DIY power box ?

[RayD]

2 minutes ago, BRUN said:

Just been to maplin, those neutrik are enormous, the cable I bought is 2.8mmx2 so it wouldn't be properly fitted on a connector so large.

They didn't seem to have an xlr that I felt would be a good fit, do I need fatter cable ?

2 x 2.8mm seems a bit big?  If you look at Dave's he only has 2 x 0.5 or 0.75.  Are you sure it's 2 x 2.8 as that's not really a standard cable size, perhaps you can post an image?

[BRUN]

That includes the insulation

[RayD]

9 minutes ago, BRUN said:

That includes the insulation

Ah ok, makes more sense then.  I'm guessing then you're cables are about the same size as Dave's, which means you may need to use a little bit of heat shrink tubing to close the gaps.

[RayD]

These are the XLR plugs I use, which work well on smaller cables:

XLR Plugs

 

The plugs I use in these sockets:

XLR Sockets

[Davey-T]

I use these also from Maplin, the thing about these connectors being big is what I like makes them easier to use.

Dave

http://www.maplin.co.uk/p/small-cable-exit-grommet-jp42v

[BRUN]

Cheers

Does it make any difference whether you have male or female on the box and vice versa ?

[RayD]

Personally I would say female box (socket) end and male (plug) end.  In real terms it doesn't matter, but if your socket side isn't switched you will have your +-12V terminals exposed which could lead to a short.

[BRUN]

cheers, ive gone for the XLR 

[cjdawson]

I've gone for a mixture of Marine 12v cig sockets, and XLR.

The XLR is used as the main connection for my scope, as people said, they're lockable and won't get confused with other connections in an astronomy setting.

Marine 12v cig sockets can accept the marine version of the 12v cig plug.  That advantage of those is that they have spikes that come out of the plug, and provide a positive lock to keep the plug in place.

 

The XLR parts I get from Farnell.

The Marine sockets came from a supplier on the web, I can't remember which one.

[SonnyE]

I take it you have much damper conditions than I do, but what a person needs depends a lot on what their climate throws at them. Connectors are but one of the needs to address.

If I were faced with very damp to wet conditions, I would probably want Marine grade connectors. But I am not. And if I was, I would also consider sealing the circuits and circuit boards as well against moisture. Putting a marine grade connector on an unsealed box and circuit board is fruitless to the job at hand. Condensation can, and will, still wreak havoc on your efforts. (I see nothing at all sealed about the switches or connectors on my Celestron mount, for example.)

So I opt to use the manufacturer supplied connectors, and where I need to extend things like my 12 volt supply for my CCD fan, I simply solder connected additional wire into that circuit. My AVX mount came with a 25 foot long cigarette type lead. For USB connected needs, I got the longer USB cables appropriate for my cameras and Mount needs. Because I am an EAA buff.

I don't want to over complicate my life with too many changes to get the job done. I also loom my wiring with a spiral wrap type of covering. No dangling loose wires for me.

[BRUN]

what kind of fuse are you all fitting, what amp, mine will just be powering my scope, nothing else (Skywatcher 250px GOTO Dob)

[RayD]

3 hours ago, BRUN said:

what kind of fuse are you all fitting, what amp, mine will just be powering my scope, nothing else (Skywatcher 250px GOTO Dob)

5A will be perfect with cable you're using 

[Alien 13]

As above, the real purpose of a fuse is to protect the wiring and should be rated at a lower current than the cabling can provide. Fuses are too slow to protect the device but can help prevent them from bursting into flames by removing the power.

Alan

[BRUN]

Thanks, I would have thought 5A would be too much, was thinking 2-3A

[RayD]

Cable should be good for up to 1440w 6A so 5A fuse is perfect

[RayD]

You can put lower in if you want, it doesn't matter, but you don't want false trips.  In reality you should fuse at a minimum of 120% maximum current but less than cable capacity, so you could most likely do anything between 3A and 5A and be ok, either will blow with a problem.

[Alien 13]

9 minutes ago, BRUN said:

Thanks, I would have thought 5A would be too much, was thinking 2-3A

The problem with astro gear is it can be very cold when powered up so the inrush current or surge can be quite large (up to 10 times the normal running current) so it would be wise to go at least 1.5 times and with a fuse that is rated for surge, usually denoted by the T prefix.

Alan

[Hicks]

I use a couple of different types. For the mains supply I use an extension cable that has these type of connectors[1] on. They're waterproof. From that extension lead I run the cable into a waterproof box for switching power on/off and to connect to the next cable from the 240v/12v convertor (also waterproof).

The two 12v outputs from the power convertor I plug into the main power cable that runs up my scope using two amphenol ATM06 connectors and the other side of the cable connects to my main box on the scope using a 6 pin screw on plug. Although only 4 pins out of the 6 are actually used.

Everything up to but not including the 6 pin screw on plug is waterproof. Everything from the 6 pin plug/socket on, is not.

Other accessories that plug into the box for 12v power, I just use regular 2.5 and 2.1mm DC sockets, although after seeing the screw on version linked earlier in this post, I might switch some of them over

As an aside, the amphenol connectors were not exactly cheap compared to other connectors and they're not rated for that many cycles, but they were quite easy to put together and make a nice solid and importantly for me with this been a ground level connection, waterproof connection.

[1]: If anyone knows the official term for those connectors, please let me know

[daz]

I think they're IP44 connectors @Hicks

[Scott]

8 hours ago, BRUN said:

what kind of fuse are you all fitting, what amp, mine will just be powering my scope, nothing else (Skywatcher 250px GOTO Dob)

whatever size fuse in in the power lead you already use. you are not protecting the cables you are using, you are protecting the circuitry in the mount/camera/etc

 

[BRUN]

Am I correct in thinking a 5A 240v fuse will blow just the same as a 5A 12v fuse ?

Just making sure

[Marci]

No. At 240v a 5A fuse will require a power load of 1200w or greater to blow. At 12v a 5A fuse will require 60w or greater load to blow.

Look at your current power pack, not the plug. On it's label it should give output voltage and ampage. Round the ampage up to nearest whole number. That's the fuse rating you need at the voltage output of the power pack, for that particular device.

[BRUN]

But the fuses are rated in amps, not watts ?

I dont have a current power pack, im making one

[NEM]

It's the current through the fuse that matters. The voltage rating is only important to stop arcing to the outside. As long as the voltage rating exceeds the voltage you're usng., it's OK.

[RayD]

A 5A fuse will disconnect at 5A no matter what voltage you have on it.  The voltage rating on the fuse is the maximum voltage the fuse will take to prevent arcing, as mentioned above.  There are special DC rated fuses for applications such as PV arrays and alike, but they're not necessary at low currents and voltages like these.

As Alan noted, for inductive loads like motors you can use motor rated or time delayed fuses to allow you to reduce the disconnect current to 20% above your nominal if you are concerned about the rating, but most fuses will cope with this momentary spike anyway unless they are specifically "quick blow" fuses, which are designed for very sensitive equipment where you expect no spiking at all, so want to see an almost instantaneous disconnect.

Above all you have to be comfortable with your selection, but what you must do is make sure the fuse protects not only load on it, but that it also disconnects before the cable melts (in the case of a direct short).  I personally would say try a 5A normal "general" type fuse, and if that blows whilst switching on, then swap it out with a time delayed fuse as it will only be the surge current and not the nominal which has caused it to disconnect.  This is of course just my opinion and every other opinion is just as valid but hopefully you get it sorted