Arclight Charges: Zenyte on rate is 9 ancient shards, Tormented Synapse is 18 ancient shards.

You only use an arclight charge now if you hit, no charges used if you hit a zero.

In arclight + med level gear at 86 str on task, you would be on rate for a zenyte with 9 ancient shards worth of charges.

In arclight + med level gear + torture amulet at 92 str on task, you would be on rate for a tormented synpase with 18 ancient shards worth of charges.