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Magneto charger magnetizer

lister man

Registered
Hi there from the uk

I have been building a magnetizer i plan to use on mains voltage , When carrying out tests i have found when my coils are connected in series the ohms reading is 35ohms, i have connected them in parallel and i get a 9ohms reading. Would it be better to have them connected in parallel as the amp draw would be higher? Hope someone can help.

Andrew
 

Scotty 2

Registered
It would all depend on how you wound the coils.
Do yourself a favour and get a book call by David Gingery entitled "How to build a Magneto Magentizer"
Well worth the read.

Cheers Scott
 

neonman

Registered
Not sure how many turns your coils have. Assuming rectified mains voltage of 240V, current through the coils in series is about 6.8A. In parallel, the total current would be 26.7A, or 13.35A per coil. So if we assume you have 1000 turns in each coil, you'd have 2000 times 6.8, or 13600 ampere-turns in series. In parallel, each coil would have 13.35 times 1000 or 13350 ampere-turns, or 26700 ampere-turns total.

Connecting them in parallel would definitely provide more ampere-turns, but the current is significantly higher. Also the heat generated would be significantly higher. Since power is current times voltage, each coil in parallel would need to handle 13.35 * 240 = 3204 watts. Not unreasonable for short duty factor.

Given the higher ampere-turns generated in parallel, I'd do that if you can safely supply the current.
 

PaulGray

Subscriber
Last Subscription Date
12/24/2019
The other thing to consider is the saturation magnetization of the pole pieces. This is how efficiently the pole pieces on your charger converts amp turns to magnetism to deliver to the magnet to be charged. https://en.m.wikipedia.org/wiki/Saturation_(magnetic)#/media/File:Magnetization_curves.svg
Certain iron alloys support a much higher field strength; cast steel and silicon steel allowing about twice the field for far less amp turns than other ferrous alloys. If your coil saturates the pole pieces, then no additional amp turns will get you more field and higher charge. So bigger is not necessarily better. I made my charger from two truck starter solenoids (several thousand turns) and at 12 volts, both coils wired in parallel and probably drawing like 15-20 amps, I’d put it up against most other home brew units. Also make sure the bottoms of your poles are connected and fit tightly against the base plate to not have any air gaps which can diminish the total field strength. I haven’t read Ron Gs book but I have working schmartz since I’m a materials guy by trade.... still, since the coils are only used momentarily, give them what the mains will handle and what the wire will take without frying the windings...
 

Molinegb

Registered
Called the Q of coil or efficiency. Basic electronics formulas. Have most memorized after 43 years.
 

radiodoc

Subscriber
Last Subscription Date
02/04/2021
I would have thought if both coils had the same resistance that in parallel the resistance would be 17.5 Ohms instead of 9 Ohms.
 

neonman

Registered
The formula for calculating resistance of parallel resistors is

1/Rt = 1/R1 + 1/R2

Going through some basic algebraic multiplication and division, you can end up with

Rt = (R1 * R2) / (R1 + R2)

So if the coils total 35 ohms in series and otherwise close to the same resistance of 17.5 ohms each, you end up with

Rt = (17.5 * 17.5) / (17.5 + 17.5)

which is 8.75, close to the measured 9 ohms.


Saturation of the core material is something I didn't consider, and would certainly factor into the decision to go in series or parallel.
 

lister man

Registered
Regarding the coils they was not wound by me i acquired the coils from someone else who had started the project.
The cores measures 2 3/4 " diameter and length 10" The wire used is 18 gauge enameled wire.

I have run some test on low volts 12v dc battery and there feels a little more magnetic pull/ flux on parallel, the amps drawn on parallel at 12v is 1.3amp and
0.3 amp when wired in series ...
 

barry ayres

Registered
look to me as if you have approx 830m of wire per coil this gives approx 3175 turns per coil

therefore in series 6350 turns at 6.8A = 43,000A/T very good for steel based magnets (horse shoe) but not enough for alnico types

or in parallel 3175 x 13.5 x 2 =85,700AT exactly what lucas recommend for charging there magneto,s

unfortunatley lucas also recommend a core area of 9sq inches but that must depend on the material the cores are made from

hope this helps

barry.
 

lister man

Registered
I have now run the magnetizer on mains 240v in both series and parallel and there is a very strong pull in parallel (even the spanners on the wall move!)

One confusing thing when i initially tested it on 12v you could change the polarity of the battery and the north and south poles would switch round , but on the 240v when i switch the + - terminals on the rectifier the poles do not change, I was just wondering why this was??
 

landreo

Registered
Changing the electrical polarity will change the magnetic polarity. Did you use a voltmeter check the polarity of the wires where the power supply connects to the magnet wires?

It is possible to remagnatize your compass if held too close to the charger which may give the impression that the field polarity did not change.

It will be interesting to see what you determined is really happening.
 

eddie bedwell

Registered
Hi Team,
back in the mid 1960's at The Cat Dealer as an apprentice I used to re-charge magneto magnets with DC voltage from a 24V battery pack used to start big Cat Diesels.

To my not very electrical mind I would think the AC voltage would change the charger pole polarity every half cycle and confuse heck out of the magnet--possibly discharging it.
I do stand to be correct by smarter electrical and magnetic minds.
Cheers,
Eddie B.
 

neonman

Registered
Lister-man did mention that he powered the charger from mains using a rectifier, which should be sufficient to keep from demagnetizing anything. I have wrecked a perfectly good compass by leaving it too close to an electromagnet. I'm still puzzled by the previous post that mentioned not being able to detect a change in polarity of the magneto charger when the + and - were reversed. That can't really happen if DC or rectified AC is used. Unless the rectifier is bad, passing AC to the magneto charger.
 

lister man

Registered
I checked the rectifier with multi meter and it is showing a dc current as it recognises a + and - but it still does not switch the north and south poles when you switch the wires on rectifier.

So i went back to my 12v battery and reversed the wires on the battery and it does switch North and south poles as expected. Maybe my rectified 240v is not giving a clean signal, the rectifier was a full wave one, maybe i have a bad one???
 

lister man

Registered
Landreo was right my compass got magnetised so was getting a bit confused:D
All sorted now and working properly .

Is there any consequences if magneto magnet polarity gets reversed?
 

barry ayres

Registered
probably not so long as its saturated as most mags produce alternating sparks any way (ie 1 & 3 positive and 2 & 4 negative thats the order of sparks produced not cylinder numbers) ideally you want all negative but very few multi cylinder mags do.
out of interest what current does your charger draw? i hope to get back to building mine soon it should theatricality draw 22A on a 240V rms supply.
 
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