Power supply to scope

[Brady]

Morning all

I am going to be running a 13.8v supply from the shed to the scope pier to run the synscan and for now 2 dew bands and was wondering if this supply would do the trick?

http://cpc.farnell.com/unbranded/in06008/power-supply-bench-13-8v-5a/dp/IN06008

I know a few of you run the Maplin or similar supplys but looking at the above specs its half the price for in theory the same output?..in fact i think this is the 5A version as the Maplin is 3A

http://www.maplin.co.uk/p/maplin-69w-dc-fixed-voltage-bench-power-supply-xm22y

The only problem i have is the power will be travelling around 7m to the pier, the supply i have at the moment which is not a bench supply i might add, drops out after 5 minutes or so which was expected...but still a downer 

The last and final option is this one also from CPC, again it looks the part on paper but hands on information is always a bonus..

http://cpc.farnell.com/unbranded/in06009/power-supply-bench-13-8v-15a/dp/IN06009

I know someone actually uses the first supply but cannot find the post or if it was even on this site...sorry...and thanks for help

Wayne

Edited June 14, 2015 by Brady

[Brantuk]

I use the XM21X direct off the mains via a very long all weather mains cable with a socket on the end - so the supply is close to the scope. I have to protect the box from dew of course and keep it well ventilated - but otherwise - it's never been a problem.

Edited June 14, 2015 by Brantuk

[Smithysteve]

Hi Wayne,

I have had a look at your examples but I am not sure of your load requirements...

You are always better off over specifying the supply unit by a factor of 2 times your full load requirements. You won't have many power issues if you do this.

Note:Your load requirements may be low at this time but may increase in the near future, so try to allow for this, so work out your full load requirements bearing in mind that dew bands are generally a continuous load.

Distance to the scope is not a problem if certain factors are taken into account. Low voltage dc circuits generally mean higher currents flowing through your cables. Higher currents (amps) result in power losses over the lengths of cable. This is due to resistance of the cables over the distances involved. This will result in a lower voltage being available at the load end. The longer the run of cable the more resistance there is, the more the losses and the lower the available voltage at the load end.

This can be overcome by limiting the distance to a minimum and using a larger csa (cross sectional area) of cable as is practical. The thicker the wires the less the resistance, the lesser the losses etc. e.g 4mm csa is better than 1.5mm csa etc.

In your case 7 or 8 meters is not far at all, but keep the length to a minimum, do not keep any excess slack on a drum (this can cause overheating of cable).

If it was 40 meters to your scope then you would have been better getting mains to your pier :-)

[stash]

I use a PSU from Mass which I believe was popular with "Ham Radio" people due to min interference(!) - it puts out 13.8 v (fixed) and whatever Amps (10a max) required. I run a long lead and have no problems running a AZ-EQ6 (the light on the mount never flickers and the MASS Amp reading max's at about 2amps)

 

something like this http://www.ebay.co.uk/itm/MAAS-SPS-250-11-BENCH-POWER-SUPPLY-13-8V-DC-25A-CB-Ham-Radio-/161615075899?pt=LH_DefaultDomain_3&hash=item25a1025a3bbut mine was cheaper.

 

What Steve says about CSA is the key even if the power source is capable. 

 

Hope that helps.

Edited June 14, 2015 by stash

[Brady]

Thanks for your input gents, i managed to get a Maplin XM19V off the bay earlier so looking forward to setting that up, i dont know how long these things are supposed to last as i know its not a newer model but at least it will give me time to get things in order, Stephen i looking at cable now and have this stuff if you dont mind taking a look..

http://www.ebay.co.uk/itm/361222860238?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I will be running the synscan and maybe two dew bands so around 4-5A total

Thanks for your time guys

Wayne

Edited June 15, 2015 by Brady

[Brady]

Sorry the supply is rated at 7A

[stash]

Don't forget thats the max Amps(short period) not continuous cycle - I would not think  that you would be running at 7amp continuously -clear skies   

[Guest peepshow]

In the old days when I had my gear outside in a field I always used white cables which show better in the dark.

Black cables are a menace at night.

 

I also buried 12v cable about 6 inches in the ground, running from the house to my mount.

Edited June 16, 2015 by peepshow

[Smithysteve]

Hi Wayne, you have now committed to a XM19V ?and 17 amp rated cable so the best thing is to see how you go. If you have worked out that your load is around 4-5 amps then you may be ok. Clive is right about the power supply, ok it is 7 amp rated, you are using less, but you will be probably be using 4-5 amps continuously for several hours so the power supply may struggle. Keep your power supply unit where air can circulate freely around it. Do not put it in a box etc, you need to keep it well ventilated to keep it cool! During the winter this should not be such a problem:-)

If it is a regulated power supply then it will try and maintain the voltage, compensating, by limiting the current output, if necessary, to do so.

The cable you are using may do the job, but there is no mention of the csa of same, so I am presuming it is about 1mm (or 1.5mm) square. This is small. Again, now you have it, see how you get on with it. Keep length to a minimum, but allow for same running freely on the ground etc not like a clothes line, or bow string :-)

Personally, I would have preferred the cable to have been a bigger csa e.g a min of 2.5mm but better at 4mm). If you have a problem with volts drop (measure the voltage at the telescope end whilst running dew bands and scope with a meter) then you could double up on the cable or get a bigger cable. But like I said, try it. If you have any probs or further queries then post it and we should be able to sort it. Hope this helps.

Cheers!

[Brady]

Cheers Stephen, its most probably how i worded it but i haven't purchased the cable yet, it was meant to read that i have it in the watching part of ebay and for you to take a look so glad i didnt buy it  , the reason why i purchased the supply is im cash strapped for a good month and this was the only available option for now so like you say should do me before i get the bands on at least, i will up the cable and post the outcome...thanks again to all

Wayne

 

Can i just check the part about the Amps, the supply is 7A continuous..shouldn't that be enough if running 4-5 continuous?

Thanks

Edited June 16, 2015 by Brady

[Brady]

[Smithysteve]

Hi Wayne, looking at the PSU it is 7amp cont, and surge protected etc, so yep, for your current setup it looks good!

I know some people go for the 10amp cont model, the XM21V I think, to be on the safe side :-)

Cable wise you are better off with a flexible cable (with multi stranded cores). it will lay on the ground better and be easier to coil up after use etc. Or, Is your pier permanently mounted? Are you thinking of running the 12 v cable underground to it? If so, I may have some cable you can have, subject to length, gratis of course :-)

Cheers

[Brady]

Hi Stephen, unfortunately due to the garden being a "modest" sized patch of baron soil it was slabbed over a few years back, as much as it would be nice to bury the cable im just going to have to lay it down as and when its needed, i have 2.5mm flexible cable with multi strand in the shed which is surplus as of now   so will try it all out at the weekend, much appreciated for the offer of the cable Stephen, i will surely call if my new plan and equipment fail, good to know the supply may still be of use..

Thanks

Wayne

[Smithysteve]

Ok Wayne,

2.5 mm should be fine, the cable I have is 4 core, 6mm csa flexible armoured (SY type), so not really suitable for running out every time you want to use it ☺ï¸

Let us know how you get on...

Cheers!

[Brady]

The cable i have used is 2.5mm cable that was an unused caravan extension cable i had made up last year at work, i have ran this off the supply which is running 13.72v, at the end of the cable which is 25m long is 13.72v?, do i need to check the output with some usage i.e the synscan powered up? or is it just that good?

Also is it wise to have an inline fuse on this setup or does the supply cover it? if so what size? 

Sorry for the questions...just don't want to have a meltdown at 2am..

Thanks

[Smithysteve]

Hi Wayne, sorry for the long winded reply :-)

Regards the fuse;

It's always a good thing to have an inline fuse, this can help protect your cable and your power supply in the event of a fault. Your power supply will more than likely have built in overload and short circuit protection, unlike, say a car battery, so that is good. If you are using 2.5mm cable, and your load is going to be around 4-5 amps then you could use a 7.5 amp anti surge fuse to be on the safe side.

Regards your voltage test;

The volts will be the same at both ends when there is no load I.e. No current flowing.

So your voltage test results are normal. But this test result is deceptive... with a similar cable say 200m long etc the volts would be the same at both ends if there was no current is flowing. Add current to the circuit and things change...

If you connected your dew bands to the 25m long cable and tested the voltage at both ends you may see a difference. The point is this difference may or may not be enough to affect a sensitive voltage dependant load, e.g. The Synscan etc, these devices will only tolerate a certain voltage reduction... But, you don't need 25 metres do you? :-) and in your case it well might be fine and dandy, but you are asking the questions what if? So I am happy to try and explain :-)

The point is when you increase load, you increase current flow which increases volts drop. The trick is to minimise volts drop by minimising cable length and increasing cable CSA size... And keeping your load to a sensible minimum, Then you should not have a problem using 2.5mm cable of less than 10 metres with a load of 5amps etc.

I am trying not to get too technical, but for your information, I will try and explain what's happening... In your case, you should be ok, I am trying to explain why you have the same voltage at both ends :-)

Volts drop depends on certain factors; e.g.

The Cable: It has a certain resistivity dependant on the conductor material, the conductor thickness and the length of its conductors. E.g. Copper conductors have less resistance than aluminium etc. ( the point here is resistance of the cable affects the following formula... See below)

The load. The Load takes power from the supply. In a dc circuit, power = volts x amps ( the point here is the higher the load, the higher the amps the more it effects the following formula... See below)

There are other factors, but let's keep it simple:-)

V = I * R

Or,

(Volts drop) V(d) = I (amps or current) * R (resistance in ohms)

This volts drop, say for example it's 2.7v, means you have 13.7vdc at the power supply and 11 volt at the load end.

Sorry for the long winded reply, in a nutshell you should be ok.

[Brady]

Thanks for the info Stephen, much appreciated, you have made the situation a lot clearer, i have decided to hide the cable so lifted some slabs, grass and wife's pots and got it buried, maybe a bit premature but i had a hour spare last night and seemed a shame to waste it in case the plan works, i fitted a twin 12v socket to the pier which would power the scope and band, as Richard says i really cant be tripping over cables at 2am  so will test tonight if this clear spell comes and see what happens...

A few pics...the pier is all stainless, a perk of the job, the mount plate was made by a good friend who is retiring in a few weeks time and this was his parting gift to me, my gift to him was a bottle of Glenfiddich...a good trade i think..i welded up the stainless myself with my trusty stick and the pier is modified to my needs i.e the extension on the right is 48mm to mimic the tripod leg so all controller fittings just snap on, The twin 12v supply is waterproof and is enough for my use...for now anyway..i hope you like it and thanks for all the help guys.

[Tweedledee]

Very nice job Wayne

[Smithysteve]

Glad to be able to help you Wayne :-)

Your pier and accessories looks brill, and will continue to look brill. I have not seen a finer one...

Getting the cable in permanently will help you set things up quicker and more safely, it's worth the effort, so we'll done!

[Brady]

Thanks guys, now let us pray for clear skies 

[Brady]

It worked a treat Stephen, so much easier to use and set up, power supply has worked fine up to now so should be good for a while yet, thanks for the advice..

[Smithysteve]

No probs Wayne, glad to help. Pleased it is all working fine...

Cheers!