teoria_del_big_bang

4 hours ago, michael8554 said:

The calculator I found seems to have been pessimistic in advising 12sq mm.

But calculating for least load is not best either.

What happens when the mount slews and draws lots more current and the voltage drops? 

Mount runaway.

Michael

Michael,

No I agree we have to consider maximum load but if you add up all maximum draw of Matts setup it is really no more than 5A at 12V  (the least load is more like 1.5 to 2A) and I think 2.5mm2 would always keep the voltage over 12v with a 13.8 V supply.

Don't get me wrong I am not recommending this at all and do think 17M is far too far. Even at 2.5 mm2 it is borderline hence why I included links to the calculators, the cable would need to multistrand so actually this probably increases the required wire size so it is not what I suggest but with the lower load of 5A max I think it would be possible.

Steve

51 minutes ago, matt_baker said:

My issue is that I have to image further up in my garden and then I'm not close to any sockets. My mains extension runs about 16m to the equipment as to why I need such a long cable but if I can have the PSU in a box outside, with the mains extension running to it so I can have a shorter cable and not have significant voltage drop, that would be great. Of course, the scope would never be outside when it's about to rain and it takes me around 15 mins to pack everything up. My main concern I guess would be moisture and how that could affect the PSU, as well as heating issues being inside a box

 

Matt

Then as I said put the extension inside a splashproof box that is plenty big enough to leave enough air round then to stop over heating, plug into a RCD. My suggestion of getting an outdoor socket near to where you image properly wired by an electrician to the consumer unit is just a better idea.

It is difficult for me to recommend this way of doing things as whilst I consider it safe if via an RCD many will shoot me down and say I should not be recommending this as electricity is dangerous - which it is if care is not taken.

I use a 240V ps in an home made box and will take a pic to show you. It is home made but I have never had any moisture get into it and is big enough to house a big 12V power supply and extension for any other smaller supplies (such as the RPI) to plug into. Only thing is I do have a proper outside socket next to the mount but this just means I do not have the extension issue and the RCD is in the consumer unit.

Oh and when using an extension always unwind all the lead, if a 25M extension and it needs to me 15 m do not leave 10M wound on extension. Even with small currents you would be amazed at how hot it can get.

Steve

35 minutes ago, matt_baker said:

Thank you all for your input.

How unrecommended is it to put the psu in a box outside with the equipment connected to a mains extension lead and have a 2-3m wire to the DSD DCHub?

Matt

You can put the power supply AND extension in a weather resistant box like this:

Outdoor IP55 Power Enclosure

Then connect the extension into a RCD adaptor:

RCD

Note that theIP55 box is not totally waterproof but more like splashproof and should not be left out in rain but then I assume you would not leave your scope out if rain was immanent either.

The RCD is essential for safety.

The RCD should protect you from shocks and will trip if a short occurs but I would also recommend if any damp about to plug everything in then switch on at the RCD and again switch off before unplugging again at end of session as stugg tends to get a bit damp if any moisture in the air. Maybe over cautions but better safe than sorry.

Much better is to get an electrician to fit a proper outdoor socket close to where you intend to image and that will go to an RCD in the consumer box. The power supply still really wants covering with an IP 55 type enclosure and make sure it is big enough to leave pleaty of air around the supply so it does not overheat.

Steve

7 minutes ago, michael8554 said:

Let's say 10 amps including the dew heaters, over 20 metres.

I found an online calculator that gave a figure of 12sq mm for a 0.5V voltage drop at 12V.

For example, probably the heaviest cable you find in a house for 240V is 6sq mm.

25M of 10sq mm black or red from Radio Spares costs about £60 each.

As wulfrum says, investigate a safe mains supply to your mount position, google "Temporary Garden Electricity"

Michael

At 10A that sounds about right but he will need less than 5A and to be fair if the supply is 13.8V he can stand a 1V drop and most of time he will niot be drawing 5A so I think 2.5 mm2 will suffice.

Steve

@wulfrun has given some good advice above.

Just as an example below are some links to calculators for voltage drops in DC circuits. Both give slightly different results but pretty close to each other and probably due to using different coefficients for the resistance of copper.

It is also very difficult to calculate exactly the current being drawn because the mount for example depends what it is doing. You state 3A that is probably the supply recommended. From what I remember a HEQ5 on average takes around 2A when slewing at full speed (even this can differ from mount to mount depending on how stiff the bearings are or how tight the gears mesh or if load is out of balance) but for 95% of the time it will just be tracking and draw 0.5 A or so. The camera cooler again needs a 3A supply but I think again draws around 2A when cooling down from ambient but when cooled may again only draw a small current and will continually be changing. The dew band should be fairly constant and I guess for a scope your size around 0.5 A.

So we may be drawing around 5A in theory but normally when all up and imaging it will be more like 2A. But we really have to take worst case and say it may be 5A.

Using the calculators for 13.8 V over 17 M using 1mm copper wire you would have a voltage drop of around 3V and only deliver 10.8V to the mount which is certainly not enough for the mount itself.

Voltage Drop Calculator 1

Voltage Drop Calculator 2

To have anything like a good 12V at the mount you would need to use 2.5 mm cable which would give a volts drop of around 1.2V when drawing the full 5A. Of course most of the time it will not draw this only around 1.5A and so the voltage using 2.5 mm cable will vary from about 12.6 to maybe 13.3 V.

When drawing 5A the cable may get a bit warm as it is displacing nearly 15W but suspect it maybe okay.

So maybe you will be okay with 2.5 mm2 cable.

Steve

Yes all about normal for a first night. 🙂

Well actually no it isn't, you got some pretty decent shots which I bet most do not on their first attempt. So well done.

I would have been more than happy with decent images of 3 targets, I think I managed to get something that looked like Orion Nebula but to be fair you can get a single shot of that to look good but for sure I think I had a similar debacle on my first night.

A lot of imaging does come with practice especially getting set-up on a target and actually taking images. I think for many of my first sessions I was two or three hours into the session before I saw a recognizable image on the screen, but in a way that was good as if something went wrong I always wanted to know exactly what so rather than just somehow getting an image in view and then start tracking so often I would sacrifice some imaging time and return the mount to home and start again till I got it right. Then eventually you will be able to set up, align in minutes and be imaging instead of hours.

Of course there are still nights it doesn't go quite to plan and from other threads I see I think most of us have these from time to time.

Well done, enjoy this great hobby obsession 🙂 

Steve

3 minutes ago, SMF said:

One down side, not very good for hiking, it’s gonna be heavy. About 24kg with battery and box but I recon it’ll only be carried over short distances anyway.

Always one drawback, but if you are not walking for miles then not an issue. Might even be able to hang it below the mount to make it more stable as well. 

Steve

10 minutes ago, SMF said:

Andy, not sure about the stats but I looked at the Maplins chart that shows expected rating in various usage examples. Didn’t look that much to me. I might be wrong.

I’ve spent a few weeks debating this subject and after Ships and Star’s suggestion have just ordered the below:

https://www.fishingmad.co.uk/31508-bison-battery-box-carrier-with-usb-charger-led-meter-breaker-and-12v-socket-.html
and

https://www.batterymegastore.co.uk/product/hankook-xv27-leisure-battery/
 

Gives me 90AH for £135.00 which I recon will last six nights and more. The bigger Celestron Powertank is 17AH and that lasts more than a night for most people.

I’m fortunate to live right on the beach and plan to use this for leisure next summer as well.

I really like that battery holder.

That should be great and give you plenty of power, just make sure you do not totally drain the battery and keep it charged, re-charging regularly if not used for a while as it will discharge slowly on the shelf. But even if the battery goes down after a few years you only have to buy a new battery and still have that great holder.

Steve

Just now, Shimrod said:

In my case I use a low power laptop - an HP spectre x2. The biggest power draw is the screen, the processor has a TDP of 15w. The laptop will go about 4 hours in the cold, and I use a cheap 20ah powertank (£30) which plugs into the usb-c port and keeps it topped up.

The other thing in favour of the LiFe-Po battery is the consistent power delivery as the battery discharges - no drops in voltage as you might find on other batteries.

Ah well yes it is certainly true that many laptops use less power than my brick and probably many of the newer models are far more lowered powered than mine. 

Steve

21 minutes ago, Shimrod said:

I have one of these as well (it can be picked up for £214 from picstop) and it is both lightweight and has all the power connectors I need. You don't have to worry about keeping it charged (like lead acid or Li-on) batteries, and the battery technology (LiFe-Po) is much safer than Li-on when it comes to possibly knocks or damage to the battery. It beats lugging the equivalent 20kg lead acid battery around and it will last for years. It is the battery technology rather than the brand that makes this expensive - have a look at tracer batteries which use the same technology and cost similar amounts.

That is actually a great price and although sounds expensive would probably work out cheaper in the long run.

The W/Hrs is about the same as the two supplies from Amazon and Maplin mentioned above at 158.4 W/Hrs. But:-

• You will get somewhere near all of that out of it if fully charged, I doubt you will from the others.
• It will last longer (i.e. more years) without having to be really careful to keep it charged, the others are liable to holding less power as it ages and maybe even failing altogether if not charged regularly.

However, not sure how you would power your laptop without some extra device such as 12V Laptop Charger

Steve

Some interesting finds and I am also particular interested how good either the Amazon one or the Maplin one is (I guess Mapling have remained an on line company as sadly I thought they went bust a while ago)

Amazon

Maplin

Both claim to be about 150W/Hrs which for a smallish imaging rig sounds good. One thing I would say is that whatever power they claim they can deliver in practice it will always will be less and in some cases maybe only half (that is a guess I cannot say for sure and sometimes you only find these things out by trying them). Many things contribute to lack of performance such as temperature, efficiency of the circuitry when creating all the different voltages.

If it was just a HEq5 size mount and a dew band drawing an average total of 1 to 2 amps at 12V throughout the night that is an average of 24 Watts so in theory would last 150 / 24 = 6.25 hours. But I would think if I were buying this I would only bargain on getting 4 to 5 hours. 

Now it may well be you actually only draw around 1A on average with this setup so long as you are not slewing from target to target every few minutes as it is the fast slewing to target that draws a high current (on HEQ5 I think it states around 2A). When tracking it will only be drawing about 0.5 A.
A dew band probably takes 0.5 to 1A depending on size, so a 100 mm dia scope probably about 0.5A but a bigger one on 200mm or bigger diameter may be 1A or a little more.
That's why I suggested maybe 2A average. But if a small scope and you are not doing a lot of slewing you may keep to around 1A to 1.5A so may get 8 hours or more, very difficult to say without knowing  exactly the current draw of each item and the efficiency of the supply.

One thing I haven't mentioned is the laptop. If use on an inverter then this will very quickly run down your battery and no actually idea how long it will last with the laptop as well. In fact it is impossible because many older laptops have woefully poor battery life so would be on mains power nearly all night. Most laptops have power supplies around 50 to 80W (I think - mine is 65W at 20V). This will be a maximum it can provide and so the laptop may not take this amount to charge or run. But lets say it takes 40W at 20V that means that with 150W/Hrs available (if it were 100% efficient - which it will not be) then the laptop alone will only run for 3.75 hrs (150 / 40).
Also the inverter will be nowhere near 100% efficient and my guess is in reality you will get only 2 to 2.5 hours running the laptop + of course what ever the battery can provide. 

So as I said very difficult without all the info of power used by each item and also how efficient the supply is with a small mount, small dew band and laptop with good battery my best  guess is you might get 2 to 3 hours from these at best.

There are things you can do to extend this life all of which are to draw less current:

• Use dew band at a lower voltage than 12V so it does its job but not over warm the scope.
• Use a low power tablet instead of laptop.
• If you use laptop then get a good battery, maybe two and hot swap them when one runs low (I do not know how feasable this is as I have never tried) but even one good battery means you can run only on battery for 2 to 3 hours before plugging into invertor.
• Do not use the invertor to run laptop but get a seperate 12V to Laptop Voltage supply (Like This) that will probably be more efficient and run it from the 12V, also only plug into supply for a short while and run most of night from battery (or ideally batteries).
• Dim screen right down and let it automatically turn off altogether when not being used.
• Install  a solid state drive rather than conventional HDD.

On a last note I think the Watt/Hrs is a better indicator of battery life than A/Hrs or mA/Hrs.
mA/Hrs is really the same as A/Hrs but rated in 1/1000's of an Amp rather than Amps. So if you divide mA/Hrs by 1000 you get A/Hrs.
If it is stated in A/Hrs or mA/Hrs then really it should state at what voltage. Some scrupulous sellers quote the A/Hrs as a ridiculous figure that makes it seem really powerful but they are quoting it from what is on the batteries which will be 3.6V for lithium-ion. But at 12V the figure will be 3.33 less than this quoted figure.

Steve

What equipment are you needing to power and is this for use in remote areas or from your back garden ?

Steve

These are perfect size I bought some a while ago

https://www.ebay.co.uk/itm/5X-Small-Transparent-Plastic-Storage-Box-Case-Clear-Square-Multipurpose-LDUK-bp/193680972846?hash=item2d18491c2e:g:XMYAAOSw-ldZZmmE

Steve

Signed

Steve

I had never thought of this before, but if I understand correctly @gilesco is concerned that the weight of the camera, FW etc on a focusser with draw-tube almost fully extended may cause it to sag and introduce tilt, but by moving the draw-tube in say 50 mm and fitting a light-weight 50mm spacer between the focusser and Flattener then with more of the draw-tube inside the focusser it will be stiffer and less prone to tilt.

It does sound a reasonable possibility to me, I think on my Esprit 100 the draw-tube is only about half way out so never considered it an issue (But so long since we had a some clear nights I have forgotten just how far out it is).

Steve

Nice clear capture 🙂 

Steve

3 minutes ago, rickwayne said:

Yeah, it admits that it's got a pink problem!

I didn't think the galaxy looked bad for colour but the stars are a bit pink. That shouldn't be too difficult to fix.

Steve

Wow, that's an absolute beauty - nice subtle colour and great detail 🙂 

Steve

Long shot but I did see a similar thread about no link to MC and it turned out to be the lead between handset and mount, I think handset had power but some of the cat5 cable wires must have been broken. Like I say a long shot but have you got a spare cable anywhere just to try it?

Steve

What did you power it with before ?

12.8 V is not too high for a HEQ5 and a fully charged battery will be 13.8 V but still fine.

The fault you are getting is not something I am familiar with but hopefully somebody else on SGL will have seen it but I would suggest going back to the power supply you last used when it all worked okay and have nothing else connected.

Steve

6 hours ago, Craney said:

Clear nights !!!!!

.......when,

1)   I have work the next day

2)  It's windy

3)  Object of interest is now behind a tree

4)  Electronics (which have worked fine on every partially cloudy night)..... now do not work.

5)  My partner has obviously not looked at the long term forecast when arranging that "not to be missed" social event......

6)  Greater than 75% Moon

7)  ... and so on....

I am glad thats the norm, I thought it was just me 🙂 

Steve

8 minutes ago, vlaiv said:

You do know that it transfers via SGL thread participation as well?

As soon as you participate in a thread when someone shows off their new gear - at least of couple of cloudy days is added on your tab

That's okay vlaiv, I am far too jealous to go looking at what other members are buying 🙂 

Steve

Living in the North of the UK I do get a bit of a hint when it may be a clear night here as they always coincide with a near full moon. So on the plus side I do not need a red light to see as it's as clear as day 🙂 

Steve

7 minutes ago, Pryce said:

Is the effect cumulative?  Simce literally every piece of gear I have is new,  will it take like 725539 weeks before I see clear skies again?😮

Is the big bossman bribeable?  I'd really like some clear skies right about now..

I am not sure how it works really. I have been good this year and not bought anything for months but last chance I got of clear skies was September and had to travel 260 miles South to get that.

I hope for clear skies for us both soon 🙂 

Steve

My first scope was a dobsonian which I bought for a good price 2nd hand from an SGL member. I think I really wanted a goto but the 2nd hand manual was a cheap option so I had nothing to loose. 
I actually ended up being very pleased with it. And in fact it was a great introduction to the hobby and the views were great.
Yes being manual was a slight pain in that I had to manually track the objects by hand but the fact I had to find the objects really helped me get used to where things are in the sky at particular times of the year.

Also, because at that stage, being very new to the hobby, I did not know where my real interests lay again it gave me time to think what I really wanted whilst having something I could use and keep the interest going.

After a lot of chatting and asking many questions on SGL (Some which really were very novice questions but that where we all start and nobody made me feel silly for asking these very basic questions) I fairly soon decided I wanted to get into astro photography and so If  I had paid a lot more money and bought a goto Dobsonian then really that would not have been the ideal start for AP and so saved myself a lot of money, although AP is not cheap so when I say I saved money that is very much debatable 🙂 

So it does very much depend on where you may think you want to go with this.
If you think you really just want to dabble into astronomy or even are keen but think you are more into observing then the goto dobsonian will serve you well and you can still take some images even very easily just with your mobile phone.
But if you are unsure, or think that the imaging side is more where you want to head then maybe get the manual and save the money to put towards an AP setup later as you will need a fair amount of cash for this as a good sturdy mount that will track the object is ideal for this.

I still have the manual Dobsonian as I love it and so long as I have the room in my garage to store it will keep it.

Steve