Designing a Tunable High Voltage Oscillator for Pulsing 5 Electromagnets 1-20Hz

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#1 21663906 28 Sep 2012 21:06

Aaron Hiniker Aaron Hiniker

Anonymous

Post #1
21663906 28 Sep 2012 21:06

First I'll say my electronic skills are quite poor. I'm trying to pulse 5 electromagnets in series between the 1-20 hz range. Apparently the 555 timer only works up to 18 volts. I'd like help designing a tunable high voltage circuit with a tunable frequency and led. First off, what information do I need to start designing the circuit, I'm not sure how much power I am going to need, I just want the EMs as powerful as feasibly possible. I'd like to just hook a dozen or so 9 volts together as the power source. Where do I begin? By the way, I'm not looking for a specific wattage or anything, it's just an experiment.
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#2 21663907 28 Sep 2012 23:47

Peter Evenhuis Peter Evenhuis

Anonymous

Post #2
21663907 28 Sep 2012 23:47

In the same store where you buy the 555 you can also buy FET`s as a switch controlled by the 555.

As a experiment you do need to know the voltage current rating from your e-magnets, as a example 120V 0,5A magnet x 5 =120V / 2,5Amp your battery is 12 x 9V = 108V / 0,4A.
As a result the battery can not give the power.
In a different setup you can burn the coil.
so they need to be in the same range.

Any DC voltage above 24V gives good burn wounds and above 80V can kill a person.
Be safe and double check always.
#3 21663908 29 Sep 2012 01:51

Steve Lawson Steve Lawson

Anonymous

Post #3
21663908 29 Sep 2012 01:51

When working with high voltages, always keep one hand in your pocket -- that way, you're less likely to form a current path through your heart.

And best bet, as Peter said, is to use a MOSFET (see diagram below). Vcc needs to be high enough to drive the MOSFET. If it's a logic level FET, then 5 volts is enough, otherwise around 10 to 12 volts. Make sure the max Vds is around 1.5 times (or more) the highest voltage applied to the coil.

If the voltage on the electromags is 300V or above, then consider using IGBTs:

http://www.irf.com/product-info/igbt/

And if that high, then REALLY KNOW WHAT YOU ARE DOING, BECAUSE SUCH VOLTAGES CAN KILL THE HELL OUT OF YOU!
#4 21663909 29 Sep 2012 01:59

Steve Lawson Steve Lawson

Anonymous

Post #4
21663909 29 Sep 2012 01:59

Also, consider using something like a 74?138 driven by a 3-bit counter.

*Edit:* That is if you want to sequence the EMs (not sure why I thought that was what you meant, 'cuz I went back and read your post and you said "series" not "sequence")
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#5 21663910 29 Sep 2012 02:09

Aaron Hiniker Aaron Hiniker

Anonymous

Post #5
21663910 29 Sep 2012 02:09

Thanks for the reply.

How would I find the current of my EMs? Divide the voltage by the EMs total resistance?

What does FET stand for?

I'm thinking since 9 volts are expensive that maybe I should take the 120v AC from the wall and rectify it (bad idea?... most likely).

How do I design the circuit. I think what I'm looking for is similar to this (with an fet, whatever that is). This is a succor punch circuit for resonating a wire around crystals at 15 hz. It just looks like gibbrish to me.
#6 21663911 29 Sep 2012 02:15

Aaron Hiniker Aaron Hiniker

Anonymous

Post #6
21663911 29 Sep 2012 02:15

Good tip with the hand in the pocket.

I hate to be the useless noobie, but I just don't know what the hell I'm doing when it comes to designing a circuit. Could you give me an example of what this should look like?
#7 21663912 29 Sep 2012 17:54

Steve Lawson Steve Lawson

Anonymous

Post #7
21663912 29 Sep 2012 17:54

Sorry, but it sounds like you don't have enough experience to be messing with such things. I suggest you enroll in an electronics course or get a book on basic electronics.
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#8 21663913 29 Sep 2012 18:02

Aaron Hiniker Aaron Hiniker

Anonymous

Post #8
21663913 29 Sep 2012 18:02

I can build circuits, I just can't design them.
#9 21663914 30 Sep 2012 01:44

Steve Lawson Steve Lawson

Anonymous

Post #9
21663914 30 Sep 2012 01:44

Well, what you are asking for takes a lot of time. I'm not willing to design the whole thing (which would involve a lengthy Q&A between us to even get to the point where I know what it is you want designed. And, then, were I to design it, apparently I would have to spell out every detail, such as what a FET is. That's a daunting task!

I suggest you start with basics and get some experience under your belt. Then, perhaps, we can talk.

Also, as you are acquiring that experience, if you should have questions along the way, by all means, ask them on this forum (but be sure to do each one as a new topic, so they're visible to everyone on the forum).
#10 21663915 30 Sep 2012 10:56

Steve Lawson Steve Lawson

Anonymous

Post #10
21663915 30 Sep 2012 10:56

OK, change of heart. I read up on the "Succor Punch" concept and realized that what you need to be thinking about is current, not voltage. The voltage will be high only if it needs to be to drive whatever coil you conceive of--and if you are winding coils that need more than 18 volts, then your getting way into OverKill!

Attached is an add-on to your Zapper circuit. The value of R5 will depend on the current you will be driving with Q1: Ic = hfe * Ib, where Ic is the current into the Collector of the transistor, and Ib is the base current (limited by R5). The hfe (also called beta) of any transistor can be acquired from it's datasheet. For this application, I suggest using the minimum hfe.

If you don't know what any of that means, then read up on Transistor basics:

* http://www.electronics-radio.com/articles/ele...-does-a-transistors-works-basics-tutorial.php
* http://www.electronics-tutorials.ws/transistor/tran_2.html
* http://www.americanmicrosemi.com/tutorials/bipolartransistor.htm
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#11 21663916 30 Sep 2012 15:49

Aaron Hiniker Aaron Hiniker

Anonymous

Post #11
21663916 30 Sep 2012 15:49

Thanks for the reply. I'm not building a succor punch I'm just using the same pulsing circuit, so I'm not looking for current. I just need to pulse some electromagnets with a high voltage.

I think what I want is something like this. Would this work? (the D of the mosfet will go to the electromagnets, I forgot to draw it in)
#12 21663917 30 Sep 2012 21:41

Steve Lawson Steve Lawson

Anonymous

Post #12
21663917 30 Sep 2012 21:41

More like this (see diagram below). Your diagram isn't complete (no connection to the Source or Drain and not sure what the line is suppose to represent (the one that seems to go from the Drain to the "90V" label)).

In my diagram, R1 can be anything from 0 ohms (i.e. a piece of wire) to infinite resistance. And L1 is the inductor (or inductors in series). Also, you might need to

But, once again, I warn you to BE _VERY_ CAREFUL WITH VOLTAGES THAT HIGH!!! If you injure or kill yourself, I take no responsibility. And, in fact, I highly encourage you to not play with such things until you have more experience!!!

*YOU HAVE BEEN WARNED!!!*
#13 21663918 01 Oct 2012 01:04

Steve Lawson Steve Lawson

Anonymous

Post #13
21663918 01 Oct 2012 01:04

And let me reiterate--if it's inductors you are driving, then it's all about the current.

And make sure the max Vdss on the FET is at least 1.5 times the maximum voltage involved. If 90, then I would go with 135V or above (and I like to take it to 2 times and above).

Also, depending on your application, you will probably want to put a rectifier across the inductor(s) with the polarity opposite to the polarity applied to the coil(s) (i.e. so the rectifier doesn't conduct while the inductor(s) are grounded by the FET (but, instead, conduct when the FET opens in order to dampen any reverse EMF generated by the abrupt interruption of current.
#14 21663919 01 Oct 2012 03:22

Steve Lawson Steve Lawson

Anonymous

Post #14
21663919 01 Oct 2012 03:22

Here's the diagram with the protection diode:
#15 21663920 02 Oct 2012 02:29

Aaron Hiniker Aaron Hiniker

Anonymous

Post #15
21663920 02 Oct 2012 02:29

Thanks again! You're awesome.

I'll do my best no to kill myself.
#16 21663921 02 Oct 2012 18:51

Steve Lawson Steve Lawson

Anonymous

Post #16
21663921 02 Oct 2012 18:51

The resistor is merely to limit the current through the inductor. In most cases that "resistor" would be zero ohms, in other words, no resistor. But, since I don't have a clear idea of what you are making, I included the resistor to cover all (or as many as I could think of bases.
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Topic summary

✨ The discussion centers on designing a tunable high voltage oscillator circuit to pulse five electromagnets in series at frequencies between 1-20 Hz. The original poster has limited electronics experience and seeks guidance on circuit design, power requirements, and component selection. Key advice includes determining the electromagnets' voltage and current ratings to match the power source, as mismatched voltage or current can damage coils. Using multiple 9V batteries in series to achieve high voltage is generally insufficient for high current demands. Safety warnings emphasize the dangers of voltages above 24V, with lethal risks above 80V. For switching, MOSFETs are recommended due to their ability to handle higher voltages and currents, with logic-level MOSFETs requiring 5V gate drive and others needing 10-12V. For voltages above 300V, IGBTs are suggested. The importance of selecting a MOSFET with a drain-source voltage rating at least 1.5 to 2 times the maximum applied voltage is stressed. A protection diode (flyback diode) across the electromagnets is advised to suppress voltage spikes caused by inductive load switching. The discussion also touches on the role of resistors to limit current, though often zero ohms (a wire) is used. The original poster is encouraged to build foundational electronics knowledge before attempting complex high voltage designs. Example circuit diagrams involving a 555 timer controlling a MOSFET switch with an LED indicator and protective diode were shared. The focus is on current control rather than voltage, as electromagnet performance depends primarily on current. Overall, the conversation highlights the need for careful component selection, safety precautions, and incremental learning in high voltage pulsed electromagnet applications.
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FAQ

TL;DR: For pulsing five electromagnets at 1–20 Hz, size for current, protect against inductive kick, and respect lethal voltages—“DC above 80 V can kill,” and “Be safe and double check always.” [Elektroda, Peter Evenhuis, post #21663907]

Why it matters: This FAQ helps hobbyists safely choose switches, voltages, and protection parts when building a tunable high‑voltage EM pulser.

Quick Facts

Size the MOSFET’s Vdss to ≥1.5× (often 2×) your highest coil voltage to survive transients. [Elektroda, Steve Lawson, post #21663918]
Logic‑level MOSFETs switch from 5 V gates; many others need about 10–12 V gate drive. [Elektroda, Steve Lawson, post #21663908]
Stacking 12× 9 V batteries ≈ 108 V but only about 0.4 A—insufficient for high‑power coils. [Elektroda, Peter Evenhuis, post #21663907]
Always add a flyback (protection) diode across the coil to clamp reverse EMF and save the switch. [Elektroda, Steve Lawson, post #21663919]
Standard 555 timer use is typically ≤18 V; use a driver stage for higher coil voltages. [Elektroda, Aaron Hiniker, post #21663906]

What information do I need before designing a 1–20 Hz electromagnet pulser?

List each coil’s resistance, inductance, and rated current. Decide series or sequence operation. Pick supply voltage that achieves target current. Choose a switch device with sufficient Vdss and current. Plan for a flyback diode and a pulse source (e.g., 555) feeding a driver. Safety rules apply above 24 V and become lethal above 80 V. [Elektroda, Peter Evenhuis, post #21663907]

Why do experts say “it’s all about the current” for coils?

Magnet strength depends on ampere‑turns, so current through the winding dominates. Voltage is only the means to push that current through coil resistance and inductance. “If it’s inductors you are driving, then it’s all about the current.” Size your supply and switch around current first. [Elektroda, Steve Lawson, post #21663918]

How do I pick the right MOSFET voltage rating (Vdss)?

Choose a MOSFET with Vdss at least 1.5× your maximum coil voltage; 2× offers more margin. Inductive transients can exceed supply voltage during switch‑off. This headroom helps avoid avalanche and device failure. Pair it with a flyback diode to limit spikes. [Elektroda, Steve Lawson, post #21663918]

Do I need a flyback diode across the electromagnets?

Yes. Place a rectifier diode across each coil, reverse‑biased to supply. It stays off when the MOSFET is on, then conducts on turn‑off to absorb reverse EMF. Without it, voltage spikes can punch through the MOSFET. [Elektroda, Steve Lawson, post #21663919]

Can I drive a MOSFET gate directly from a 555 timer?

Yes, if you use a logic‑level MOSFET that fully turns on at 5 V. Non‑logic MOSFETs may need about 10–12 V gate drive. Keep gate leads short, and include a small series resistor if ringing appears. [Elektroda, Steve Lawson, post #21663908]

Are stacked 9 V batteries good for powerful electromagnets?

No. A dozen 9 V cells give about 108 V but only around 0.4 A. That low current starves the coils, delivering weak magnetization despite the high voltage. High‑current supplies are a better match for strong EM pulses. [Elektroda, Peter Evenhuis, post #21663907]

Is rectifying 120 V AC for this project a good idea?

Not for beginners. Mains‑derived DC is lethal and unforgiving. The forum cautions that DC above 24 V can burn and above 80 V can kill. Use isolated, current‑capable low‑voltage supplies and proper training before attempting mains work. [Elektroda, Peter Evenhuis, post #21663907]

What is a MOSFET, and why use it here?

A MOSFET is a transistor that acts as an efficient electronic switch. It handles coil current with low loss and is easy to drive from logic if it’s a logic‑level type. Choose adequate Vdss and current ratings, then add a flyback diode. [Elektroda, Steve Lawson, post #21663908]

When should I consider an IGBT instead of a MOSFET?

Use an IGBT when coil voltages approach a few hundred volts and you still need pulsed current. The thread suggests IGBTs for 300 V‑class applications, with strict safety discipline. Ensure proper isolation and protection networks. [Elektroda, Steve Lawson, post #21663908]

How do I estimate coil current from resistance?

Measure DC resistance (R). For steady current, I ≈ V/R once inductive transients settle. Ensure the supply can deliver that current continuously. Size wiring, switch, and diode for at least that current. [Elektroda, Aaron Hiniker, post #21663910]

How should I wire five electromagnets that must pulse together?

Place the coils in series if they must share the same current. Drive the series string with one MOSFET low‑side switch. Add one flyback diode across the entire string, observing polarity. Verify the MOSFET’s Vdss margin. [Elektroda, Steve Lawson, post #21663917]

What’s a logic‑level MOSFET gate requirement in plain terms?

Logic‑level MOSFETs reach low Rds(on) with a 5 V gate. Standard MOSFETs often need about 10–12 V to turn fully on. Match your driver to the device type to avoid heating and voltage drop. [Elektroda, Steve Lawson, post #21663908]

Can I limit coil current with a series resistor?

Yes, but it wastes power. The thread shows an optional series resistor to cap current when coil specs are unclear. Prefer setting current via supply voltage and proper coil design when possible. [Elektroda, Steve Lawson, post #21663921]

How do I add a safe switching stage to a 555 pulser?

Use the 555 to generate 1–20 Hz, then drive a MOSFET gate. Choose Vdss ≥1.5× supply and add a flyback diode across the coil. Keep control ground and power ground common and short. [Elektroda, Steve Lawson, post #21663918]

What’s a quick three‑step to protect my switch from coil kick?

Wire a diode across the coil, cathode to supply, anode to the switch side.
Size diode current to at least the coil current.
Verify MOSFET Vdss margin and layout short leads. [Elektroda, Steve Lawson, post #21663919]

Any final safety guidance for high voltage coil drivers?

Work one‑handed around energized circuits, verify isolation, and double‑check wiring. Respect thresholds: above 24 V causes burns; above 80 V can be fatal. “Be safe and double check always.” [Elektroda, Peter Evenhuis, post #21663907]

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