Mount Power Fuse Box

[mapstar]

Great news Gina

Glad it's working

Damian

[Gina]

Thank you William   And Damian

Yes, battle is right!  I feel a bit of a fool - should have thought of checking the RJ45 connector.  The contacts look gold coloured but I think they're brass   Gold doesn't go a greeny blue!!

All that messing about with printed boxes containing fuses and digital A/V meters etc.   Provided I use a thick enough cable I see no reason not to feed the mount from the warm room as before.  Also I think the one 15A switch mode PSU can be used to run both mount and the imaging rig.  I think I'll use separate cables though - just commoned at the warm room power box.  I may use a common 0v or ground wire with the 4mm earth cable I have on order. 

[Gina]

I now need to think about the whole power and USB distribution including the imaging rig.  The earlier arrangement was to have separate cables through the umbilical cable trunking for the mount USB, imaging USB with powered hub on the dovetail feeding cameras and filter wheel, power to mount and power to imaging rig.  The mount ran off a separate PSU.  Now my thinking is to streamline everything. 

I don't think there's any need for separate power supplies for the imaging rig and the mount.  I have a 15A PSU which is more than enough to drive everything.  And I can have one backup battery to power everything in event of a mains power failure.  Likewise it seems unnecessary to run two USB cables - the data bandwidth requirement for the mount is negligible.

[mapstar]

Keep things simple is my moto with electrics.

Bit of a poor design there with the connector, a little bit of contact lubricant may help keep the condensation off the contacts

Just my two Penneth

I would try to shield the power cable from the USB but it shouldn't be a problem. If the umbilical is a tight fit I'd also run two USB cables too just in case if not then just the one

You've had a fair fight with this mount and hopefully we'll see some photo's soon? ;-)

[Gina]

Yes, I like "simple" too

I think the USB cables I'm currently using are shielded but if I get any further problems I'll look at replacing them with screened video cable.  There is plenty of room in the trunking and the flexible umbilical up to the scope is longer than needed so far from tight

It's a great relief to have the EQ8 working again   And yes I'm now back on the road towards imaging, at last   A few thinks to do - sort out the wiring and do any small alterations to boxes required.  Take EQ8 back and remount it on the pier, connect up and test again then, when we get a clear night re-do the PA.  Then hopefully I shall be imaging again and will indeed post the results   Thank you

[Gina]

Still working this morning   The manual controls enabled me to adjust the mount to "point" to the moon even though it's below the horizon, pointing into the ground.  I then parked the mount to the Home position successfully and closed down

[Gina]

Been looking into the A/V displays.  The problem is that the ammeters require the current sensor in the -ve side making dual ammeters to monitor dual outputs with a common -ve/gnd impossible without having two independent PSUs.  I would like to have a common PSU and backup battery but independent monitoring of the current fed to the mount and imaging system.  I know there may be the view that once working why bother watching the current but I like to keep an eye on things - maybe even go for automatic monitoring with facility to close down if things start going wrong.

For remote reading (and needed for auto monitoring) there is the DS2438 Smart Battery Monitor, a 1-wire device that measures battery voltage and current (both charging and discharging) and which is dead easy to read with an Arduino - all the required code is available in the Dallas 1-wire library.  I have used these chips in the past for my weather station and other projects.  However, these have the same problen as the digital ammeters (or A/V meters) - the current sensing is in the -ve battery connection.  Fine for monitoring the battery but not for reading output currents where there's one battery and two independent loads with common ground.

What to do then... It would be nice to monitor individual camera and other loads (OK so maybe this is overkill) but at least monitor the mount separately.  No doubt there are designs "out there" to do this but I think it would probably be as quick to just design my own than do a long Google search when it's difficult to know what search terms to use.  I want to monitor current in the +ve side, mostly at +12v or so.

Tried Google search and found this.  Now to read through it ...

[Gina]

Definitely some ideas there   The LT6100 looks an interesting OP amp with input voltage upto Vcc

[Gina]

Just doing some designing until the weather improves enough to take the EQ8 back out.

I've decided on my own design for measuring current in the +ve power line.  A low resistance shunt followed by an op amp feeding one of the analog inputs to an Arduino.  So the idea is to take a volt drop up to say a quarter of a volt in the shunt resistor at 13.8v and transform it into a range 0f 0-5v to feed to the Arduino.  It doesn't matter whether 5v represents 5A or 0A an same with 0v input so with no current we can have 5v (or slightly less) and at the desired FSD of 5A the voltage can drop down towards zero.

Here is the circuit diagram.

The 13.8v is divided down to 5v by the resistor chains either side of the shunt.  So the + opamp gets 5v and the - gets 5v less the shunt volt drop divided by 2.8.  This difference is multiplied by the amplifier such that at the desired 5A full scale current takes the output voltage down to zero.

I'l probably add diode protection to stop the amp output going below 0v to protect the Arduino in event of over current.

[Gina]

Has nobody noticed a glaring error in that diagram???   OOOPS   The opamp inputs are the wrong way round

Here's the corrected diagram.

[Stu]

I was just waiting to see if anyone else spotted it Gina.........honest

[mapstar]

Isn't there a current sensing module for the arduino's about already? other Idea a CT instead if a shunt resistor? 

[Gina]

I don't know - I'll have a look   Umm... excuse my ignorance but what's a CT?

[mapstar]

Current transformers/ transducers 

[Gina]

Isn't there a current sensing module for the arduino's about already?   

Indeed there is - like this   Didn't think of that   Thank you   Much better idea than mine

And UK sourced and quicker delivery - this   I've ordered one to try out.

[Gina]

I now have the EQ8 back on the pier   I'll take the laptop out and set up a test setup shortly.

[mapstar]

Indeed there is - like this   Didn't think of that   Thank you   Much better idea than mine

Thought you needed something a bit easier after your EQ8 battle, Just keep those connection's clear and protected we can't go through another thread like this   Electrolube is good 

[Gina]

Thank you

Maplin 0-20v 5A bench PSU feeding EQ8 at 13.5v - laptop set up nearby running on mains power with EQ Dir adapter plugged into LH USB port and EQ8.  Now running pointing at the moon in CdC.  Test begun

TEST FAILED

[mapstar]

Oh no I think that must've been me that Jinxed it in my last post!

[Gina]

Probably not

Disconnected laptop power and ran EQ8 from battery.  Battery started at 12.6v and gradually dropped to 12.3v after a minute or two at 12.3v the data connection dropped out - the mount continued lunar tracking judging by the sound.

Next test - connected charging circuit to bench PSU set to 13.8v.  Battery reading 13.5v on digital ammeter.  Ran a bit longer but now gone again

I do have EQ8 on the pier top so there could be leakage through the concrete pier.

AARRGGHH :(

[mapstar]

Have you used the original data lead Gina? 

[Gina]

No, the new one.

[mapstar]

No, the new one.

Beginning to think your mount doesn't like being cold 

[Gina]

I don't think it's had time to cool down all that much but it's a thought

Guess I should have put the EQ8 on the packing case and tried it there first but I thought I'd found the cause of the problem, of course.  I've got fed up with one micro step between tests

Shut everything down outside now - too much tramping in and out through the mud that's supposed to be grass is not good, particularly at night and it's raining again now

[mapstar]

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

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