Mount Power Fuse Box

[Gina]

Laptop battery showing just 15m and 11% left and I think it shuts down at 10% so I'll go and connect the mains power...

A bit later...  Laptop now on mains power and mount battery voltage dropped to 11.3 at the mount.  SW tell you not to let the supply voltage drop below 11v so I've connected the Mains PSU for that too.

Still working

[Gina]

Still workling   So the problem with the EQ8 when out in the observatory now seems to be interference from the electric fence.  With the fence disconnected the EQ8 is behaving well with or without mains power through the 13.8v PSU.  Likewise, mains power on the laptop doesn't cause any problem.

Have I at last found the cause of all the mount problems?   Certainly seems like it

[Gina]

Now I need to work out how I want to arrange the power and USB feeds to the imaging systems.  There are three imaging rigs I might use on the EQ8 :-

1. MN190 single scope with OAG guiding.
2. 400mm triple imaging rig with Esprit 80ED and two ST80s all with 460EX cameras, separate guiding system with lens and LodeStar.
3. Widefield imaging rig with 3 lenses and 3 460EXs - not decided on guiding.

I strikes me as wasteful to have separate power and USB distribution sets for each rig, duplicating the fuses and control for focusers and maybe dew heaters.  So I would like to have one box with everything in and swap this between rigs.  I don't want to put it on the pier head as that would mean lots of cables fed through the umbilical to the focusers, cameras and dew heaters.  I will have to swap the 460EX cameras over anyway so it makes sense to me to put the control box on the imaging part of the mount and avoid long cables flexing as the mount tracks the stars.

The place for it would be on the dovetail but then again, I will be having different dovetails on the three different imaging rigs, so I guess it has to be a box that can be taken off and swapped to another imaging rig.

Another point is that it makes sense to run the USB for the mount from the powered USB hub rather than from a separate long USB cable from the laptop in the warm room.  The serial cable from the EQ Dir adapter to the mount could go through the umbilical from the imaging rig back to the mount.  One powered USB hub and one 5v regulator to run it from the 12v feed makes sense to me.

[Gina]

I think I made a mistake in an earlier post about the resistance per metre of the power cable I'm using.  This is the real "gen" :-

Current rating 16.5 Amps Resistance per metre at 20°c 0.0185 ohms

I'm actually using a bit less than 5m so the total resistance for the "round trip" of 10m would be <0.18 ohms.  So the volt drop when running the mount from this twin cable would be :-

2.5A slewing - 0.45v

1.3A tracking - 0.234v

For the imaging rig power - the 460EX takes 2A max and nearer 1A, other loads amount to no more than 2A including dew heaters on the triple rig.  So 8A is well over the normal current.  8A in 0.18 ohms is 1.44v.

I bought 6m of 4mm earth cable which could be a bit short for what I'm now proposing, viz. from earth rod to mount, through cable ducting to warm room and up to bench and across to power box.  When I ordered it I hadn't thought of using an earth rod   Might just reach - have to see...  If it does then the return power path should be much lower resistance than with the 16.5A cable.

[Gina]

The earth cable came today, it's long enough and I have partly installed it   Connected to the earth rod and fed into the scope room, up the pier to the pier head plate.  Then down the cable trunking, across to the warm room, up through the cable hole and across to the power switch and fuse box.  Only the earth ron end connected ATM.

[Gina]

Wiring diagram.

[Gina]

To make use of the fuse/switch/ammeter box already made I've drilled a hole in the side for a nut and bolt to connect the earth cable.  This is connected on the inside to the ammeter output (0v).  I've added an internal fuse to provide a second output for the mount +ve supply.  With just the one swich in the box the designed switch for the mount has been left out, relying on the power switch on the mount.  The remaining switch is used for the power to the imaging system as before.  The 0v side of both mount and imaging rig is connected to the thick earth cable at the pier top.

[Gina]

I now have the warm room part of the power distribution finished and all connected up.  The pier top earth cable has been stripped and bent into a loop of the right size to fit an M4 bolt and penny washers to provide the connection.  The earthing and 0v wires will have crimped ring connectors to go on the bolt and I'm using crinp on spade connectors for the power connections.  I have addeed heat shrink sleeving to the female connectors to to prevent shorting.  These are designed for use in damp conditions.

This photo shows the power cable for the imaging rig which goes from the pier top through the umbilical to the imaging rig, and the earth connection nut bolt and washers with crimp connectors attached.

Here's a close up of the connectors.

[frugal]

I am sorry, but there is something that really amuses me about 7 pages of detailed analysis and investigation of voltage drops, amperage, earthing, many circuit diagrams, only to find out the answer was "goats"...

[mapstar]

I am sorry, but there is something that really amuses me about 7 pages of detailed analysis and investigation of voltage drops, amperage, earthing, many circuit diagrams, only to find out the answer was "goats"...

I think it's shocking he he

[Gina]

Seems my dectecive powers and technical/scientific faultfinding prowess have taken a tumble in recent years - I'm just not as young as I was and I think it's showing   But don't worry - no offence taken and I can laugh at myself   Daft thing about it is that I did have "interference from the electric fence" as a possible cause of the problem way back in this thread

[mapstar]

Seems my dectecive powers and technical/scientific faultfinding prowess have taken a tumble in recent years - I'm just not as young as I was and I think it's showing But don't worry - no offence taken and I can laugh at myself Daft thing about it is that I did have "interference from the electric fence" as a possible cause of the problem way back in this thread

Hi Gina

As many would agree one thing that definitely doesn't show is your age. With your enthusiasm and commitment I'm sure others could learn a lot.

As usual a great read and lots of details.

Damian

[Gina]

Thank you very much Damian

[Gina]

New wiring now completed and running a mount test as before.  EQ8 is now running from Tritan 200W 13.8v PSU feeding SLA battery and fed across to the pier through the cable trunking.  Using the new thick earth cable and 16.5A cable.  From the pier head distribution wiring the feed goes up to the mount.  The mount is earthed from the azimuth fixing screws to the main earthing piont.

Here are some photos.

EQ8 power cable connectors.

Pier head power distribution and earthing.

EQ8 earthing

EQ9 power connection.

Warm room fuse, switch, ammeter box with no power on.  Showing earth connection on side.

Power on and feeding EQ8 which is slewing in one axis as it finishes its slew towards an imaginagr moon.

The power units in the warm room showing the mount in tracking mode.

[Gina]

Here's CdC showing the EQ8 tracking the moon which is only showing as a circle as the real thing is below the horizon

[Stu]

I am sorry, but there is something that really amuses me about 7 pages of detailed analysis and investigation of voltage drops, amperage, earthing, many circuit diagrams, only to find out the answer was "goats"...

You're not kidding.......... [emoji12]

[Oddsocks]

Looking good Gina.

If everything works well I would drill and tap an extra hole in the mount casting and fit a ring terminal and shake proof washer for earthing rather than relying on good contact through the painted surface although maybe Skywatcher have grounded 0v to chassis in the mount anyway?

I guess the big test will be what happens when you switch the electric fence back on.

Just curious, I know you said the EQ cable was not screened, I was wondering if they have used a straight-though cable or twisted pairs for the Rx and Tx wires as you would normally for a serial comms cable?

My project for the summer is to build a working USB to OPF converter as no one seems to make them. I have about 200 Mtrs of twin 1mm plastic optical fibre and thirty or so twin visible light transceiver modules left over from when I used to do a lot of CAN networking.

Since there is very low latency on the plastic fibre I should be able to run any USB device up to 500 mtrs away with 19-20,000 bps and the plastic fibre can be stood on and generally abused without breaking, it would make a good way of galvanically isolating computer from device over large distances, host end and client end would need external 12V for the light transceivers but otherwise can't see any problems. If it works I see no reason why I couldn't build an EQ cable using a plastic optical cable either.

[Gina]

Thanks

Yes, I was thinking of drilling and tapping a hole in the mount for earthing.  The current arrangement really justs earths the piertop plate as (like you say, the paint won't conduct).  I think I'll drill the main body of the pier where all the electronics live.

I may try connecting the electric fence again tomorrow though I think I would prefer not to have the electric fence near the observatory at all.

The EQ serial cable is just a standard flat phone cable with parallel wires.  I would prefer twisted pairs for the data.

Must say, I like the idea of fibre optic cables 

[Oddsocks]

I rather thought the EQ cable might be like that from the pictures I have seen on the web, a strange way to do a serial link.

In that case it will act just like an ariel and pick up any old EMI/RFI floating about.

I wonder why HiTech Astro haven't considered that, perhaps it has never been a problem before but seems unlikely since even a mobile phone on standby near an unscreened or un-twisted parallel cable will induce interference and upset data transmission, but of course it takes quite a bit of work to determine cause from the effect, I guess there are not to many astronomers about with a goat issue 

If I get the USB to POF converter working I know who to send it to for testing......

[Gina]

I might replace the EQ Direct adapter with my own construction and use either twisted pairs as in CAT5 cable or screened cable.  I think I favour twisted pairs.  I could use a CAT5 cable in fact.  Pity the Hand Controller connections don't match CAT5 (even though it has an RF45 socket!) so it will need a special cable making up anyway.  I have RJ45 plugs and a IDC tool.

I imagine the power line is to supply the hand controller from the mount and that only Rx, Tx and Gnd connections are required for the EQ Direct connection.

[Oddsocks]

I imagine the power line is to supply the hand controller from the mount and that only Rx, Tx and Gnd connections are required for the EQ Direct connection.

I think that is right Gina.

If doing twisted pairs for Rx and Tx you would need four wires for the Eq connection,  Rx and 0v twisted together and Tx and 0v twisted together, the 0v's commoned together at either end.

I am not sure if in a Cat5 cable the twisted pairs are also twisted around each other but it really doesn't matter. I did have some Cat6 cable, UTP? laying about which was twisted pairs, twisted bundle and screened but having dug it out of the shed this evening it seems mice have been at it and shredded it in several places. Time to get the mouse traps out again....

[Gina]

OH dear!   Dreaded rodents   A lot of my cables have been attacked by rats

Yes, I've used twisted pairs for data transmission a fair bit

[Gina]

Checked out the electric fence for earthing and tidied it up where it had come undone.  Found a place where it was sparking to the ground and fixed that.  Sparking like that will cause an enormous amount of RFI - effectively a spark transmitter!    Reconnected and set up the mount testing again from the obsy.  By the time I came indoors and connected TeamViewer it had gone again.  Have now re-set the mount test via TeamViewer and watching it in another window while I type here in Firefox.  So far it's held...

Next I plan to move the laptop back into the warm room and set up the MN190 on the mount.  It has all the power and USB distribution already done.

[Gina]

It's still going so maybe I'll leave the fence connected for the next test...

[Gina]

Connecting up and tidying cables is going well - now indoors for a break and to find some cable ties.  MN190 is now on the mount together with the power and focus control box and powered USB hub. 

Sunny so far so if it holds I might put the solar filter on the scope and try some white solar imaging later...