Raspberry Pi Grounding

[pete_81]

To all those interested and especially @symmetal and @7170 for the latest comments... I'm presently imaging M51, 23:10, so some time to spare!

The RPi is indeed working fine with the buck converter, was slightly worried as the RPi4 I think runs on more power than the zero and so on, but no issues at this time. I've not measured the leakage, more in effort to get a good setup before it got too dark.

I can confirm @fozzybear that the phone charger + USB-C cable suffered the same issue as the original supply, albeit with a significant reduction in the 'tingle'. Another point of note - I've got a monitor on the RPi (Conky) which nicely displays some of the hardware stats. The reason for saying this is that I noted the temperature of the CPU when running with the original PSU was >40ºC but the phone charger cable had this lower at ~35ºC during testing this earlier today, and the same low temperature with the buck-converter presently running (USB-A to USB-C cable from buck-converter to RPi) the setup at present.

Guess closing this topic as solved with the final note that all works with the Nevada supplying power to mount (via cigarette adapter) and 12V-5V buck converter supplying the RPi4 with no issues. I've made no connection to the GND on the back of the Nevada, but it appears the issue is solved (or a solution has been found!). Thanks again to all for suggestions, comments, help and patience!

[symmetal]

Glad it's all working fine now Pete. 😀 It's possible the Pi power supply was giving slightly over 5V leading to the Pi itself running a bit warmer.

Having no switch mode power supply powered from a 2-pin mains plug in the system means there won't be any AC leakage tingles so earthing the Nevada isn't required for that, but it's beneficial having exposed metalwork like your mount earthed in case of any mains mishaps, so there's certainly no harm in bonding the Nevada -ve to the Earth terminal with a reasonably thick wire. 

I assume you have an RCD in the mains supply feeding your extension cable anyway for safety. 

Alan

[pete_81]

@symmetalYep, RCD in place each time 👍

Thanks again folks

[pete_81]

So back in the summer, I started this topic as I had been getting 'tingles' from my mount, camera and RPi which wasn't good!
I'd reported in my last note that I had purchased a buck converter to power the RPi (5A, 12V-5V USB Buck Converter) which had solved my issues of any 'mains leakage' and tingling sensations.
My Nevada PS-08 unit now powers my setup with no issues - cigarette socket to AZEQ6 mount using the supplied SW adapter, and banana plugs powering the RPi (via the buck above) and DSLR via a 12V-8V step-down connector. No issues with this and the PSU seems to have no trouble in supplying the power required.

Coming into winter months for imaging, obviously colder with hopefully more imaging time, I'm now thinking about keeping frost (& dew) off the optics. I've got 2 dew heaters both USB, 5V,2A so have to think about getting these into the mix.
So also to keep cables everywhere and reduce load on the RPi (put the load elsewhere), I've got a powered USB and debating my main supply now. Obviously the Nevada PS-08 is rated at 12V 6A (8A max).
Using 2x dew heaters at max, (2A @5V x 2)= 20W (hopefully mid setting so not quite at this)
The RPi wants 3A@5V=15W
Camera=10W (recommended value is 2A when using 5V and converting to 8V)
Mount=48W (slew only)
Total power = 100W when at max draw => 12V,8A.

I've worked out that I can have a single supply powering everything above (mount, dew heaters, camera and RPi) with a single cable going to the mount (really tidy!), supplying everything from one source and no need for a return cable (unless using ethernet to the RPi).
However, this is on paper at the limit of the Nevada. So I think I'm going to be looking at an alternative power source, 12V 10A (120W), similar to the post above that @7170 recommended, rather than the Nevada? I'd assume the 12V holds stable when under load as I've read several posts about the mount supply failing outside of 11-16V (incl appendix 1 in manual)?
Also driving at closer to the current limit when slewing, I'm assuming all would be fine with a 10A supply when in regular tracking/guiding mode (when the total load should be closer to 12V,5A)

On closing, if my calculations are right, this suggests that the Nevada "may" be OK, but not sure how to connect it - max of 5A through the cigarette plug is all the info I can find ("Output current 6A continuous (8A surge). Max 5A via Cigarette Socket") , but does anyone know the current limit across the banana plugs? What I don't want to do is connect a total of say 5A (8A surge when starting slew), to just the banana plugs, if the cigarette socket is max 5A and the banana plugs max is 4A (assuming then nobody would be using 2A on the cigatette adapter to put it over the 6A max). Not sure that's worded well, so can anyone confirm the current limits on the Nevada connections based on the following quick table:
Cigarette adapter:           Banana Plugs:
0A                                    6A
1A                                     5A
2A                                    4A
3A                                    3A
4A                                    2A
5A                                    1A
5A  (max)                        0A

Anyone else care to share about 10A supply they're using? FLO go to max of 5A switch mode before jumping to the Nevada PSW30, which I don't think I need (just yet!)
Cheers

Edited November 1, 2021 by pete_81

[symmetal]

Hi Pete,

The Nevada PS-08 can supply 6A continuous, so as long as the total current of that supplied via banana plugs, added to that supplied via the cigar socket, is less than 6A you're fine. The two outputs are most likely wired in parallel internally anyway. There may be an internal 5A fuse just for the cigar socket but probably not. The 5A specified is just because these cigar connectors have a small contact area, so potentially a higher contact resistance on the centre pin, so are not suitable for higher currents. This would cause a voltage drop on the cigar output and possible burning of the centre contact if the current is significantly above 5A.

I'm assuming you're hoping to power the 5V dew heaters from the powered USB hub. You really need the hub to have dedicated 'charging' outputs if you're expecting to supply 2A from a USB socket. A standard single USB2 outlet can only theoretically supply 0.5A, while a single USB3 outlet can supply 1.0A. If it's a USB hub with 5V power in rather than 12V, then the power adapter supplying it also needs to supply up to 4A for the dew straps plus whatever else is plugged into the hub. If it's a 12V power input hub with dedicated charging outputs specified at at least 2A, then you're fine. If you didn't already have the 5V dew straps, I would have recommended getting 12V ones as it saves all that hassle, and they take only half the current to deliver the same power.

It's not recommended to run power supplies continuously near their specified rated output power and the Nevada PS-08 does run quite hot at 6A too, being a linear design.

The supply that 7170 recommended gives you a better overhead margin on the current, and isn't expensive, so is worth considering. It's a switch mode supply off course, but having a 3 pin mains input with a connected earth means you're safe from the 'tingles'. 😉

I personally use open frame switch mode supplies like this from Meanwell, a known reputable company, and mount them in a metal enclosure so can't give personal advice on the brick style supplies, though other forum members can give their recommendations.

It's always worth considering the Nevada PSW-30 or similar if you think you'll be expanding operations in the future, and you can afford it, as it future proofs you, and you don't need to worry about such things. 😀 

Alan 

 

[pete_81]

Hi @symmetal Alan,
Many thanks for your response.
Just to detail this further, plan is a 4-way CCTV splitter that will feed from the main supply, and split into the 4x 2.1/5.5mm DC barrel connector, with each of these supplying:
1) RPi, powered via the buck converter you recommended previously (so input to the buck will be DC 2.1/5.5 female and get fed via the splitter), and BC-USBC to RPi as present
2) Anker USB3 powered hub (12V,60W with 3 USB-power output and 7x USB3.0), which as you point out correctly, will indeed power the dew heaters (also using the USB ports to connect guide camera, DSLR, USB-wifi dongle and the AZEQ6 USB connection)
3) DSLR, so 12V-8V reducer which already has the 2.1/5.5 connection
4) AZEQ6 power, 12V up to 4A, so I'm making a GX12-DC connector that will just again plug into the 4-way splitter (yes, will be checking polarity and triple checking it(!) long before it's plugged into the mount.

I had looked at the open frame type supplies but kinda dismissed them as they don't 'look' as safe, although they do seem to review higher than the other brick types. Only concern about it is that it'd be outside - how do you house yours? I'm tempted to do the frame one and house it in this for example (alternatives). I'd also looked at the idea of waterproof LED supplies (example), a disadvantage is the short output cable but would need to extend a frame type anyway. The more I think about it, I'm still debating the PSW30.
In summary, am I right in thinking that any supply rated at 12V will be OK, provided that it can supply (more than) adequate current/power to the setup?
Thanks again!

Edited November 3, 2021 by pete_81

[symmetal]

Hi Pete,

Your setup using the Anker USB3 hub looks fine. 🙂

I use the reputable brand power supplies as mentioned as they have a full data sheet giving full specifications which includes over voltage, short circuit and overload protection. The brick type supplies have less information available and often don't mention such features. The LED supply you mentioned does say it has those features but how reliable are those features. For led displays low noise and ripple is not a priority for the supply so it may be higher compared to others. An advantage of the open frame types is that the output voltage is adjustable over a small range, and at maximum setting is 13.8V for the 12V supplies which is useful.

The open frame ones have a thick metal base plate which is meant to be mounted onto a metal surface to aid in heat dissapation when used near its maximum output. Although the brick type ones are generally smaller and in sealed plastic boxes which do run hot at full current, so for your usage where the current will be modest, using the box you mentioned should be OK. 

I have mounted mine in metal boxes like this one with the power supply screwed to the bottom plate and a panel meter along with fuses and connectors on the front plate. They also have ventilation holes. They aren't waterproof of course, though the one on my fixed pier is under a little roof on a wood frame screwed to the concrete pier, so has no direct water getting to it and the normal heat from operation prevents any dew forming. If used in the open with another mount I put it in a large Really Useful strong plastic box with the lid just resting on top to let the cables out along with a 4 way mains splitter and laptop PSU for polar aligning if needed.

The PSW30 isn't waterproof either of course, so would need to be in a plastic box or similar anyway.

Alan

[pete_81]

In closing, thanks again to Alan @symmetal for the tremendous help on this with the tips and checks.
Just done the PSW30 with PX of the PS08. Think this works best for my present usage and future proofs things too.
Might add a final photo once everything is operating on next clear night. Tidy cables, here we come!