I successfully recharged the magnets for my '24 Speedster engine today, using a setup I built a couple years ago from information on the forum. At that time I used three 12-volt batteries in series, this time it was a battery charger on the boost (100 amp) setting.
Of the 16 magnets, only two were strong enough before recharging to lift a bare Ford iron piston (839g). I understand a charged magnet should be able to lift a two lb weight (908g). After a dozen flashes per magnet, they now lift minimum 1375g to a maximum of 1820g (the bare piston plus all those misc fasteners inside). I suspect that those magnets that lifted the lesser weights (1375g to 1500g-ish) may have been compromised by less-than-ideal contact between the magnet poles and the piston.
So far, so good. Now my questions...
1. What is the best way to store recharged magnets prior to installation? I currently have thin metal keepers across the poles, and keep the magnets on a board several inches apart.
2. What is a good 'home garage" technique to check the magnets for cracks? I gave each one a good DING with the little brass hammer and they all rung about the same tune. That, and the fact that they all took a pretty good charge, would indicate they are OK. On the other hand, noted authorities like Ron the Coilman say they rarely test a set without finding at least one cracked magnet. So maybe I'm missing something. I'd sure like to be sure before I put this engine together!
First....AWESOME WORK CHRIS! CONGRATS!
Next, how about a piece of cardboard?
Maybe arrange them like it says in the book, like they are on the flywheel like so -++--++--+
Tape in place and fold the cardboard over them.
Professor Jim Cowart, USNA has two charged Model T magnets on his desk that he measures periodically. One has a keeper and one does not have a keeper. Neither one has lost any magnetism to date.
The professor also built a device to measure that magnetic charge and he has determined a good Model T magnet that will lift 2 pounds measures about 375 Gauss.
Recently, I disassembled a 1925 Model T engine that had been used on a saw mill and stored inside for over 40 years. I was surprised to find the magnets were still charged enough to lift the Model T piston.
Paul Vitko demonstrated another interesting fact with those magnets, if the ends are ground and polished straight across, they will lift a 16 to 18 pound smooth iron weight.
The magnets will also pick up more weight when positioned this way, as there is more metal contact.
Hold 'em at the peak of the 'V' and ding 'em against an anvil or vise. If they break in two, they have a crack. If they stay in one piece, they don't.
Don't be bashful with the "ding".
If they are cracked they will break into two pieces and look something like this.
Ron the Coilman
Thank you all for the replies. Here's an update...
My weight lift testing was done with the magnet ends as factory finished, lifting on the curved side of the piston. This resulted in a four point contact, with (probably) line contact between the pair of points.
Test magnet lifting on the curved piston wall: 1,378g pull
Same magnet lifting on the flat piston top: 1,504g pull
Same magnet with ground flat contact surface (roughly 1/8" wide contact line): 1,998g pull
Same magnet with flat contact and after several more flashes in the recharger: 2,563g pull — see photo (2,954g less the 391g magnet)
Then I got ruthless with my crack testing. Gave the first 14 magnets a couple of pretty solid whacks each against the vice: no breaks, no problem.
For the last two, I last two I really banged them against my anvil. Both broke with on first wallop. Looking at these broken magnets (photo below) I saw no evidence of a pre-existing defect on the top one, and only a slight anomaly in the valley of the second. Neither looked anything like the cracked magnet in Ron's post, so methinks I was just too hard on these two.
All of the magnets showed some loss of strength after the crack testing, so the blows must have discombobulated the magnetic orientation. Recharged 'em all again and they seem just fine.
Well now that the magnets are broken can they be welded? Or does somebody make new ones?
Try welding one and see. I don't think new ones are being made.
Chris, I have plenty of magnets if you need some.
The magnets are forgings and some have stress risers in the vee. In my opinion you are far better off finding the questionable ones now than later. Rarely do you find a flywheel without at least one cracked magnet.
Ron the Coilman
I wonder if the two that cracked are the two that had the somewhat lower reading after recharging?
Kenny, thanks for your kind offer — I do have a few loose ones kicking around plus a whole 'nother rusty flywheel with a full set.
Ron. do you think its possible to break a good magnet with a real hard wallop against an anvil? If there was any chance my two that broke were compromised obviously I am glad to find out now. My question is for next time I test magnets.
Warren. the two that broke tested had at 1,493g and 1,820g after the initial recharge. The 1,820g magnet (upper one in photo above) was my top performer, which leads me to suspect it broke from the trauma and not from an inherent defect.
As Warren questioned I noticed that if they are cracked and after a recharge they will not produce as high a Gauss reading.
I have never seen a magnet break where there was not some sort of flaw in the vee and sometimes you have to look very closely. They usually ring like a tuning fork if they do not break.
Ron the Coilman
If you lay a steel flux bar accross the ends while chargeing the weight lifted with my setup went from 15 to 16 1/2 pounds.
I dont know if its true but was told that steel will lift better then iron.
Was also told that the comercial chargers load a capasitor with amps then dump a bunch of amps into a magnet for a good charge in one hit.
Regarding the commercial chargers, that's correct. My brother worked for such an outfit for a while. Said that when they unloaded the capacitors to charge the magnets, it sounded like a rifle shot. I believe they wore ear protection.
I think one point should be made on magnet testing with weight. Bob B-Zero from Seattle posted a good link about a year ago on how magnets are tested with the big boys.
Weight is not dead lifted as these posts show.
The magnet is placed on a flat fixed surface and pulled from it with weight.
I can lift some where close to 12 pound on a dead lift but it would have to be a perfect lift and its much easier and more accurate lifting from a fixed plate.
I am sure most of the chargeing methods tested in the past would actually test well above ten pounds on a good test platform.
The differance is shocking.
Here is a conversion chart to make life simpler.
Grams Pounds and/or Ounces
1000 2 Lb 3.2 Oz
1170 2 Lb 9.2 Oz
1260 2 Lb 12.4 Oz
1350 2 Lb 15.5 Oz
1500 3 Lb 4.8 Oz
1750 3 Lb 13.6 Oz