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CHEAP CASE NECK INDUCTION
ANNEALER EXPERIMENT
By Wayne McLerran
Posted 12/7/18

Please note that the experiment was not successful but the details should be
interesting and you should learn something from the article.

If you’re already annealing your brass case necks or considering doing so you’
ve no doubt researched the subject to some extent on the Internet.  There have
been numerous threads on reloading forums discussing annealing brass cases to
soften the work-hardened necks, extending the life of the cases and arguably
increasing the accuracy of the ammo.  Induction technology seems to be the
latest trend when designing case annealers.  But induction annealers are very
expensive, typically around $1,000 or more.  Therefore I thought I’d take a shot,
pun intended, at configuring a cheap solution with $100.00 being the maximum
expenditure.

Run a search on eBay or Amazon.com for “induction heaters” and you’ll find
many, many units in the $30 to $40 range with some as low as $12.  They’re
typically used with a round ceramic crucible that fits inside a 2” diameter coil
made from 5mm outside diameter (OD) copper tubing.  Made by companies in
China and Hong Kong, the heaters are used to melt precious metals and other
materials and, depending on the unit, run off of 12V to 48V DC.  They could be
connected to a car battery for 12V or two batteries in series for 24V, etc.  But a
much better solution is to purchase a switching power supply, also available
cheaply from similar sources.  Although I have a very nice propane-powered
Vertex Bench Source brand annealer, I was curious enough to purchase one of
the Chinese 12V to 48V units and a switching power supply to see if it could be
modified to work for annealing case necks.

If you research the suppliers of ready to use albeit expensive case-neck
induction annealers you’ll find they’re rated at around 1000W (watts) in order to
anneal a typical case neck in 3 seconds or so.  Therefore, since power measured
in watts is equal to voltage (V) x current measured in amps (A), an equivalent
unit powered by 48V would require a power supply capable of supplying
approximately 21A.  But since $100.00 was my self-imposed limit a 24V 20A
setup was selected.  The combination of induction heaters and power supplys
are available on eBay for around $60, and lower power combinations are
available for less.  Will they work annealing case necks?  There was only one
way to find out.

A 1000W ZVS induction heater and a 24V 20A switching power supply were
ordered off eBay from Chinese and Hong Kong suppliers.  The total cost was
$59.26.  The heater came with a fan attached to aid in cooling the electronics.  In
less than two weeks the units arrived.  A 2” diameter coil came with induction
heater electronics.  There were no instructions but after inspecting the unit
closely it was obvious how to install the induction coil and how to connect the
required power.
Although the induction heater could handle up to 48V DC, the recommendation
was to use it with a 24V power supply.  By the way, while researching the
subject of cheap Chinese or Hong Kong induction heaters I ran across several
warnings not to apply power without the induction coil installed or the heater
electronics will be damaged.

Induction heaters work on the principal of creating “eddy currents”, which are
localized electric currents induced in a conductor by a varying or changing
magnetic field.  When current flows through a coil, a magnetic field is created
around and inside the coil.  When a conductive material is inserted into the coil
the quickly changing magnetic field produces eddy currents in the material.  The
materials resistance to eddy currents generates the heat.

The 2” diameter coil supplied with the induction heater was designed to heat
precious metals in a ceramic crucible.  Although it quickly heated iron rods of
various diameters red hot, it would not heat a solid brass rod or .45-70 case
neck when inserted in the coil.  Ferrous metals such as iron and steel are much
easier to induction heat than non-ferrous metals such as aluminum, copper and
brass.  Non-ferrous metals, especially those with low resistance to electrical
currents, require a higher concentration of magnetic fields and eddy currents.  
One method to increase the frequency and concentration of magnetic fields and
eddy currents is to reduce the coil diameter.  After experimenting with different
size coils made from 12-gauge copper wire, the unit would very quickly heat
case necks with a 1” inside diameter (ID) coil.  Since a 1” coil would be hard to
form using the 5mm outside diameter (OD) copper tubing supplied with the unit,
one was made from 4mm OD copper tubing ordered on Amazon.com from a
Chinese supplier.  The 1 meter length of tubing was $7.81.  The coil was formed
by slowly wrapping it around a 1” diameter wooden dowel, allowing for
sufficient length on each end to attach to the heater electronics and vinyl tubing
for cooling.

By the way, I quickly realized why the supplied 2” diameter coil was made of
copper tubing rather than solid copper wire.  Even with the unit running without
an item inserted in the coil, the coil eventually gets warm due to the eddy
currents created in the coil by the coil itself.  And when used to heat metal, the
radiant heating from the metal will definitely heat the coil.  Therefore the coil is
made from copper tubing to allow pumping cool water through it for extended
use, which is especially important when the diameter of the coil is reduced.

To cool the coil a small cheap 115V (AC) submersible water pump was
purchased from Amazon.com, one made for fish aquariums and bird baths.  The
price was $8.65 and a length of 0.170 ID, 1/4” OD clear vinyl tubing was
purchased from a local hobby shop for $1.95.  After connecting the tubing to the
induction coil and pump, the pump was submersed in a bowl of cool water.  It
worked great and supplied plenty of cooling as long as the water was not
allowed to get excessive hot.

Finally, due to the induction heater design, a switch must be used to connect the
output of the power supply to the induction heater.  The switch does provide the
capability of turning the heater on and off as needed rather than unplugging or
turning off the power supply.  But more important, it’s required to “shock” the
heater circuitry into running correctly.  If the heater was connected directly to
the power supply, as the supply was turned on the relatively slow increase in
power supply voltage would destroy the MOSFETs (transistors in the heater).  
Suffice it to say that the coil circuitry must be “kick started” to oscillate or ring
properly to create the quickly changing magnetic field, which is accomplished
by the switch.  Therefore the power supply must be on and running prior to
engaging the switch to the heater.  Adding a switch was less than $5.

Once everything was setup and connected (the induction coil connected as noted
earlier, the water pump running and water flowing through the coil), the power
supply and then the induction heater was turned on.  A .45-70 case neck was
inserted into the coil.  Only 4 seconds was required to anneal it which was
obvious by the neck color change.  So, for less than $83 I had a functional and
cheap case neck induction annealer.  But there was a problem!

After annealing several case necks I became aware of an unusual burning
smell.  It turns out the bottom of the circuit board was blistered and burned
close to the input to the coil and some of the large capacitors were getting
extremely hot.  The smaller diameter coil more than doubled the current
requirement of the heater circuitry.  As illustrated in the photos below, without
an item inserted in the coils (unloaded) the original 2” diameter coil setup
current draw was 3A with 24V.  With the 1” diameter coil the unloaded current
draw was 9A.  Inserting a metal rod or case neck into the coil essentially
doubled the unloaded current draw of both setups.  After attempting some
modifications to the circuitry to fix the problem it was obvious the circuit board
design and some of the components were not adequate to handle the increase
current.  So the experiment was not a success.  No doubt a beefier circuit board
could be designed to work, which I may tackle at a later date.
Although the original goal of the experiment was not realized I learned a good
bit during the process.  By the way, after repairing the burned section of the
circuit board and with the original larger coil installed, the setup works fine and
the heater can be used as designed.  Without the multimeter and amp gauge
components, the setup will be kept handy in my workshop for quickly heating
up smaller metal parts for hardening and other applications.

Wishing you great shooting.
Wayne