Mount Power Fuse Box

[Demon Barber]

Hi Gina,why not bite the bullet and try the psu i emailed you the details of?

They just work.

Mike

[Gina]

Which one was that, Mike?  I did buy one that several people recommended.

[Gina]

Winning a war is about more than one battle and it looks like this is now a campaign!

So it seems!! 

Best to sleep on it then you'll sort it straight away ;-D

I'm going to do exactly that   But as for sorting it out straight away...

The 4mm earth cable is due to arrive tomorrow so then I can produce a proper earthing system

[Demon Barber]

Hi Gina this one,link here:http://www.rapidonline.com/electrical-power/rapid-smps-25a-40a-65063   

I really think a lot of your problems would be aleviated,you thought them pricey,but they save you time and money in the long run.

Hope you get sorted soon.

Regards,

Mike

[Gina]

Thank you Mike   They certainly look good, I have to say

[Gina]

Today's campaign plan :-

Search for and locate a length of copper water pipe, squeeze one end flat and drill a hole for the cable connection.  Clean off corrosion.  If the weather holds drive pipe into ground just outside scope room.

While waiting for the cable to arrive I guess I could unscrew and lug the EQ8 off the pier and onto the packing case.  Not sure I want to do this as the earthing rod and cable in conjunction with the earthing scheme should cure the possible pier leakage problem.

The failure of the data connection consistently occurs when the supply voltage to the EQ8 drops down to 12.3v though the tracking is maintained.  I conclude that the serial data control and feedback is sensitive to supply voltage.   Pity I didn't think of testing this while I had the mount indoors but if anyone thinks I'm going to lug that beasty back indoors again, think again 'coz I'm NOT   I plan to have more than 12.3v available anyway even on backup battery.

I think I might go for a larger capacity SLA battery for backup when I can afford it and I've been looking at 62AH, 72AH and up to 120AH calcium car barreries and deep cycle batteries.  There's a huge 120AH deep cycle SLA battery on ebay weighing in at a massive 24Kg    It's BIG too.  I think that just might be overkill   Though something that will run all the gear for a whole night's imaging would be quite something

[Gina]

Been thinking about what is/may be different out in the observatory as compared with indoors.

1. Colder and damper though the humidity is held below 50% RH by a dehumidifier.  Indoor reading is 35% RH.
2. Mains power is currently fed through a 15m 15A extension cable from the house.
3. Possible interference from electric fence a few feet away - though if this were the problem I would expect immediate problems, not after several minutes.
4. Leakage through concrete pier.

[mapstar]

We're all here listening.

Is the supply run from the PSU to the mount a long one? Just thinking about volt drop? Have you extended the cable in any way and is it of decent cross sectional area?

[Gina]

It's the original cable cut down to a bit above half and it's quite thick so I wouldn't expect much volt drop.  I'll pop out and measure it.  I would estimate the thickness as around 1.5mm diameter from memory when I soldered it to the fuse and ammeter.

[Gina]

It's 1.4m long and I've measured the resistance of one wire as 0.2 ohms.  Current reading was 1.3A - total cable resistance 0.4 ohms so total volt drop would be around 1.3 x 0.4 = 0.52v.  So when the digital voltmeter read 12.3v the voltage at the mount would be about 11.8v with an estimated error range of 0.3v (voltage resolution 0.1v, resistance resolution of 0.1 ohms, x2 for both wires).  So anything between 11.5v and 12.1v.  So the voltage at the mount electronics could be getting close to the specified minimum.

That might explain the data problem below the DV reading of 12.3v.

[Gina]

Found a 3ft length of 22mm OD copper pipe.  Hopefully that should be long enough.  How far I can get it into the ground depends on location and size of stones in its path

[mapstar]

Just a little query?

The meter leads have a resistance too and did you deduct that or can you zero it on the meter before measuring like an old Avo (showing my age now)

You seem a bit low on volts though?

[Gina]

The voltmeter is in the output side of the shunt and fuses.  I don't think the shunt drops much voltage as it's about 20mm of 2mm copper.  I have now disconnected the EQ8 cable and connected a short cable to a matching plug.  The cable used is the thin insulation 16.5A 0.18 ohms per meter cable.  So the digital voltmeter will be reading the voltage at the mount power input.  I checked calibration of the DVM against my 4 digit autoranging DVM and the power box DVM is reading about 0.1v low.  That's within the resolution of these cheapo digital A/V meters.

Here's a photo of the new connections - I've removed the battery connections as I don't have any way of holding the battery that high up.  But I can feed the battery into the box with a longer cable.

[Gina]

Managed to get the earth rod (copper pipe) about 2 ft into the ground after several attempts to miss stones   Now I need to clean up the top and provide connection for the cable.

[mapstar]

I'd not realised you'd still got all the monitoring bit's in the power feed Gina?

I know you probably want to have it but I would dispense of it for now and see if the mount then works just to be on the simple side? narrowing the fault finding a bit?

Just thinking it worked in your house did you just use a straight lead with nothing in?

[Gina]

I had the meter & fuse box in the circuit when I had it indoors but not the battery.  Power was from my Maplin 0-20v 5A bench PSU.  I tried the same arrangement when it was on the pier anongst others.

I can easily connect the mount directly to the PSU without the metering.  And I could take it up to 15v as recommended by Skywatcher

[Gina]

The earth cable didn't come today   Hopefully tomorrow...

But I have got the earth rod all ready to connect it when it does come.

[Gina]

Well, I'm running yet another test   Running all gear off batteries, meter box is showing 12.8v with the supply from the battery in the warm room which has been fully charged with a final charging current of 0.1A off 13.8v.  PSU now disconnected.

I have disconnected the electric fence.

Test started at 15:47.

[Gina]

20 minutes...  30m...  40m...

[mapstar]

Well, I'm running yet another test   Running all gear off batteries, meter box is showing 12.8v with the supply from the battery in the warm room which has been fully charged with a final charging current of 0.1A off 13.8v.  PSU now disconnected.

I have disconnected the electric fence.

Test started at 15:47.

Electric fence

[Gina]

Yes - electric fence   Goes round two sides of the observatory about a foot from it.

50mins...

If the electric fence turns out to be the problem I shall have to rethink fencing to keep the goats in.  ATM they are in the top paddock so I've been able to disconnect this section

I have some high voltage insulated cable so I could run the fence supply round the other side of the house.  Then get some pig netting to go from the goat shed to the observatory along eastern boundary.  There is already pig netting on the south boundary.

One hour and counting...

[mapstar]

Is the fence there to protect the Goats from the Astronomer 

[Oddsocks]

You might find once you have an effective earthing arrangement on the 0v common that the signal cable for the EQ serial comms will then have a proper shielding function and not pass through the RF from the fence (assuming the EQ cable is shielded).

[Gina]

LOL   To stop them getting out into the neighbours fields and possibly from there out onto the road.

Yes, I'll try that first   Actually the EQ cable is not shielded but I could add shielding.

[Gina]

90 minutes have passed since the start of the test.  The voltage at the mount has dropped to 11.5.