Newbie Here and Newbie to electronics. My apologies for asking what I believe is a way too simple question for this group. I have just begun and online course to learn more. In the meantime, I am hoping to get some guidance in a immediate problem.

My goal is to create a magnetic coil with the greatest magnetic field from a 28v AC circuit. The potentiometer is computer based managing the input of frequencies form 25 hz to 20,000 hz via the headphone jack on my laptop.

Problem: Frequencies below 1000 hz overheat the resister I have in the system. All other frequencies work well without overheating. I would like to be able to turn the system up to full power and just leave it there.

Here is what i have:
24v - 1A powered amplifier
28 AWG Speaker wire to the resister
Resister: 68 ohm-1/2 watt
Coil is circular ring with 38 AWG magnet wire with 150 turns around the ring (not around a core...just circular around the ring. (probably 150 ft)
The coil itself is not overheating, only the resister.


1. If I increase the wattage of the resistor will it reduce the size of the magnetic field.
2. Can I decrease the ohms and increase the resistors wattage to increase the magnetic field without over heating the system? Say...33 ohms and 2 watt resistor?

 

No, increase in resistor wattage wont affect the magnetic field, it stops the resistor from burning up, if you have 28Vac at 1amp, thats 28W of power, so ideally a 25W resistor is better, lowering the resistance will increase the magnetic field.

At the moment you have 12W in the resistor wasting, a 33ohms resistor needs to be 24W.. Formula is VxV/R =W

 

Thanks...I will work with it...my resistor is way too low then...Any good reference material come to mind. I am looking at various intro courses on magnatism and electronics...most are either too far advanced or way too simple...

 

Coil is circular ring with 38 AWG magnet wire with 150 turns around the ring (not around a core...just circular around the ring. (probably 150 ft)

If that's a toroidal coil then are you aware there will be only a small magnetic field external to the ring? Most of the magnetism is trapped in the ring itself.

 

Just to expand a bit in case it isn't clear, your coil has an inductance. Impedance of an inductor is proportional to frequency. So at high frequency, the coil impedance is a much larger factor than the combined DC resistance of the coil and resistor. As frequency drops, the impedance of the coil drops. At pure DC, you have only the resistance of the coil plus that of the resistor. It sounds like your coil can dissipate more heat than your resistor, so your resistor is the weakest link, like a fuse.

You should consider a fuse, by the way. If your coil gets hot and melts some of the insulation, you won't be happy.

 

You can substitute the resistor for a capacitor in series with the coil, a 100uF cap will be Approx 30 ohms at 50hz, Or 26 ohms at 60hz, and it wont get hot...

 

If you do try a cap as DD mentions, make sure it is a non-polarised type.

 

...Any good reference material come to mind. I am looking at various intro courses on magnatism and electronics...most are either too far advanced or way too simple...

Try watching some of the training videos under EDUCATION of All About Circuits

http://www.allaboutcircuits.com/video-lectures/inductors-part-1/

 

Thank you all...I have one last question regarding the system (for now). I noticed an increase in the magnetic field after inserting a 50ohm 10 watt resister. the magnetic field increase 5 fold from the smaller lower wattage. It could be that the 1 watt resistor is mostly burned out already?

Not understanding fully what all the relationships are (I am ordering an amplifier kit with teaching materials today), is there a change the increased wattage will damage the adapter that translates the sound frequency to pulsed electricity? It is an adapter unit that cost $650 so I want to be sure I keep it safe? It is designed to handle 24 volts DC. I have checked with the company but not sure if they have a clear handle on this. I have not opened the unit to look at the contents and would not know at this point what I am looking at. Hopefully that will change in the next month!

 

I'm reluctant to say much without more detail about your hookup. But usually an amplifier has high impedance (very low current) inputs that are isolated from the low impedance (high current and power) outputs. So with a normal sound system, you might do things that blow the speakers or even overload the amp, but none of that would put the input signals at risk.

I'm having trouble imagining why you had to spend $650. That would buy a lot of power in an audio amplifier.

 

I'm reluctant to say much without more detail about your hookup. But usually an amplifier has high impedance (very low current) inputs that are isolated from the low impedance (high current and power) outputs. So with a normal sound system, you might do things that blow the speakers or even overload the amp, but none of that would put the input signals at risk.

I'm having trouble imagining why you had to spend $650. That would buy a lot of power in an audio amplifier.

I understand and agree...the unit in discussion is an adapter type amplifier that transfers the frequency generator signal to electrical impulses for the the magnetic coil and several other devices. It is powered by a 24 DC amp wall plug and then provides an outlet for several devices of varying voltages....hence the high price!

I started down this venue looking at the impact of Schumann Resonances on myself and others via binaural beats and isochronic tones. I have since expanded my focus to magnetic, sound and light. So I begin my journey down the electronic's road with Electronics for Dummies and a number of practice items!

I plan on setting up an intermediate box to manage the resisters and amps for the coils and sound systems. return to either an amplifier or the adapter to protect them. Not hard I assume if one knows what they are doing.....! More later.