12"LB Secondary Heater

[astronut]

After carrying out a lot of mods to my 12"LB over the last two years, I'd thought I was done but........... with a few lost nights to the dreaded dew, I knew that it was time for a secondary heater.
Now the one recommended for the LB's wraps around the sec holder, (and works well) its only drawback is that it uses a lot more power than the conventional heaters (having to heat the holder & mirror) attached to the back of the secondary.
So I decided that it was time for a project.
I bought the Astrosystems DG-1 heater.
Since I powered the rest of my heaters and fan through my 12V system, I opted for the same for this.
The most difficult part was removing the mirror from the holder,(I think they use a very strong glue at G.S.O.) you must gently lever it out (this takes a bit of time and patience) both the holder and the back of the mirror are cleaned with Metho.
After marking the position of the heater on the mirror, two holes have to be made into the holder. To keep wires from fraying over time I inserted grommets into the holes.
The heater is mounted on the mirror using Automotive Silicon. The heater was also sealed around the edge of the circuit board to prevent heat loss.
Then came the installation of the mirror, three small blobs of silicon would gently hold the mirror. To prevent further loss of heat I packed the inside of the holder with cotton balls.
After allowing to cure overnight, the holder is reattached to the spider.
From one hole comes the L.E.D. (This lets you know when the heater is on)
and the external sensor. The other is for the leads to the power supply.
I ran the power wires over the spider. I drilled a hole in the U.T.A. and down to a plug.
This was then fed down the (inside) of the truss and off to the switch box and power supply.
For a non standard job it went off very well (I didn't curse once:lol:)

Result? Works brilliantly!!:thumbsup::thumbsup:

I'd like to thank Chris (Omaroo) Dick Everett (M.A.S. member) and Jay Scheurle (CN member) for their invaluable advice and help.

[Screwdriverone]

Hi John,

Nice Job!

Looks a very professional install and sounds like its a great addition.

Chris

[Starkler]

Sounds great but is there silicone between the heating element of the DG-1 and the secondary? Silicone rubber would be a thermal insulator which isnt what you want.

I also have an Astrosystems secondary heater built into my scope. Works great.

[astronut]

Thanks Chris.
Geoff, the circuit board is held around the edges onto the mirror with the silicone.
The heater contact points have a 1 -2mm layer of silicone.
This was recommended by astrosystems.
I've used it a couple times since building it.
I've left the scope pointing straight up, and though the rest of the scope was saturated the secondary was fine:thumbsup:

[CoombellKid]

This looks very interesting.

Geoff, how is yours powered? do you use the 9v battery up in the SC or
do you run power to it. If you do use a 9v battery, how long does it last
and can you use rechargables

regards,CS

[astronut]

Hi Rob,
I can answer some of your questions.
1. You can use a 9V, it lasts from 3-12 hours depending on the setting that you use and the amount of times the heater turns on.
2. You can use rechargables.:thumbsup:

John.

[CoombellKid]

Thanks John, have you ever tried powering with a 9v?

regards,CS

[astronut]

Rob,
I haven't, but one of the CN members that helped out with advice does.
He told me that it works very well.
The reason I went for 12V is because the rest of the heaters and fan already run on it and are controlled by the box in the photo's.:thumbsup:

[Starkler]

Mines wired into 12v as is everything else on my scope except the telrad.

[astronut]

Well, after two weeks of use, I have to say that this was an invaluable addition.
I've used the scope on the wettest nights (without) the dewshield, just to place extra load on the heater.
It came through with flying colours.
Since the Lightbridge shares the sec mirror holder with the Guan Sheng branded scopes, if dew is your major opponent I would recommend this as a worthwhile project.:thumbsup:

[CoombellKid]

Geoff,

Is your Argo Navis powered through your scope?

I'm toying with the idea of sending power up my truss poles and building
a power rail into the SC I can run 3-4 things off.

Sorry for the off topic John

regards,CS

[astronut]

I've added another feature to the secondary holder.
Since the mirror is siliconed back onto the holder, it's not easily removed (unless you really have to)
If the setting on the heater has to be changed, the mirror would have to be removed.
So I decided to make an inspection- adjustment port on the holder.
To stop the heat from escaping, the hole is easily covered using a wiring plug.
Now I can adjust the heat setting easily.:thumbsup:

[erick]

Good idea, before I start the project. But, sorry - "a wiring plug" - what's that, please?

[astronut]

Sorry Erick, I'm getting technical:lol:
It's just a simple plug (I bought it from Supercheap) to fill a hole that may have had a wiring loom pass through it.
It will prevent loss of heat from the holder.

[CoombellKid]

I was wondering how you were going to get around that. I got a DG2, just
waiting now on the spider and holder from AstroSystems. Which already has
the inspection/adjustment hole built in, I think????:whistle: . In anycase, if I need
to fill it I know what to use :thumbsup:

regards,CS

[erick]

The DG-2 ain't going to fit in the GSO 12" secondary mirror holder. I measured the mirror dimensions and ordered the DG-2 which is the perfect size for the mirror, BUT it will not fit into the step down section of the mirror holder. One could design a new holder for the secondary with a bigger diameter, I guess - but I gave up on that idea after a while - haven't got the materials or tools. So I will get the DG-1 instead. I had noticed John was using the DG-1, but I didn't think to ask myself why! Obviously John's experience is that the DG-1 works, though the mirror size would benefit from the DG-2, if it were possible to fit it. (It would fit perfectly on the mirrored side! :P )

[erick]

John, you used cotton balls to pack behind the heater, inside the secondary holder? I'm a bit worried about the moisture they might soak up when the heater is off - eg. during transport etc.

Anyone suggest an alternative packing that might not soak up moisture? I 've discounted using a piece of fibreglasss batt! Fibres drifting everywhere - Yikes! I was thinking of either:-

1. Some of the synthetic acoustic packing used in loudspeakers?

2. Cutting a piece of styrofoam into a plug that fits into the secondary holder and up against the heater? I could then drill a small access hole through that, aligned exactly with the temperature adjustment pot?

Thanks in advance
Eric :)

[astronut]

Erik,
I was going to buy the DG-2 as well. But after some advice from a CN member (and LB12 owner), he recommended the DG-1.
As you've found out, the DG-2 doesn't fit.
You can experiment with different packing materials, I was encouraged to use the cotton balls by one of our very experienced ATmer's in my club.
It won't rot or cause any other problems.
Even on the wettest nights, the cotton has stayed dry.
The only tools I used was a "Dremel" style mini drill.
Jaycar have them on special for $44, or see if you can borrow one.
The plugs and grommets were purchased from Supercheap, though most motor acc places should carry them ($6)
The reason I made my inspection hole bigger than necessary was just in case I had to remove the mirror, this would allow better access to be able to lever it out.
Since the heater was a little smaller than the DG-2, I would recommend that you increase the heater setting to allow for this.
How much you ask? Experimentation is the only way.
If you need further help, please ask.
Good luck:thumbsup:

[erick]

Commenting on removing the secondary mirror from the holder (12" GSO reflector). Not being sure what I would find, I took it slowly. Removed the retaining clip at the bottom end of the long axis. Ran a knife blade (not too broad since you have to turn around the sharp radii at the long axis ends of the ellipse) around the edge of the mirror. It made lots of glass crunching sounds, but as it turned out, it didn't achieve anything - there was no adhesive along the edge. Started gently pushing a small flat blade screwdriver between the mirror and plastic holder and levering. As it turned out, you won't be breaking this mirror - it's thick. But you might chip a little off the lower, non-aluminised edge and, of course, you always run the risk of a slip generating a nice scratch across the mirror surface.

Graduated to a larger flat blade screwdriver and could feel some form of adhesive releasing . Got braver and willing to lever it enough to bend the plastic holder. I did try putting a longer phillips head screwdriver down through the centre screw hole at the top of the plastic secondary holder, but wasn't brave enough to push hard when I couldn't see what I was doing and the screwdriver was touching the mirror at 45 deg angle. Finally one end raised enough so I could see what was going on. Then I could get my fingers on the edge of the mirror and pull it out. The thickness of the mirror means that it wants to come directly out of the holder, not at an angle - but you have no choice then to lever it up at an angle initially, bending the holder. I guess you could get a lever under two opposite sides of the mirrror (probably along the long axis) and lift - but you'll need a second pair of careful hands holding the holder. Perhaps a third to catch the mirror before you shoot it across the room! The holder seems to have sprung nicely back into shape.

The mirror sits on the diameter step-down edge of the holder - probably a good 1 cm wide ledge all the way around. At three points were short pieces of double sided adhesive (about 1 mm thick), doing a very good job of holding the mirror in place. There were also a couple of random blobs of silicone which didn't look to be doing much of use at all. Cleaned it all off the mirror back and the holder. Hopefully I'll reinstall with small blobs of silicone, around four should do.

In practice, given the thickness of the mirror, if I put it back into place with no adhesive and screwed the clip back on, that mirror won't fall out - but will wobble all over the place. Hence the adhesive is really to hold the mirror rigid to the holder and only plays a minor role in stopping the mirror falling out of the holder.

Will post some pics at some stage - probably this weekend when I do more work on it.

[astronut]

Good news Eric,
My mirror had a few flakes of glass come off the bottom end as well, but nothing to worry about.
I placed 4 small blobs of auto silicone under the mirror, these along with the clip do a great job of retaining it on the holder.
Remember to clean the back of the mirror and the holder with metho before you put everything back together.:thumbsup:

[erick]

I'm even going to give it a wash - pop it in the dishwasher? With the primary?? :D

[astronut]

:lol::lol:

[erick]

DG-1 heater has arrived. That looks so small for such a big mirror :confuse3: OK, I'll give it a go. I think I'll connect it to the mirror, let it cure, then sit the mirror out facing the sky on a dewy night and give it a blast and see what happens - worst case testing.

Wish I could have fitted the DG-2. I'd suggest anyone following this path look for a way to make a new secondary holder into which the DG-2 will fit.

[astronut]

It will work, just remember to turn it up from the standard setting.
Have fun Eric.:thumbsup:

[CoombellKid]

Why would you suggest that, when John has proved it works a treat on
his 12".... you haven't even tested yours yet :shrug:. You would probably
find a DG2 overkill. Either that or they must stick oversized secondaries
in the GSO's

regards,CS

[erick]

Fair enough. I'll let you know how it goes....... This weekend, I hope. :)

[jayscheuerle]

Nice John! I'm on my 3rd secondary (the 2nd with the heater) and this one's NOT going to be astigmatic! When I sent #2 to Mark Harry for testing, he tested it with the heater both on and off to see if it would affect the flatness. It did not. I haven't had to adjust my settings yet, but I'm hoping that I can reach them through the 9v battery hole. :thumbsup:

- j

[JethroB76]

Jay, I remember following your original CN thread; did your recent problem end up being the new secondary?

[jayscheuerle]

Yep. On my 3rd now... :)

[Jen]

:eyepop: Eric you need to wash your mouth out with soap hahahha :lol:

Nice idea John this thread has been reborn i think now that dew season is kicking in :D