Variable vs constant power supply

[Ephant]

I have a CCTV camera using the ordinary 12 volts AC to DC adaptor that has higher voltage (like 15 volt) when there is no load. I decided to buy a Meanwell adaptor but the datasheet (below) I got doesn't give the no load voltage.

What do you call power adaptor in which the voltage is higher at no load versus the power adaptor where the voltage is constant even at no load. And what would happen if you used a constant adaptor (with constant voltage) on devices that uses ordinary adaptor where voltage is higher at no load. Can it damage it?

In the case of the 12v Meanwell I got (with datasheet below). Since there is no no-load voltage data. Does it mean it would measure 12 volts even with no load? Can it work in my CCTV camera or destroy it? I decided to get one with very low leakage current to avoid damaging the electronics of the CCTV in case there is failure.

https://www.meanwell.com/webapp/product/search.aspx?prod=GSM60B

 

[DaveE]

The data sheet you linked to clearly states an output voltage tolerance of +/-3% (including mfr tolerance, load regulation, line regulation). Since it doesn't list any restrictions in the footnotes, you can assume it applies over the entire load range.

Your camera will also have a specification for input voltage, although you may not be able to find it.

 

[Ephant]

The data sheet you linked to clearly states an output voltage tolerance of +/-3% (including mfr tolerance, load regulation, line regulation). Since it doesn't list any restrictions in the footnotes, you can assume it applies over the entire load range.

Your camera will also have a specification for input voltage, although you may not be able to find

For ordinary AC/DC adaptor like voltage of 9v, the no load can reach as high as 13v. Yet in the Meanwell, the no load is only less than 10v. In the ordinary adaptor, why can't they make the no load also less than 10 volts? is it because of costs? What terms do you refer to them, variable vs constant power supply?

it.

 

[DaveE]

is it because of costs?

yes

 

[DaveE]

What terms do you refer to them, variable vs constant power supply?

I read the data sheet. The whole thing, especially the footnotes. The rest is marketing crap. Sorry, I just don't trust most marketing, especially for low cost parts.

OK, but given that I claim you can't trust it. I would assume the term "power supply" for this type of part means regulated. "Adapter" would make me suspicious. To cheap to be real makes me extremely suspicious. Within a given supply channel/manufacturer you will get what you pay for.

 

[Vanadium 50]

Dumb question - why does the no load voltage matter? It only matters when you are not drawing any power. Once you start, the voltage will sag.

 

[DaveE]

Dumb question - why does the no load voltage matter? It only matters when you are not drawing any power. Once you start, the voltage will sag.

It can overstress components that are exposed to that voltage. There may be things like transient suppressors or filter caps that you don't really want to see that stress. Maybe just for lifetime/reliability concerns.

EEs will often also use this as a marker for other potential problems. If you buy a Yugo that doesn't have a good defroster, it may also have a crappy suspension and an unreliable engine. It can represent a difference in kind, a different market segment.

Also in some industries, like Mil/Aero-space it can make a big paperwork burden: "prove it's OK".

But your point is well founded, that's why they are so common in consumer electronics. More expensive because of better performance isn't necessarily a good thing. There's a reason Toyota makes more money than McLaren or Boeing.

So, in short: Read the data sheet. The whole thing. Buy what suits your requirements.

 

[Ephant]

For ordinary adaptors, the sag can be large like 45% for no load. For branded adaptors like Meanwell, the sag can be only 3%. Both can power the CCTV fine? What electronics components are involved inside that can make the sag 45% vs 3%?

 

[DaveE]

For ordinary adaptors, the sag can be large like 45% for no load. For branded adaptors like Meanwell, the sag can be only 3%. Both can power the CCTV fine? What electronics components are involved inside that can make the sag 45% vs 3%?

Sorry, you can't ask us about a generic camera. We don't know anything about what it requires. Why would we?

 

[Ephant]

Not just the camera. But any electronics like router or anything that needs adaptor. Now I just need to know what components in the adaptor can create 45% vs 3%. Isn't the latter like regulated power supply? You can use regulated power supply for all devices that can accept ordinary adaptors that can sag in voltages?

 

[DaveE]

For ordinary adaptors, the sag can be large like 45% for no load. For branded adaptors like Meanwell, the sag can be only 3%. Both can power the CCTV fine? What electronics components are involved inside that can make the sag 45% vs 3%?

Oh, sorry, are you asking about what's in the power supply?
This can be kind of complicated, there are lots of different designs. Basically, it's an issue of power control and feedback. Did they pay to control the output parameters or just convert things in a rough, approximate way.

Ask a more detailed question if you really want to know more about transformers and power supplies. There are lots of people here that can help.

 

[DaveE]

You can use regulated power supply for all devices that can accept ordinary adaptors that can sag in voltages?

Each device will have an input power specification. They should tell you what is acceptable. This is often not shown to consumers, particularly if they are selling you a system that includes the device plus it's adapter.

You can get a feeling for this if you get a magnifying glass and read the writing on your adapter. People that work in this industry know what all of that stuff means.

 

[Ephant]

Maybe this the first simple question I wanna ask. For all gadgets like router or even cheap cctv camera that can accept 12v that can sag in voltages 45%. What would happen if you use regulated power supply that supply purely 12v? Won't it damage the gadgets or do the gadgets need adaptor that can sag in voltage (at no load) largely to work (if this does even make sense).

 

[DaveE]

Maybe this the first simple question I wanna ask. For all gadgets like router or even cheap cctv camera that can accept 12v that can sag in voltages 45%. What would happen if you use regulated power supply that supply purely 12v? Won't it damage the gadgets or do the gadgets need adaptor that can sag in voltage (at no load) largely to work (if this does even make sense).

No it will work fine. Each device that has a voltage input will work over the entire specified range. They will specify a minimum and maximum voltage. You needn't worry about breaking it within that range.

Edit: can't type today. LOL.

 

[Vanadium 50]

If you buy a Yugo that doesn't have a good defroster, it may also have a crappy suspension and an unreliable engine.

Ah yes. The Yugo. For people looking for a Fiat with even less reliability.

Good explanation, thanks.

 

[DaveE]

Ah yes. The Yugo. For people looking for a Fiat with even less reliability.

Why does the Yugo have a rear window defroster?
To keep your hands warm while you're pushing it.

 

[Ephant]

The data sheet you linked to clearly states an output voltage tolerance of +/-3% (including mfr tolerance, load regulation, line regulation). Since it doesn't list any restrictions in the footnotes, you can assume it applies over the entire load range.

Your camera will also have a specification for input voltage, although you may not be able to find it.

I read other specs. I think the 3% is for full load. Even for unregulated power supply, the tolerance at full load is also low like 3% to 5%. It is when there is no load that the voltage will reach high. My question is whether the particular Meanwell in my original thread is unregulated too or regulated. It has no "no-load" data.

For the term switching power supply, does it mean unregulated or regulated?

 

[DaveE]

I think the 3% is for full load.

Which 3%? There is a reason the parameters on the data sheet have names. If you read the name of a spec and don't know what it is, ask google. Careful, detailed reading is required here. Those data sheets are written for EEs that know the subject.

My question is whether the particular Meanwell in my original thread is unregulated too or regulated

It is regulated. It has to be to achieve those line and load regulation specs. Learn what those mean.

It has no "no-load" data.

Because they left that reference out, by implication, it doesn't matter. For a counter example look at footnote #5 for line regulation. This is a case where they thought a defined range was worth communicating.

They can't write a data sheet that describes every possible application scenario. Reading data sheets is something that new EEs have to learn. Think of them as a contract between the manufacturer and user; "this is what it will do, this is what you have to do". They are also often the basis for the testing they will do before they ship it to you.

For the term switching power supply, does it mean unregulated or regulated?

Yes, 99.99% of the time it means that the output parameters are controlled to meet the published specifications. There are some interesting (to me) examples of SMPS systems that are not. You won't encounter those unless you are a working EE in a particular field.

But still, it begs the questions "what's regulated?" and "how well is it regulated?". That's why data sheets are written. To first order, it doesn't matter how they do what they promise.

 

[Vanadium 50]

Why does the Yugo have a rear window defroster?

To keep your hands warm while pushing it.

Think of them as a contract between the manufacturer and user

That's a very good way to think about it. And, just like a contract, one assumes what is meant but not written down at one's own peril.

 

[gmax137]

Well in 1987 a Yugo was $4000, compared to a VW Rabbit at $13000. The phrase I remember is, "you go crazy looking for parts."

 

[DaveE]

one assumes what is meant but not written down at one's own peril.

In my time as a designer, it wasn't uncommon for us to evaluate, tear down, talk to manufacturers, and test components to establish or verify the important things we needed. This was, of course, all for expensive, high performance products. The data sheets aren't perfect, but they are definitely the starting point. Every word written on them was chosen carefully. They have been the subject of legal settlements from time to time.

 

[Vanadium 50]

The data sheets aren't perfect, but they are definitely the starting point. Every word written on them was chosen carefully.

I was in the market for some (20K channels worth) Analog Front End/ADC chips. Some of the best documented ones are used in medical ultrasound. This is why.

 

[Rive]

Dumb question - why does the no load voltage matter?

My guess is, that the cheap one is barely more than a cheap wall-plug transformer, a graetz and a cap, without regulator parts (I've seen such things). If you mess up the order-of-pluggin' then you put a 15V charged cap on your 12V equipment. If you are lucky, then the equipment may have a sufficiently tolerant regulator.... But maybe not...

Also, these cheap ones are often prone to turn-shorts on the primary, and that may raise the output voltage significantly. (Seen some 12V pieces with above 18V output, the plastic casing already soft...)

I hope these will get a ban someday.

 

[Ephant]

Which 3%? There is a reason the parameters on the data sheet have names. If you read the name of a spec and don't know what it is, ask google. Careful, detailed reading is required here. Those data sheets are written for EEs that know the subject.It is regulated. It has to be to achieve those line and load regulation specs. Learn what those mean.Because they left that reference out, by implication, it doesn't matter. For a counter example look at footnote #5 for line regulation. This is a case where they thought a defined range was worth communicating.

They can't write a data sheet that describes every possible application scenario. Reading data sheets is something that new EEs have to learn. Think of them as a contract between the manufacturer and user; "this is what it will do, this is what you have to do". They are also often the basis for the testing they will do before they ship it to you.Yes, 99.99% of the time it means that the output parameters are controlled to meet the published specifications. There are some interesting (to me) examples of SMPS systems that are not. You won't encounter those unless you are a working EE in a particular field.

But still, it begs the questions "what's regulated?" and "how well is it regulated?". That's why data sheets are written. To first order, it doesn't matter how they do what they promise.

Checking my adaptors. I think there is an easy way to tell which one has higher voltage at no-load. It seems only the transformer type adaptors have this higher voltage at no-load. So there are only 2 kinds of adaptors. The switching and the transformer type. Only the former is regulated.

Switching adaptors are now so cheap that it costs like candy. Why do they still make transformers type? Maybe it's even cheaper?

For 2xMOPP isolation at 4000V with very low leakage current. Doesn't this need some kind of transformers? Or can 2X MOPP be used also for switching type?

https://www.digikey.pl/pl/articles/medical-power-solutions-standards-deliver-safety

 

[DaveE]

Maybe it's even cheaper?

Yes.

Doesn't this need some kind of transformers?

Yes. But in a SMPS they operate at much higher frequency which makes them much smaller.

 

[Ephant]

Yes.Yes. But in a SMPS they operate at much higher frequency which makes them much smaller.

so based on the Meanwell with 2 MOPP with spec you saw in my first message. Does it use Transformer or SMPS or Hybrid of both Transformer and SMPS to achieve 2 MOPP.

It is used in medical devices to produce low leakage current. In the Large Hadron Collider, what kind of power adaptor do they used for some small components.. should it require low leakage current too? Is this important in sensitive particle detection, to reduce noise?

 

[DaveE]

so based on the Meanwell with 2 MOPP with spec you saw in my first message. Does it use Transformer or SMPS or Hybrid of both Transformer and SMPS to achieve 2 MOPP.

It is a SMPS with an internal transformer (like most of them).

In the Large Hadron Collider, what kind of power adaptor do they used for some small components.

Probably all of the different types. The LHC is a huge machine with lots of subsystems, contractors, suppliers, and parts.

should it require low leakage current too? Is this important in sensitive particle detection, to reduce noise?

I have no association with the LHC. I don't know what they require. However, I am confident that to get such a large, high tech system to work, they must have system engineers that write specifications for the subsystems they use. They should tell you what they require, ask them.

 

[nsaspook]

I have a CCTV camera using the ordinary 12 volts AC to DC adaptor that has higher voltage (like 15 volt) when there is no load. I decided to buy a Meanwell adaptor but the datasheet (below) I got doesn't give the no load voltage.

What do you call power adaptor in which the voltage is higher at no load versus the power adaptor where the voltage is constant even at no load. And what would happen if you used a constant adaptor (with constant voltage) on devices that uses ordinary adaptor where voltage is higher at no load. Can it damage it?

In the case of the 12v Meanwell I got (with datasheet below). Since there is no no-load voltage data. Does it mean it would measure 12 volts even with no load? Can it work in my CCTV camera or destroy it? I decided to get one with very low leakage current to avoid damaging the electronics of the CCTV in case there is failure.

https://www.meanwell.com/webapp/product/search.aspx?prod=GSM60B

It's unlikely the camera operates internally at 12-15 VDC (other than maybe the IR led array that draws usually a large percentage of the total current when on). Usually the first thing after a fuse is the switching DC to DC converter and/or regulator that changes the bus distribution voltage (when designing for 12V systems you need allow for the upper range absorption voltage of a battery charger for a SLA battery bank of at least 15+ volts for the bus voltage with a nominal 13.6 volts DC operating voltage) to the proper voltages for the logic, sensors and processor for the camera.

 

[Tom.G]

If you look at pg. 2, line 3 of the datasheet you will find CURRENT RANGE,
that is the range over which the load can vary and the Specifications are valid.

Since the CURRENT RANGE is 0 - 5A, the output voltage will be within spec at ANY load between no-load and full-load.

Cheers,
Tom

 

[Ephant]

If you look at pg. 2, line 3 of the datasheet you will find CURRENT RANGE,
that is the range over which the load can vary and the Specifications are valid.

Since the CURRENT RANGE is 0 - 5A, the output voltage will be within spec at ANY load between no-load and full-load.

Cheers,
Tom

How does this differ to the unregulated where when the current drawn is less than 5A, the voltage will be greater like 18V (for no load). It is only when the current drawn is 5A that the voltage will be 12V at full load. In both case the power in watt is maintained from voltage times ampere).

In your description, did you mean the voltage is always 12V even when current vary from 0 to 5A? Or did you mean the power is always maintained even if the voltage varies like described above, in which case, it is really unregulated?

 

[Tom.G]

In your description, did you mean the voltage is always 12V even when current vary from 0 to 5A?

Yes!

when the current drawn is less than 5A, the voltage will be greater like 18V (for no load). It is only when the current drawn is 5A that the voltage will be 12V at full load. In both case the power in watt is maintained from voltage times ampere).

Sorry, not quite correct, the delivered power is not constant. Please see the datasheet below for a table of how the output voltage of an typical unregulated supply varies as the current changes.
Beware of the graph on that page, the x-axis is nonlinear. At low currents the voltage drops rapidly with increasing loads.

You will see that at 50mA load the delivered power is 1Watt;
but at 300mA load the delivered power is 4.8W!

https://assets.omega.com/manuals/M1388.pdf

Cheers,
Tom

 

[Ephant]

Yes!Sorry, not quite correct, the delivered power is not constant. Please see the datasheet below for a table of how the output voltage of an typical unregulated supply varies as the current changes.
Beware of the graph on that page, the x-axis is nonlinear. At low currents the voltage drops rapidly with increasing loads.

You will see that at 50mA load the delivered power is 1Watt;
but at 300mA load the delivered power is 4.8W!

https://assets.omega.com/manuals/M1388.pdf

Cheers,
Tom

How do you know what wattage is the right one, 1Watt for 50mA load or 4.8W for 300mA load? If both is wrong, how do you check the right wattage?

 

[Tom.G]

how do you check the right wattage?

"...right wattage?"

That is sort of like asking "What is the weight you can lift?". There is no "right" answer because you can lift your limit or anything below your limit.

The Maximum wattage that the power pack can supply is stated, sometimes indirectly, on the pack itself or in the data sheet.

If not explicitly stated, the Wattage is the normal output voltage, V, times the rated output current I; in other words W = V x I -- where V is the output voltage, and I is the current that the load is using (drawing from the power pack).