Adding Fans to a Newtonian

[PeterC65]

While they are seeing little use over the Summer, I've been modifying my two Newtonian scopes (Explorer 150PDS and Explorer 200PDS). First up is the addition of fans, mainly to get warm air flow to the secondary to prevent dew, warmed by the primary dew heater. Here are the finished results ...

Explorer 150PDS

Explorer 200PDS

I started by purchasing 3mm thick plastic disc from PlasticSheets.com. The ones I bought are black matt Perspex, and you can get them cut as circles (and other shapes) to a specific size, so I measured the diameter of the inner part of the mirror holder for both scopes and ordered this size. The discs come covered with a plastic film and to this I glued a piece of paper so that I could mark out the holes that I needed. I cut the holes mostly with wood cutting twist bits (the lip and spur type), using a Forstner bit for the larger collimation adjustment screws and a tank cutter for the central hole (in both cases, cutting the holes from both sides of the plastic sheet). You do need to support the plastic on a flat block of wood to prevent the twist bits from breaking out. Here are the plastic baffle disc with the required cut-outs ...

The fans I used are Noctua NF-R8 redux-1200, purchased from Amazon. They are low noise but with sufficient air flow from what I've read online. There are three connections, red is 12V, black is ground, and yellow is a speed control which is not required. I connected the red and black to a chassis phono socket fitted into the plastic disc to allow the fans to be powered from my dew heater supply, via a phono to phono cable. I then attached some double sided tape to the inside of the plastic disc to fix them to the scopes. Here they are just before assembly to the scopes ...

Hopefully this will keep dew at bay from the secondary during my long Winter EAA sessions.

My next modification is to change the spiders, improve the collimation adjusters, and fit covers to the secondary mirrors to further reduce the chances of dew.

 

[bosun21]

4 hours ago, PeterC65 said:

While they are seeing little use over the Summer, I've been modifying my two Newtonian scopes (Explorer 150PDS and Explorer 200PDS). First up is the addition of fans, mainly to get warm air flow to the secondary to prevent dew, warmed by the primary dew heater. Here are the finished results ...

Explorer 150PDS

Explorer 200PDS

I started by purchasing 3mm thick plastic disc from PlasticSheets.com. The ones I bought are black matt Perspex, and you can get them cut as circles (and other shapes) to a specific size, so I measured the diameter of the inner part of the mirror holder for both scopes and ordered this size. The discs come covered with a plastic film and to this I glued a piece of paper so that I could mark out the holes that I needed. I cut the holes mostly with wood cutting twist bits (the lip and spur type), using a Forstner bit for the larger collimation adjustment screws and a tank cutter for the central hole (in both cases, cutting the holes from both sides of the plastic sheet). You do need to support the plastic on a flat block of wood to prevent the twist bits from breaking out. Here are the plastic baffle disc with the required cut-outs ...

The fans I used are Noctua NF-R8 redux-1200, purchased from Amazon. They are low noise but with sufficient air flow from what I've read online. There are three connections, red is 12V, black is ground, and yellow is a speed control which is not required. I connected the red and black to a chassis phono socket fitted into the plastic disc to allow the fans to be powered from my dew heater supply, via a phono to phono cable. I then attached some double sided tape to the inside of the plastic disc to fix them to the scopes. Here they are just before assembly to the scopes ...

Hopefully this will keep dew at bay from the secondary during my long Winter EAA sessions.

My next modification is to change the spiders, improve the collimation adjusters, and fit covers to the secondary mirrors to further reduce the chances of dew.

 

Nice neat job Peter, and well documented 👍.

[NGC 1502]

Good to see that DIY modifications are still a part of astronomy, neat job, well explained.
 

Lots of cloud and summer twilight to get stuff done👍

[Alan White]

Now that is very tidy work indeed, super job.
As Ed says above, its nice to see DIY mods still going on.
 

[wimvb]

I once made a similar fan holder for a friend's 8" ONTC albeit with a cheaper, and much smaller fan. It was kept in place with velcro tape. The fan caused bad vibrations that showed as fatter stars, and these weren't suppressed by the small velcro pads. You might want to do a fan on/fan off comparison just to be on the safe side.