I feel like the easiest way to fund open source is to offer dual licensing and somehow charge businesses. There have been many that have done this and it seems to work well, most notably IMO is mperham with Sidekiq, but there are many others. Open source developers are too timid of charging for their code.

Relying on donations seems like a bad move, business-wise, because I'd guess (no data to back this up, just gut feeling) that most donations will come from individuals and not busineses, yet the businesses are the ones making money off of your code.