output to the coils please
 

DickCappels

Joined Aug 21, 2008
10,152
Can I use a transistor like a bc108?
Maybe somewhere in the circuit, but you would probably need many of them in parallel to drive a single coil.

The first order of business is to tell us what you are trying to make <= affects that might be subtle in some applications may be major effects in other applications.

The second order of business is to determine how much current you need and what voltage you can use to obtain it (for example: 6V motorcycle battery). From that you can obtain some solid recommendations for a driver circuit. Until the first two questions are answered, we are only guessing at what you need, which is inefficient at best.
 

Thread Starter

Tony Spence

Joined Dec 20, 2013
64
Maybe somewhere in the circuit, but you would probably need many of them in parallel to drive a single coil.

The first order of business is to tell us what you are trying to make <= affects that might be subtle in some applications may be major effects in other applications.

The second order of business is to determine how much current you need and what voltage you can use to obtain it (for example: 6V motorcycle battery). From that you can obtain some solid recommendations for a driver circuit. Until the first two questions are answered, we are only guessing at what you need, which is inefficient at best.
I am making a motor using magnets. When I first made the circuit it was an Led chaser I took away the LEDs and added a bc108 and the coil and Im sure I only used one bc108 but the coil worked then now I think I've lost power and need to bump it up
 

DickCappels

Joined Aug 21, 2008
10,152
Second order...have you determined how many amps you need? In Post #71 Bernard calculated that this coil would take "@ 9 V,
I = 6.4 A, 5 V = 3.6 A." That is a whole lot of amps, the BC108 cannot do that without serious loss of power.

If you were driving your current coils with a BC108, you were not getting the full voltage across your coils, so the current (also because of the BC108 saturation characteristics) would not be even near 3 amps or you would have observed some very hot parts, even at a low duty cycle.

You wrote that you need to boost the output of your coils. The output of the coil is proportional to the (current x turns)/ (average distance from one end of the coil through to the other end taking into account all possible paths in space). A magnetic core would help concentrate this magnetic energy -notice that in the elementry school electromagnet experiment the wire is wrapped around a nail?

You need to design your magnetic circuit using the principles above. I suspect that you will want to use many more turns so you can get more of a field with lower current. Once you get something working, measure the current with a steady voltage applied to it, then measure the resistance. We have some people here who are very good at designing driver circuits, but they need to know the coil resistance and the voltage across the coil. Reporting the number of turns can be useful to obtain suggestions at improving your coil design.
 

wayneh

Joined Sep 9, 2010
17,496
There are a number of current pinching points in your circuit. The first one that jumps out at me is the breadboard. They're not intended for large currents.

But there may be many other, starting with the battery and including the hookup wires and active components (ie. transistors). It's tough to make a judgement without details. Length and gauge of the coils, for instance. (Sorry if you've already provided this.)

And as Dick has noted, you'll get a lot more bang for the buck – magnetic field per amp – if you use a core in the coil and provide a return path for the magnetic field.
 
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