magnetic switch/ relay question

is there a way to have one magnetic switch power on two devices, each with there own battery. maybe a (flyable) dual relay?

I'm sure it could be done, but holding a relay coil energized during the whole flight doesn't seem like a good way to ensure sufficient battery life. Maybe a latching relay?

Yes it can be done, by making the switched leg a common leg and then running the other leg seperate. If your talking about the featherweight magnetic switch with say two altimeters it switches the positive line so you would put both batteries positives to the switch in, a line from the switch out to each of the altimeters positives, one of the batteries ground to the switches ground and the first altimeter, and the second batteries ground to the second altimeter. In this way one battery powers the featherweight switch and one atimeter and the other battery powers the other altimeter. This in not technically a truly redundant system because if the battery powering the switch fails both altimeters fail. However if your doing this to separate your altimeter power from your charge power then this would work fine. In this case the battery powering the altimeter should power the switch since the charge battery can experience voltage drops when firing the charge (the reason for seperating them in the first place) and the power battery is more stable.

I thought about doing this so that one Featherweight mag switch could power both a Raven and a BRB GPS. I pursued using a solid state latching relay, thereby allowing separate batteries for the two devices controlled by a common switch. In the end, it added a lot of complexity and additional points of failure, so I ended up simply using two mag switches.

Worsaer said:

I thought about doing this so that one Featherweight mag switch could power both a Raven and a BRB GPS. I pursued using a solid state latching relay, thereby allowing separate batteries for the two devices controlled by a common switch. In the end, it added a lot of complexity and additional points of failure, so I ended up simply using two mag switches.

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Do you have any issues with magnets interacting at close range while trying to trigger the switches?

The group projects I am involved in moved to screw switches after problems like that. I imagine spacing them far enough would help, but we were awful tight on space to begin with.

I've put magnetic switches at opposite ends of a sled that goes in a 4" rocket (my Excel w/DD). By opposite ends I mean same distance from the nose, but 180° separated on the airframe. This has worked fine for me, the range at which the featherweight switch works with it's provided magnet is fairly short, certainly much less than the ~3.5" separation between the two. Now if they were side-by-side that might be a problem, and in a much smaller diameter rocket maybe it would be a problem. The other thing I've noticed is that the magnetic switch seems to be pretty sensitive to the orientation of the magnet, the way I have it mounted in some of my rockets requires me to swipe the magnet vertically along the airframe to activate/deactivate, and when I mount it rotated 90° in other rockets I find I have to swipe around the curve of the airframe to activate/deactive reliably. So I wonder if you might be able to place them more closely by having the two different orientations, I doubt that would be fool-proof though. I find that even in the right distance/orientation it is possible to get the switch to toggle twice (ON->OFF->ON or OFF->ON->OFF), so I try to position a vent hole right over the switch, both as a reminder of where I need to swipe and so that I can see the LED to make sure it turns on/off as expected.

The large magnet is SO worth it, as it extends the range quite a bit. Could be problematic with multiple switches, though.