Voltage drops?

[matt_baker]

I've got a HEQ5 Pro and I'm using a RPi with astroberry. I also have a 1600MM hooked up with the cooler running at about 30%. This is all running from a DeepSkyDad DCHub2 through a 12v 10A power brick I bought from Amazon

My guiding is okay at about 0.8"RMS but at random points (not periodic), either the RA or DEC will spike massively then recover quite quickly but this does mean I'm having to throw away quite a few subs which of course I don't want.

The possibilities of this being an issue would be either a dodgy extension reel since it is quite old, the DCHub, the extension lead or the power brick which could be potentially causing voltage drops.

I did have a dew heater but I've unplugged it since it was actually causing voltage drops when slewing and caused the mount to act sporadically. I doubt it's the mount either since I very recently serviced it myself and it still happens

Any thoughts?

 

Edit: Also to note that the extension reel is 10A not 13, could that be an issue? 

Edit 2: Not sure how safe it is to be doing this either but the extension reel is 30m long and I'm probably only using half of it so how much of a problem does that cause too?

 

Matt

Edited November 5, 2020 by matt_baker

[fozzybear]

Matt,

Is the extension reel at 30m 230v then attached to the power brick 12v then attached to your hub? or is the extension 12v

[matt_baker]

Just now, fozzybear said:

Matt,

Is the extension reel at 30m 230v then attached to the power brick 12v then attached to your hub? or is the extension 12v

It's reel > extension lead > power brick > DCHub

The only reason I don't plug directly into the reel is that it doesn't have surge protection. Obviously with a new one I could do just that

[Jonk]

11 minutes ago, matt_baker said:

It's reel > extension lead > power brick > DCHub

You should never daisy chain extension leads - if the main extension reel is over 12-15m long then it should have a thermal cutout. If it doesn't, you shouldn't use it.

It's unlikely to be sags or spikes on the mains, as the AC-DC switched mode PSU would probably absorb these due to the capacitance in the circuit. If the PSU output is dropping, then it's probably best to replace it.

Large spikes in RA or DEC on the guiding can happen for a number of reasons.

[symmetal]

The extension reel won't be the issue here. It's 10A rating is for the 240V mains. Your 10A 12V SMPSU at around 90% efficiency, uses around 0.8A from your extension reel. Not a problem, and being partially wound doesn't matter at such low currents.

The main issue is I expect the voltage drops from your 12V PSU to the equipment via the DC Hub. I assume they are all using 2.1mm DC connectors and not very thick cable, which will cause significant voltage drops. It's the main reason that 13.8V PSUs are often used, to reduce the chance of the voltage falling below 12V at the equipment and causing issues. Your dew heater making it worse confirms this. 

The easiest solution is a 13.8V supply. The alternative is either to upgrade all the DC wiring/connectors which isn't easy, or possibly use a DC boost converter on your 12V supply to generate 13.8V or thereabouts. Not very elegant but it should work.

Alan

[Tomatobro]

It does not sound like a voltage droop issue from the description but one way to find out is to introduce a controlled voltage drop and see if you can replicate to guiding glitch.

I would wire a 12 volt stop and tail light bulb in series with a switch across the power supply and by switching the bulb on and off you can cause a momentary voltage droop to the mount. The bulb filament will have very low resistance at first but the resistance rises rapidly as the filament heats up.

Should result in a fast momentary voltage droop which will test your theory

[matt_baker]

The only thing I can test at the moment is if me daisy chaining the extensions caused something as I've currently got the setup outside

I've plugged the brick straight into the reel so now I'll wait and see

[fozzybear]

Could the problem lie with the OS running on RPi? maybe a gander on the Indilib forum is the 1600MM camera plugged into the Rpi. Also what RPi are you running Rpi4 4gb? Could be a bottleneck problem

[matt_baker]

I really don't want to jinx it but I think it was down to daisy chaining the extension lead

Edit: I literally just jinxed it 

On a side note, the freq. is barely ever so I can cope with it. Of course it shouldn't happen anyway but oh well, at least I'm not throwing away a 1/3 of my frames

Edited November 5, 2020 by matt_baker

[matt_baker]

Okay, gone out tonight and it's still doing it. I guess I'll have to buy a 13.8v power supply? Only thing is I want the portability and not have to lug around a big PSU

[fozzybear]

c'est la vie

That's life I've luckily kept from my amateur radio days one of these bad boys.  albeit not light at 8kg

https://www.radioworld.co.uk/second-hand-watson-w-25am-power-supply

 

[Tomatobro]

 Switch mode power supplies are small, light weight, low cost and efficient when compared with linear types but switch mode PS's don't cope well with transients.

From experience SM's also vary a lot in design and quality where low price is a key factor in achieving volume sales.

[fifeskies]

Not had any power issues since I swapped over to a 13.8v linear supply.

Previous switch mode power brick would lead to mount LED flashing when slewing.

I now run everything , mount , dew heaters etc from the chunky linear and everything seems to go smoothly even with a heavy payload on the mount.

 

You could also , if you invest in some thick 2 core cable , keep the Linear supply under cover and only run out the low voltage outdoors, but don't use the long thin cables that you get as 12v extensions with the dc connectors on , they are way to thin.

Thick cable to a low voltage splitter , the last short part can then use those thin connectors to hook up with.

Use a waterproof box for the PSU if the nearest building is too far away so you can keep all the mains stuff under cover, mains outdoors is a risky thing , so make sure there is RCD protection.

[david_taurus83]

+1 for a linear 12v supply. I have a Nevada 30A supply sat in the window by the back door. I run a 1.5mm² cable out to the mount.( Yellow rubber type we use on building sites for 110v, cheap and stay flexible even when cold) Banana plugs on the PSU side, cigar plug type terminal at the mount, one with voltage reading. I set the PSU to output 14v and at the mount through 15m of cable I'm still getting 12.5v with camera cooling, dew straps heating, mini PC computing. I have 1 cigar plug feeding the DSD DC Hub 2 and never have any issues.

[matt_baker]

It's still doing it unfortunately, not as often, but it sure is still there.

I used a separate power supply completely to rule out it being the PSU that goes to the distribution. Albeit not a 13.8, just a 12v 5A brick.

I find it odd because only in the last 2 months has it done it, before it was completely fine.

In other news, I have managed to tune the backlash on my DEC nicely and I'm getting a consistent 0.6" with the HEQ5 since I've also recently serviced it

[matt_baker]

I was wondering that it might be a potential software issue too. I can post my guide logs if anyone wants to have a look along with the EKOS indi logs

[symmetal]

On 22/11/2020 at 18:46, matt_baker said:

It's still doing it unfortunately, not as often, but it sure is still there.

I used a separate power supply completely to rule out it being the PSU that goes to the distribution. Albeit not a 13.8, just a 12v 5A brick.

I find it odd because only in the last 2 months has it done it, before it was completely fine.

In other news, I have managed to tune the backlash on my DEC nicely and I'm getting a consistent 0.6" with the HEQ5 since I've also recently serviced it

It's possible your adjustments to reduce backlash have moved the worm gear closer to the wheel, and it's binding slightly at some positions. When I adjusted the backlash on my AZ-EQ6, I put an ammeter in the power supply feed and measured the current taken as it slew throughout its operating range. Although it looked and sounded fine, at one section the current taken doubled meaning more effort was required to move the mount at those sections. I backed off the backlash grub screws very slightly and the problem cleared. You end up with slightly more backlash but the mount doesn't run the risk of sticking at certain points when guiding.

Alan

[Jonk]

2 hours ago, symmetal said:

It's possible your adjustments to reduce backlash have moved the worm gear closer to the wheel, and it's binding slightly at some positions. When I adjusted the backlash on my AZ-EQ6, I put an ammeter in the power supply feed and measured the current taken as it slew throughout its operating range. Although it looked and sounded fine, at one section the current taken doubled meaning more effort was required to move the mount at those sections. I backed off the backlash grub screws very slightly and the problem cleared. You end up with slightly more backlash but the mount doesn't run the risk of sticking at certain points when guiding.

Alan

Interesting, was it repeatable?

Did you try at the tight spots at sidereal rate? Obviously this would take a lot longer to monitor.

[symmetal]

18 minutes ago, Jonk said:

Interesting, was it repeatable?

Did you try at the tight spots at sidereal rate? Obviously this would take a lot longer to monitor.

Yes it was consistant at those positions. I didn't try it at sidereal rate though.

Alan

[Jonk]

Ok, I ask as I may do the same with my az-eq6 at slew speed, and then at sidereal rate using a data logger of some sort.