Does this wiring diagram look okay?

[michaelmorris]

I'm about to embark on a journey bodgery and minor burns.  I'm going to attempt to make a simple (ha ha!) 12 v power switching box for my new observatory set up.  It will consist of a single 12v DC input cable and 2 x out RCA phono sockets as outputs.  Each circuit will have an on/off switch with a built in red LED light and a 10A fuse for each output.  Output 1 will only feed the mount (an EQ8). Output 2 will go to a 12v distribution box mounted on to of the mount.

Does this wiring diagram look correct?

 

Thanks

[Alien 13]

5 minutes ago, michaelmorris said:

I'm about to embark on a journey bodgery and minor burns.  I'm going to attempt to make a simple (ha ha!) 12 v power switching box for my new observatory set up.  It will consist of a single 12v DC input cable and 2 x out RCA phono sockets as outputs.  Each circuit will have an on/off switch with a built in red LED light and a 10A fuse for each output.  Output 1 will only feed the mount (an EQ8). Output 2 will go to a 12v distribution box mounted on to of the mount.

Does this wiring diagram look correct?

 

Thanks

Looks fine but I would perhaps have a single LED at the input for power ON and two others after the fuse to indicate the status of the equipment supply/fuse.

Alan

[Davey-T]

You'll need a couple of resistors for the LEDs unless you get 12volt ones, it's surprising how blinding red LEDs can be in the obsy at night.

Dave

[Woolnut]

Looks good to me, short and sweet  (Alan's comment i second, seems like a logical thing to do and won't require much more effort!)

 

[Mr niall]

looks good

[Jonk]

I would probably put the fuses before the LEDs, that way you'll know if the fuse has blown straight away, as the LED won't be on (unless the supply fails of course).

Are RCA plugs rated to 10A?

[ronin]

What is the voltage drop by the LED's? Seem to think they take out something like 0.7v so if it is specifically 12v in then you could get 11.3v out. Is that sufficent to happily power whatever is attached?

If the Input side is sort of lead acid battery then they tend to output more the 12v so likely that even with a drop at the LED's you could get 12v output.

[michaelmorris]

39 minutes ago, Mr niall said:

1 - You should consider fitting a diode to the 12v output, especially if it's permanently connected to anything that draws power.

 2 - Are you planning on running the full 120 watts? 

1 - Excuse my ignorance, but what would a diode do?

2 - A worst case scenario is with all the dew heaters switching on simultaneously (3A), the mount slewing (max 4A peak), the camera cooler having to work really hard (1A) and the USB hub having to power the guide camera and focus controller and USB filter wheel (3A).  This makes a maximum of 11A .  In reality is very unlikely that the focuser will be running with the scope slewing as is the case of this combination running with the filter wheel operating with either of these.  

The power supply is rated at 10A output with a 12A peak, so my guess is that I'm unlikely to be asking the power supply more than it can deliver. 

[michaelmorris]

5 minutes ago, ronin said:

If the Input side is sort of lead acid battery then they tend to output more the 12v so likely that even with a drop at the LED's you could get 12v output.

The input is regulated bench power supply with an output voltage of 13.8v.

https://www.amazon.co.uk/QJE-QJ1863-10-12AMP-Linear-Supply/dp/B01KXUIXFU

 

[michaelmorris]

1 hour ago, Davey-T said:

You'll need a couple of resistors for the LEDs unless you get 12volt ones, it's surprising how blinding red LEDs can be in the obsy at night.

Dave

The LEDs are actually built into the switches.

[Davey-T]

Any way you can find out if they're OK for 12 volt direct ?

I think separate components would be more flexible.

LEDs have a data sheet that includes what's called their forward voltage from this you can work out the resistor value needed to lower the voltage supplied to them as they don't like being run continuously at 12 volts or in your case 13.8 volts.

A diode only allows current to flow one way.

Dave

[michael8554]

Ronin said:

"What is the voltage drop by the LED's? Seem to think they take out something like 0.7v so if it is specifically 12v in then you could get 11.3v out. Is that sufficent to happily power whatever is attached?"

Quite right about the led voltage drop, but the led should be across the supply, not in series- so 12v in, 12v out.

 Michael

 

[Gina]

Most LEDs I've come across drop about 2v.  They have various ratings with 20mA about average.  But I don't recommend 20mA in a observatory - 1mA should be enough so something like 10K in series with each should be suitable.  I think the switches you have may have a separate pin for the LED - ones I've used in the past are like that.

[michaelmorris]

44 minutes ago, Gina said:

 I think the switches you have may have a separate pin for the LED - ones I've used in the past are like that.

That raises another issue.  I assumed that the three pins on the back of the switch are +ve in, +ve out, and -ve (for the LED).  Is this correct?

[Gina]

Ah yes, probably.  Means you can still reduce the brightness by having a resistor in the -ve feed to the LED but the +ve for the LED will be at the switch.  I think the switches probably had 4 pins, can't remember now.

[michaelmorris]

(Hopefully) finished.

[Stub Mandrel]

Sorry to be a wet blanket, but most phono connectors are rated at 2 amps max...

Having had a connector with 15 Amps on the side of it melt on my 3D printer's RAMPS board when notionally taking 10Amps...

[michaelmorris]

19 hours ago, Stub Mandrel said:

Sorry to be a wet blanket, but most phono connectors are rated at 2 amps max...

Having had a connector with 15 Amps on the side of it melt on my 3D printer's RAMPS board when notionally taking 10Amps...

Hi Neil

You're not being a wet blanket at all.  I'm keen to get this right.  What type of connectors would you suggest as an alternative?  

I could simply use cigar lighter sockets like this,

http://www.ebay.co.uk/itm/12V-24V-20A-Cigar-Lighter-Accessory-Power-Supply-Socket-Durite-0-601-01-/221214835614?hash=item33816e839e:g:1G4AAOSw74FXPbBz

If not, what about XLR connectors?

http://www.maplin.co.uk/p/3-pin-xlr-line-socket-bw91y

[Stub Mandrel]

3 hours ago, michaelmorris said:

If not, what about XLR connectors?

Apparently 15A with thick enough wire, so yes XLR should be a good choice. They are used for high-power speakers.

They are my weapon of choice for my rig, as you can get ones with different pin patterns and colours that make getting the right one in the right socket easier.

[michaelmorris]

10 minutes ago, Stub Mandrel said:

Apparently 15A with thick enough wire, so yes XLR should be a good choice. They are used for high-power speakers.

They are my weapon of choice for my rig, as you can get ones with different pin patterns and colours that make getting the right one in the right socket easier.

Thanks.  It should be relatively easy to swap these for the phono sockets.

[Horwig]

The industry standard XLR connectors for 12V is the 4 pin variety, with pin 1 0V and pin 4 +V, with volts on sockets.

Don't be tempted by some of the no-brand cheap ones on Ebay, go for recognised manufacturers like Neutrik, they are much better built, I fell for the ebay bargains, and in some of them the pins are loose, not good at all.

Here are the relevant pieces you need.

Chassis socket:

http://www.ebay.co.uk/itm/Neutrik-XLR-Panel-Socket-4Way-NC4FDL-1-/272430962258?hash=item3f6e269652:g:NdwAAOSwzJ5XaT2g

 

Cable mounted plug:

http://www.ebay.co.uk/itm/Neutrik-NC4MXX-4-PIN-Male-XLR-Cable-Connector-Plug-Audio-PRO-/281886258073?hash=item41a1baf399:g:kUwAAOSwYaFWcDcT

 

Huw

[michaelmorris]

54 minutes ago, Horwig said:

The industry standard XLR connectors for 12V is the 4 pin variety, with pin 1 0V and pin 4 +V, with volts on sockets.

Don't be tempted by some of the no-brand cheap ones on Ebay, go for recognised manufacturers like Neutrik, they are much better built, I fell for the ebay bargains, and in some of them the pins are loose, not good at all.

Here are the relevant pieces you need.

Chassis socket:

http://www.ebay.co.uk/itm/Neutrik-XLR-Panel-Socket-4Way-NC4FDL-1-/272430962258?hash=item3f6e269652:g:NdwAAOSwzJ5XaT2g

 

Cable mounted plug:

http://www.ebay.co.uk/itm/Neutrik-NC4MXX-4-PIN-Male-XLR-Cable-Connector-Plug-Audio-PRO-/281886258073?hash=item41a1baf399:g:kUwAAOSwYaFWcDcT

 

Huw

Thanks

[Stub Mandrel]

I buy mine from CPC but don't buy the cheapest ones they sell...

[symmetal]

I use 4 pole Neutrik XLRs from CPC too. As Horwig says pin 1 ground and pin 4 +12V. It changed to this around the mid 1980s I believe. Before then it was pin 1 ground, pin 2 +12V, pin 3 +24V, pin 4 +48V. They were widely used in the broadcasting industry. The +24V was for illuminating bulbs in sound desks and consoles (before LEDs were around) and the +48V was for 'phantom powering' of microphones. Now that desks generate their own phantom power the 24 & 48 became redundant with just pin 2 used for 12V. This was later changed to pin 4 (to reduce the chance of short circuits). The 4 pole XLR connector was kept as it is widely identified it as a DC power connector.

Nothing to do with astronomy but thought you might like a bit of history.  

It might be too large to fit in the box in your photo though, as it needs a hole about 22mm diameter and the mounting flange is 26 x 31mm. The depth behind the flange is 28mm.

[MarkyD]

I use Tiny XLR connectors.  Pins only rated to 5A but should be plenty for dew heaters etc but a fraction of the physical size

https://www.rapidonline.com/tiny-xlr