How Does a DC Power Supply Function and What Are Its Key Features?

[PainterGuy]

hi everyone,

here is picture of power supply:--
http://img696.imageshack.us/img696/8841/powersupplyg.jpg

at top it says power supply can give 3A. would this mean when resistance is 10 ohm is used and voltage is set at 30v. then current will be 3A. please tell me.

what is the function of silver color port at right hand side bottom corner.

i am very happy for any help you can provide me. much thanks.

cheers

 

[vk6kro]

hi everyone,

here is picture of power supply:--
http://img696.imageshack.us/img696/8841/powersupplyg.jpg

at top it says power supply can give 3A. would this mean when resistance is 10 ohm is used and voltage is set at 30v. then current will be 3A. please tell me.

what is the function of silver color port at right hand side bottom corner.

i am very happy for any help you can provide me. much thanks.

cheers

If there is 30 volts across a 10 ohm resistor, then there will be 3 amps flowing.
This power supply is rated at 3 amps maximum, so it should be able to cope with this.

The silver terminal at the bottom is an Earth or ground connection.

If you connected the negative side of the power supply to this then the other side would be 0 to positive 30 volts relative to ground.

You could connect the positive side of the supply to this terminal and get a supply thet was 0 to negative 30 volts relative to ground.

Or, you could leave the power supply floating by not connecting anything to this connector.

Quality power supplies often have this option.

 

[PainterGuy]

thank you, vk6kro. it is nice that you helped me. i am a beginner.

The silver terminal at the bottom is an Earth or ground connection.

If you connected the negative side of the power supply to this then the other side would be 0 to positive 30 volts relative to ground.

what i understand is that if i connect one wire to this silver terminal and other to +ve terminal then i can get volts from 0-30. is this what you said?

and when i have wires connected to +ve and -ve terminals on power supply (as in the picture) even then i can get same range of volts. then what is benefit?

You could connect the positive side of the supply to this terminal and get a supply thet was 0 to negative 30 volts relative to ground.

i understand you are saying if connect one wire to this silver ground terminal and other to -ve terminal of power supply then i can get volts from 0 to -30. is this correct.

why would someone do this? what benefit of 0 to -30 volts. please tell me.

Or, you could leave the power supply floating by not connecting anything to this connector.
Quality power supplies often have this option.

i think the power supply in the picture has this floating option. doesn't it?

i am very much grateful to you for helping me with this. many thanks.

cheers

 

[vk6kro]

These voltage ranges may be useful or they may give you the option to choose some voltage in that range.

For example, if you want to test something that needed 12 volts, you could just select it.

In a laboratory, you might be checking on how a transistor behaves with different voltages on it. So, you could take voltages in steps of 2 volts, maybe, and apply voltages from 0 to 12 volts like this 0, 2, 4, 6, 8, 10, 12.

Some devices like PNP transistors and P chanel Mosfets can operate with negative supplies, so these could be operated from this supply but with the positive lead grounded.

Yes, this supply does give a floating output unless you connect one of the outputs to the ground terminal.

 

[PainterGuy]

hi everyone,

i am sorry to say this. but i think vk6kro missed many of points i raised in my post# 3 above. i know it is difficult to understand my posts because of my bad english. please read it again and try to clear the confusion.

and let me tell you that i think of +ve terminal on power supply as the terminal where the electrons from -ve terminal of power supply flows. in terms of 'electron current' -ve terminal is at high potential.

cheers

 

[sophiecentaur]

You're doing it again painterguy. I'm not hounding you but I read your post and wondered why you don't stick to Current? Imagine you are in the year 1900. You can answer ALL of your circuit questions without using electrons (which haven't been invented properly, yet). Current flows from + to - and you don't need to cloud the issue by saying it's electrons - because it might just NOT be. It could be positive ions flowing as well!

AS for the positive or negative supply query. It is very common for equipment to have supply of both polarities. You only need to google Audio Amp design. You will see dozens with two power 'rails'.

 

[vk6kro]

Reading your post no 3 again, you seem to have another wrong idea.

To use the "silver thing" or ground terminal, you would connect the negative side of the floating supply to it and then you would have a 0 volts to +30 Volts supply with the most negative side of the supply grounded.

You would take one output from the junction of the negative wire and the ground wire, and the other output from the + lead.

Or, you could do the reverse and connect the positive side of the floating supply to ground and then use the supply as a grounded positive, variable negative supply.

 

[PainterGuy]

hello everyone,

You're doing it again painterguy. I'm not hounding you but I read your post and wondered why you don't stick to Current? Imagine you are in the year 1900. You can answer ALL of your circuit questions without using electrons (which haven't been invented properly, yet). Current flows from + to - and you don't need to cloud the issue by saying it's electrons - because it might just NOT be. It could be positive ions flowing as well!

sorry. i understand your advice. one of my teacher from some previous class taught us this way. but i promise i will get rid of this soon.

Reading your post no 3 again, you seem to have another wrong idea.

To use the "silver thing" or ground terminal, you would connect the negative side of the floating supply to it and then you would have a 0 volts to +30 Volts supply with the most negative side of the supply grounded.

You would take one output from the junction of the negative wire and the ground wire, and the other output from the + lead.

Or, you could do the reverse and connect the positive side of the floating supply to ground and then use the supply as a grounded positive, variable negative supply.

thanks vk6kro. you have touched it on the spot. the connecting of the negative side of the floating supply to the ground terminal isn't useless. because i can have 0 volts to +30 volts even without doing it - connect one wire to negative terminal and the other wire to positive terminal of the supply and i have 0 volts to +30 volts.

and yes, connecting positive side to the ground and getting 0 volts to -30 volts makes sense.

many thanks for helping me out with this. much grateful.

cheers

 

[PainterGuy]

Reading your post no 3 again, you seem to have another wrong idea.

To use the "silver thing" or ground terminal, you would connect the negative side of the floating supply to it and then you would have a 0 volts to +30 Volts supply with the most negative side of the supply grounded.

You would take one output from the junction of the negative wire and the ground wire, and the other output from the + lead.

Or, you could do the reverse and connect the positive side of the floating supply to ground and then use the supply as a grounded positive, variable negative supply.

hello vk6kro,

i think one question i asked above was not clear that is why you didn't get it. i will ask it again to make it more understandable.

don't you think the connecting of the negative side of the floating supply to the ground terminal is useless? because i can have 0 volts to +30 volts even without doing it - connect one wire to negative terminal and the other wire to positive terminal of the supply and i have 0 volts to +30 volts.

is this any clear now. please tell me if possible. many thanks

cheers

 

[vk6kro]

don't you think the connecting of the negative side of the floating supply to the ground terminal is useless? because i can have 0 volts to +30 volts even without doing it - connect one wire to negative terminal and the other wire to positive terminal of the supply and i have 0 volts to +30 volts.

No, it isn't useless.

Grounding one side of the supply helps to reduce noise pickup and makes the supply compatible with other devices which may have one side of their inputs grounded.

This supply gives you the choice. With it floating, you could possibly put two of these supplies in series to get extra voltage. With it grounded you could have dual supplies from two such supplies with one giving positive and one giving negative output.

With audio devices, often it is best to only ground the system at one point to avoid Earth loops. This may be at the power supply and, if so, then this power supply is able to do it.

Incidentally, responding to questions here is optional. A non-reply does not mean someone did not understand your question. Less abrasive questions tend to get answered more readily.

 

[PainterGuy]

Incidentally, responding to questions here is optional. A non-reply does not mean someone did not understand your question. Less abrasive questions tend to get answered more readily.

many thanks vk6kro. was my question abrasive? i didn't intend to it to be? perhaps it was because of the reason that i don't yet understand the subtleties in meanings of the words used. once again, thanks

cheers

 

[sophiecentaur]

I think the word "useless" was just referring to 'without use or purpose' rather than a quality judgement of the suggestion.

 

[PainterGuy]

I think the word "useless" was just referring to 'without use or purpose' rather than a quality judgement of the suggestion.

hi sophiecentaur,

i am sorry i did not understand what you said above. was you saying something to me? please let me know if this is the case.

i see only i have used "useless" word above in one of my posts.

don't you think the connecting of the negative side of the floating supply to the ground terminal is useless?

cheers

 

[sophiecentaur]

Don't worry PainterGuy. I think your use of that word was mis-interpreted. You meant it literally and it was taken as a bit of an insult, I think.

 

[PainterGuy]

Don't worry PainterGuy. I think your use of that word was mis-interpreted. You meant it literally and it was taken as a bit of an insult, I think.

you are so nice sophiecentaur.

thank you for the clearing this up. i did not mean any such thing as to insult anyone a bit. never ever. i would not really blame vk6kro for this misinterpretation. actually i am also new to this english learning so sometimes i don't understand subtle differences in meaning - though i am struglling a lot to learn it. once again i am grateful for your understanding i didn't mean anything bad.

cheers

 

[Jiggy-Ninja]

You're doing it again painterguy. I'm not hounding you but I read your post and wondered why you don't stick to Current? Imagine you are in the year 1900. You can answer ALL of your circuit questions without using electrons (which haven't been invented properly, yet). Current flows from + to - and you don't need to cloud the issue by saying it's electrons - because it might just NOT be. It could be positive ions flowing as well!

AS for the positive or negative supply query. It is very common for equipment to have supply of both polarities. You only need to google Audio Amp design. You will see dozens with two power 'rails'.

Damn, it's a good thing they weren't patented. Just IMAGINE the royalties!

Your English is quite fine, PainterGuy. Misinterpretation can happen for a million different reasons entirely unrelated to your choice of words: mood, personality, distracting thoughts, incomplete reading, etc.

And sometimes, it's just your natural speaking style that gets misinterpreted. A lot of times, I have a very terse and efficient way of conversing, preferring to get to the point and not waste words. People with a different personality can misinterpret that as rude, arrogant, mean, or several other things.

I can't count the number of times I've said something and gotten "the look' from my parents, and wondering what I said that they thought was rude.

And that's with face-to-face talking. Online, you don't have voice tone and body language to give you clues, you just have the words. Much more room for misinterpretation.

 

[PainterGuy]

Your English is quite fine, PainterGuy.

many thanks for these encouraging words Jiggy-Ninja. i am happy. and i have been working very hard on my english for last few months.

i have used power supply twice. each time i used it i used it as a voltage source - i mean to say i was able to control the voltage not the current. though there is a current knob too. so this means this can be used as a current source. so this time i tried to play around a little.

this is the picture when i was using it as voltage source so can notice current display does not show anything:---
http://img842.imageshack.us/img842/5833/powersupplyvoltage.jpg

then i started to play around to find how current source function can be used. i connected +ve terminal of the wire coming from the supply to +ve side of DMM and -ve wire from the supply to -ve terminal on the DMM. have a see on this picture i took then:--
http://img810.imageshack.us/img810/4475/powersupplycurrent.jpg

at the top power supply says 30V/3A, but if you see the current display it is reading 4.45 A and voltage display reading 2.5V. what do you understand from this?

tell me what is this please. it will be highly helpful of you.

cheers

 

[Averagesupernova]

You see the LED switched from constant voltage mode to constant current. Look closer at the spec of this supply. It may say more about the 3 amp vs. the 4.5 amp that it is obviously putting out.

 

[Jiggy-Ninja]

many thanks for these encouraging words Jiggy-Ninja. i am happy. and i have been working very hard on my english for last few months.

And yet you forget to capitalize "I" and the first letter of your sentences. Though it could just be laziness. You wouldn't be the first.

Also, English, being the name of a language, is a proper noun. It gets capitalized too.

at the top power supply says 30V/3A, but if you see the current display it is reading 4.45 A and voltage display reading 2.5V. what do you understand from this?

tell me what is this please. it will be highly helpful of you.

cheers

What does the DMM read? Is it different from the power supply's reading? It could be a mis-calibration in the power supply's ammeter.

 

[Perfection]

The power supply is probably okay, it's pretty typical for power supplies to supply more current then the sticker says, especially at lower voltages. What I'd be more worried about is what device he's dumping over 10 watts into. He could be at risk of damaging it.

If the thing is still setup, I'd photograph it with the power off.

 

[PainterGuy]

You see the LED switched from constant voltage mode to constant current. Look closer at the spec of this supply. It may say more about the 3 amp vs. the 4.5 amp that it is obviously putting out.

thanks Averagesupernova. okay i didn't know it. so "CC" and "CV" on the power supply mean constant current and constant voltage. i do not access to this power supply. i am sure even the owner does have its specs.

And yet you forget to capitalize "I" and the first letter of your sentences. Though it could just be laziness. You wouldn't be the first.

so sorry. this is because of my addiction to text messaging. but i promise to change it from now onward. Happy!

What does the DMM read? Is it different from the power supply's reading? It could be a mis-calibration in the power supply's ammeter.

I don't really remember reading of DMM. I don't even know was DMM set as an ohm meter, ammeter, or voltmeter. Actually the power supply almost always work as a voltage supply. So I was trying to find out how I can use it as a current source. Could you help me with it? The LED above the current knob turned on when I connected +ve lead from the power supply to the +ve side of the DMM and -ve side of the power supply to the -ve side of DMM. I don't know if this is correct to do. Could you tell me how to use this supply as a variable current source? It always is working as a variable voltage source. (Seriously, I had read this post of me at least four times to correct the capitalization and mistakes ).

The power supply is probably okay, it's pretty typical for power supplies to supply more current then the sticker says, especially at lower voltages. What I'd be more worried about is what device he's dumping over 10 watts into. He could be at risk of damaging it.

If the thing is still setup, I'd photograph it with the power off.

Thanks Perfection. It was connected to a DMM.I do not access to the setup so sorry I can not take any picture.

cheers

 

[Averagesupernova]

Here is how you use it as a constant current source: Turn the voltage all the way up. Turn the current all the way down. Short the output terminals. Turn the current up until you get the current you want. Now, no matter what kind of load you put on there it will supply the current you set it to as long as the loads resistance doesn't get so high that it requires more than the maximum voltage the supply is able to put out.
-
For example: Suppose you want a constant current source of .25 amps. You set the supply as I described. Now you plug in a 100 ohm resistor in. The supply will attempt to supply a constant voltage until it realizes that 30 volts (in your case) across a 100 ohm load requires .3 amps which is more than you set the max current for. So it will settle down to 25 volts and supply you with .25 amps. Now try that with a 130 ohm resistor and the supply does not have enough voltage to push .25 amps through the 130 ohm resistor. If the supply were designed to have a max output of 33 volts it would be enough to reach the .25 amps.

 

[sophiecentaur]

You may find that the output is not a steady current when in 'constant current' mode. Unless the power supply has been deliberately spec'd to be a proper constant current supply, the current setting may only be there to protect equipment from frying. You would need to test how good it is, using a hefty rheostat that could stand a good few Watts of dissipation.
If you want a good constant current supply then you might use a regulator chip in a configuration that the manufacturer recommends in its data sheet.
Also, it may be worth checking for 'dark brown' smells when using the Constant Current setting. The PSU may not be up to supporting continuous use in this mode.

 

[Averagesupernova]

Sophie, I would say that if it has CV and CC LEDs it is a safe bet it can handle it. It looks like a lab-grade supply to me. BTW, these supplies are EXCELLENT for charging batteries.

 

[sophiecentaur]

Go for it then. Sounds like a useful piece of kit.

 

[Jiggy-Ninja]

so sorry. this is because of my addiction to text messaging. but i promise to change it from now onward. Happy!

Texting. I should have known. My mom almost does that crap in her emails. It's like a curse that needs to be exorcised from some people.

And that's nothing compared to teachers that get assignments from their students with "u" and "gr8" on them.

I command you, in the name of the Grammar, the Syntax, and the Proper Speech, begone, foul texting!

I don't really remember reading of DMM. I don't even know was DMM set as an ohm meter, ammeter, or voltmeter. Actually the power supply almost always work as a voltage supply. So I was trying to find out how I can use it as a current source. Could you help me with it? The LED above the current knob turned on when I connected +ve lead from the power supply to the +ve side of the DMM and -ve side of the power supply to the -ve side of DMM. I don't know if this is correct to do. Could you tell me how to use this supply as a variable current source? It always is working as a variable voltage source.

It was probably plugged into the ammeter part, given the voltage and current readings. The voltmeter terminal would have a massive amount of resistance.

Then it's just a matter of tuning it on and checking if it reads the same as the supply.

Though I don't think those are right. As Perfection noted, that's 10W of power, and I don't think most DMMs can handle that kind of power. I know the $30 one I put together from a kit used only 1/4W resistors.

(Seriously, I had read this post of me at least four times to correct the capitalization and mistakes ).

Much better. Now it's just a matter of mastering the subtler points grammar and word usage, which could take the rest of your life.

Thanks Perfection. It was connected to a DMM.I do not access to the setup so sorry I can not take any picture.

cheers

IF you don't have access to it, how are you getting these pictures?

 

[PainterGuy]

Hello everybody,

Here is how you use it as a constant current source: Turn the voltage all the way up. Turn the current all the way down. Short the output terminals. Turn the current up until you get the current you want. Now, no matter what kind of load you put on there it will supply the current you set it to as long as the loads resistance doesn't get so high that it requires more than the maximum voltage the supply is able to put out.
-
For example: Suppose you want a constant current source of .25 amps. You set the supply as I described. Now you plug in a 100 ohm resistor in. The supply will attempt to supply a constant voltage until it realizes that 30 volts (in your case) across a 100 ohm load requires .3 amps which is more than you set the max current for. So it will settle down to 25 volts and supply you with .25 amps. Now try that with a 130 ohm resistor and the supply does not have enough voltage to push .25 amps through the 130 ohm resistor. If the supply were designed to have a max output of 33 volts it would be enough to reach the .25 amps.

Many thanks Averagesupernova. I think your post is going to be most helpful in making that power supply a current source. Much grateful for telling me simple way to do this.

I understand what you say but to be on safer side I would ask it anyway. Do you mean by "way up" and "way down" to set it at maximum value and lowest value respectively? I hope you will keep helping me in this simple way in future too.

You may find that the output is not a steady current when in 'constant current' mode. Unless the power supply has been deliberately spec'd to be a proper constant current supply, the current setting may only be there to protect equipment from frying. You would need to test how good it is, using a hefty rheostat that could stand a good few Watts of dissipation.
If you want a good constant current supply then you might use a regulator chip in a configuration that the manufacturer recommends in its data sheet.
Also, it may be worth checking for 'dark brown' smells when using the Constant Current setting. The PSU may not be up to supporting continuous use in this mode.

Hello sophiecentaur,

Thanks for telling me this point. I will check whether it can supply steady current and will keep on checking for 'dark brown' smell! Thanks for being there to help me out.

Sophie, I would say that if it has CV and CC LEDs it is a safe bet it can handle it. It looks like a lab-grade supply to me. BTW, these supplies are EXCELLENT for charging batteries.

Good thing to know.

Texting. I should have known. My mom almost does that crap in her emails. It's like a curse that needs to be exorcised from some people.

I assure you that you have exorcised this curse from me. But there are still many millions of them out there who still need your service!

Much better. Now it's just a matter of mastering the subtler points grammar and word usage, which could take the rest of your life.

Now I believe it is worth investing your life and energy to learn something useful! In studies I face a lot of difficulties because I started studying things in English just some time ago. Almost everything on the net is in English.

IF you don't have access to it, how are you getting these pictures?

No, no. I have access to it. I wanted to say I get access to it only occasionally. Last time I had the power supply in front of me I took its pictures with my friend's phone.

Cheers

 

[Perfection]

I understand what you say but to be on safer side I would ask it anyway. Do you mean by "way up" and "way down" to set it at maximum value and lowest value respectively? I hope you will keep helping me in this simple way in future too.

That would be correct.

 

[PainterGuy]

Grounding one side of the supply helps to reduce noise pickup and makes the supply compatible with other devices which may have one side of their inputs grounded.

This supply gives you the choice. With it floating, you could possibly put two of these supplies in series to get extra voltage. With it grounded you could have dual supplies from two such supplies with one giving positive and one giving negative output.

Hello again,

1:-- I was reading this thread again. I was wondering what really happens inside the supply when one of the leads connected to -ve terminal on the supply is grounded. Can you please shed some light on this? I have though -ve terminal is simply taken ground but here I mean mt previous understanding shatters.

2:-- If I have two supplies and each one has one lead connected to the ground terminal and other to the +ve terminal. Can I connect them in series (connecting ground of one supply to the +ve terminal of other supply to get double voltage (e.g. If both the supplies have same maximum voltage, say 30V, then double will be 60V).

3:-- When lead is connected to -ve terminal and other lead to the ground. The supply will supply the voltage from 0V to maximum negative voltage the supply can deliver. If the supply can supply 30 volts, then it would be from 0V to -30V. So now the current is flowing from ground terminal which is at 0V to -ve terminal which is at lower voltage. Correct me please.

Many thanks for all your help.

Cheers

 

[sophiecentaur]

Nothing different "really happens" inside a power supply whatever you connect one of the outputs to. (Within the limits of the insulation) It's irrelevant.

All the power supply does is to maintain a Potential Difference between its two terminals - just like a battery. You can stack them 'one on top of another' just as with batteries, in a whole chain. Remember that a PSU has a transformer somewhere inside it which decouples DC between the supply and the output.

I can't see your problem. If you can accept that a 6V battery will probably have 4 1.5V cells connected in series, inside it, the why shouldn't you be able to connect four 12V PSUs in series and get yourself + and -24V by grounding the mid point?

Just look at a few diagrams of circuits involving multiple power supplies and multiple voltages. It really is obvious what will happen.

 

[Jiggy-Ninja]

For most purposes, you do not need to use the Earth tie. I'm 1.5 years into my education and have not once had to hook anything to the Earth tie on the power supply, though some dorks at school still do it for some reason. vk6kro brought up a couple of specific situations that it might be helpful, but other than those you likely won't need to bother with it.

 

[PainterGuy]

For most purposes, you do not need to use the Earth tie. I'm 1.5 years into my education and have not once had to hook anything to the Earth tie on the power supply, though some dorks at school still do it for some reason. vk6kro brought up a couple of specific situations that it might be helpful, but other than those you likely won't need to bother with it.

Hello,

Some days ago I had the lead coming out of +ve terminal connected to the lead coming out from the ground which formed a junction. Then I attached the +ve terminal of the DMM to this junction, and the other terminal of the DMM to the -ve terminal of the power supply. The DMM gave me -ve readings.

And Jiggy-Ninja, the power supply has 2 prong plug .

Now I will try to ask what is puzzling me.

If I connect one lead to the ground terminal and the other one to -ve terminal, I will have 0V to -30V. Right? But what does this really mean? What is the direction of electrons? Before you answer this, I would request you to go through the rest of post.

I have always thought -ve terminal is simply taken as the ground because conventional current flows towards this terminal.

In 'actuality' electrons flows from -v terminal toward +ve terminal. I could get 0V to 30V when I have leads connected to +ve and -ve terminals. But I could also get the same range of voltage, 0V to 30V, when I have one lead connected to the +ve and the other one to the ground. Is then the ground also a '-ve' terminal because there should be something which is pumping electrons into +ve terminal?

And I was also able to set the current supply as constant current source following the instructions of Averagesupernova.

Many thanks for your help.

Cheers

 

[sophiecentaur]

Bringing electrons into this is a total red herring and doesn't help in any way. It's the equivalent of writing half of each post in French and half of it in English and expecting that it would help to make things clearer. We all agree (?) that electrons flow against the 'conventional current'. This will always be the case and I assume that you are not introducing it in a hope of showing some inconsistency(?). So please just talk in normal terms of V and I, resistance and PD etc..

There is not necessarily a reason for using the negative terminal as an Earth / Ground except that it is a very mild sort of 'convention'. The choice of ground connection is of no consequence to the internal workings of a circuit but it is relevant to how you connect between circuits. The 'negative earth' convention is usually adopted if you want to pass DC signals from one module to another if each module has a 'single sided' power supply. All voltages in a 'positive supply' circuit will be above ground and all voltages ing a 'negative supply' circuit will be below ground: not a convenient situation for connecting signals. For battery operated equipment, a single battery is usually the cheapest option and that dictates using a convention - if you want to pass DC signals in a straightforward way.

Hum and interference can be embarrassing without using some grounding system and often using an oscilloscope (and there is no option, using many other RF measuring devices) dictates using a grounded unbalanced signal connection. It is possible, on some 'scopes, to decouple the outer of a probe cable from ground but you can't rely on it being possible. None of this is magic- it's just pragmatic.

 

[vk6kro]

And Jiggy-Ninja, the power supply has 2 prong plug

In my country, this would mean that the case of the instrument was not grounded and that it wouldn't matter if you connected the outputs to the ground terminal or not.

Where are you?

 

[sophiecentaur]

And Jiggy-Ninja, the power supply has 2 prong plug

In my country, this would mean that the case of the instrument was not grounded and that it wouldn't matter if you connected the outputs to the ground terminal or not.

Where are you?

I am now confused. Are we supposed to be discussing a DC Power Supply problem or are we discussing the Mains Supply to a House?