help building a heating coil

Thread Starter

bootlegengineer

Joined Dec 5, 2016
60
Hi! So I'm building a heating coil powered directly from the wall outlet of 120V 15A. To achieve this, I wired a standard outlet plug to a center tapped transformer (the one from my previous thread) that transforms voltage to 12V or 24V. I then wired a 25 V 10,000uF capacitor to the two outside wires to produce 25V across the capacitor, which is then attached to each end of a thick, 5ft steel bar compacted to a 1ft spring. But before I plug this in, I need to know something very important. When I calculated the energy going across the capacitor, I got 3,125,000 Joules per second, which converts to 3,125,000 watts!! Did I just figure out a way to pump insane amounts of power or am I just a jabroni? If I really did, I'm terrified that I might melt my entire circuit!
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
What are you hoping to achieve with a capacitor in this AC circuit? Apart from loading the transformer.
Induction tank circuit?
Max.
 

wayneh

Joined Sep 9, 2010
17,496
The capacitor serves no purpose.

What is the cross sectional area (wire gauge) of your bar?

Do NOT try this until you are fairly sure it'll be safe. It sounds really bad so far. It'll blow your circuit breaker.
 

Alec_t

Joined Sep 17, 2013
14,280
DON'T plug it in! Unless you use a rectifier bridge between the transformer secondary and the capacitor you will destroy the capacitor if it is a polarised electrolytic type. Also, the peak voltage from the secondary will be at least 24 x 1.414 = 34VAC (more if the transformer regulation is poor). For safety's sake your capacitor needs to be rated for 50V or more. Your 25V one is inadequate and may explode.
 

Thread Starter

bootlegengineer

Joined Dec 5, 2016
60
DON'T plug it in! Unless you use a rectifier bridge between the transformer secondary and the capacitor you will destroy the capacitor if it is a polarised electrolytic type. Also, the peak voltage from the secondary will be at least 24 x 1.414 = 34VAC (more if the transformer regulation is poor). Allowing for voltage drop in the bridge the bridge output will be about 32VDC if only lightly loaded. For safety's sake your capacitor needs to be rated for 50V or more. Your 25V one is inadequate and may explode.
then should i just use the center and one side wire for 12 volts instead?
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
Im trying to prevent the circuit breaker from tripping by lowering the current.
The only hope you would have there on AC is if the coil and capacitors represented a resonant tank circuit at 50/60hz.
This is the theory behind induction heating.
What is your reasoning for the capacitor?
Max.
 

Thread Starter

bootlegengineer

Joined Dec 5, 2016
60
The only hope you would have there on AC is if the coil and capacitors represented a resonant tank circuit at 50/60hz.
This is the theory behind induction heating.
What is your reasoning for the capacitor?
Max.
if the current is alternated between one side and the other, wouldn't the coil heat up? its how an induction heater works i believe.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
The maximum current would be the coil alone across the AC supply, all you would achieve by adding a capacitor is to reduce or control the actual current.
Your frequency is fixed.
Max.
 

Kermit2

Joined Feb 5, 2010
4,162
A voltage of 1 volt
Will cause 1 amp of current to flow
Through a 1 ohm resistor.

A voltage of 12 volts will make

1 amp of current in a 12 ohm resistor.
2 amps of current in a 6 ohm resistor.
12 amps of current it a 1 ohm resistor.

What is the resistance of your steel bar?
That will determine the amount of current that will try to flow through the bar when attached to a voltage source like your transformer.
 

Thread Starter

bootlegengineer

Joined Dec 5, 2016
60
A voltage of 1 volt
Will cause 1 amp of current to flow
Through a 1 ohm resistor.

A voltage of 12 volts will make

1 amp of current in a 12 ohm resistor.
2 amps of current in a 6 ohm resistor.
12 amps of current it a 1 ohm resistor.

What is the resistance of your steel bar?
That will determine the amount of current that will try to flow through the bar when attached to a voltage source like your transformer.

its about 4 gauge (just remeasured it) so the resistance would be about 0.001 ohms
 

Thread Starter

bootlegengineer

Joined Dec 5, 2016
60
my problem is i cant afford a resistor big enough to support a high wattage, which i need to heat up the coil. so im trying to find a way around that
 

wayneh

Joined Sep 9, 2010
17,496
id say about 00 gauge
Standard wire 00 gauge is 0.08mOhm per foot, so you're looking at about 0.4mOhms total resistance across your coil. This will carry more current than you can supply without getting warm. Resonance or not won't matter.

Same story with 4 gauge. 1.25mOhm total resistance.
 

Thread Starter

bootlegengineer

Joined Dec 5, 2016
60
Standard wire 00 gauge is 0.08mOhm per foot, so you're looking at about 0.4mOhms total resistance across your coil. This will carry more current than you can supply without getting warm. Resonance or not won't matter.

Same story with 4 gauge. 1.25mOhm total resistance.
is there a way to decrease the current without a giant resistor then?
 
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