rw950431 on How to update a long string? And How to reconnect and upload again when Wifi is dead.

Sadly thingspeak is limited to 8 fields per update and updates no less than 15 seconds apart.

If you wish to use thingspeak maybe you can summarize your data (take an average, max/min etc) to reduce its frequency.

There are other logging services which allow more frequent updates but they usually have restrictions in other ways such as only retaining a certain number of days or a certain number of datapoints.