Electronics > Projects, Designs, and Technical Stuff
How do you tell what "type" of power a DC power supply is?
DW1961:
--- Quote from: TimNJ on July 26, 2020, 06:48:19 am ---
--- Quote from: DW1961 on July 25, 2020, 05:08:52 pm ---
--- Quote from: AndyC_772 on July 25, 2020, 06:55:42 am ---
--- Quote from: DW1961 on July 24, 2020, 07:40:54 pm ---Good information, but why does that power supply I linked to above have a CE mark on it and say "LED use only?" Also, how could you test it to make sure it is compliant? I'd love to know that. Does complaint mean ripple and etc are in spec?
--- End quote ---
The standards in question relate to EMC (radio interference) and safety, not functionality. The ripple voltage, for example, could be atrocious, but that wouldn't make it non-compliant from a legal standpoint.
To test it properly, you'd need to take it to an approvals lab where they'd put it in a screened enclosure, connect it to a load (which in this case is an LED lighting strip) and measure the radio emissions from it. It's also tested for its conducted emissions back up the mains cable, immunity to spikes, surges and drop-outs in the mains supply, and immunity to radio interference generated by other nearby equipment.
In terms of safety they'll look at things like electrical isolation between the mains and the low voltage output, the temperature of the case when it's under full load, flammability, current leakage to earth, and whether or not it's correctly marked with voltage and current ratings, type of fuse and so on. A lot of the process is about paperwork.
--- End quote ---
Got it. I would hope those PSU would at least be safe. A scope could test for voltage and ripple and other undesirable, though, correct? I'm less worried about burning to death than protecting my equipment :)
--- End quote ---
Just be aware that there is a lot more sketchy stuff on Amazon than you might think. I don’t know the vetting process for items like power supplies, but there are certainly many which have slipped through the cracks. Some may have questionable safety and/or lack relevant safety documentation. Others might be safe but do not comply with mandated efficiency or EMC requirements. As expected , these items tend to be cheap and thus appealing to consumers, but in reality may be ignoring some regulations intended to help the consumer and protect society as a whole. Not to mention, undercutting legitimate manufacturers who ARE abiding by the laws.
By the way, technically power supplies for LED lighting should be IEC61000-3-2 “Class C” compliant for line frequency harmonic current. This is a measure of current drawn by the power supply at harmonics of the line frequency (50/60Hz). Drawing large currents at the harmonics can cause line voltage distortion, which in turn can mess up other systems on the same power distribution network.
--- End quote ---
Well, let's hope they test enough of them to keep them relatively in compliance, but I have my doubts too. The only way to tell is to scope them under load. It would be interesting to do.
james_s:
--- Quote from: DW1961 on July 24, 2020, 07:38:29 pm ---I have three DMMs. All capable of doing current test. What could I use for a power source instead of getting a bench supply? I mean, they're like $120.00 bucks on Amazon.
--- End quote ---
I didn't see this earlier.
I used various salvaged "wall wart" type adapters for years, batteries, power supplies salvaged out of scrapped equipment. Now there are a lot of cheap modules you can get from China to build a bench power supply, just add a surplus laptop charger or other similar PSU and put it in a box and you're good to go, I think Dave did a review on one of those a while back. If you have a decent thrift store around those can be a good place to get power adapters, used to be one down near our cabin that had a whole bin of cast off AC adapters and power cords for 99c each, I got several good ones from there. Those all in one scanner/printer/fax things get junked all the time and often have an adapter that puts out around 32V at several amps.
DW1961:
--- Quote from: james_s on July 27, 2020, 05:22:25 pm ---
--- Quote from: DW1961 on July 24, 2020, 07:38:29 pm ---I have three DMMs. All capable of doing current test. What could I use for a power source instead of getting a bench supply? I mean, they're like $120.00 bucks on Amazon.
--- End quote ---
I didn't see this earlier.
I used various salvaged "wall wart" type adapters for years, batteries, power supplies salvaged out of scrapped equipment. Now there are a lot of cheap modules you can get from China to build a bench power supply, just add a surplus laptop charger or other similar PSU and put it in a box and you're good to go, I think Dave did a review on one of those a while back. If you have a decent thrift store around those can be a good place to get power adapters, used to be one down near our cabin that had a whole bin of cast off AC adapters and power cords for 99c each, I got several good ones from there. Those all in one scanner/printer/fax things get junked all the time and often have an adapter that puts out around 32V at several amps.
--- End quote ---
That's a good idea, but those bench supplies on amazon are like 50-70 bucks. Also, I want t make sure the power is clean. Who knows what the ripple is in those other types of supplies is, for instance? a bench supply would make things so much easier.
On the other hand, if I had a decent scope, I could test the supply under load and see how it performs - lol.
cdev:
--- Quote from: DW1961 on July 26, 2020, 08:33:01 pm ---
--- Quote from: TimNJ on July 26, 2020, 06:48:19 am ---
--- Quote from: DW1961 on July 25, 2020, 05:08:52 pm ---
--- Quote from: AndyC_772 on July 25, 2020, 06:55:42 am ---
--- Quote from: DW1961 on July 24, 2020, 07:40:54 pm ---Good information, but why does that power supply I linked to above have a CE mark on it and say "LED use only?" Also, how could you test it to make sure it is compliant? I'd love to know that. Does complaint mean ripple and etc are in spec?
--- End quote ---
The standards in question relate to EMC (radio interference) and safety, not functionality. The ripple voltage, for example, could be atrocious, but that wouldn't make it non-compliant from a legal standpoint.
To test it properly, you'd need to take it to an approvals lab where they'd put it in a screened enclosure, connect it to a load (which in this case is an LED lighting strip) and measure the radio emissions from it. It's also tested for its conducted emissions back up the mains cable, immunity to spikes, surges and drop-outs in the mains supply, and immunity to radio interference generated by other nearby equipment.
In terms of safety they'll look at things like electrical isolation between the mains and the low voltage output, the temperature of the case when it's under full load, flammability, current leakage to earth, and whether or not it's correctly marked with voltage and current ratings, type of fuse and so on. A lot of the process is about paperwork.
--- End quote ---
Got it. I would hope those PSU would at least be safe. A scope could test for voltage and ripple and other undesirable, though, correct? I'm less worried about burning to death than protecting my equipment :)
--- End quote ---
Just be aware that there is a lot more sketchy stuff on Amazon than you might think. I don’t know the vetting process for items like power supplies, but there are certainly many which have slipped through the cracks. Some may have questionable safety and/or lack relevant safety documentation. Others might be safe but do not comply with mandated efficiency or EMC requirements. As expected , these items tend to be cheap and thus appealing to consumers, but in reality may be ignoring some regulations intended to help the consumer and protect society as a whole. Not to mention, undercutting legitimate manufacturers who ARE abiding by the laws.
By the way, technically power supplies for LED lighting should be IEC61000-3-2 “Class C” compliant for line frequency harmonic current. This is a measure of current drawn by the power supply at harmonics of the line frequency (50/60Hz). Drawing large currents at the harmonics can cause line voltage distortion, which in turn can mess up other systems on the same power distribution network.
--- End quote ---
Well, let's hope they test enough of them to keep them relatively in compliance, but I have my doubts too. The only way to tell is to scope them under load. It would be interesting to do.
--- End quote ---
Some of the designers of the cheap power supplies should go to jail for cutting corners the way they do. I say that because they kill people, usually poor young people, all of the time.
james_s:
--- Quote from: DW1961 on July 27, 2020, 10:43:25 pm ---That's a good idea, but those bench supplies on amazon are like 50-70 bucks. Also, I want t make sure the power is clean. Who knows what the ripple is in those other types of supplies is, for instance? a bench supply would make things so much easier.
On the other hand, if I had a decent scope, I could test the supply under load and see how it performs - lol.
--- End quote ---
If you have the budget then a proper bench supply is better, I'm just trying to give you options.
Don't forget there are also a lot of good quality used power supplies available from places like ebay. Others may have some specific recommendations.
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