Horrible power adapters.

[Traceless]

Hi everyone,

am I being picky here or is this just a really horrible 14V supply?

[janoc]

And how did you measure that? You did put a 20MHz bandwidth limit on, right?

100-200mVpp of ripple and noise is par for the course on cheap power adapters. They are cheap for a reason.  Those larger spikes will likely be gone with the bandwidth limit enabled.

[Traceless]

Why do I need a 20 MHz bandwith limit for that measurement?

[janoc]

Why do I need a 20 MHz bandwith limit for that measurement?

Because it is the standard way ripple is measured. You will get a lot of those very short and narrow spikes from almost any switching supply but in reality they don't mean much because they get filtered out by the various bypass capacitors and parasitic inductance of the load wiring. So putting that filter in place removing all the high frequency junk gives you a more realistic view of what the load will actually see.

[Kean]

That high frequency noise may not all be coming from the power supply at all, but rather RFI/EMI from the environment and very possibly picked up due to bad probing techniques.

Check out this for some tips on measuring it correctly: https://www.cui.com/blog/how-to-measure-ripple-and-transient-in-power-supplies
This is also available in video form:


The other thing you may want to test is the supply under load.  Some cheaper power supplies may have higher noise under no load conditions.

Beyond that you may want to do load transient tests, as a low noise power supply is not necessarily enough if it cannot handle any load transients if may face in operation.

[Traceless]

@janoc: Thank you, I hadn't heard about the 20 MHz bandwitdth limit for the ripple measurements.

@Kean: Thank you for the explanations and the link.

That screenshot was actually taken under ~60% load. The measurement was taken at the contacts between the SMPS and my DC load wiring. So if I get janoc's comment right:

.... they don't mean much because they get filtered out by the various bypass capacitors and parasitic inductance of the load wiring...

at that point at least some of the spikes should have been already filtered. On the other hand, based on your source Kean I have the problem of a super long ground loop because I used the scopes alligator clip attached to the ground wire connecting the SMPS and the load. The probe tip contacted the DC+ line. The problem is that you can't really measure those SMPS adapters using the paper clip method suggested because you can not non-destructively open them to get to the output caps. So you always have a super long ground loop unless you crack the adapter case open.

[beanflying]

The thing to worry about as much as noise with some of the garbage out there is does the supply float way above earth potential creating issues with potential for human or electronic smoke release 

[Kean]

You just want to minimise the ground loop in your probing as it acts as an antenna for RFI.

Probe as close to the output of the PSU as possible and maybe add extra 10uF & 100nF caps at the probing point as you see him do on the terminal block in the video.

And don't forget to enable the 20MHz BW filter on your scope.

[Kean]

The thing to worry about as much as noise with some of the garbage out there is does the supply float way above earth potential creating issues with potential for human or electronic smoke release 

Validating product safety is a whole other investigation, as there are so many things that are not immediately obvious.

If you've ever put a mains powered product through safety certification the labs can be blasé or crazy picky.  Not sure which I prefer.... 

[Traceless]

Thanks for the tips Kean. I'll give it a try with bandwidth limit and  extra capacitance.

@beanflying: Yeah sounds like my PinePower desktop supply. Here is a short demo video of the unit from the other thread.

[Kean]

@beanflying: Yeah sounds like my PinePower desktop supply. Here is a short demo video of the unit from the other thread.

That is quite normal leakage current for an double insulated (unearthed) power supply, and is from current flowing through the EMI suppression capacitor which sits across the AC/DC isolation boundary.  The 10M ohm input resistance of the DMM puts very little load on the leakage current.

Here in Australia (nominal 230V AC) I will often measure 100-150 VAC (approx half mains voltage) on the output side of such a PSU when referenced to earth.  If you measure the current from this to Earth it will be less than 1mA, quite likely about 150-250uA depending on the Y capacitor value.

If you are unsure about the isolation and don't want to risk blowing up your meter, a simple setup it to place a 100k resistor between the output and earth and measure the AC voltage across that.  If I do that I measure about 15-17V AC, so that is 170uA.

The lets say there is a typical Y2 capacitor of 2.2nF being used for EMI suppression.  At 50Hz that has a reactance of 1/(2*Pi*f*C) = 1/(2*3.14*50*2.2e-9) = approx 1.45 Mohm.  And 230V across 1.45 Mohm is ... about 160uA.

[beanflying]

You are assuming the clever Muntzers making these supplies didn't save the $0.02 on EMI caps

While the leakage current is generally tiny it could be enough to cause issues depending on what you are hooking up. The Feeltech 6600 Sig Gens were a classic example of this with the 90-100V floating output of the PSU going straight across to the output of the BNC's  I did retrofit a fix to mine to tame it but they are out there.

[Traceless]

@Kean: My Brymen meter shows ~123µA of leakage current.

@beanflying: It does cause issues. I ordered the supply along with my Pinecil soldering iron. Unfortunately when I use the iron with the Pine Desktop on anything connected to earth ground (e.g. a board on top of my pre-heater) the iron blacks out randomly and reboots. I bought an IEC C13/C14 laptop supply for the iron. That solved the issue.

[vk6zgo]

Some "230v" power supplies are designed for the US 240v system, where there are two "actives", with the centre tap of the "pole pig" transformer doing duty as common for both.
These often have two capacitors, one from each "active" to the metal chassis, which is at a virtual "zero-volt" point.

Such supplies will work perfectly well on Australian Mains, but the capacitors now constitute a voltage divider, with the chassis at around 115-125 v, depending on how close the "230v" spec is met by the Mains.

[macboy]

Some "230v" power supplies are designed for the US 240v system, where there are two "actives", with the centre tap of the "pole pig" transformer doing duty as common for both.
These often have two capacitors, one from each "active" to the metal chassis, which is at a virtual "zero-volt" point.

Such supplies will work perfectly well on Australian Mains, but the capacitors now constitute a voltage divider, with the chassis at around 115-125 v, depending on how close the "230v" spec is met by the Mains.

That doesn't sound right. As I understand it, if a product has a metal class it must be built in one of two ways: it has a plug with ground and the chassis is grounded, or it has a 2 prong plug and double insulation between anything live and the chassis, so the chassis is isolated. Never should there be caps from live to chassis if that chassis is allowed to float above ground potential.

[BrokenYugo]

The confusion goes back to some goofy 240V appliance designs approved for many decades that used/abused the safety earth connection on 30/50A 240V range/dryer sockets as a neutral for small 120V loads in the machine, works because the center tap of the pole transformer is used as a neutral for 120V circuits and neutral and earth are bonded at the pole and breaker panel. To be fair these are chunky connectors with full size earth pins, the 3 pin welder sockets with a smaller earth pin are for 240V loads only. This is no longer permitted and range/dryer outlets now feature a dedicated neutral (4 pin connector, 4 wire run) for this, since sometime in the 90s I think. If you have the old 3 wire setup you just bond earth/neutral in the case when installing the cord (sold separately).

If the currents in L1 and L2 are balanced, there will be zero current on the third wire.

Don't ask me why they encouraged this stupidity rather than save a wire and just mandate 240 everything in the big appliances and limit earth current to like 5mA.

[vk6zgo]

Some "230v" power supplies are designed for the US 240v system, where there are two "actives", with the centre tap of the "pole pig" transformer doing duty as common for both.
These often have two capacitors, one from each "active" to the metal chassis, which is at a virtual "zero-volt" point.

Such supplies will work perfectly well on Australian Mains, but the capacitors now constitute a voltage divider, with the chassis at around 115-125 v, depending on how close the "230v" spec is met by the Mains.

That doesn't sound right. As I understand it, if a product has a metal class it must be built in one of two ways: it has a plug with ground and the chassis is grounded, or it has a 2 prong plug and double insulation between anything live and the chassis, so the chassis is isolated. Never should there be caps from live to chassis if that chassis is allowed to float above ground potential.

Maybe not with modern designs, but my Drake SSR1 Communications Receiver back in 1977 was wired like that, & even in the 1980s/'90s, there were pieces of equipment made similarly.
I remember getting nice little "zaps" from the coax sockets of VCRs which had 2-conductor cables.

Even using a 3-conductor cable with the ground extended from the wall socket, there is a problem, in that the two capacitors I mentioned were often rated at 200v & sometimes as low as 160v.

All perfectly OK with the US 240v system, where neither of the "hots" are more than 120v above ground, but use it in Australia, & one cap has the full "230v" (sometimes up to 250v) across it, as there is only one "active" ("hot") conductor & Neutral is very close to ground potential.

The second cap is effectively bypassed by the ground to Neutral connection where the Mains enter the building.

Some North American equipment we used in TV work was also technically non-compliant to Australian standards because they had fuses in both legs of the internal Mains connections of the device.
Perfectly logical for the NA system but in Australia, one of those fuses is in the Neutral line, which is a "no-no".
They somehow slipped by---probably because they weren't "consumer equipment".

[Someone]

Perfectly logical for the NA system but in Australia, one of those fuses is in the Neutral line, which is a "no-no".

Citation required. Fusing both live and neutral is perfectly acceptable for single phase appliances under both AU and EU standards.

[vk6zgo]

Perfectly logical for the NA system but in Australia, one of those fuses is in the Neutral line, which is a "no-no".

Citation required. Fusing both live and neutral is perfectly acceptable for single phase appliances under both AU and EU standards.

Until fairly recently, it was not.
It looks like we have signed up for another one of those "world's best practice'" things.

[themadhippy]

Citation required. Fusing both live and neutral is perfectly acceptable for single phase appliances under both AU and EU standards.

Certainly not in the uk regs,the ONLY exception is if the fuse breaks both live and neutral simultaniously

[boB]

Could also be common mode noise and not ripple.

[AVGresponding]

Citation required. Fusing both live and neutral is perfectly acceptable for single phase appliances under both AU and EU standards.

Certainly not in the uk regs,the ONLY exception is if the fuse breaks both live and neutral simultaniously

Our supply while the same voltage and frequency might be different. Not sure if the antipodeans use something similar to the split-phase system the septics have, where earth would be centre tapped at 240V   
It would make some sense in that case, but if they use any kind of PEN system it would be a big mistake.

[Someone]

Citation required. Fusing both live and neutral is perfectly acceptable for single phase appliances under both AU and EU standards.

Certainly not in the uk regs,the ONLY exception is if the fuse breaks both live and neutral simultaniously

Our supply while the same voltage and frequency might be different. Not sure if the antipodeans use something similar to the split-phase system the septics have, where earth would be centre tapped at 240V   
It would make some sense in that case, but if they use any kind of PEN system it would be a big mistake.

a) split phase (balanced power/centre tapped) as US uses is permissible in Australia though unusual.
b) pretty much every Australian install has a dedicated earth electrode and RCDs (some legacy installs still exist but are dwindling in number) so a dropped PEN on the supply side is of little danger.

On the consumer side, neutral is treated as live.

[fmashockie]

Some North American equipment we used in TV work was also technically non-compliant to Australian standards because they had fuses in both legs of the internal Mains connections of the device.
Perfectly logical for the NA system but in Australia, one of those fuses is in the Neutral line, which is a "no-no".
They somehow slipped by---probably because they weren't "consumer equipment".

It's pretty common to see double fusing (L and N) employed internally in electronics.  It can help prevent faults caused by polarity reversal. 

For the original OP, here's a great document put out by Agilent/Keysight/HP on how to performance test power supplies.  https://xdevs.com/doc/HP/pub/5952-4190.pdf

[Traceless]

Thanks fmashockie, something nice to read this weekend!