Making A Magnet - Off topic

Richard J. Nelson rjnelsoncf at
Sun Jul 20 09:15:40 MDT 2014

What an interesting idea.


I will have to test this with known wire sizes.  Circuit breaker
characteristics vary greatly and they don't respond very fast unless the
current is many times their rating.  I wonder how long you could get away
with, say, 100+ ampere current draws and I suspect it could be several AC
cycles.  Certainly a piece of wire is much cheaper than using an actual


Another thought is to use an NTC thermistor inrush current limiter.  They
make some very low resistance (as low as 0.2 ohms) high energy values (30
Jules) these days.


My favorite way to make a magnet is to use an iron rod hanging on a string.
Orient it parallel with the earth's magnetic field (pointing to magnetic
north - check where it is these days because it is moving 20 miles a year
into Canada - and tilted slightly upwards if you are in the US - and then
rapping it sharply with a hammer.  Presto, it is detectably magnetized.


I use magnets a lot and I use a dozen magnetic tool holders.  My Philips
head screwdrivers get magnetized all the time and I use a demagnetizer I
made ten years ago as shown in the photo below.  The coil ID is 2-3/4" and
it is very effective.  There is a transformer inside the old data cable
switching cabinet.  The power switch is a spring loaded off type.  I have
tried all kinds of demagnetizers and none of them are as effective as this
one.  The coil is 14 Ga. house wiring and the turns were determined for
maximum 2x current draw from the transformer.





Perhaps I can use the same coil and add a switch to magnetize or demagnetize
adding a small wire fuse holder/fixture as shown in the second photo.




X < > Y,




-----Original Message-----
From: hhc-bounces at [mailto:hhc-bounces at]
On Behalf Of Richard
Sent: Saturday, July 19, 2014 10:21 PM
To: 'Handheld Computing Conference discussion list'
Subject: RE: zapping NiCAD Cells


You reminded me of the old procedure for magnetizing an iron bar.   Wrap it

with heavy insulated wire, and wire it in series with a much finer wire that

acts as a fuze.   Then plug it in.   Current rises as rapidly as the AC

power waveform and the inductance will allow until the fine fuze wire blows.

The current gets very high, more than enough saturate the iron bar beyond
its magnetic capabilities.


The fuze wire must be fine enough to blow in a small fraction of one cycle
of the 60 Hz AC power.


I tried this method when I was about 15.   My dad smelled the burned wire

and came running in.   When he saw what I had done, he was really angry.

But the house circuit breaker did not blow.   I guess my fine fuze wire was

fine enough. 




-----Original Message-----

From:  <mailto:hhc-bounces at>
hhc-bounces at [ <mailto:hhc-bounces at>
mailto:hhc-bounces at]

On Behalf Of Roger Hill

Sent: Sunday, July 13, 2014 9:51 PM

To: Handheld Computing Conference discussion list

Subject: Re: zapping NiCAD Cells


Hi all,


The capacitor method would undoubtedly be better, though my model train
power supply did work every time for the cells in HP printer (or tape drive)
battery pack.  I didn't aim for any particular amount of power applied.


Actually, I do use a 3500-uf capacitor charged up to 30+ volts to operate
the electromagnets used to throw the track switches on my model railroad
layout.  The switch machines have coils designed to operate on 12-15 volts
AC/DC, but by giving them a good "wallop" from the capacitor they are much
more powerful, and because the pulse is very short, the coil is less likely
to burn out (which could happen if a steady voltage is applied for too
long).  I use relays and other capacitors to control the time (around 1

second) for charging the main capacitor so that it is ready to throw another


Looks like the recommended procedure (below) is similar to my
switch-throwing circuitry but with a bigger zap.  And agreed, the zapping
procedure can effective for cells that won't hold their charge (due to
shortage from internal conducting "whiskers" or filaments), but would
probably not be effective from a cell that is weak for other reasons (or has
too many whiskers).


-- Roger


------------ On Richard N's messages ------------


> The usual procedure is to charge a capacitor and discharge it into the 

> cell. This provides an energy controlled pulse.  Check the Internet 

> for UF values and voltages.


> "To zap a NiCd battery, a 47,000mF capacitor is charged to 90V, after 

> which the raw power is discharged directly across a single NiCd cell 

> of 1.2V. After the shock treatment, the cell is cycled and then zapped 

> once more. Experts say that once a cell is treated and used in 

> service, zapping will no longer improve performance, nor does it 

> regenerate a weak cell."



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