As promised, I brought the Gauss meter (it measures magnet strength) home and did some testing. I have two magnet chargers. One I made from a Growler and one I made from an industrial demagnetizer. Here is what I found :
Magnetic strength output at the poles :
North Pole - 2550 Gauss
South Pole - 2600 Gauss
Converted Demagnetizer :
North Pole - 3560 Gauss
South Pole - 3510 Gauss
I recharged several magnets. Initially, none would pick up my 3 pound test weight. I gave the magnet an initial charge (end on)on one of my chargers, then measured the strength. Then Whacked it while charging, then measured the strength. Then charged it on it's side, then measured it.
The initial charge brought them up from less then 200 Gauss to about 700 Gauss. They would pick up the test weight easily at this point. Any additional charging, whacking, laying down, etc. made less then 2 % difference.
Has anyone else made any measurements?
Has anyone determined what Ford's measurement relates to in modern terms? I know the manual states a minimum of 50 "units" on Ford's tester but there's no definition of what the units are. I suspect it may have been Maxwell per square inch but I don't know for sure. It it was, that would equate to about 320 Gauss as a minimum for a magnet pole pair (NN-SS-NN...).
Note: 50 units was stated as a test for mounted magnets using Ford's hand-held tester.
Ops, that's not right either. I multiplied instead of dividing. Must not be Maxwells. Sorry. If the "unit" is Gauss, 50 seems pretty low for a minimum. Any thoughts?
Interesting Bob-- I am tempted to send you a few magnets charged with my Mickey Mouse setup and see what the real story is!
You send them and I will measure them ... or ... come on up on a Saturday
50 Gauss wouldn't pull the hat off of your head. Around 700 Gauss will pick up 3 pounds and hold it pretty firmly.
I'll have to take some before and after Gauss readings and report back later today.
Murray Fahnestock wrote the Ford magnet required 1500 Ampere/turns to saturate the magnet core fully up one side of the Hysteresis curve. I have a photo of the tool used in the factory and I can certainly beleive it from the size of the windings.
Ron the Coilman
Exactly Bob. I was referring to the test shown below. For magnets out of the car, the tester should read 35 units or more. My question was; What are the "units" Ford is referring to during the test? Certainly, this is not Gauss. I'm interested in a "unit" conversion to modern terms.
With the in-car test, are you really reading the field of two north (or south) poles at a time?
Apparently so Tom. With the magnets mounted, as shown in the test photo, 50 units or better should be read on the meter. With a magnet removed and tested individually, a reading of 35 or better is the target. The flux density of the dual poles must be interacting.
On Thursdays I take my Bride to lunch so I only had a few minutes in the shop this morning.
I have a set of older analog field strength meters made by Electro-Matic. The largest of the three has a scale 2000North-0-2000South. I spoke to a technical representative at the manufacturer and was told these meters are calibrated in Gauss and are generally used to check machine tool spindles and construction steel for residual magnetism that could affect tool accuracy or construction problems.
I selected three used Model T magnets, checked them for cracks and ground the ends flat so they made good contact with the flat surface of the weights I used for test lifting. Before recharging each magnet would lift only 1 lb 10 oz and the ends of the INDIVIDUAL magnets read as follows using the Gauss meter.
Here is a photo of my magnet charger.
I connect the magnet charger to a large battery charger which is capable of 250 Amps in shorts bursts in the “start” mode in parallel with a 12 volt battery to act as a filter to flatten the ripple riding in the top of the DC. I have a hand pushed starter switch to energize the current to the charger.
I recharged each magnet with five one half second bursts and rechecked the field strength.
After recharging each magnet would lift 4 lbs 10 oz. I plan to leave them undisturbed for a week and recheck the filed strength and lifting capacity and report back. I also noticed that when you paired TWO ADJACENT recharged magnets as they would be mounted on the flywheel the field strength was off the 2000 scale in both N and S directions.
One additional observation; when the starter switch was energized the current through the charger measured 18 amps. I do not know the exact number of turns in each charger pole, but estimating the wire size, core diameter and core outer diameter there has to be at least 90-100 turns on each pole core creating at least 1500 ampere/turns per core.
I will report back on any declining magnet strength in one week.
This was fun.
Ron the Coilman
Hmmmmmm. There seems to be a substantial difference between the readings Bob got on recharged magnets and yours Ron. Would anyone care to explain?
Years ago I got a 6 volt magnet charger ,the magnets can lift 5 kilogram = 11pounds, that gives about 30 - 35 volt AC magneto output
Some thing is wrong with the weight, Hope the pictures come through. The scale is close, if you look at the picture of the weight with the one pound magnet on it the weight is exactly four pounds.
The second picture has a 8 3/4 pound boring bar holder with a exactly 2 pound weight setting on top of it plus a 1 pound magnet. It appears the weight you are lifting would have to be much larger to equal 11 pounds.
I might not understand the scale--- if the weight the magnet is setting on is attached to the base and the counter weights on the opposite end are used to pop it loose then I am wrong.
I don't know what you mean whith your last message I think my Englich is not good enough'
can you translate it to Dutch ????
Think I have it now Toon!-- Ingenious design.
There seems to be such a large difference in the weight lifted but now I think its the testing method yours is much more accurate then mine!
Question? is the block the magnet is setting on steel or iron?
My English is so poor don't know how I could ever speak Dutch!!
Paul, it appears to me that there's three weights on Mr. Boer's scale. The round base on the left is probably attached to the base and used strictly as a magnetic pull surface for the hanging magnet. All the weights on the right, two on bottom and one on top, must add up to 5Kg. Mass does not equal density. The weights could be lead.
Dang nice test stand I might add.
Here is a definition of Pull Force and how it is measured by one manufacturer:
Pull Force - The force required to pull a magnet free from a flat steel plate using force perpendicular to the surface. The limit of the holding power of a magnet. The pull force listed is actual data acquired by testing using our state-of-the-art force test stand. A comprehensive table of the pull force for all of our stock magnets is available here: Pull Force Table.
We test for two different values of pull force using two different setups.
TEST SETUP :
11. How is the pull force of each magnet determined?
All of the pull force values we specify have been tested in our laboratory. We test these magnets in two different configurations. Case 1 is the maximum pull force generated between a single magnet and a thick, ground, flat steel plate. Case 2 is the maximum pull force generated with a single magnet sandwiched between two thick, ground, flat steel plates. Case 3 is the maximum pull force generated on a magnet attracted to another magnet of the same type.
The values are an average value for five samples of each magnet. A digital force gauge records the tensile force on the magnet. The plates are pulled apart until the magnet disconnects from one of the plates. The peak value is recorded as the "pull force". If using steel that is thinner, coated, or has an uneven or rusty surface, the effective pull force may be different than recorded in our lab.
I would like to know if its iron or steel the magnet pulls against. As I understand it a magnet will not pull iron as well as it will pull steel. Also wonder if that size block might have some thing to do with it. I intend to make some thing simple possibly from wood so it will compare. The best I could lift with my method was about 5.35 pounds
Big difference from 11 pounds.
Paul, Ken ;
The round steel block on the left is attached to the base , for the test I grind the legs of the magnet flat so there is more surface .
Thanks Bob, Toon,
Now I can make something comparable!
Test rig made from two wheels, string, and a free ground plate from a G sale.
Now I can get 11 pounds!
As promised I checked the three magnets I recharged a week ago using the same field strength meter. During the interval they were just laying on the bench with no keepers. There has been a 2-3% decrease in strength and all three will still dead lift 4lbs 10oz.
Ron the Coilman
Sort of think your lift test platform has a health problem as mine did. I just took a legenth of 1 1/2"---- 8 1/2 pound square tubing ground off the center and easily dead lifted it after centering on my test stand.
I am sure your magnets will dead lift more then that.
Now that I know how a magnet should be tested it starts to be come obvious what the testing problems are.
I can now see why they test with a fixed plate rather then something that can move when you test it.
After posting the test with the two wheels a second look at it I noticed that I had pushed the magnet to the side. Look at the angles of the string from the magnet to the wheel above it then compare it to the angle of the string from the pot of weights to the wheel above it. you will notice they are different. The reason could be several things-- slightly only a degree off grind to flatten the ends, or one leg 1/16 shorter then the other.
The point is if you are not exactly center on the pull point between the two legs AND exactly center on the weight AND if the center of the V is off center of the bottom of the two legs you will lift an edge of the magnet way before its true power and it will release.
The string helps a bunch because you can slide it to one side or the other to get the center of the pull.
The way I tested was to put a pull on the string to the magnet by holding the string tight to the wheel and put a pull on it, if the magnet started to lift on one side it was adjusted to get a straight pull.
If it would be of interest to you. I can pretty well test and inform you of the number of turns of wire on each of your cores. There exists some electronic measurement equipment that can determine pretty accurately the number of turns on a given core. The procedure is pretty simple. You need a stable AC oscillator or signal source which probably could be the AC wall power and then a very accurate digital AC voltmeter. You then wrap say 10 turns additional around your existing coils using a small gauge wire. You measure the exact value of the voltage that is exciting the main winding and the amount of Voltage being induced into the 10 turn winding using the same meter. The ratio of the 2 voltages is the turns multiplier. Since there basically is no load on the 10 turn winding there is no copper loss involved in it and thus the voltage ratio is the winding ratio - get it? Have fun but be careful.
Sometimes doing this using 60 cycle AC is NOT a good idea because you can get "beat frequency" interference in the meter circuit caused by the test signal and the power supply of the meter being the exact same source. This can be a big problem if the AC out of the 10 turn winding is very small. Better to use an AC oscillator that produces a low voltage AC at some frequency not harmonically related to 60 Hz. Thus don't use 120, 180...etc. I would probably use 1000 Hz myself. If you want to haul that beast to my house - I could show you the method and use it to determine how many turns are on that thing and since you know the amperage - that would tell you the amp-turn force you have there.
Is there anything else on a T that weighs about 3 pounds that I could use to test my magnets?
At the moment, I have a 1913 flywheel apart with 5/8" magnets. I would assume they will not lift quite as much weight as the later 3/4" magnets.
The standard Ford recommended dead lift criteria was a cast iron piston with rings and pin which is 2 3/4 lbs. All the other heavy lifting magnets observations cited here are obtained by physically tuning the magnetic air gap.
Ron the Coilman