I can’t take credit for this idea. I had to bite the bullet and sort out some dew control stuff because my C9.25 dews up even if there’s a forecast for a clear sky. A few people have mentioned making one the same way, but here’s what I’ve done with mine.
It’s not hard to find 12V 8A controllers on ebay intended for use with strings of LEDs. In fact the labelling looks like 12V .8A, but reading the instructions it definitely says 8A not 0.8A, and I’m really not sure you’d be able to power a very long string of LEDs with 0.8A. Anyhow, someone suggested that it should be possible to use these to make a dew controller so I thought I’d have a go. I read a few comments suggesting that they can fail because of overheating, so I decided to strip the parts out of the box they come in and mount them all in a large box that would have room for a cooling fan if I decided I needed one. They weren’t too hard to remove from the original boxes once I’d worked out how to split the input and output connectors. I remounted the pots for controlling the power on the lid of the box and fed the output through a panel fuse into a BNC socket for the dew controller cable to plug into. Power comes from a two-core mains cable that I plug in to my 12V PSU. The PCBs are fixed to the bottom of the box using double-sided sticky foam pads.
That’s about it, really. Here’s what it looks like inside:
and all put together:
Overall it works very nicely and the C9.25 stays clear of dew, though it works far better getting the straps on early and maintaining the temperature before the corrector starts to dew up rather than having to clear dew that has already formed.