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Author Topic: Reed switches, Hall sensors, trigger coils... discuss  (Read 17962 times)

Offline dieter

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Reed switches, Hall sensors, trigger coils... discuss
« on: April 11, 2014, 01:35:49 AM »
I currently have some issues in determing a perfect power switching system with a magnet sensor, for use in pulse motors.


Reed switches:  They are great in that they are passive, so they don't waste any energy, and they are quick, causing a true square signal, but they tend to burn out quickly. Although their livespan can be increased by several principles:
-don't let the back emf go trough the reed switch.
-don't let any high power go trough a tiny switch .
See also here:

 www.reed-sensor.com/Notes/Protection_Circuits.htm

Also, big Reed switches for watts are expensive and they also attract the rotor, and did I already say that they burn out on a regular basis?

.........

Hall sensors, ideal one might think. I have just designed a pulse motor with a hall sensor. It works, although the problem is:  the hall sensor needs 5 V in, so I need to lower the supply voltage, wasting maybe 15mW already. Then I have to use a transistor for the hall sensor output. I use a tip 2955, works well, but is easily burned when the coils induction or the supply power or the heatsink is wrong. Also, the turn off isn't as sudden as in a reed switch, which is bad for back emf harvesting. This whole circuit, together with a 1.6 kOhm pulse coil, dissipates 300 mW, but the coil alone only about 25mW... a lot of circuit loss.

So I wonder, did anybody ever try to build a long living reed switch, eg. one that is filled with oil to suppress sparking??

Regards
 

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Offline TinselKoala

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Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #1 on: April 11, 2014, 05:39:37 AM »
MHOP:
http://www.youtube.com/playlist?list=PLml9VdOeqKa8F1PebS_EX7AX2aA_ZZtb9

Long-lived reed switches are mercury-wetted (not oil) and are protected from arcing by external capacitors etc. They are the simplest way to produce fast risetime pulses but as you note they are delicate and expensive and do fail in various inconvenient ways.

You may not be using the "best" Hall sensor for your application. Try Allegro Microsystems Hall sensors: Unipolar non-latching switch, and ratiometric types.






Offline conradelektro

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Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #2 on: April 11, 2014, 09:49:26 AM »
I like trigger coils very much, because they are simple and can easily be wound at home. Also coils from relays can be used as trigger coils (because they have many turns of fine wire).

The best idea concerning trigger coils came from TinselKoala who uses an OpAmp to increase the sensitivity of a trigger coil.

I attach a circuit from TinselKoala (TL082, which he published in this forum) and a circuit which I developed based on his idea (LM311, for a low power pulse motor).

A very good OpAmp would be the MAX931, but I never got around to use it myself.

Greetings, Conrad

Free Energy | searching for free energy and discussing free energy

Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #2 on: April 11, 2014, 09:49:26 AM »
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Offline dieter

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Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #3 on: April 11, 2014, 11:39:47 AM »
Thanks a lot for your answers, some interesting information.

Offline conradelektro

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Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #4 on: April 11, 2014, 02:55:32 PM »
A method of driving a pulse motor just with the drive coil interested me for some time. The drive coil can also be the sensor or trigger coil.

http://www.youtube.com/watch?v=OqQSJjRJ6EQ  I made a video of such a pulse motor and also show the drive circuit in the video.

As far as I know this circuit was invented by a person with the nick name DadHav. Look at the INFO of the video where I put a link to DadHav's video.


I also attach a very simple pulse motor drive circuit (which needs at least one drive coil and a trigger coil) and the photo of a ring magnet spinner (diametrically magnetized) driven with this circuit. All this has been discussed in this forum (but I have forgotten in which thread). The coils were taken from relays.

The coils need a very high DC resistance (very many turns of very thin wire). The coils I use had a DC resistance of ~4 K. If the DC resistance is smaller you have to use a different transistor.

Greetings, Conrad

Free Energy | searching for free energy and discussing free energy

Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #4 on: April 11, 2014, 02:55:32 PM »
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Offline TinselKoala

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Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #5 on: April 11, 2014, 03:53:13 PM »
Those are great and handy circuits. I've never been able to get them to "self start" when power is applied, it always seems to take a pretty good spin. I also don't know if the power-take-off can work with those circuits. Can you siphon off the spike from the coil and charge a capacitor to higher voltage than the supply?

I guess I should build another one and try. I can't find my proper magnets, though, I'll have to make some kind of special rotor out of separate magnets.

 

Offline conradelektro

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Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #6 on: April 11, 2014, 06:06:09 PM »
Those are great and handy circuits. I've never been able to get them to "self start" when power is applied, it always seems to take a pretty good spin. I also don't know if the power-take-off can work with those circuits. Can you siphon off the spike from the coil and charge a capacitor to higher voltage than the supply?

The circuits I showed do not self start, one has to give the rotor a spin by hand.

I was mostly interested in building a very low power pulse motor and this made the spike very weak. To do something interesting with the spike you need a good solid current running through the drive coil first (1 Ampere or more).

The attached Hall Sensor circuit produced interesting spikes. The drive coils had 260 Ohm DC resistance. But with coils having e.g. 50 Ohm DC resistance the spike would be even more interestingly strong.

I observed that harvesting the spike reduces the speed of the rotor.

Greetings, Conrad

Free Energy | searching for free energy and discussing free energy

Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #6 on: April 11, 2014, 06:06:09 PM »
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Offline synchro1

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Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #7 on: April 11, 2014, 08:07:59 PM »

Quote from Conradelectro:

"The best idea concerning trigger coils came from TinselKoala who uses an OpAmp to increase the sensitivity of a trigger coil".

Milehigh originated the idea for the OpAmp circuit, not Tinselkoala!

The Tesla series bifilar power coil projects a "Magnetic Scalar" wave at high speeds that propels the magnet spinner with additional velocity. Try to power your reed switch spinner with a series wrapped bifilar solenoid, and compare the speed to input ratio over the single wire coil.

Offline TinselKoala

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Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #8 on: April 11, 2014, 08:28:55 PM »
Quote from Conradelectro:

"The best idea concerning trigger coils came from TinselKoala who uses an OpAmp to increase the sensitivity of a trigger coil".

Milehigh originated the idea for the OpAmp circuit, not Tinselkoala!
That's right, that's why it is called the MHOP: Mile High Op-Amp driver.

He had the idea, I just did all the work. Credit where credit is due!

Quote

The Tesla series bifilar power coil projects a "Magnetic Scalar" wave at high speeds that propels the magnet spinner with additional velocity. Try to power your reed switch spinner with a series wrapped bifilar solenoid, and compare the speed to input ratio over the single wire coil.

That's a crock of cheese. Even if there is a difference in speed that does not require a "magnetic scalar wave", whatever that is.

Free Energy | searching for free energy and discussing free energy

Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #8 on: April 11, 2014, 08:28:55 PM »
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Offline synchro1

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Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #9 on: April 11, 2014, 08:33:24 PM »
@TK,


       You're the Liederkranz! The "Vortex": This wave has the magnetic poles trailing one another at 180 degrees, and resembles a smoke ring that's shrinks and expands as it travels. However, the series bifilar solenoid generates a transverse wave along with the longitudinal, with the magnetic poles at 90 degrees! The series bifilar spiral toroid that I created reduces the transverse wave and projects an even more powerful longitudinal EG wave. Professor Meyl has determined there are two varieties of "Scalar Waves": The electric and the magnetic.

Offline kEhYo77

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Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #10 on: April 11, 2014, 08:48:57 PM »
Why not to use a reed switch to apply a voltage to the gate of a mosfet, with a pull down resistor?

Free Energy | searching for free energy and discussing free energy

Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #10 on: April 11, 2014, 08:48:57 PM »
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Offline synchro1

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Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #11 on: April 11, 2014, 09:02:18 PM »
The series bifilar coil no longer even needs a switch over the self acceleration threshold. The "Scalar Wave" increases in power and begins to drive the spinner at a new pitch way over the rated circuit switch speed. The longitudinal magnet wave has a back to back pulse included in it! Take another look at the schematic in the comment above!

Offline conradelektro

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Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #12 on: April 11, 2014, 09:34:49 PM »
Why not to use a reed switch to apply a voltage to the gate of a mosfet, with a pull down resistor?

Yes, one can do that and it will help to have a long life of the reed switch.

The main advantage of a reed switch usually is that one does not need any electronic component besides it (just a battery, reed switch and drive coil). If you are prepared to use a transistor (MOSFET) then it costs very little more to add a hall sensor in order to get a reliable and accurately switching circuit.

A reed switch can not switch at high frequency, can not switch a high current and is probably more expensive than the transistor plus the hall sensor.

The modern pulse motor circuit would be a hall sensor and a MOSFET. One could throw in a little microprocessor in order to generate some fancy timing (hall sensor, microprocessor, MOSFET).

A trigger coil (instead of the hall sensor) plus an OpAmp is a nerdy solution just for the fun of it.

A trigger coil plus a transistor is a nice home made solution, but there really is no valid reason not to use a hall sensor.

But if we want to be cynical, there is no valid reason to use a pulse motor in the real world. Use these new three phase brushless motors which you see in quadro copters or model airplanes. Some good drive circuits use hall sensors on the face of the motor.

Greetings, Conrad

Offline dieter

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Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #13 on: April 11, 2014, 10:17:56 PM »
Conrad,


I agree, for BEMF harvesting a low impedance and a high inductance is required. Few Ohms, but enough mass to create a strong field. I had problems with too little resistance, at a higher RPM the tip2955 would simply go in a on mode, maybe because the supply voltage dropped, the hall sensor latched? It does so whenever there is a contact interruption, eg. by a loose aligator clip when touched. So a few dozen of ohms should it be at least IMHO.


For a good square waveform, it may be useful to use a nand gate chip like the 4011, that will make 0 and 1 out of an analog signal, it may dissipate less than an OA and can trigger any Transistor easily, and it's cheap.


Harvesting the Back EMF may indeed reduce RPM, but maybe this can be optimized by:


Let the BEMF flow trough the drive coil with a rather high load at the "end", the load should not delay the BEMF as capacitors or inductors do. But finally, the BEMF is not for free, so a certain reduction in RPM is to be expected.


High Voltage peaks of a BEMF may however be used in a Bedini Style Battery reconditioning System, at least.


A quick diode like a schottky should be used to catch the BEMF, as well as a cap with a few hundred volts to be able to collect the preaks, I guess.
As it was mentioned, mercury tipped reed contacts are used... doesn't that evaporate? Could gallium be used instead?


Regards

Offline TinselKoala

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Re: Reed switches, Hall sensors, trigger coils... discuss
« Reply #14 on: April 11, 2014, 10:21:35 PM »
The motor that probably shouldn't work, but does: the Marinov Slab. (bottom view)

One Hall sensor, one capacitor, one resistor, one mosfet, one battery, no cores, two rotor magnets, one switch. No armature back-reaction. Or so it could be claimed.


 

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