Novice needs help with relays

[initagain]

I have read several posts on this forum concerning the application of relays in operating various postwar Lionel accessories and for train control, etc. There are obviously some real experts on this subject.  However, I have several questions, which I would like the experts to answer in the clearest, most concise way possible.  Let's call this post relays 101, or relays for dummies (the dummy being me).

Do solenoid-driven accessories operate better on DC as opposed to AC.  If the answer is DC, do I need to get a DC output transformer (HO powerpack or the like) to provide the relay with DC output, even though the relay itself would be powered by AC from a normal Lionel transformer.  What type of relay should I be looking for;  i. e. a 12 volt input to the relay with a ? volt DC output to the accessory. What type of amperage capacity would the relay need so it doesn't self-destruct.  I hope all this is making sense.  Remember the words in the first paragraph of this post, "relays for dummies"-me.  By the way, I would prefer to use solid state vs. solenoid type relays. 

[lionelsoni]

They're quieter on DC.  But why do you want to use relays?  You can operate most of that type of accessory directly from a control rail.  You can use a power supply meant for HO or make your own easily from a smallish transformer and a rectifier.  What accessories are you thinking about?

If you do need to use relays for something, you will find that DC relays are a lot easier to find than AC relays.  If you're going to have a DC supply for whatever the relay is controlling, you might as well use it for the relay coil as well.  I see no reason to avoid conventional electromechanical relays.  In any case, you would have to avoid the type of solid-state relay that is intended only for AC loads.  The only "solenoid type relay" I am familiar with is an automobile starter solenoid, which I'm sure is not what you intend.