If I wanted to build a DIY magnet recharger would some of these caps work for that?

http://www.goldmine-elec-products.com/p ... ber=G22715

Figure I could put the 5 in parallel and charge through a resistor using a resistor and neon to indicate full charge.

A switch of some sort could be used to dump the charge into a wire around the magnet.

The ones I looked up look like they can be built from scrap around the house.
Can you tell us what your trying to achieve. Someone recently made a post on doing one from a fan motor, I've used a Weller Soldering Gun.

Thanks,
Jason

The way I've seen it done has always been a quick discharge of a dc voltage usually a high voltage.

That induces a momentary high current in the coil of wire around the magnet which recharges the magnet.

This would be mostly for the 1920's speakers.

1980's, I once had access to a magneto repair shop. There was an olde tyme magnet charger bolted to the bench and a couple of parallel connected 6 volt L/A batteries under the bench. I called the day before and the batteries were put on charge. Setup the magnet to be charged on the pole piece and held the old car starter floor button in, while holding the button gave a couple whacks to the magnet at the "U" bend. Released the button, done...

Name plate on charge only gave specs. "6 volts 300 Amps"

I charged the magnet on the Kohler Eisemann magneto and magnets for Teletype Polar relays. The Eisemann magnet got overcharged I could not shut the engine down by shorting the points... So I put a shunt of iron bar across the outside of the horseshoe, that killed enough magnetism to properly stop the engine. Years later I removed the shunt, the magnet had lost enough strength for the magneto to shut down normally.

There are many plans for the high current charger on the web. I was going to build one but lost interest as I haven't had the need to recharge magnets lately. I also retired, lost my access to a free machinist to make the armature and sundry pole pieces...

The old engine and tractor collectors always have a need for the chargers...

Chas

My other hobby is Model T Fords ... I have a 1916.
The model T has 16 horseshoe magnets mounted on the flywheel
that generate an AC voltage that provides power for the ignition coils.
I have recharged many Model T magnets over the years.

The key to recharging a magnet is applying a momentary intense magnetic charge to the magnet.
The intensity of the charging field is determined by how much current
you can push through how many turns of the charging coil.
i.e. Ampere-Turns.
10 Amps through 1000 turns is the same as 1000 Amps through 10 turns.
Guess which one is easier to handle.

The test for Model T Flywheel Magnets is if it will pick up and hold at least a two pound dead weight.
I have two homebrew methods of recharging magnets.

First is a Demagnetizer I found on eBay.
It was originally powered with 120 VAC.
I did some testing and determined that the electromagnet had about 3200 turns.
I use a 12 Volt battery to pulse the coil which will draw about 23 Amps.
This yields a charging field of about 73,600 Ampere-Turns.

The second is a Growler (Armature Tester for Starters and Generators).
Instead of applying 120 VAC, I bridge rectified the 120 VAC and applied the DC to the Growler.

In both cases I only pulse the power to the magnetizing coil (less than 0.5 seconds).
I both cases both recharged magnets pass the "Model T Test".

I once used an EICO power supply/battery eliminator that I had at least 20,000uF of capacitance as the filter caps which put out 30Vdc unloaded for recharging an AK E3 speaker magnet.

Wound a few turns around the magnet then turned the supply on and back off and connected the other end of the wire to the other terminal.

Seemed to work, but somewhere it was mentioned that a higher voltage was a better way to do it versus something like a low voltage boostcap.

Saw those caps yesterday and figured they would easily work for the intended purpose and would hold up given they are photoflash caps.

Of course a bit more dangerous given the higher voltage.

This is very interesting!

I picked up a growler at a yard sale for $8 a while back, never considered passing DC as a magnet charger. I'll keep that in mind and give it a look over as to how much DC current it can with stand.

So what is the value in ampere turns to charge an atypical tungsten magnet?

I would suspect the "overcharging" does no harm or good, as the stronger charge would soon fade?

Somewhere in an old hand book I read that recharged tungsten magnets have to be boiled in hot water for "several hours" to normalize the charge, aging would be more appropriate, your thoughts?

Would the same ampere turns figure apply to Alnico?

I have a few horseshoes that probably came from magnetos. Since I will probably never encounter a mag with missing magnets where can I unload them or just scrap?

Chas

I have a meter for a GR 1800 A/B VTVM. These meters are precision calibrated with shunt resistors for 50 uA. The one in question calibrates at exactly 50 uA without a shunt resistance.

I've heard that heat is bad for magnets, and the GR 1800X VTVMs have no cabinet ventilation and the manual instructs to keep them turned on as long as possible to minimize drift. I don't think it's a stretch to conclude this particular meter came from a VTVM that was kept on.

The question now becomes is it possible to remagnetize properly a magnet that came out of an old movement like that? These were top of the line movements back in the day, and spares like I have are rare and getting rarer every day. It might work fine for years, possibly even decades if used minimally, but eventually it will need recharging, and being overcharged would be just as bad as being undercharged.

Just a thought.

Exactly, changing the strength of a meter magnet essentially, changes it's sensitivity.

If no access to a meter facility then altering shunts to keep the meter in range may be the answer. Possibly using an error chart against a standard.

ARF does have at least two (more?) resident meter experts ( by trade).

Posing the question in a separate topic may bring it to their attention for a more professional answer.

Magnet charging for "non-calibrated" devices is something that can be done without the need for an exact measurement in gauss.

YMMV

Chas

I have calibrated my other similar meters by changing the shunts. They've all aged to some extent, and needed recalibration. Unfortunately, you can only reduce the shunt to zero, and then shunts don't do any good because you can only further reduce sensitivity below 50 uA.

One could possibly change the VTVM circuitry to keep it calibrated overall, but I consider that cheating, quite honestly, and I'm not entirely certain what other effects that might have.

Not sure if a 'meter facility' even exists. I know there was at least one person here on ARF that would repair meters, but I don't think even he had any capability for remagnetizing. I'm not even sure if he's around any more.

Chas,

Tungsten is at best only very weakly magnetic.
I have not encountered a tungsten magnet before.

As far as overcharging goes, once a material reaches magnetic saturation, additional magnetizing energy will have no effect.

Heat does reduce magnetic strength over time.
This is why Model T Flywheel Magnets need to be recharged every 30 or 40 years.
The magnets are internal to the engine.

I have never tried to recharge an Alnico magnet - I can't comment on this.

Check some of the Old Engine websites for magneto repair guts - then might be interested in the spare horseshoes.
https://www.smokstak.com/

I used to use the field coil for a Magnavox R-3 horn speaker as my magnet charger. But some years ago I bought a couple of 1/2" diameter x 1" long super magnets. The kind you soon remember how bad you can get pinched if you don't handle them right... Just stroke them on a horseshoe. If you can't do that, stick to one pole and then tap the old magnet with a brass hammer a few times...

Works for me...

Robert

That just might be a good way to add a little magnetism at a time.

Thanks Robert.

Chas,

I did a little research into the metallurgy of Model T flywheel magnets.

Ford had a 'magnet steel' that was listed as :

.82 -.90 Carbon
.30-45 Manganese
2.5 - 2.6 Chrome
.25 - .40 Silicon
Normal trace of Phosphorous
Normal trace of Sulfur

There is no Tungsten in Model T magnets.

Interesting, since FORD made and alloyed the various metals for there vehicles likely to keep the processes under close supervision. Tungsten magnets may have been covered by a patent at the time. Having to pay a "alloy royalty" was not a good idea.

Thanks Chas...