In my survival game (hard mode) I observed that a zombie spawner never stops making zombies even if the population of converted drowned rises well above any mob cap that may be in effect. I haven't noticed this happening until recently. I also haven't spent much time in my flooded dungeon drowned farm, so I don't know when this started happening.
Instead of harvesting any of the converted drowned, I decided instead to manage the items in the collection chest: smelting gold and chainmail armor into nuggets, keeping a few interesting enchanted pieces and discarding the rest. After 30-45 minutes I took the attached screenshots, showing (a) a view of the drowning room with what seems to be about 50 drowned crowded into it, most of them packed into the left end, and (b) the spawner dungeon room crowded with over 40 drowned that managed to climb on top of other drowned to get back into the room from the drowning room below (with a few zombies visible). It took probably 30-45 minutes to accumulate this many.
This farm is beyond the despawning range from my home base, so whenever I visit the farm, it's empty but starts producing zombies when I arrive. At this point I'm using the farm only as an inefficient source of iron because I'm playing an island survival game ("Ocean Monument Ahead" seed from the seed picker) and there are no villages around to construct a real iron farm, and I've already mined much of the iron around my area.
Update: Still happening in 1.17.0.
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@GoldenHelmet - The Minecraft Wiki content is all user-generated and I can attest (being an active editor there) that some information may not be accurate or complete. It is especially a problem for any technical information about Bedrock Edition, because the code cannot be decompiled and examined as it can with Java Edition. The Bedrock rules in the wiki are typically based on experimentation.
Nevertheless, my zombies are being moved 6 blocks below the spawner, so they would be outside a 16x10x16 volume centered on the spawner, and therefore not be capped according to the Minecraft Wiki, and after 30 minutes I would have about 180 zombies and drowned milling around, which looks about right.
The real question is, did the developers intend to have no mob cap at all? It seems ridiculous to have dozens of zombies and drowned all clustered together, as you can see in the screenshot. But if that is the intent, this ticket can be resolved as "works as intended" – although I am not noticing that all of these zombies and drowned have any effect on environmental spawning.
I was referring to surface mobs too. In my case, according to the Minecraft Wiki's spawn article, "Structure-spawned mobs and converted mobs (i.e. drowned converted from zombies...) always count toward the cave cap, and spawner-spawned mobs always count toward the surface cap." Because I have both zombies and converted drowned here, and plenty of them, both the surface and cave caps should be in effect around this farm. This particular spawner in the screenshots is below a deep ocean floor. I do see other naturally spawned drowned around, which is why I suspected the environmental spawns aren't capped. But those monsters could have been there before the spawner built up the population.
I'll have to devise some sort of test. One can find spawners reasonably near the surface. So if I contrive things to create zombies and converted drowned above the mob cap, there should be no monsters spawning for 72 blocks around (4.5 chunks). That's a large area.
@Goldenhelmet I just saw on https://minecraft.fandom.com/wiki/Talk:Spawn#Bedrock_edition_mob_cap that I started a discussion on this topic some months ago, and you corrected the article. I had forgotten about that discussion and I missed your reply until just now.
There's a skeleton spawner under my home base island (it no longer generates with the same seed in 1.17.0), quite shallow underground, and there were several skeletons in the cave where I found the spawner – enough skeletons that I had never seen a hostile mob anywhere on the island. After I cleared out those skeletons, bang! instantly the island got hostile mobs on it. Now that I made a skeleton farm and the skeletons in the killing room remain close to the spawner, there are never more than 4 or 5 skeletons so I see only occasional hostile mobs on the surface (mostly patrols, strangely). If I allowed the skeletons to wander farther from the spawner, the island would go back to having no monsters appearing on the surface at all.
I don't need that farm anymore so I should disable it. The skeletons constantly standing in the kill room are likely causing my nearby slime farm to be underproductive.
I have this marked for Mojang review, as I could not find an official source that it is working as intended.
Believe it or not, I didn't recognize your name from the wiki until you menitoned it!
Patrols have their own separate cap, btw (pillagers, actually).
FWIW, I'm having the opposite problem at my drowned conversion farm – zombie spawners just randomly seem to stop producing zombies, even though the wiki says that spawners should ignore mob caps, and even after the drowned are all cleared via trident killer, the spawners still won't produce zombies. If I leave the area and comback, the spawner works again. Maybe I should file a ticket for this...
Reply from @unknown: that issue is tracked at MCPE-142285.
@Ninja Dankinate - I assume you are within 16 blocks of your spawner for it to spawn zombies. If you are too far away, the spawner doesn't work.
If it doesn't spawn zombies when you are in range, then yes you should file a ticket if this is reproducible. Be sure to include the seed and location of the spawner in question.
The only cap on monster spawners is as follows (from the Minecraft wiki):
This means that if you move even zombies far enough from a zombie spawner there is effectively no cap on them. However both the zombies and converted drowned still count toward the caps on environmental spawning.