On Fri, 8 Jul 2016 20:16:52 +0800, Rheilly Phoull
wrote:

snip
I know this is an old post, but I find it interesting. Would using AC
on the electromagnets instead of DC solve the problem?

Remember the power in these systems comes from a backup battery to make
it fail safe. It would involve major rebuild costs to do that.

For this service, loss of power would invoke the fail safe condition,
without a back-up battery. Fail safe is the de-energized state.

RL