Which goes where...confused about wiring....

[SkyBound]

Hi, 

am making a new power lead, and wondered if anyone can help, I will have 4 core cable carrying +12v -12v +5v -5v and it will be wired into a 5 pin Din plug as the picture shows, but my question is where does the -5v go and what goes onto the "common" pin.. ? Anybody...

[Dr_Ju_ju]

The general rule is that the 'common' pin has the 0v\earth wired to it...

[SkyBound]

17 minutes ago, Dr_Ju_ju said:

The general rule is that the 'common' pin has the 0v\earth wired to it...

So can I just put one of the negative wires on there..?

[Dr_Ju_ju]

That would only work if your 0v wire is common to all your +ve\-ve supplies

[SkyBound]

59 minutes ago, Dr_Ju_ju said:

That would only work if your 0v wire is common to all your +ve\-ve supplies

No I am more confused, sorry but electronics is not my strong point, hence the original question..

[RayD]

It depends what you have in your socket.  If it's a unique plug going in to a unique socket you can literally put what you want where you want so long as the pin outs in the socket match those in the plug.  However, I think what Dr_Ju_ju is saying is that if you are taking the +12v and +5v from the same supply i.e. a single power supply or battery with a DC-DC convertor for the +5v, then you can tie the negatives together.  If the 2 +ve values are derived from totally separate supplies then you will need two separate -ve cables, but again if you're only plugging in to one matching socket then make the pins whatever you want, but good practice would be +/- space -/+

[SkyBound]

3 minutes ago, RayD said:

It depends what you have in your socket.  If it's a unique plug going in to a unique socket you can literally put what you want where you want so long as the pin outs in the socket match those in the plug.  However, I think what Dr_Ju_ju is saying is that if you are taking the +12v and +5v from the same supply i.e. a single power supply or battery with a DC-DC convertor for the +5v, then you can tie the negatives together.  If the 2 +ve values are derived from totally separate supplies then you will need two separate -ve cables, but again if you're only plugging in to one matching socket then make the pins whatever you want, but good practice would be +/- space +/-

Thanks

it will be a single 12v supply and an inline 12v to 5v converter in two of the cable cores, (4 cores in all) and the socket it is for an SBIG CCD camera, so can't alter that, but the pins for the camera are shown in the picture above, but I will only have 12v - 12+ and 5v- 5V+ so as you see in the picture the 12v - & +  are shown but only the 5v+ is shown and no -, so I wondered where that went, and what I should connect to the common pin...

hope that explains a bit better

i need to make one as I have no working power supply for the camera and I use 12v on all my kit, so,thought I would make one....

[RayD]

Ah ok well in that case you may need to be a bit careful as to what is termed as common and -ve as they could be different things (one being tied to earth).  Which SBIG camera is it?

[SkyBound]

8 minutes ago, RayD said:

Ah ok well in that case you may need to be a bit careful as to what is termed as common and -ve as they could be different things (one being tied to earth).  Which SBIG camera is it?

It's the ST7 it's an old one, and had a 5 pin Din socket, with pins wired as shown above, but that diagram is from the 240v AC supply that comes with the cameras, which are not available anymore, so though I would make a 12v DC one, so maybe that complicates things...as there is no earth I guess....!

[RayD]

Just now, SkyBound said:

It's the ST7 it's an old one, and had a 5 pin Din socket, with pins wired as shown above, but that diagram is from the 240v AC supply that comes with the cameras, which are not available anymore, so though I would make a 12v DC one, so maybe that complicates things...as there is no earth I guess....!

No I wouldn't think there is an earth but sometimes you can find common pins tied to the plug casing.  I would think that the common would be the common bus for the -5v as this would make sense, but I wouldn't want to advise that as it may not be. 

I'll see what I can find out.

[RayD]

Well I found some details and it notes pin 5 as the DC ground, so yes this would indicate this as the -5v, with a separate -12v on pin 4.  Pin 6 (case) is earth.

 

[SkyBound]

8 minutes ago, RayD said:

Well I found some details and it notes pin 5 as the DC ground, so yes this would indicate this as the -5v, with a separate -12v on pin 4.  Pin 6 (case) is earth.

 

That's great, many thanks for your time on this

so i just connect as shown with pin 3 left empty, and the 5v- on pin 5, and as it's 12v dc there is no earth is that correct ? 

I don't connect one of the - to the case too...? Or do i

[RayD]

Just now, SkyBound said:

That's great, many thanks for your time on this

so i just connect as shown with pin 3 left empty, and the 5v- on pin 5, and as it's 12v dc there is no earth is that correct ? 

I don't connect one of the - to the case too...? Or do i

Yes that's how I would read this.  I suspect they call it DC common as there are a few 5v circuits in the camera, so presumably they all tie in to this common rail.  Pin 3 stays empty.

No I wouldn't think there is any need to connect an earth unless you're using shielded cable.  Personally I would just mark the cable for use with battery supply only, just so in the future you don't forget and get a new power supply and plug it in, but if you have no intentions of this then it won't be necessary.  Definitely don't tie -ve to the case.

[SkyBound]

8 minutes ago, RayD said:

Yes that's how I would read this.  I suspect they call it DC common as there are a few 5v circuits in the camera, so presumably they all tie in to this common rail.  Pin 3 stays empty.

No I wouldn't think there is any need to connect an earth unless you're using shielded cable.  Personally I would just mark the cable for use with battery supply only, just so in the future you don't forget and get a new power supply and plug it in, but if you have no intentions of this then it won't be necessary.  Definitely don't tie -ve to the case.

Like I said many thanks for your help it is much appreciated, and I have now just gotten past 500 posts.... ??

[RayD]

No problem at all 

[Gina]

Looks like the camera needs three supplies - +12v, +5v and -12v.  This is the sort of thing the ATX PSU used in computers provides.  In addition to the power lines you have a Ground or common connection - this is the DC Ground in your table.  Hope that makes sense.  I'm not at my main computer at present or I'd draw you a diagram.  I can do that tomorrow.

[RayD]

12 minutes ago, Gina said:

Looks like the camera needs three supplies - +12v, +5v and -12v.  This is the sort of thing the ATX PSU used in computers provides.  In addition to the power lines you have a Ground or common connection - this is the DC Ground in your table.  Hope that makes sense.  I'm not at my main computer at present or I'd draw you a diagram.  I can do that tomorrow.

Yes this would definitely make sense as to why they are showing the -12v as a separate pin.  ATX supply below showing the power outs, so maybe the original power supply is a mini version.

[SkyBound]

46 minutes ago, RayD said:

Yes this would definitely make sense as to why they are showing the -12v as a separate pin.  ATX supply below showing the power outs, so maybe the original power supply is a mini version.

So your original thoughts are still correct yes, or has something now changed....?

[Stu]

Is this for one going on sale on your site Stewart? I hope it's correct!

[RayD]

7 hours ago, SkyBound said:

So your original thoughts are still correct yes, or has something now changed....?

Not necessarily.  You may actually have to run it from a power supply.  This could be why they suggest in the manual to run it from a battery by using an inverter.  

 

[SkyBound]

2 hours ago, RayD said:

Not necessarily.  You may actually have to run it from a power supply.  This could be why they suggest in the manual to run it from a battery by using an inverter.  

 

Well all I know is that 12v DC supplies for these cameras, were available, and came with crocodile clips for battery connection, so I guess it is possible to do..! 

 

[Gina]

You can get the +5v from the +12v with a buck converter but I don't know if there's anything available to give you the -12v.  I've never actually done this.  I've made many a power supply with all sorts of voltage outputs from 240v AC with transformer, rectifiers, etc. but not -12v from +12v.

[SkyBound]

10 minutes ago, Gina said:

You can get the +5v from the +12v with a buck converter but I don't know if there's anything available to give you the -12v.  I've never actually done this.  I've made many a power supply with all sorts of voltage outputs from 240v AC with transformer, rectifiers, etc. but not -12v from +12v.

So it isnt just a case of using the negative wire from the 12v supply then as we thought...?

[Gina]

No, I'm afraid not - there would be 24v between the -12v and +12v, if you see what I mean.

[Gina]

Done some Googling but the only way to get -12v from +12v I can find involves a good knowledge of electronics.  The problem is that the usual step down or step up buck converters have the -ve side of input and output joined.  I have used both sorts.  With the +12v on the input you can only get positive output voltages - either lower or higher.  To get a negative output voltage would mean modifying the circuit which would need a good knowledge of electronics.

I'm sorry but I don't think I can help - I'll do some more thinking about it though.