I built two types of mob traps. One
MFR based: mob spawners(from vanilla minecraft) + grinder.
As you can see there is tesseract which transfers mob drops and MobEssence to Auto-Enachnter (MFR) and Auto-Anvil (MFR) which do the work.
The second one is
OpenBlocks/ThermalExpansion based. Couple of Autonomous Activators filled with swords (possibly made of Tungstensteel which have durability about 5000 and enchanted on durability and looting) which will attack nearby mobs, and a Vacuum Hopper (OpenBlocks) to suck dropped items and, the most important - experience orbs. After - transfer it to
Auto Enchantment Table (OpenBlocks):
Something like this. I use this trap to kill mobs one by one by teleporting them using portal gun. So the question is - is there common sense to build such complex (comparatively to the first one) mob trap to get liquid XP instead of Mob Essence? I can see that Auto Enchantment table from OpenBlocks works much faster (instantly), does not require energy and liquid XP is more bright (which is just good looking) and has more uses - it can be absorbed using xp shower or tank (OpenBlocks). But HUGE disadvantage of Auto Enchantment table from OpenBlocks is that it doesn't enchant books.
So how can I calculate real cost of liquid xp and mob essence? Other words - how can I calculate how many zombies should I kill by each trap to get 30 lvls cost enchantment?