NEQ6 Power Supply issues

[morls (Stephen)]

I've installed my pier, but have now run into some power issues. When slewing on both axis simultaneously the voltage drops below 10V, which is causing the hand controller to malfunction.

The power supply I'm using is a Powertech DC Regulated Power Supply, supplying 13.8VDC at up to 12A. I think the problem might be that the cable from power supply output to mount input is somewhere around 12 metres long, and is in 3 sections spliced/soldered together through a conduit. Without a load, the voltage at PS terminals is 13.9, and is the same at the mount connection.

Would it make sense to assume this long cable run is causing a voltage drop under load?
The reason I have the PS in the garage is that it has a fan, which is very noisy. Has anyone disconnected this fan? Would the PS overheat without it? Photo of PS is attached.
Cheers
Stephen

[xelasnave]

When using 12 volt dc you really need to look carefully at the wire you use..a bit of old 240 volt extension cord wire will not do...get correct wire and your problem will go away I expect. A Google should find out what you need.
Alex

[RyanJones]

Hi again Stephen,

A simple conversation with Edison and Westinghouse if they were around would provide you with the answer. DC power does not like to travel long distances. It’s slightly more complicated than that simple answer but you get the idea. You are going to need to take the power supply closer to the mount unfortunately. A long A/C extension will have no issues over 12m. The issue with the fan being noisy has 2 potential solutions, neither of which are disconnecting the fan. You may get away with it given you’re not likely drawing the full 12A constantly but in the long term it won’t like it. You could replace the fan with something quieter or change your power supply. I use a laptop style power supply that I bought from Jaycar. It’s a 12v 15A unit and it has no fan.

Hope this also helps

Ryan

[luka]

You can use this calculator, for example, to work out the voltage drop for various distances, cables, currents etc.

A fatter wire will work, you may get away with 18AWG (10A mains extension cord wire size) to keep the voltage around 12V. A fatter wire would be a safer bet.

Alternatively use a smaller power supply without a fan next to the mount. NEQ6 will draw up to 2A when slewing both axis, 10A is an overkill.

[gregmc (Greg)]

The electrical current that a wire will carry, governs the thickness of the wire. Also, the higher the voltage used, the less the current needed to transfer the same amount of power.

Low current and thinner wire also mean a lower cost. Its why the power companies have very high voltage power lines. Running a thick 12v cable 12m is a much higher cost due to the amount of extra copper in the cable.

If for example, you are using 10A at 12V (or 120 watts of power), you would need about 3.57mm dia cable for that 12 metres. (see table)
To run 240V that 12m and carry the same 120 watts of power, you only need about a 1mm dia cable to carry the 0.5A



Other considerations that come to mind:
240V MAINS can be a lot more dangerous and should be restricted to licensed people if doing anything other than running a ready made extension lead.

You should also not run 240v AC cable next to low voltage DC (on long runs) or next to data cables (ie. USB cables) as they could pick up signals/noise from the adjacent 240v AC cables.

Note the attached table is from a Victron battery cable guide.

[morls (Stephen)]

Thanks for all the replies, it's a great help.

The 12m DC cable run was inside a conduit, alongside and wrapped around an AC extension cable, so it didn't really have a chance. I moved the power supply much closer to the mount, connected with 2.2m of 12AWG cable. The voltage is much better, staying above 12V 95% of the time, although it droppped to 11.9V at one point (slewing on both axis with scope fully loaded). I'm going to get thicker wire, just to be sure of some headroom.

I also got in touch with Skywatcher/Tasco, and got a good email from a support agent, Graeme, who said
I always suggest no less than 7.5 AMPS for a NEQ6. 5 amps should be OK but I have had issues with that amps which was rectified after upgrading to 7.5A MPs

I think I'll get a silent power supply - it's hard to contemplate space and time with a noisy fan running.

Thanks for the help.
Stephen