If your train hesitates over any permanent magnet uncoupler, you may end up uncoupling cars that you don't want to uncouple. With experience, that should not be an issue. I use the #308's in a few locations that are out of the reach of a hand uncoupling tool. As long as the track is level and your couplers function well, false uncoupling should not be a problem--certainly not enough of a problem that you would want not to use them.
John Timm
Thanks, everyone, for your responses so far. I'm not so concerned with appearance (of between the rails magnets) as I am with reliable operation as I do a lot of my layout operations with computer control.
Lee
Experiment with mounting the magnet further below the track. If you've got it directly beneath the ties, try moving it under the roadbed. It sound like the magetic field is too strong. By moving it further away from the track, you'll reduce the field strength.
Set up a test track to do this. You don't want to mess with glue, scenery and ballast until you find the right position for these things.
I've got a number of the above-tie Kadee permanent magnets, and they work pretty well. I found that I had to mount them a bit lower than the position recommended by Kadee, because one of my engines (P2K S1) has very low clearance, and it ran aground on the magnets. They still work fine down a bit lower.
I've also got one of the electromagnets on my main line. It works well, too. Since the track was already installed, I put the whole thing in from below. Believe me, that's not the way to do it. It would have been easier to rip up the track and just follow the directions.
It takes an iron man to play with a toy iron horse.
I use the unter the tie magnets, too. But two magnets in one track give problems.
Therefore I've made a few of my magnets movable. This is helpful with two tracks. I can move the magnet from one track to the another.
Wolfgang
Pueblo & Salt Lake RR
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I've been cutting them in half for years with no decrease in performance when mounted under the ties. Started doing it because the HOn3 cars are lighter and would pull up to the magnet. Spotting the cars is a bit more critical though.
Tom.