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  #1  
Old 12-04-2018, 06:11 PM
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darrellx (Darrell)
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Hey look! A new Dome has popped up.

Hi All

In another thread, I have detailed some of the new equipment I have purchased, and more is expected. With all this new gear I figured I needed somewhere suitable to use it.

Briefly, I settled on an Observatory at an appropriate site.

And here it is.

Back to the beginning, the Site Survey was the fun part - too many choices. I settled on a high part of a ridge line with excellent views all round. The attached shows the star trails view to the South. I should have no trouble getting a good Polar Alignment.

The electrical and data fit out will begin weekend of the 21st.

It have had a lot of enjoyment getting this far.

Darrell
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  #2  
Old 12-04-2018, 07:14 PM
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You will never look back, well not true you will time travel with style
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  #3  
Old 14-04-2018, 09:47 AM
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darrellx (Darrell)
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Houghy

I like that - time travel with style.


Hi All

I think I have my plan for power and data connectivity mostly sorted. But I do have one issue I am trying to resolve. Cable Management.

With my old Pier, I simple velcro'ed a USB Hub, Dew Controller and power cable to the side. The cables then just looped up to the relevant device, and generally, all was fine. (EQ6 Pro)

Now that I am in an Observatory, I have been rethinking this.

I am making a power distribution box, and looking to get a new USB 3 Hub. Conduit has already been run under the floor.

My dilema is, how do most attach their "rigrunners" or equivalent to the equipment? From what I have read, the three options seem to be attach to the Scope, the Rings, or a Base Plate.

All this might be irrelevant because I am waiting on a Mach1. This I believe has through-the-mount cabling. So, for those of you who have this option already, would it be more straight-forward and suitable to still velcro boxes to the Pier, then run cables through the mount? Because I have essentially used this successfully in the past (attaching to the Pier), I am much more comfortable with this option.

Thanks
Darrell
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  #4  
Old 14-04-2018, 11:14 AM
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Darrell, I reckon stay attached neatly to the pier instead of running it through the pier, easier to access if needed, and I have heard that running through a pier could cause some electrical interference

But at the end of the day it is your choice, when i did my set up it worked well for me.

Leon
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  #5  
Old 15-04-2018, 10:19 AM
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FlashDrive (Col)
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Darrell .... nice bit of gear you have there....
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  #6  
Old 15-04-2018, 03:16 PM
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Leon

Yes, I am thinking of running all the cables on the outside. I think it will be easier in the long-run for me.

I also think I will leave the power box and the USB hub on the Pier. It has worked for me in the past, and unless somethings goes awry I will stick with what has worked.



Col

Thanks. It has been a long time in the planning. And despite the efforts of some local cows, it took four days of effort to erect.
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  #7  
Old 20-04-2018, 03:20 PM
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darrellx (Darrell)
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Hi All

Steady progress is being made on finishing the observatory. But I have one niggling issue I am having trouble getting my head around. I am hoping someone here might be able to help me with electrical theory.

My Laptop and the current draw on a 240 volt system compared to a 12 volt system.

I have a MSI laptop that I use exclusively for astro work.
On the transformer, the Output is stated as 19.5v 7.7a
The Input is listed as 240v 2.7a

When I use my Amp meter, plugged into 240 volts, during boot it peaks at 0.31 amps.
During normal use, it sits around 0.22 amps. In terms of watts, it moves around 42 to 48.
The laptop is fully charged.

Now, when I plug this onto a 12volt battery with an Inverter, the figures essentially stay the same.

All good so far.

What I don’t understand is the impact on the battery.

My thoughts on this.
- Forget the Output on the transformer. The listed 7.7amps is a maximum.
- The important figure for the laptop is the third of an amp it seems to draw at maximum.
- The other important figure is the 2.7a listed on the transformer.


So, ignoring any loss and inefficiencies, the transformer requires 240v at 2.7a. It is then delivering the 0.31 amps that the laptop requires.

Does that mean that the loss from the battery is still only the 0.31 amps or 2.7? I don't think so.

240v 0.3amps = 72 watts
72watts at 12 volts = 6amps

So, to run the laptop for say 6 hours - 36amps

I suppose if I wanted to get picky I would say 240v 0.22amps = 53watts
53watts at 12 volts = 4.4 amps

6 hours of runtime would then be 26.4 amps

Does that seem correct?

Thanks
Darrell
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  #8  
Old 26-04-2018, 09:38 PM
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darrellx (Darrell)
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Hi All
I have now got all my power needs setup in the Dome – well, almost. I do have one problem to solve.

But first, the power. 2x 100amp hour deep cycle batteries with an 80watt solar panel and dual battery charge controller. All nicely housed in a matching white box. I have a third battery on standby – 75 amp hour deep cycle.

Okay, the problem. I have four pieces of conduit installed under the deck that was put in place at the time of construction. I have pulled the power and data cables through three of the them.

The fourth one, that is one of the runs from the Distribution box to a point across the Dome for some lights is the problem. When I tried to pull the cable through, my draw line came free of the end of the wire I was trying to pull. Now, no draw wire. The conduit run is 1400mm, with three bends (gentle curves really).

So, short of pulling out the conduit, how can I get my electrical wire through? So far, I have tried, in order;
Heavy gauge fencing wire, but it got stuck
I taped two pieces of 5mm twin electrical cable together and tried to push push it through, but it got stuck
If you know yellowboard, the construction flooring, also called yellowtongue, I tried to use a long piece of the yellow plastic stuff use in the groove to join two pieces. But it got stuck.

So I figure I have two options.
Go to Bunnings and spend a few hundred on the flexible wire thing electricians and builders use
Remove the conduit, hold it vertically and start again by dropping a reasonable sized nut through tied to a piece of string.

Has anyone got any other ideas?

Thanks
Darrell
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  #9  
Old 26-04-2018, 09:42 PM
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darrellx (Darrell)
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And, by the way, I did also install a Bunker Light at the door. It now has a 12volt red LED strip inside. It gives a nice light. So I have a porch light if I get any visitors.

Thanks
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  #10  
Old 27-04-2018, 07:26 AM
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Hello Darrell,

Consider getting some braided nylon fishing line (the stuff that don't snap), wrapping it through a slightly undersized styrofoam ball, and blowing it all through the pipe with compressed air. Seen some mates do it with fibre optic cable with a shuttlecock-like tool.

Best of luck!
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  #11  
Old 27-04-2018, 08:57 AM
Wilso (Darren)
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Make sure there's no sharp ends on the cable and use a cable lube.
As long as the bends in the conduit are not too sharp will work ok.
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  #12  
Old 27-04-2018, 04:11 PM
noswonky (Peter)
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What are your impressions of the NexDome?

Any problems with it?

Did you get the automation options or is it manually operated?
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  #13  
Old 28-04-2018, 11:34 AM
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darrellx (Darrell)
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Andy/Darren

Bloody wonderful. It worked. I didn't have any styrofoam, so I used a piece of that puffed rice packaging and wrapped the fishing line around it and formed a ball. The only compressed air I had was from a battery powered compressor to pump up tyres. So I couldn't get that initial strong, almost explosive burst of air. It took a while, but it got there.

I spayed a fair amount of cable lube down the conduit before I started.

All good. Thanks for the tips. So happy I didn't have to go under the deck and remove the conduit.

Darrell
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  #14  
Old 28-04-2018, 11:41 AM
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darrellx (Darrell)
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Hi Peter

Overall I am very happy with the Dome. I settled on this style of dome because it is situated in a reasonably windy area. Not particularly high wind, but constant wind. It is high on a ridge, with fairly constant wind from the south. So I thought the slit style would be better. I think I made a good choice. As a side note, given the location and the wind, I am thinking of calling the dome "Windy Ridge Observatory".

I did encounter a few issues. Just minor problems that should not happen. But I will start by saying that Sidereal Trading were great with the help and guidance.

There were a few items that didn't initially get shipped. The missing rubber door seal was noticed by Sidereal before I noticed and they shipped it immediately. Great. But there were also some nuts and bolts missing. I was told that should this happen to let them know and the parts would be shipped straight away. But for a few dollars I couldn't be bothered waiting so I went to Bunnings and bought them.

I will be blunt and say that the assembly instructions are ..... atrocious. I was warned about this, and it is not a real big issue, at least for me. And the tips I got from Sidereal were really helpful. But this is one area that Nexdome should focus on.

And the last issue, and really the only one concerning the product, is that some of the holes on the walls were drilled too small for the bolt I had to use. So I had to redrill about a dozen holes. Once again, not a big issue really.

My dome, at the moment is fully manual. I do intend to automate, but I thought I would take small steps and get it built first. I am glad I have. There is a yahoo group for Nexdome and there is a lot of discussion about automation.

Overall, very happy. And I think it looks good.

Btw – don’t be fooled – I read on one of the o/s forums that its a half day job to get this done. It took me and a mate 2 days.

Hope this helps with your decision. If you want any more detailed info, let me know.

Darrell
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  #15  
Old 28-04-2018, 01:18 PM
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Thanks for the write up on the Nexdome Darrell.

I've been considering one for a while now.

Just wondering what you think about the locking mechanism for the door, is it secure enough or is it to keep the honest people out?
I was looking at it in one of your photo's but couldn't really tell.
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  #16  
Old 28-04-2018, 03:41 PM
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darrellx (Darrell)
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Ric

Thats a good one (question). It was point of discussion during assembly.

The actual mechanism on the door is quite good. It feels strong and heavy. The amount of "throw" on the locking bolt is nice and long, so it engages well in what would be a strike plate.

Being made of ABS, the door, door frame and hinges are a bit flexible. I think the answer to the question about only keeping honest people out is, yes. If someone wanted to get in, I think they could, but I am still satisfied with it. I usually work on the assumption that all locks only keep honest people out. A determined criminal will find a way.

BUT.... I think with two simple mods, I can fix that. First, each wall panel bolts to a vertical piece of aluminium square tube. The piece that is on the hinge side of the door panel just needs to be a bit thicker and have 5 bolts instead of three. That would stiffen that part of the Dome wall significantly. Thats an easy one.

Second, I think they have used the wrong hinges for the door. The door does have a bit of a tendency to sag. They have used a smallish Butt Hinge. I think they should have used something like a Strap Hinge or a Tee Hinge. Once I get the aluminium wall frame swapped out, I will consider if I can easily change to a different hinge. I am concerned about changing the "look" of the Obs if I put larger hinges on the door. My alternative will be to put on a Padbolt.

From a security point of view, my other concern was the Slit opening. As supplied, the Dome Slit can be simply opened from the outside. I have modified a stainless steel balustrade kit with a turnbuckle and plastic coated stainless steel wire. All nice and secure now.

I should mention that there are two straps supplied that secures the Dome to the Walls and stops the Dome from rotating. This is mainly aimed at wind, but still has the effect of securing the Dome.

While I really have nothing to compare with (regarding other observatories), I am comfortable with the security of the Dome.

Hope this helps.
Darrell
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  #17  
Old 29-04-2018, 10:45 AM
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Thanks Darrell,

That's really good info, appreciated.
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  #18  
Old 03-05-2018, 09:05 PM
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Hi All

I thought I would provide a bit of a final update on the Observatory. I am happy to say that I think it is now “operationally ready”. The final piece of construction was the installation of some LED lighting. Three strips of red and one white for inside and one red for outside.

I think it is a bit of overkill. I am surprised at how the light seems to bounce around inside the dome. Just having one turned on provides more than enough light. Some pics attached. The bright red strip of grass being lit up is caused by the outside "porch" light being turned on. Way too bright I think.

I say operationally ready because I am still waiting on my new mount to arrive. So far, I have only used my GoPro.

Thanks
Darrell
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  #19  
Old 03-05-2018, 09:27 PM
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Hi All

Following on from my last post, I wanted to add a bit about my assessment on the dome. Anyone interested in purchasing this or something similar may find this helpful.

Originally, I was going to go with a roll off option. I had a few concerns about the dome option. I was worried that it would become a hotbox sitting in clear full sun all day. I was worried about water getting into the dome. And I was concerned about how it would handle the wind. I felt comfortable that all these issues could be addressed in building a roll off. It was the potential for wind and the slit design that convinced me to go for this style dome.

I should also add that I was intending to build a solid floor on the deck, using blueboard or something similar. This was to attempt to better seal the dome from water and crawling things (snakes and scorpions). The advice I got was to have a gap between floor boards to allow water to run through. Concerning! But I heeded the advice, and it has worked well. The floor boards have a 5 mm spacing and I put down a layer of flyscreen under the boards.

The temperature issue. I have very good clear horizons and the Dome gets sunshine pretty well from sunrise to sunset. But it hasn't been a problem. On day 1 at 1 pm the outside temperature was 29.5 and the inside temperature was 22.4 degrees. The next day, at 1 pm the outside temperature was 33.5 degrees and the inside temperature was 25.7. On the first day, at 6 pm the outside temperature had dropped to 14.3 and the inside temperature was 15.4. The daytime temperatures in the Dome were taken with the Dome totally closed. I am quite happy with that.

The water issue. There have been two storms since I constructed the Dome. So far, not a drop of water has come inside. Not a drop. Nothing. Totally dry. Extremely happy with that. And I didn't use any sealant or glue on any joins.

The wind issue. As I have previously said, we get fairly constant wind from the south. Last night I was in the Dome with a strong wind coming in from the south east. I would guess somewhere around 20km/h with gusts to 25. I was expecting it to be draughty, and maybe a bit noisy. Nope. I moved the Dome around and it was very rock solid. The only time it got a bit of a windy howl was when the slit pointed about 45 degrees into the wind. Once again, very happy.

Now for my new mount and some clear sky.

Darrell
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  #20  
Old 03-05-2018, 11:37 PM
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E23 (Andras)
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Quote:
Originally Posted by darrellx View Post
Hi All

Steady progress is being made on finishing the observatory. But I have one niggling issue I am having trouble getting my head around. I am hoping someone here might be able to help me with electrical theory.

My Laptop and the current draw on a 240 volt system compared to a 12 volt system.

I have a MSI laptop that I use exclusively for astro work.
On the transformer, the Output is stated as 19.5v 7.7a
The Input is listed as 240v 2.7a

When I use my Amp meter, plugged into 240 volts, during boot it peaks at 0.31 amps.
During normal use, it sits around 0.22 amps. In terms of watts, it moves around 42 to 48.
The laptop is fully charged.

Now, when I plug this onto a 12volt battery with an Inverter, the figures essentially stay the same.

All good so far.

What I don’t understand is the impact on the battery.

My thoughts on this.
- Forget the Output on the transformer. The listed 7.7amps is a maximum.
- The important figure for the laptop is the third of an amp it seems to draw at maximum.
- The other important figure is the 2.7a listed on the transformer.


So, ignoring any loss and inefficiencies, the transformer requires 240v at 2.7a. It is then delivering the 0.31 amps that the laptop requires.

Does that mean that the loss from the battery is still only the 0.31 amps or 2.7? I don't think so.

240v 0.3amps = 72 watts
72watts at 12 volts = 6amps

So, to run the laptop for say 6 hours - 36amps

I suppose if I wanted to get picky I would say 240v 0.22amps = 53watts
53watts at 12 volts = 4.4 amps

6 hours of runtime would then be 26.4 amps

Does that seem correct?

Thanks
Darrell
Darrell

I note that no one actually taken up your request for help with your electrical theory. Well here it goes:

Your analysis of the issue is largely correct. The figures for the transformer (power supply?): input 2.7A is nonsense, probably refers to fuse rating. Output 7.7A max. at 19.5VDC is consistent with your measured max input current of 0.31A. (0.31A input translates to 0.31x(240/19.5) = 12.3A, but only at 100% efficiency).

For the battery and inverter case, again the efficiency of conversion has a significant impact.

If your inverter supplies an accurate 240VAC output the draw from the battery will be 0.31x(240/12)= 6.2A but more likely about 7A due to inefficient conversion. Your calculation based on power is correct at 6A.

Now, about battery capacity. Your calculation is correct but what you got was 36 Amp hours not amps. You need a minimum battery size of 36 Ampare Hours, AH for short. This is basically a good car battery. Nasty things car batteries, better to use SLA (Solid Lead Acid) batteries. At 36AH they are not cheap if availably. The largest one at JAYCAR is 17AH but they may have larger. Need to check.

Andras
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