Re: ES-G11-PMC8 power options

Steve Lang

Thanks Jeremy.

I'll read up on your posts soon. What you have done here is very close to what I had done before (pic attached).

I had two buck/boost DC-DC converters - one pushing out laptop voltage (19V) and one pushing guaranteed 12V (not battery input which was ~11V - 12.8V). Also had a slew of buck modules pushing 5V (usb hub), 7.8V (from my DSLR days..., not now) and I'm not sure what else.

I picked modules carefully, and had a common negative - the common pin. Each other pin was a different voltage so I made up cables for each device which picked the right voltage off the right pin, hence didn't need to care which one it was plugged into.

The switch is to switch off the common negative, but that's bad, wrong and dangerous. Turns out that switching off laptop negative rail (for example) whilst still connected to a powered USB hub just meant that the laptop was powered through the USB hub ground. Learnt not to do that again... Switch should be on the volgtage input into the DC-DC converter.

This was brilliant, as I fed it with 12V (well, more like 13V) from a good mains supply (still switchmode) or a number of battery options (including one remote site where I have 4 batteries and some solar panels (and spare counterweights...) permanently there.

This one got too wet, so I need to rebuild/replace, hence re-evaluating everything.

I don't use a DSLR these days and am replacing USB hub with one that takes 'nominal 12V', so apart from laptop, don't really have much requirement for DC conversions, so long as things like PMC-8 can run at battery voltage, hence my original question.

On 3/05/19 2:01 AM, Jeremy Parker wrote:
Hi Guys,

I recently moved from a bunch of individual wall warts on a power strip to a single 12V ac adapter to power everything through a PowerPole panel. To power my Nikon DSLR and USB hub, I bought a couple of buck converters on Amazon to convert down to 9V and 5V respectively. In addition to just cleaning up my setup and making things quicker to set up and break down, I can now easily choose whether to power from my AC adapter at home or from batteries in the field. They both plug right into the the PowerPole panel, which now has a handy power meter to help me monitor voltage, current, wattage, and watt-hours. I have both sizes of the Celestron Powertank Lithium batteries, which are LiFePO.  The larger one (~160Wh) can easily power my entire rig for a night of imaging (PMC-Eight, Surface Pro, dew heaters, USB hub, DSLR and guide camera). I think the last time I was out with the rig, I only used 100Wh. In case anybody's interested, I've got all the details on my Cloudy Nights post here:

For what it's worth, I saw no performance difference or image artifacts that I can attribute to moving to the single switching supply I use at home, compared to the mess of wall warts, compared to the batteries. When I first used the stock wall wart that came with the PMC-Eight, I did make an interesting discovery though. I had my hand on the counterweight shaft and felt an AC voltage on my skin, so I measured the PMC eight chassis ground compared to earth ground on the power strip. Sure enough, there was 59VAC rms on my meter. Since none of the power supplies in my setup were IEC class I, there was no earth ground anywhere in the system. And these universal switching AC-to-DC supplies, like the one for the PMC-Eight, have higher leakage current to neutral than the older style linear power supply wall warts (transformer-based). So the 'ground' output of these switchers aren't fully isolated and may sit at some relatively high AC voltage compared to earth ground. So I added a earth ground jumper wire to one of the serial cable housings that connected to the ground of the power strip. My new DC supply has a grounded (3 prong) AC power connection, so I don't use the jumper anymore.


On Thu, May 2, 2019 at 7:19 AM Chris Tardif <christardif@...> wrote:

I bought this:


Works perfectly.





Sent from Mail for Windows 10


From: <> on behalf of Wes Mcdonald <wesmcd6@...>
Sent: Wednesday, May 1, 2019 10:39:42 PM
Subject: Re: [ESPMC-Eight] ES-G11-PMC8 power options

Yes the mains supplies are switchers if they are the small brick type. 

My feeling is that DSLRs at least are going to be immune to interference, in fact I run my Nikon with its 120v brick, with the brick powered by an inverter, with the inverter powered by my battery.  No artifacts.  No telescope processor crashes.  But I also make sure things are wired to preclude ground noise and to add some nice low impedance paths to ground with wiring inductance between different power feeds.  This helps choke any high frequency crap from running around.  But like you, I get so balled up with just getting everything right I'm a ways off from being where a bit of poop in a picture file is gonna be visible. Haha.  One day perhaps.


Wes, Southport NC
PMC-8, ES ED 127, 10" LX200GPS, Astro-Tech 8" Newt, ETX-90
Polemaster, Orion ST-80 and SAG
Electrical Engineer, Retired

Scope: StellarVue SV102T  & Optimus Eyepieces
Mount:  Explore Scientific PMC-Eight G11, Spring-loaded OPWB on DEC, O-Vision Worm on RA
Cameras: Nikon D5300 H-alpha mod
Guiding & Alignment: StellarVue F50 GuideScope & ZWO ASI290MM Mini Guide Cam, QHY Polemaster
Computer & Software: Surface Pro Windows 10, ExploreStars, ASCOM POTH, CdC, PHD2 Guiding, Backyard Nikon
Accessories: Williams Optics clear Bahtinov Mask, 1000 Oaks Dew Heater Controller, Astrozap Dew Heaters, Celestron Lithium / Lithium-Pro Powertanks

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