It has been suggested that the magnetic strength of the magnets in the T's magneto might degrade over time, requiring a recharge. I have now found that this does happen right after the magnets have been recharged. In a previous thread of mine, http://www.mtfca.com/discus/messages/411944/499231.html?1417815376
I described a charger that I built and a device to measure the strength of the magnets before and after charging. The increase in strength that I measured was almost to good to be true, and someone suggested that it might be a temporary high, and that they would weaken soon after charging. Unfortunately I had already installed the magnets on the flywheel so I couldn't go back and recheck them. But I did still have one magnet that I got from a vender. The vender recharged the magnet before he sent it and I was surprised that its strength was lower then any of the ones that I recharged with my charger. I checked my magnets strength right after recharging but the vendor's magnet had been recharged 1-2 weeks before I checked its strength. I recharged the venders magnet and it went from 6.8 to 7.9 lbs pulling strength, and set it aside. That was three weeks ago (and 30 deg warmer); I went back and checked its strength and found it to have dropped back down to 6.6 lbs strength, which was just about the strength that it originally had.
This was only one magnet tested but I think it warrants further testing. I don't have any more magnets to test but if someone out there in T land has some magnets that they could send me to test I would be most grateful. I would return them after testing fully charged up. I would like to test the effects of temperature as well as time on the magnets strength. I live in Wisconsin.Thanks!
It's been a while since having magnets on my mind but I've read different specs for Model T magnet saturation. And saturation is critical to strength and longevity. If I recall correctly, figures ranged between 8,000 and 25,000 amp/turns but I bet Ron has that fact on the tip of his tongue. It might even be on the drawing.
Temperature is a factor. These magnets will loose all magnetism above around 1200F and seriously degrade above 500F. I think the normal operating temperature of the engine shouldn't be a problem. Magnets degrade over time and the drop from right after the charge is normal.
Robert Send me your address I will send you magnets that do not have to be returned.
Robert, did you put a pole piece across the magnet before you took it off the charger?
If you didn't, you should, or it will loose some until you get it back on the flywheel, and don't take the pole piece off until you get the face plates back on the ends of the Magnets.
I have designed a few magnetic devices like transformers and coils and want to give you a heads up that you need to be aware that all magnet cores have a curie temperature. The curie temperature is such that if you exceed it you destroy the magnetic properties of the thing. I have no idea where that temperature is for a T magnet but it would seem to logically be below the boiling temperature of the radiator which would then likely be an upper limit for the oil and parts that the oil hits like the magnets but I don't really know. Just don't get out your torch when heating the magnets unless you want to find that temperature in which case you can keep checking the magnet and raising the temperature. When you exceed the curie temperature the magnetism will essentially be erased very completely and without much warning. It may not be a good magnet at all anymore. Again can't say for sure so just be careful when heating up the magnet and testing things. Rare earth magnets typically have a somewhat low curie temperature and I wrecked one once by accident when I got the device too close to my bench soldering iron. It was a very small refrigerator magnet size thing.
Oops - it looks like others were all typing at the same time as me.
The curie temperature for iron is 1043K (1417F) That would be getting into the cherry red heat and not anywhere close to that in a operational motor.
The temperature range I planned to cover would be from freezer temp to boiling water temp, which would be found in the typical life of a model T.
Yes, I did store the single magnet with a keeper pole piece on it. The lack of a keeper on a magnet and its effect on its strength is one of the things I want to test. I have a sneaky suspicion that this is an "old wives tale" (like not storing batteries on a concrete floor) because the installed magnets on the flywheel don't have keepers on them.
For some fun reading is this 1915 article on Google Books. Author says keepers are un-needed.
http://books.google.com/books?id=xNc7AQAAMAAJ&lpg=PA415&ots=XDtdnye9pq&dq=use%20 of%20keeper%20for%20magnet%20recharging&pg=PA414#v=onepage&q=use%20of%20keeper%2 0for%20magnet%20recharging&f=false
Think this is the right link...if not will repost.
Your link worked. There seem to be some disagreement about keepers.
Thanks to Dean, I recieved a box of magnets from him and now have some results of the study. I measured the magnetic strength of the magnets (no keepers) when I recieved them with a newly built gauss meter.
I measured the strength of one magnet at 10 degrees F (-12C), and then at 212 deg F (100C). There was no change in the strength.
I then charged 6 of them up with my charger. They went from an average of 130 gauss to an average of 345 gauss, a gain factor of 2.7. Right after charging I placed a keeper on 3 of them and left the other three unkept. After 10 days the strength decreased by 3.9% without keepers, and 1.4% with keepers. Not much change either way. But I leave shortly on a 2 month trip and will measure them again when I get back and report any significant findings.
There is always a warning to charge magnets to their original polarity. To test that I "accidentally" reverse charged a magnet, flipping its polarity. It charged up just as well as the rest, and only went down by .2% after ten days (no keeper).
To do these studies I needed an accurate, consistent way to measure the strength of the magnets. The tester I built in my previous thread,
worked well but was very sensitive to the smoothness of the ends of the magnets. So I decided to build a gauss meter using a magnetic probe I found online and a circuit wired up inside a phone jack housing to read its output. It works great and the most expensive part was the 9V battery! See the pic below. My former tester measured the strength at the ends of the magnet but the model T coils use the sides of the magnets. So I measured the strength on the same spot on the sides of all the magnets with the probe. I found that the decrease of strength going from the ends to .030" (about the recommended gap to the coils) above the steel clamping piece between two magnets decreased by about 30% I also calculated that a model T magnet (unfinished ends) needs about 40 gauss to lift 1 lb.
When installed in the engine, there are no keepers on the magnets. The hold downs are at like poles which are pushing each other away, the mounting bolt at the V is in the middle and the ends are held in air by none magnetic brass screws and brass or aluminum stands. The center in the mag coil is .025 to .035 air gap from the mag clamp plates if the magnets and them are lined up right. So is that not in fact the same as not having keepers?
Robert Please post the drawing and information on building the gauss Meter.
I agree Mark; my initial results are showing very little benefit to keepers (so far). But if your magnets are going to be knocked around and frequently come into contact with other metal, keepers might be a good idea.
Dean, the circuit is quite simple. The probe is part #A1301KUA-T that I ordered from: http://www.digikey.com/
It has 3 terminals; 5V input, com, and the output. At 0 gauss, it puts out around 2.5V. A N field will decrease the output, and S will increase the output by 2.5mV/gauss. The 5V is produced from a 5 volt regulator, (LM7805CT, from DigiKey) also a simple 3 terminal device that uses 9V from the battery, center pin com. I have posted the probe and circuit below. The crossed out items are nice but not necessary.
Neat idea building your gauss meter on a telephone jack base!