Power supply issues

[Ptarmigan]

As I understand it the correct way to treat terminal posts is to crimp or solder the wires into ring lugs.  Just wrapping wires round the posts and tightening down is not satisfactory - they can easily come loose.  Unsealed plugs and sockets can suffer from corrosion in a damp atmosphere.  Alright in a warm room but not exposed to the damp in the scope room with the roof open.

Yes, yes, yes, yes, and yes

in that order

but "easily come loose" needs some caveat, more a case of if the right copper, number of strands etc&etc is not blah blah then the connexion can 'relax' and oxidation blah

and another but :-

to be fair to plugs and sockets, they are supposed to be removed and replace _from time to time_ ! and if correctly designed ( spring tension, wipe action etc) can provide a servicable wotsits within the design crit blah blah

In summary, good news on your working 11v, now what about all these lost electrons on the  5v

There is sometimes something to be said for no reusable connectors, just bare the wires, twist and solder. No probs !

then, if/when you need to re-design some time later, snip, ,  whats a few mm count ? re run twist and solder.

[Martin-Devon]

Just a quick note to followers of this thread - Gina contacted me today to say that her internet connection is down. She has to change providers, but expects to be back on line and posting by next Thursday.

Martin

[Gina]

I'm back   Missed you all enormously - it's been a hard time and very frustrating and depressing.  Hopefully back to normal now and I'll be updating my threads in due course.

[Gina]

Damn - my post has just disappeared - I'll have to try to remember what I said and re-post it tomorrow.  All the phone and ISP problems have stressed me out beyond measure

[Gina]

This is the main project I have been working on while I've been off line.  I thought I had the power distribution and focus control box almost done but when I brought all the gear indoors to fit together I found I had designed the box the wrong way round   The connectors faced the wrong way.  I have always had trouble with getting my left and right moixed up and I guess this was just another example   So it was back to the drawing board or rather SketchUp

I have the twin 13.8v PSU from Tantronics and heavy duty 16A twin cable.  This is considerably thicker in copper than what I have been using but with the thin insulation and multi-wire inners, is quite small overall and nice and flexible.  Definitely a good choice for this application

[Gina]

This is the circuit diagram for the incoming 13.8v power.  Firstly a fuse which protects against short circuits then an over-voltage crowbar which will shunt the supply and blow the fuse if the voltage exceeds the zener diode conduction voltage plus the thyristor trigger voltage.  This is set so that a PSU failure resulting in a high output voltage will very quickly trigger the thyristor and blow the fuse rather than destroying the equipment connected.

The top connection on the right goes on to feed the astro imaging cameras plus the dew heaters and stepper motors.  With the cameras costing several thousand pounds, the few pence spent on the fuse and components is well worth it even if the PSU developing an over-voltage fault is very unlikely.

Next is the L78S05CV +5v regulator chip that feeds the USB hub which in turn powers the Arduino and guide camera.  Ceramic capacitors of 330nF and 100nF provide decoupling.

[Gina]

I hope to provide better circuit diagrams soon with the component values and part numbers added.  I have so far failed to find Windows circuit diagram drawing software so I'm making do with ordinary drawing software.

I'm planning to set up a Linux box in the store room and run XCircuit on it.  Then connecting it to the wi-fi LAN and using TeamViewer to control it from my main Win 7 machine.

[Tinker1947]

Design Spark is a free circuit designer from RS Components just a form to fill in and then a download.......

[Gina]

Thank you - I'll check that out

[Gina]

Couldn't get the registration to work - I'll try again later.

[Gina]

Having my initial design for the power distribution box scuppered gave me the opportunity for a complete rethink.

With some of the stepper motors being quite a long way from the power box I had a good think as to whether the driver module was best in the power box or in a little box of its own near the focuser it was driving.  With the driver in the main box I would have to extend the motor cable - not a problem but is it necessary?  With the driver in its own little box one continuous cable would run from the power box to the driver and the motor cable would plug into that.  A separate little box to 3D print but a smaller main box.  One advantage would be that the driver module with its LEDs to show it's working could be near the focuser being controlled and hence less confusion.

Now if anyone wants to know why I'm using these ready built driver modules, there are several reasons. 

1. I already have a number of them
2. It saves me making up a circuit board
3. The LEDs (which can be disabled by removing a link) can help with diagnostics in the event of problems

[Tinker1947]

Couldn't get the registration to work - I'll try again later.

I remember it was a bit finicky but it did go through and download....

[Gina]

I have designed and printed the little box to take the driver for the Esprit focuser.  Here's a screenshot of the SketchUp design and some photos.  The side next to the LEDs and the top are just 1.5mm thick so that the LEDs are visible through the transparent ABS (translucent when printed).  Little clips on the sides hold the box onto the ali bar.  The front can be closed in with a piece of foam rubber to keep moisture out.

[Tinker1947]

Have a look at this designer,,,,,

http://www.expresspcb.com/index.htm

[Gina]

Have a look at this designer,,,,,

http://www.expresspcb.com/index.htm

 Thank you   But I don't want to design PCBs - I can work out my own layouts for Veroboard.  That is adequate for my little projects.  Now if I could work out how to modify a 3D printer to print conductive tracks on an insulating base, a PCB layout designer could be a useful app   What it needs is a conducting thermoplastic that melts around 200C-260C and that will take solder to attach components.  Of course, this is the temperature at which ordinary solder melts.  I wonder if it would be possible to use components with preformed, cut and pre-tinned ends, fed through the holes in perf board and laid ends up on the 3D printer with solder in place of thermoplastic filament.  Then solder tracks could be drawn by the 3D printer.

OH gawd - I feel yet another project coming on    RESIST RESIST

[Gina]

Been working on the power and focus control box today.  Not finished yet, I have the output wiring to add including the data and power connections for the 4 stepper motor drivers.  The power input connector is a 2 pin screw on type, the same as used on the SW EQ8 mount.  The +13.8v input goes to the fuse carrier via a red insulated wire and is distributed to the over-voltage crowbar and 5v regulator circuits (on a small piece of stripboard) plus all the dew heater sockets (phono type) with orange wires.  The connector next to the power input is a 3.5mm stereo socket for the focuser system control lines.  +5v to the USB hub and power to the cameras and FW will be on cables going out through the plain hole in the case.

[Gina]

Box mounted on ali plate with 5v regulator chip screwed to it for a heat sink and also fuse holder screwed onto the plate.  All holes drilled and tapped.

[Tinker1947]

That's nice and tidy.......

[Gina]

Thank you

[Gina]

Made some more progress on the power and focus control box wiring.  Now connected all four stepper motor drivers to the Arduino plus +ve and gnd.  These are connected with coloured ribbon cable soldered directly to the driver PCB and to blocks of four pins for the data and to the power and earth points.  A total of 48 connections each needing separating, stripping, tinning  and soldering (plus bending into a loop with tweezers for the pins).  My fingers ache now!  So do my eyes.

I was hoping to be ready for some imaging tonight with clear skies but everything seems to take at least ten times as long as expected!  There are still a few jobs to do before I'm ready so I won't be imaging tonight - I'll be too tired.  In fact I think I'll "knock it on the head" for tonight.  There is a possibility that I may finish it tomorrow and maybe even set up in daylight.  The forecast is for some clear periods tomorrow night

Before connecting the drivers I checked the over-voltage crowbar with my variable bench PSU.  I set current limit to 0.5A and for the test gradually advanced the voltage. It triggered at 14.3v so I count that as satisfactory.  I've made a slight change to the circuit.  Used two 6.8v zeners in series as I didn't have a 13v one.  I also added a resistor between the gate of the thyristor and earth to prevent accidental triggering from stray spikes.

[Gina]

Still to do...

1. Ground connection for Arduino
2. Resistors from Arduino +5v to analogue inputs (part of the focus control resistor networks)
3. Print a couple more little boxes for stepper motor drivers
4. Power cable for cameras and filter wheel
5. Focus control box :- Add cable connector and extra switches to select which focuser to control
6. Connect resistors to switches and push buttons (values have changed)
7. Thread stereo cable through conduit for focus control
8. Assemble everything and connect all cables, PSU etc.
9. Test.

[Ptarmigan]

Do we assume that this crowbar can pull the volts down quicker than stuff downstream can blow ?

All is ok on your lower line because of the power conditioning between the crowbar and your pride&joys.

But what about your high rail ? Anything happening to your sense rail ( the feed to the zenner ) is also feeding your load (some of which may be fast blow ! ) I would like to see power conditioning on the top rail as well ??  Which would mean a higher volts supply tho'

At least then if you lose anything it is only the regulators outside of your main toys.

I dunno, I was always downstream of my power allocating peeps

[Gina]

Do we assume that this crowbar can pull the volts down quicker than stuff downstream can blow ?

Well, that's the theory.  Or at least it was several decades ago when I was in the business.

All is ok on your lower line because of the power conditioning between the crowbar and your pride&joys.

But what about your high rail ? Anything happening to your sense rail ( the feed to the zenner ) is also feeding your load (some of which may be fast blow ! ) I would like to see power conditioning on the top rail as well ??  Which would mean a higher volts supply tho'

At least then if you lose anything it is only the regulators outside of your main toys.

I dunno, I was always downstream of my power allocating peeps

I would have liked to have had voltage regulators for all the 12v devices as well as the 5v but as you say, needs a higher supply voltage.  I guess I could get a 2 or 3 volt supply to add in series with the 13.8v.

Another idea is to run the kit off a car battery and feed that from a 13.8v supply (with a fuse).  I have one in the scope room to power a hoist.

[Gina]

Progressing...  Done the following :-

1. Ground connection for Arduino
2. Resistors from Arduino +5v to analogue inputs (part of the focus control resistor networks)
3. Print a couple more little boxes for stepper motor drivers

[Gina]

I think the wiring of the power and focus control box is now finished   I have taken the assembly out to the obsy and mounted it on the EQ8, added the MN190 and ST80.  After connecting up I may be ready to try out the ST80 though I still have the focus remote control box to finish.  May be able to finish that tonight.

Here's a photo of the box having added the camera/FW cable and tidied up the wiring a bit.