Mains power to mount with extension cable

[lrh]

Hi all,

I'm coming back from a (very long) break from astrophotography, and looking to power my Skywatcher NEQ-6 with mains power. I used to use a powertank, but I was hopeless at remembering to charge it, so I'm looking at something I can just plug in and wheel out of the house when the skies are clear.

Does anyone have experience with using an outdoor-rated cable reel to provide power to a mount in a back garden? The idea being I'd wheel it out through the window and plug my NEQ-6 and dew-heater band controller (with 12v adapters) into the cable reel. I'm a bit concerned about damp/dew forming somewhere in this chain and potentially causing a surge which could damage the mount electronics.

I'm thinking of something like this for the reel: https://www.diy.com/departments/masterplug-2-socket-grey-outdoor-cable-reel-20m/33670_BQ.prd?fbt1=true ; i've just bought two of these 12v adapters for the mount + dew controller: https://www.harrisontelescopes.co.uk/acatalog/universal-mains-telescope-power-supply.html

Cheers,

Luke

Edited January 28 by lrh

[symmetal]

Hi Luke,

Personally, I would get a heavy duty storage box like this which can hold a cable reel and the power supplies etc. At the scope run the cables out the top of the box and lay the lid on top to keep any possible dew from the inside. This way you don't need to get the 'outdoor' type cable reel which should be cheaper.

Just remember that when you plug the cable reel into your house mains outlet, you connect it via an RCD adapter like this for added safety.

Alan

[mikerr]

Hi Luke, regardless of how you get the 240 volt mains out to the scope, consider getting a 13.8 volt dc power supply for the EQ-6 instead of 12 volts. I have an AZEQ-6 and it performs better on  the slightly higher input voltage. 
 

Rgds

Michael

[lrh]

Hi both,

Thanks a lot - really useful stuff there! I'll definitely pick up a heavy-duty box to manage the dew. Looking around, I've seen several suggestions to get an RCD adapter, which I'll also definitely pick up. Can't be too careful.

Michael, regarding the 13.8V supply, in what way does your mount perform better on the higher input voltage? Is the tracking better?

Cheers,

Luke

[PhilB61]

When at home I always power via a mains extension reel, if dew is going to be a problem I have found just putting the end of the reel with sockets in a plastic bag is sufficient, obviously not as robust as a box but one less thing to carry out and store.

[PhilB61]

I think pretty much any house built or rewired in the last 25 years will have RCD devices already in the the mains circuits (in the UK). I had assumed this would be sufficient protection?

[mikerr]

Luke, the higher input voltage ensures that the required running voltage doesn't drop too low during high demands like slewing. It does not improve normal tracking or other functions, just allows them to perform as intended. 
There is a section in the users manual regarding supply voltage problems and recommendations. Pages 13-14.

Michael 

[900SL]

12V nominal (eg car battery) is usually  ~ 13.2V at terminals when fully charged

Most regulated linear 12V supplies are actually 13.5 - 13.8V at the terminals. These are good supplies for astro gear and provide clean regulated DC

12V switching PSU's (like laptop bricks) can be noisy and may be 12V in service, which may not be enough for some 12V rated equipment like mounts, which have high current draw when slewing or starting up. 

I run all my gear from a regulated linear PSU delivering 13.6V  to a Pegasus mini power box. No issues at all 

Edited January 29 by 900SL

[Swoop1]

I used to roll out a reel to my pier then roll it back in again then store it in the shed. That got a bit tedious so I cut out some of the work by fixing an external socket box to the end of a length of arctic rated cable with a plug at the other end- effecgtively a do it yourself extension. Hand looping the cable is a lot less problematic than rolling in cold stiffened flex.

You could perhaps do the same for your mount (tripod?) and have the cable wire into an outdoor waterproof encloure?

[900SL]

Silicone insulated cable is good at low temperature. As Swoop notes the standard extension cords stiffen up at low temperatures. Get one that has sealed cover at the socket end (IP rated)

1.5mm2 wire should not be used more than 20m length from memory, or voltage drops start to get significant, but check that on line as I am going on memory.

Use an RCD at the supply end

[PeterC65]

Depending on the distance from inside to the mount, you could keep the mains power supply inside and just run the DC supply outside.

I use a Nevada PS-08 mains power supply which stays just inside the patio door and gives me 13.8V which I run outside through 5m of cable to the mount. I selected the low voltage cable so as to ensure that the voltage drop along the cable was small enough to still maintained at least 12V at the mount when it was drawing the current needed for the mount, cameras, and dew heaters.

The cable I use is AMC TW0203BRB.30 which is a 32/0.2 cable with a resistance of 0.0185 ohms per metre. When supplying 5A, this cable drops 0.185V per metre (counting the drops in both the positive and negative conductors) so you should be able to use it for distances up to 9m. It is possible to get cables with even lower resistance, but this one is happens to be 5mm in overall diameter which is convenient for most connectors.

 

[lrh]

Thanks all, much appreciated. To address a few points:

1 hour ago, mikerr said:

Luke, the higher input voltage ensures that the required running voltage doesn't drop too low during high demands like slewing. It does not improve normal tracking or other functions, just allows them to perform as intended. 
There is a section in the users manual regarding supply voltage problems and recommendations. Pages 13-14.

Thanks Michael, that's good to know. I'll give the manual a read over.

Regarding the voltage drops due to cable length, i'll measure the distance from the mains outlet to the place where I normally setup my tripod + mount and estimate the voltage drop. I'd be fine with slewing etc. being a bit slower, as long as the tracking is alright.

Unfortunately I'm renting at the minute, and will be for the foreseeable future due to somewhat frequent relocation for my line of work, but I'll have a think about maybe getting a semi-permanent (but reversible) power solution in place the next time I'll be somewhere for 2+ years. Maybe a mains extension from the house out to the observing site with silicone insulted cable.

Luke

[PhilB61]

Be aware that many of the provided power bricks only put out barely enough voltage, my Altair Astro camera supply is 12.3v and the Ioptron 12.6v this is okay with short cables but the 5m one suggested above would cause too much voltage drop, it only works because a higher rated power supply is being used. I often take power from my campervan which provides a nominal 12.7v and also use a 5m length of cable but opted for 2mm sq cross section to reduce voltage drop. I previously used a much thinner and longer cable which caused low voltage warnings on my mount. The 12Volt Planet website has a simple to use voltage drop calculator.

[lrh]

I got all of my gear out tonight to take advantage of the intermittently-clear skies, mainly just to verify that everything (that has been in storage for 6+ years!) still works. I used the advice in this thread to power everything via mains: an IP54-rated cable reel plugged into a mains socket via RCD adapter, with everything (including 12v converters for the mount + dew heater controller) inside a heavy-duty plastic box. It worked a treat - the electronics inside the box kept dry, and despite the cable being 20m long, the mount worked fine. Although, as mentioned by Michael, the slewing was a bit slow.

Thanks all again for the suggestions - I very much appreciate you taking the time.

I did, however, quickly remember how much I hate polar alignment. Thankfully, my guide camera and dovetail for my guidescope arrived today. I keep buying the wrong screws (🙄) to mount it to my imaging scope, but once that's sorted, I'll use a plate-solving method for the PA with the guider.

Cheers!

Luke

[PhilB61]

You don't normally have to worry about voltage drop on a mains cable, as the higher voltage is not affected so much, one of the reasons overhead power cables run at many thousands of volts. 20m or more should not have any effect and is unlikely to be the reason your mount was slewing slowly.

[lrh]

1 hour ago, PhilB61 said:

You don't normally have to worry about voltage drop on a mains cable, as the higher voltage is not affected so much, one of the reasons overhead power cables run at many thousands of volts. 20m or more should not have any effect and is unlikely to be the reason your mount was slewing slowly.

Thanks for the clarification Phil; I had assumed that was the case. I was referring instead to the fact that I'm supplying my mount with 12v, not 13.6v (I believe, I'll need to check the adapters I'm using in detail).

Thinking about it now though, it's entirely possible it's slewing fine - I haven't used it in 6+ years, so I could be misremembering the slew speed.

Luke

[PhilB61]

Yes it does seem some of the supplied power bricks are marginal at best. I found using the NINA Three Point Power Align plugin drastically improved my PA experience, no more kneeling on damp ground squinting into the polar scope.