Great Q&A !! Thanks for the shout out !! I totally respect the amount of work it takes to make one of these videos - and your discussion of the work details in this session increased that respect tremendously !!
Great content James! I believe UA-cam is smart enough to recognize video times and create links if you just include them in the video description/comment. 00:39 Why does AC Change direction? 03:17 What do home appliances run on? 06:44 Is analog or digital more accurate? 08:36 When to use pull-downs? 11:16 Comment on LM7805 part number. 13:24 What diode to use for fly back? 16:23 Do I draw my own animations? 18:51 What does "AddOhmns" mean? PS: I thought I spent a ton of time on my videos, but I think you spent even more! Thanks!
Hello JL, I think I asked you about this a while back... I add a low value ceramic cap to the trace side of the PCB after _replacing_ a bad, high ESR cap. Here's a video that clarifies this important point! ua-cam.com/video/WytU5uj78-4/v-deo.html P.S. Your content is top notch and the A/V & lighting are all great!
There are certain cases in the industry where pull ups are important over pull downs. Imagine an "emergency stop" button which disactivates that skull crushing machine. If you push the button, the signal turns off, and the machine stops. OR if some current turns off, OR if you pull the cord to the button altogether. It's just a security mechanism to make sure that, if it is uncertain what might happen, it's better to make sure and turn off the skull crushing machine. AKA if in doubt, don't kill
AC vs DC: "There were several technical factors that drove the adoption of alternating-current over direct-current. The direct-current system generated and distributed electrical power at the same voltage as used by the customer's lamps and motors. This required the use of large, costly distribution wires and forced generating plants to be near the loads. With the development of a practical transformer, alternating-current power could be sent long distances over relatively small wires at a conveniently high voltage, then reduced in voltage to that used by a customer. Alternating-current generating stations could be larger, more efficient, and the distribution wires were relatively less costly." --Wikipedia-- in short AC is much cheaper to distribute than DC
You are so cool! And I appreciate you!! Keep teaching us!! And you are smarter then I am :) Some people would say I set the smart bar low and others would say I set the bar high.
what is the diffrerence betwen constant current source and current mirrors? if both of them provide constant current, what are the advantages and disadvantages?
Very interesting. I got some MOSFETs and the logic gates I built seem to work with the inverted CMOS style. But they drained the 9V battery so quickly that I couldn't complete the tests (after the inverted CMOS gate, I made a normal CMOS gate to remove any voltage drop cascade).
Thank you for making these videos. I have learned a lot watching them. Congratulations too on doing all of that yourself; I do video editing a too and I know how much time you can put sometimes on projects that may seem basic for some people. Keep up the good work !
For LEDs, it was covered on "LEDs and Current Limiting Resistors": ua-cam.com/users/edit?o=U&video_id=81zNcctopBI. For other uses, the math is still the same. Use the voltage drop of the device in series with the resistor and a bit of ohm's law (like shown in that video.)
+Tommy Nolips yes. It is common to drop the unit and only leave the prefix. n for nano. k for kilo, u for micro. Have to be careful with m. Lowercase should mean milli and uppercase should mean Mega. But not always the case. If it’s a cap it’s farad, if it’s a resistor resistance, and heneries for inductors. Sometimes on caps no unit might mean pico. Bad convention in my book, but it happens.
+00Skyfox I still need to glue him together. After a lot of fine tuning, it was my first major print. And it turned out great. (Actually is a gift for a friend.)
The use of AC for power distribution is not just a matter of history. The DC transmission systems of the time was useless for this purpose. The amount of energy wasted would have been enormous. AC was chosen because back in the day it was far more efficient when they wanted to distribute power between nearby houses etc. AC was the only viable efficient low cost option for household use.
+Tech Tins "It's more than history" and then you proceed to explain the historic reasons. You even end with "back in the day." Another phrase for "history." But thanks anyway.
Yes that was a little long winded I agree (I have cut it down). The point I was trying to make was that the choice of AC over DC was for very good commercial reasons, it was not an arbitrary choice which was how I interpreted your presentation. Which was prompted due to your description here, quote "Its not entirely because one is better than the other. It's just what was picked a very long time ago" But it was not just picked, it was because AC was far more efficient (hence better) than DC. But, I see what you were trying to convey now, having re-watched it. But it may well confuse others as it did me, who already know why AC was the far better choice.
I'm into wildlife. I'm putting together an underground camera system where the recorder and battery will be housed in a water proof box underground, and the small lens will be above ground. The recorder will accept a USB charge/plug in while functioning. So I figure, if I made a power supply which would be a large battery? The unit will run a lot longer than if it were just running on the batteries in the camera. So, I need a USB connection to from a large battery like a scooter battery 11.1 volt to a USB power, which I guess would be a 5v? Anybody who can help me would be greatly appreciated!!
That's not true. It is exactly the opposite. Most newly built high voltage line transmits DC because of losses in the AC. en.wikipedia.org/wiki/High-voltage_direct_current
DC is actually a better transmission medium than AC. The only reason that AC was used is that up until the 80s, thyristors that were used to step DC up to very high transmission voltage cost too much compared to AC transformers. But today there is no reason not to use DC. You already know the math, DC is always less lossy than AC because AC impedance is DC resistance plus reactance at given frequency. Our future transmission and home systems will be DC.
This is why I said "most countries" in my response. I'm not aware of any, but I wouldn't be surprised if a developing nation built a DC grid instead of an AC grid. As for the future, I don't see path to transition to a DC grid. The cost involved would be enormous and probably not outweigh the benefit.
AddOhms Again, the benefit would be clear in saving electricity due to absence of AC reactance. You also don't need to run new cabling. Another benefit is needing only two cables instead of three. Not to mention the absence of 60 cycle hum in our electronics, safety improvements from not charging the metal chassis with AC, etc. There are HVDC projects already, check out Wikipedia for HVDC.
It's a great theory. In practice though, the switching cost (no pun intended) is very high. I can see it happening at certain points of the infrastructure, but at the end of the day you're going to have 50/60 Hz 120/240/480 VAC coming into your house or industrial plant for a long time.
AddOhms Maintaining the AC network has the slow cost as well, but yes changing to DC would cost more than just continuing to use AC. The future is definitely with DC though.
High voltage is dangerous to transport whether it is AC or DC. So "AC is safer" is not valid. Unless you are Thomas Edison trying to disprove AC. As for transmitting longer, DC may actually be ideal. You don't have a reactive component to deal with. However, as I said in the video, the infrastructure was originally designed to carry AC and still does today. It was originally designed for AC because transformers easily allow stepping it up to very high voltage. The key to long distance is not AC or DC, but high voltage.
That is absolutely false. Many people have suffered injury from their hand being paralyzed when coming in contact with a mains wire. Voltage causes the muscles to contract whether it is DC or AC. Period. As I said, high voltage is dangerous REGARDLESS if it is AC or DC. Neither is safer than the other.
@AddOhms. I dunno - @electroboom has some tongue/foot/face/hands on experience with AC/DC voltages and he argues that human body capacitance results in higher, more painful current for Vrms = Vdc. :]
I have a bryant AC outdoor unit model 180ANA060-b outdoor unit board shows solid light that means stand by but not starting if anybody knows the problem thanks.
I really like your channel but that explanation of AC/DC was terrible. Just tell the person because if not we would have massive transformers every few suburbs and AC allows us to send current really long distances but at really high Voltage. Its not History, its that it is just not cost effective to do DC
If the common question were: "why was AC originally picked" versus the more common, "why do we use AC today" then I would have limited it to: "transformers." I picked the historic answer because, well, it's why. 60+ years ago, we only needed AC for everything in our lives. Which, in itself might be a historic reaosn. It's only been in the past 30 years that "DC" was even a real need for most (electrical) consumers. If since the 1880s DC was a "need", who knows if AC would still haven been used as the primary transmission method? Light bulbs really don't care. How soon, if not already, can an inverter be just efficient as a ferrite-core transformer?
James Lewis I think you are overlooking the power generation and distribution system. What we need in our homes is only part of the question, and even in the home, you overlooked some important items. AC works better for generation and distribution. There are some specialty sub-cases where DC is better, but they are sub-cases. In the most common situations, AC is considerably more practical to generate and distribute. The "Current Wars" historical discussion, unfortunately, tends to give the, false, impression that the choice between AC and DC distribution was largely a matter of commercial interest. It was not. Edison and the DC camp had invested in a system that was technically inferior to the AC systems that were being developed. DC lost out because, particularly in the areas of generation and distribution, it was inferior. AC works better for the most common motor applications. In a residential setting, three of the biggest power consumers are motors: 1. refrigerator/freezer 2. Furnace/AC blower(s) 3. Air conditioner (heat pump) compressor Incandescent light bulbs are AC/DC indifferent, but the much more efficient fluorescent bulbs were, until recently, dependent on AC to generate their higher operating voltages. LEDs are inherently DC, but what voltage? White LEDs operate around 3.5 volts, but they require current limiting that imposes voltage overhead. Most household lighting applications need more light than a single LED can provide, so series wired LEDs are common. But how many in series should be the standard, and what voltage should we distribute to feed them. I'll bet that won't be standardized for some time.
No, I'm not overlooking power generation and distribution. In fact, that's the argument I'm making. We have 120 years of experience, or history, generating and distributing AC power. And almost none (relatively speaking) with a DC grid. And it is unlikely the infrastructure would change anyway.
Mark Holm this is correct, AC was chosen due to the impracticality, losses and costs in DC distribution. This means that AC is actually better for generation and distribution hence why we use it.
I'm-a gonna sound like this meme i.imgur.com/DpQ9YJl.png but "ACKCHYUALLY" A 120V light bulb will work exactly the same with 120V dc as it would with 120V AC RMS. If you mean rectified AC, which is closer to 170V (not accounting for voltage loss in rectification or ripple) then you'ld be right. It would burn twice as hot almost twice as bright, and will live half the life. Reason being that 120Vac rating is the RMS rating of AC, and because it is a sinusoid, the peak voltage is actually sqrt(2) = 1.414 times higher. The bulb filament intensity is basically the same as the long term average of the product of voltage and current. If you assume that the bulb has a constant resistance (which, since the filament has thermal mass and a not-so high thermal temp-co, that is basically true over a 1/60th of a second interval) then the power dissipated is the square of the voltage, so integrate that over time, and divide that by the by the limits of the integration, and you'll be left with Root Mean Square! Coincidentally, "square, then mean, then root" approach is also used to figure out variance, it is useful to apply in a lot of places.
Your math is correct, in theory. But theory and practice aren't the same. In practice, tungsten filaments aren't perfect resistive elements. Their chemical properties affect their life. Look up "filament notching."
AddOhms Intresting! Yup, I am very familiar with practical engineering challenges, deal with them all the time in the lab and when working on things! but 5 minutes on Google, I didnt really find much supporting evidence that DC is indeed a contributing factor to premature life. It seems logical that a more stable supply of power would yield longer life, whereby tempurature fluctuations, on/off cycles, lower operating voltage (for halogen lamps) and physical vibration/shock or even high frequency operation (due to the skin effect) would have much more substantial and detrimental effects.
I think it'd be fun to setup an experiment. Run two bulbs at the same time. One powered directly from mains and another from an DC supply at the same, effective, voltage. See which dies first and by what (if any) margin. Might be interesting to see the difference from a 12V and a 120V rated bulb.
For statistical purposes, you'd probably want at least 10 or 100 or so, half running on 120Vdc, and the other half on 120V RMS AC. I don't know of any regulator that can generate that high a voltage at many amps required, that would be a challenge! I have seen many people run incandescent lamps off several lithium batteries (particularly aVe, PhotonicInduction, and a few others)
This becomes more complicated as I think about it. Found a Linear Tech Part last night (can't find it again now) that can output up to 120 VDC at 500 mA. (Not sure if the passives are available, but at least the switcher is.) So 40 or 60 W bulb at 120 VDC would do the trick. Since their rated lifetime is based on an average, at least 100 of each would need to be tested. Then the average results taken. Okay, so there's that. Then is the simple fact of their life. Average is on the order of 1000 to 2000 hours. That means 1 to 2 months per test, if only testing 1 set (AC and DC) at a time. So then would it be valid to switch the bulbs on and off, and what would the ideal rate be? Put bulbs in parallel and we're back to the problem of generating 120 VDC with lots of amps. The alternative would be to step up the wall's 120 VAC and rectify it back down to approximately 120 VDC. But I'm not sure I want to build that rig. Too bad Mythbusters isn't still on. :)
Great Q&A !! Thanks for the shout out !!
I totally respect the amount of work it takes to make one of
these videos - and your discussion of the work details in this session increased
that respect tremendously !!
Great content James!
I believe UA-cam is smart enough to recognize video times and create links if you just include them in the video description/comment.
00:39 Why does AC Change direction?
03:17 What do home appliances run on?
06:44 Is analog or digital more accurate?
08:36 When to use pull-downs?
11:16 Comment on LM7805 part number.
13:24 What diode to use for fly back?
16:23 Do I draw my own animations?
18:51 What does "AddOhmns" mean?
PS: I thought I spent a ton of time on my videos, but I think you spent even more! Thanks!
Thanks. Had no idea. Wish more people did this on long QA videos!
Hari Wiguna I
Hello JL, I think I asked you about this a while back...
I add a low value ceramic cap to the trace side
of the PCB after _replacing_ a bad, high ESR cap.
Here's a video that clarifies this important point!
ua-cam.com/video/WytU5uj78-4/v-deo.html
P.S. Your content is top notch and the A/V & lighting are all great!
Thank you for all the hard work you put into these videos. I've learned a ton from you. Subscribed and excited for the next chapters.
There are certain cases in the industry where pull ups are important over pull downs. Imagine an "emergency stop" button which disactivates that skull crushing machine. If you push the button, the signal turns off, and the machine stops. OR if some current turns off, OR if you pull the cord to the button altogether. It's just a security mechanism to make sure that, if it is uncertain what might happen, it's better to make sure and turn off the skull crushing machine. AKA if in doubt, don't kill
Thank you for making these videos. I have been learning a lot from these.
I really Like the channel!! It's refreshing and is refreshing my basics in electronics! Thank you so much for your work!!
AC vs DC:
"There were several technical factors that drove the adoption of alternating-current over direct-current. The direct-current system generated and distributed electrical power at the same voltage as used by the customer's lamps and motors. This required the use of large, costly distribution wires and forced generating plants to be near the loads. With the development of a practical transformer, alternating-current power could be sent long distances over relatively small wires at a conveniently high voltage, then reduced in voltage to that used by a customer. Alternating-current generating stations could be larger, more efficient, and the distribution wires were relatively less costly."
--Wikipedia--
in short AC is much cheaper to distribute than DC
You are so cool! And I appreciate you!! Keep teaching us!! And you are smarter then I am :) Some people would say I set the smart bar low and others would say I set the bar high.
what is the diffrerence betwen constant current source and current mirrors? if both of them provide constant current, what are the advantages and disadvantages?
Great job on YT. Thanks!
the description makes these times codes 4:20 aswel for easy acces
You have a video named switching regulator but ı dont understand why we use diodes in boost converter circuits?
sorry my bad english
nice job your videos are so useful and practical thanks man
Can you explain to me why there are no inverted CMOS logic gates (N-Channel on Voltage side and P-Chanel on Ground side)?
Vgs for N-Channel needs to be positive and Vgs for P-Channel needs to be negative. That wouldn't happen if you swapped them.
Very interesting. I got some MOSFETs and the logic gates I built seem to work with the inverted CMOS style. But they drained the 9V battery so quickly that I couldn't complete the tests (after the inverted CMOS gate, I made a normal CMOS gate to remove any voltage drop cascade).
excellent videos! Appreciate your efforts! Keep up the good work!
Thank you for making these videos. I have learned a lot watching them. Congratulations too on doing all of that yourself; I do video editing a too and I know how much time you can put sometimes on projects that may seem basic for some people.
Keep up the good work !
Very nice! But, what's the problem with the BRUSHLESS lol
So I have a question on current limiting resistors. I never saw anything on how to determine what value should be used. Can you elaborate?
Thanks!
For LEDs, it was covered on "LEDs and Current Limiting Resistors": ua-cam.com/users/edit?o=U&video_id=81zNcctopBI. For other uses, the math is still the same. Use the voltage drop of the device in series with the resistor and a bit of ohm's law (like shown in that video.)
Thanks. I left you a note in that video's comments.
Good Q&A video!! Congrats!!
On some diagrams, capacitors are labelled 1n, 100n, etc. What are these? nF?
+Tommy Nolips yes. It is common to drop the unit and only leave the prefix. n for nano. k for kilo, u for micro. Have to be careful with m. Lowercase should mean milli and uppercase should mean Mega. But not always the case.
If it’s a cap it’s farad, if it’s a resistor resistance, and heneries for inductors.
Sometimes on caps no unit might mean pico. Bad convention in my book, but it happens.
Thanks James .Great videos. Gez.
Great video James!
That was nice. Please do more of these videos. BTW love the tshirt :D
I was halfway through the video before I noticed the Pointy Haired Boss!
+00Skyfox I still need to glue him together. After a lot of fine tuning, it was my first major print. And it turned out great. (Actually is a gift for a friend.)
Vous faites du bon boulot
The use of AC for power distribution is not just a matter of history. The DC transmission systems of the time was useless for this purpose. The amount of energy wasted would have been enormous. AC was chosen because back in the day it was far more efficient when they wanted to distribute power between nearby houses etc. AC was the only viable efficient low cost option for household use.
+Tech Tins "It's more than history" and then you proceed to explain the historic reasons. You even end with "back in the day." Another phrase for "history."
But thanks anyway.
Yes that was a little long winded I agree (I have cut it down). The point I was trying to make was that the choice of AC over DC was for very good commercial reasons, it was not an arbitrary choice which was how I interpreted your presentation. Which was prompted due to your description here, quote
"Its not entirely because one is better than the other. It's just what was picked a very long time ago"
But it was not just picked, it was because AC was far more efficient (hence better) than DC. But, I see what you were trying to convey now, having re-watched it. But it may well confuse others as it did me, who already know why AC was the far better choice.
I'm into wildlife. I'm putting together an underground camera system where the recorder and battery will be housed in a water proof box underground, and the small lens will be above ground.
The recorder will accept a USB charge/plug in while functioning.
So I figure, if I made a power supply which would be a large battery? The unit will run a lot longer than if it were just running on the batteries in the camera.
So, I need a USB connection to from a large battery like a scooter battery 11.1 volt to a USB power, which I guess would be a 5v?
Anybody who can help me would be greatly appreciated!!
Re: the name Addohms. I thought it was a play on the name "Adams" family!!!!
Let me correct you: actually AC wired transition loses are less than DC
That's not true. It is exactly the opposite. Most newly built high voltage line transmits DC because of losses in the AC.
en.wikipedia.org/wiki/High-voltage_direct_current
What are you correcting? Actually, I never said anything about losses.
Indeed. Ye olde skin effect.
DC is actually a better transmission medium than AC. The only reason that AC was used is that up until the 80s, thyristors that were used to step DC up to very high transmission voltage cost too much compared to AC transformers. But today there is no reason not to use DC. You already know the math, DC is always less lossy than AC because AC impedance is DC resistance plus reactance at given frequency. Our future transmission and home systems will be DC.
This is why I said "most countries" in my response. I'm not aware of any, but I wouldn't be surprised if a developing nation built a DC grid instead of an AC grid.
As for the future, I don't see path to transition to a DC grid. The cost involved would be enormous and probably not outweigh the benefit.
AddOhms Again, the benefit would be clear in saving electricity due to absence of AC reactance. You also don't need to run new cabling. Another benefit is needing only two cables instead of three. Not to mention the absence of 60 cycle hum in our electronics, safety improvements from not charging the metal chassis with AC, etc. There are HVDC projects already, check out Wikipedia for HVDC.
It's a great theory. In practice though, the switching cost (no pun intended) is very high.
I can see it happening at certain points of the infrastructure, but at the end of the day you're going to have 50/60 Hz 120/240/480 VAC coming into your house or industrial plant for a long time.
AddOhms Maintaining the AC network has the slow cost as well, but yes changing to DC would cost more than just continuing to use AC. The future is definitely with DC though.
AC is safer and easier to transfer on longueur distance than DC
High voltage is dangerous to transport whether it is AC or DC. So "AC is safer" is not valid. Unless you are Thomas Edison trying to disprove AC.
As for transmitting longer, DC may actually be ideal. You don't have a reactive component to deal with.
However, as I said in the video, the infrastructure was originally designed to carry AC and still does today. It was originally designed for AC because transformers easily allow stepping it up to very high voltage. The key to long distance is not AC or DC, but high voltage.
AddOhms AC is safer because if you touch a wire on AC current will be pushed but if DC your muscles will contract then you will stuck then die .
That is absolutely false. Many people have suffered injury from their hand being paralyzed when coming in contact with a mains wire.
Voltage causes the muscles to contract whether it is DC or AC. Period.
As I said, high voltage is dangerous REGARDLESS if it is AC or DC. Neither is safer than the other.
AddOhms i'm just trolling . i know . take care ;)
@AddOhms. I dunno - @electroboom has some tongue/foot/face/hands on experience with AC/DC voltages and he argues that human body capacitance results in higher, more painful current for Vrms = Vdc. :]
I have a bryant AC outdoor unit model 180ANA060-b outdoor unit board shows solid light that means stand by but not starting if anybody knows the problem thanks.
I really like your channel but that explanation of AC/DC was terrible. Just tell the person because if not we would have massive transformers every few suburbs and AC allows us to send current really long distances but at really high Voltage. Its not History, its that it is just not cost effective to do DC
If the common question were: "why was AC originally picked" versus the more common, "why do we use AC today" then I would have limited it to: "transformers."
I picked the historic answer because, well, it's why. 60+ years ago, we only needed AC for everything in our lives. Which, in itself might be a historic reaosn. It's only been in the past 30 years that "DC" was even a real need for most (electrical) consumers.
If since the 1880s DC was a "need", who knows if AC would still haven been used as the primary transmission method? Light bulbs really don't care.
How soon, if not already, can an inverter be just efficient as a ferrite-core transformer?
yeah good point, I can see where you were coming from then.
James Lewis I think you are overlooking the power generation and distribution system. What we need in our homes is only part of the question, and even in the home, you overlooked some important items.
AC works better for generation and distribution. There are some specialty sub-cases where DC is better, but they are sub-cases. In the most common situations, AC is considerably more practical to generate and distribute. The "Current Wars" historical discussion, unfortunately, tends to give the, false, impression that the choice between AC and DC distribution was largely a matter of commercial interest. It was not. Edison and the DC camp had invested in a system that was technically inferior to the AC systems that were being developed. DC lost out because, particularly in the areas of generation and distribution, it was inferior.
AC works better for the most common motor applications. In a residential setting, three of the biggest power consumers are motors: 1. refrigerator/freezer 2. Furnace/AC blower(s) 3. Air conditioner (heat pump) compressor
Incandescent light bulbs are AC/DC indifferent, but the much more efficient fluorescent bulbs were, until recently, dependent on AC to generate their higher operating voltages.
LEDs are inherently DC, but what voltage? White LEDs operate around 3.5 volts, but they require current limiting that imposes voltage overhead. Most household lighting applications need more light than a single LED can provide, so series wired LEDs are common. But how many in series should be the standard, and what voltage should we distribute to feed them. I'll bet that won't be standardized for some time.
No, I'm not overlooking power generation and distribution. In fact, that's the argument I'm making. We have 120 years of experience, or history, generating and distributing AC power. And almost none (relatively speaking) with a DC grid.
And it is unlikely the infrastructure would change anyway.
Mark Holm this is correct, AC was chosen due to the impracticality, losses and costs in DC distribution. This means that AC is actually better for generation and distribution hence why we use it.
I'm-a gonna sound like this meme i.imgur.com/DpQ9YJl.png
but "ACKCHYUALLY" A 120V light bulb will work exactly the same with 120V dc as it would with 120V AC RMS. If you mean rectified AC, which is closer to 170V (not accounting for voltage loss in rectification or ripple) then you'ld be right. It would burn twice as hot almost twice as bright, and will live half the life.
Reason being that 120Vac rating is the RMS rating of AC, and because it is a sinusoid, the peak voltage is actually sqrt(2) = 1.414 times higher. The bulb filament intensity is basically the same as the long term average of the product of voltage and current. If you assume that the bulb has a constant resistance (which, since the filament has thermal mass and a not-so high thermal temp-co, that is basically true over a 1/60th of a second interval) then the power dissipated is the square of the voltage, so integrate that over time, and divide that by the by the limits of the integration, and you'll be left with Root Mean Square!
Coincidentally, "square, then mean, then root" approach is also used to figure out variance, it is useful to apply in a lot of places.
Your math is correct, in theory. But theory and practice aren't the same. In practice, tungsten filaments aren't perfect resistive elements. Their chemical properties affect their life. Look up "filament notching."
AddOhms Intresting! Yup, I am very familiar with practical engineering challenges, deal with them all the time in the lab and when working on things! but 5 minutes on Google, I didnt really find much supporting evidence that DC is indeed a contributing factor to premature life. It seems logical that a more stable supply of power would yield longer life, whereby tempurature fluctuations, on/off cycles, lower operating voltage (for halogen lamps) and physical vibration/shock or even high frequency operation (due to the skin effect) would have much more substantial and detrimental effects.
I think it'd be fun to setup an experiment. Run two bulbs at the same time. One powered directly from mains and another from an DC supply at the same, effective, voltage. See which dies first and by what (if any) margin.
Might be interesting to see the difference from a 12V and a 120V rated bulb.
For statistical purposes, you'd probably want at least 10 or 100 or so, half running on 120Vdc, and the other half on 120V RMS AC. I don't know of any regulator that can generate that high a voltage at many amps required, that would be a challenge! I have seen many people run incandescent lamps off several lithium batteries (particularly aVe, PhotonicInduction, and a few others)
This becomes more complicated as I think about it.
Found a Linear Tech Part last night (can't find it again now) that can output up to 120 VDC at 500 mA. (Not sure if the passives are available, but at least the switcher is.) So 40 or 60 W bulb at 120 VDC would do the trick.
Since their rated lifetime is based on an average, at least 100 of each would need to be tested. Then the average results taken. Okay, so there's that.
Then is the simple fact of their life. Average is on the order of 1000 to 2000 hours. That means 1 to 2 months per test, if only testing 1 set (AC and DC) at a time. So then would it be valid to switch the bulbs on and off, and what would the ideal rate be?
Put bulbs in parallel and we're back to the problem of generating 120 VDC with lots of amps.
The alternative would be to step up the wall's 120 VAC and rectify it back down to approximately 120 VDC. But I'm not sure I want to build that rig.
Too bad Mythbusters isn't still on. :)
For the first answer, I thought that AC was more efficient for carrying over wires than DC that produce more heat, no?
Common misconception. It’s because it is easier to step AC up and down to high/low voltage. AC RMS power losses are the same as DC power losses.