CR4® - The Engineer's Place for News and Discussion®

 Previous in Forum: Surge Protector Selection Next in Forum: Transformer Temperature Rise in 54C Ambient
Power-User

Join Date: Jun 2008
Posts: 121

# 277VAC Output

04/23/2012 2:47 AM

I need to test a 150W device that runs on a 277vac input, but on hand what I have is only 240VAC supply. Would it be better if I ask vendor to make for me a custom made transformer with an input of 240, and output 277 OR request an autotransformer with an input of 240 and output variable up to 0 to 300VAC?

Thanks.

__________________
"Shallow men believe in luck. Strong men believe in cause and effect." -- Ralph Waldo Emerson
Interested in this topic? By joining CR4 you can "subscribe" to

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting ["brexit" - ugh] as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 27039
#1

### Re: 277v ac output

04/23/2012 3:42 AM

Either.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Power-User

Join Date: Jun 2008
Posts: 121
#2

### Re: 277v ac output

04/23/2012 6:54 AM

Thanks PW,

Since my country do not have a 277 power source to power up the device, what would be the power rating of the transformer if i need someone to manufacture it.

The transformer is to be power up a power supply that is rated as follows..

AC input = 100-277VAC/2.1A , DC Output 5A- 7.6A (adj) 22 -27V.

So based on these specifications, what would i specify for the wattage or KVA of the transformer ?

277*2.1 = 581W or 27*7.6 = 205W?

thanks

__________________
"Shallow men believe in luck. Strong men believe in cause and effect." -- Ralph Waldo Emerson
Guru

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting ["brexit" - ugh] as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 27039
#3

### Re: 277v ac output

04/23/2012 7:10 AM

Ah! If the load and the input are both as stated, then the equipment to hand is immediately suitable for use without an interposing transformer. Just plug and play (in a manner of speaking).

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Power-User

Join Date: Jun 2008
Posts: 121
#4

### Re: 277v ac output

04/23/2012 7:21 AM

Hi PW,

I do not understand what u are trying to say. We haave only 240v input lines here in our country, and i need a transformer to convert 240 to 277 in order to operate the equiptment i mentioned earlier. So what would be the rating of the transfomer ?

Iput 240 / Output 277 Power rating ??

I need to operate two equipments at one go.

I just need the power rating and how u derive it.

thanks

__________________
"Shallow men believe in luck. Strong men believe in cause and effect." -- Ralph Waldo Emerson
Guru

Join Date: Aug 2010
Location: Resting under the Major Oak
Posts: 4283
#5

### Re: 277v ac output

04/23/2012 7:40 AM

The power supply will work at any voltage between 100 to 277V and still give a 24V output at it's rated current.

A universal power supply.

__________________
The reports of my death are greatly exaggerated.
Guru

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting ["brexit" - ugh] as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 27039
#6

### Re: 277v ac output

04/23/2012 8:51 AM

It will even work at 110VAC.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Power-User

Join Date: Jun 2008
Posts: 121
#7

### Re: 277v ac output

04/23/2012 9:06 AM

Yes i understand all that .. All i want is , i want to burn in ( meaning ALT ) on the two devices, so i hve to operate them on its operating voltage, which is 277V.

I do not hve 277V AC in my country of origin. Of course i can plug and play at 240V, but i am not interested because i want to burn in at its typical operating volltage , which is 277 or even better 300V for 24 hours.

So in order to do that I need a transformer that will convert my incoming 240V to 277V, and so based on the device rating given in my first inqury, what would be the rating of the transformer? Thats all i am wanting to know. I got to hve the vendor to make it custom made for me.

Thanks

__________________
"Shallow men believe in luck. Strong men believe in cause and effect." -- Ralph Waldo Emerson
Guru

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting ["brexit" - ugh] as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 27039
#9

### Re: 277v ac output

04/23/2012 9:10 AM
__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Guru

Join Date: Oct 2008
Posts: 40516
#8

### Re: 277v ac output

04/23/2012 9:07 AM

Both the gentlemen who have responded to you are well known here as experts in this, and other fields.

I'll add a third vote to support their responses.

Power-User

Join Date: Jun 2008
Posts: 121
#10

### Re: 277v ac output

04/23/2012 9:20 AM

Of course lyn , i too agree in total with ur vote !. I hve got excellent responses from them in my earlier discussions with them on different matters.

Anyway PW, i m back at home now, and i cant exactly recall the manf. name, but the ps is from china.

But wherever the origin is, I just want to fabricate a transformer that whose output voltage is 277. I just need to know the power rating only based on the above spec that i specified in my first query.

By the way why do we need the manufacturer's name?

Thanks

__________________
"Shallow men believe in luck. Strong men believe in cause and effect." -- Ralph Waldo Emerson
Guru

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting ["brexit" - ugh] as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 27039
#11

### Re: 277v ac output

04/23/2012 10:57 AM

"Undefined we" alarm!

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Off Topic (Score 5)
Guru

Join Date: Jul 2005
Location: Stoke-on-Trent, UK
Posts: 3947
#12

### Re: 277v ac output

04/23/2012 4:18 PM

That's a transformer and rectifier you're talking about. Where does the DC come into it? You didn't mention it in the original post.

__________________
Give masochists a fair crack of the whip
Guru

Join Date: Sep 2008
Location: Where the sun sets on OZ
Posts: 1319
#35

### Re: 277v ac output

04/24/2012 6:41 AM

Is the power supply the device that you want to test?

OR do you want to build the power supply so that it will operate from 100v ac to 277v ac?

__________________
Where's the KaBoom? There should be a KaBoom!
Guru

Join Date: Sep 2008
Location: Where the sun sets on OZ
Posts: 1319
#36

### Re: 277v ac output

04/24/2012 7:02 AM

In post 34 you state that this device will be run on a line voltage of 277v, where in the world is that?

If you want to run this device where the nominal line voltage is 277v you don't need to do a burn in test, it will blow up when the line goes over the nominal voltage by 10%.

__________________
Where's the KaBoom? There should be a KaBoom!
Guru

Join Date: May 2006
Location: Placerville, CA (38° 45N, 120° 47'W)
Posts: 4717
#38

### Re: 277v ac output

04/24/2012 11:29 AM

JIMRAT 277VAC is a standard voltage here in the USA, used for halide arc lighting. It would be logical for someone to make LED replacement units that would run on the same voltage.

Here's the label of our 277V transformer:

On the other hand, to MOOMOO, According to the label specs you've given, 277V is the UPPER LIMIT for the input to your power supply. If you "burn in" the supply for 24 hours on a transformer correctly designed to put out 277V, you will almost certainly be exceeding that value at some point during those 24 hours. Even a 5% variation would put 291V on the device rated only to 277V. You will definitely void your warranty on those devices!

__________________
Teaching is a great experience, but there is no better teacher than experience.
Guru

Join Date: Oct 2008
Location: City of Roses.
Posts: 2060
#39

### Re: 277v ac output

04/24/2012 3:29 PM

Here Here!

__________________
Don't believe everything you read on the Internet!
Guru

Join Date: Sep 2008
Location: Where the sun sets on OZ
Posts: 1319
#40

### Re: 277v ac output

04/25/2012 12:02 AM

In reading the posts on this forum i have learnt that the U S of A has both 110v and 220v and now i am told also 277v. This must cause some headaches and there must be one hell of a distribution system. Do you also run three phase? At what voltage/s?

__________________
Where's the KaBoom? There should be a KaBoom!
Off Topic (Score 5)
Guru

Join Date: May 2009
Location: Richland, WA, USA
Posts: 20094
#41

### Re: 277v ac output

04/25/2012 12:23 AM

Three-phase at 208Δ/120Y, 240Δ with center tap between 2 phases, or 480Δ/277Y.

Single-phase residential 240/120 (center tapped neutral).

Some other oddballs in a few locations.

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Off Topic (Score 5)
Guru

Join Date: Sep 2008
Location: Where the sun sets on OZ
Posts: 1319
#42

### Re: 277v ac output

04/25/2012 12:36 AM

In a single phase residence with 240v and 120v are there different socket types/configurations to prevent burnout and or fires?

__________________
Where's the KaBoom? There should be a KaBoom!
Off Topic (Score 5)
Guru

Join Date: May 2009
Location: Richland, WA, USA
Posts: 20094
#44

### Re: 277v ac output

04/25/2012 10:07 AM

Yes; the plug configurations differ.

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Guru

Join Date: May 2006
Location: Placerville, CA (38° 45N, 120° 47'W)
Posts: 4717
#45

### Re: 277v ac output

04/25/2012 11:09 AM

It is interesting that you used 110 and 220V in your previous post, and used 120 and 240V in the last one. All four of those values are commonly used in ordinary talk here, as well as 117V for the residential voltage.

Tornado is absolutely correct in the standard values he provided, but even with a major (although barely adequate, sometimes not quite adequate) grid, there is variation from place to place and from time to time. When demand is high, there are greater losses in the transmission, so the actual voltage at the end user drops. I've seen our 480V line drop to 440V when a lot of air conditioners are running.

I've also seen quite a few cases where the "120V" sockets actually had 126 Volts in industrial buildings. Fortunately, most devices are designed to handle ±10% variation, so in theory anything from 108 to 132V is acceptable.

In modern US buildings, there is a single wall socket design for all "standard 120VAC" devices, but there are literally dozens of connectors intended for use at different voltages and currents, including twist-lock connectors for "heavy duty" 120V devices. Unfortunately, many of these connectors are pretty expensive, so people have a tendency to use whatever they have on hand, rather than get the correct connector. Occasionally this does lead to destroyed devices...

__________________
Teaching is a great experience, but there is no better teacher than experience.
Guru

Join Date: Sep 2008
Location: Where the sun sets on OZ
Posts: 1319
#46

### Re: 277v ac output

04/26/2012 7:52 AM

In my youth there were a few U.S. made devices in OZ, such as Bell and Howell 16mm projectors. These were plugged into a ( locally made ) transformer to bring our 240v down to 110v. So i have always "known" that the U.S. is 110v. It is only as a result of this forum that i have learnt that this is not so much of a fact as i thought. I am going to take a wild stab in the dark and suggest that most, if not all, of your power utilities are private enterprise. Here they were until very recently Government run. Also we are a young country and the first power was provided by mother England when we were still a colony. ( federation in 1901 ).

Enough of the history.

Jim

__________________
Where's the KaBoom? There should be a KaBoom!
Off Topic (Score 5)
Guru

Join Date: May 2009
Location: Richland, WA, USA
Posts: 20094
#13

### Re: 277VAC Output

04/23/2012 4:39 PM

How about a 250VA single-phase boost/buck autotransformer that includes the option of 240 x 277 volts. (This allows for a 150W load with PF as low as 0.60.)

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Guru

Join Date: Oct 2008
Location: City of Roses.
Posts: 2060
#14

### Re: 277VAC Output

04/23/2012 6:16 PM

I'm still having a hard time understanding why you must use the Max rated input voltage of the power supply, when it clearly states it will operate anywhere from 100VAC to 277VAC. It would work perfectly well at 240VAC with no transformer. (according to the information you have provided thus far)

What have I missed?

__________________
Don't believe everything you read on the Internet!
Power-User

Join Date: Jun 2008
Posts: 121
#15

### Re: 277VAC Output

04/23/2012 6:50 PM

Yes of course u can operate it at 240Vac RVZ.

The device i have is an LED parking lamp that is operated at 277V. The Power supply of the parking lamp is specfifed as follows.

The transformer is to be power up a power supply that is rated as follows..

AC input = 100-277VAC/2.1A , DC Output 5A- 7.6A (adj) 22 -27A

The Leds are operated on 24VDC. But i wanted to burn in the unit for 24 hours just to make sure i weed out any infant mortality failures.

What i want is a power transformer whose input is 240v and output 277v. But I do know know the Power rating of the transformer. I can have the transformer custom made for this application here.

Thanks

__________________
"Shallow men believe in luck. Strong men believe in cause and effect." -- Ralph Waldo Emerson
Guru

Join Date: Oct 2008
Location: City of Roses.
Posts: 2060
#16

### Re: 277VAC Output

04/23/2012 7:31 PM

I understand what it is you are asking, What I'm having trouble with is WHY?

You need to provide 24VDC to your lamp for 24 hours, correct?

The device you plan to use as a power supply has a 24VDC output, correct?

The allowable input needed for your power supply to provide 24VDC on it's output is anywhere in between 100VAC and 277VAC.

Thus the power supply you have will provide 24VDC all day long to your lamp with a 240VAC input without the need for any transformer. (as stated, you could use 110VAC if you wanted, to achieve the same result)

You do NOT need to run your power supply at it's MAX input power to achieve 24VDC on it's output. In fact 240VAC input signal is probably MORE desirable than running right on the maximum input, and possibly having a slight power spike and frying your power supply, or blowing a fuse.

LED's are very low power devices. you don't need much current at your 24VDC to operate them at full power.

Go back to what it is you really need to achieve. Forget HOW you plan to do it, focus on what it is you need to do, and listen to those who are attempting to give you advise.

__________________
Don't believe everything you read on the Internet!
Power-User

Join Date: Jun 2008
Posts: 121
#17

### Re: 277VAC Output

04/23/2012 8:41 PM

Yes, i undersand ur explanation my dear fren, and also the explanation of all others thus far. Yes I could use even the 100V input to power up the power supply module to get the 24V to operate the leds.

But if i were to stress the power suppy module at 277v, then i am also checking the input stage of the power supply module that do have components rated at 277 or higher.

Please understand that I am doing a burn in test, testing the electronics of the whole system , not only the 24v dc output stage.

I need also to stress the incoming power components as well.

Shalom..

__________________
"Shallow men believe in luck. Strong men believe in cause and effect." -- Ralph Waldo Emerson
Guru

Join Date: Sep 2007
Location: Japan
Posts: 2716
#18

### Re: 277VAC Output

04/23/2012 9:16 PM

Then buy what PWSLACK proposed in post #9 or something similar

__________________
From the Movie "The Big Lebowski" Don't pee on the carpet man!
Power-User

Join Date: Jun 2008
Posts: 121
#19

### Re: 277VAC Output

04/23/2012 9:28 PM

QUite right! But its quite expensive. I can ask a local suppler to fabricate it at a much cheaper cost!

All I want is what should be the power rating of the transfomer! Input 240 , Output 277, Power rating : KVA or Output current : 12 AMps?

Well , I will just close this subject. Thanks for all the inputs anyway.

Moomoo

__________________
"Shallow men believe in luck. Strong men believe in cause and effect." -- Ralph Waldo Emerson
Power-User

Join Date: Sep 2007
Location: Christchurch, New Zealand
Posts: 169
#21

### Re: 277VAC Output

04/23/2012 10:43 PM

Hi Moomoo,

If you really want to test your product at maximum input voltage then you should specify a 240VAC to 277VAC transformer rated to cater for 2.1A on the output side ( I.E. 277VAC side). Thus the rating shouldbe 582 watts. Although power factor is probably not going to be less than 1.0, you could allow a little leeway and assume 0.9. Thus VA rating should be 582/0.9 = 647 VA ( I.E 650 VA or next nearest size up).

Do be aware, as others have said, that when your mains supply goes above its' nominal 240 VAC, you will then be powering your UUT ( Unit under test ) with greater than 277 VAC. I.E. you may be overstressing the design and end up causing unnecessary failures!!!

Cheers,

MPM

Guru

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting ["brexit" - ugh] as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 27039
#43

### Re: 277VAC Output

04/25/2012 5:31 AM

It cannot be as expensive as the procrastination excercised within this thread....

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
4
Power-User

Join Date: Aug 2008
Location: Melbourne, Australia
Posts: 476
#20

### Re: 277VAC Output

04/23/2012 10:26 PM

When I need minor changes from normal mains I use a standard transformer with a secondary voltage and current rating that adds/subtracts the difference.

If you were to obtain a transformer with a 32 volt secondary (1 Amp would be enough), then series the secondary in phase with the 240 volt input, you would end up with 272 volts at full load. It will be closer to your 27 volts at the .6 Amp load you will be giving it.

__________________
johny451
Guru

Join Date: Jan 2008
Posts: 1756
#22

### Re: 277VAC Output

04/23/2012 10:51 PM

The idea is right for somebody, who thinks he needs 277VAC the worst way. Except, the add-on trafo needs full amperage, over 2 A, hence 2,5A and above. It appears to me, it is for a temporary desktop stress setup, with a who cares design. A breaker is recommended.

Power-User

Join Date: Aug 2008
Location: Melbourne, Australia
Posts: 476
#23

### Re: 277VAC Output

04/23/2012 11:17 PM

...sorry about the typo - 277 Volts at the 0.6 Amp load.....

__________________
johny451
Power-User

Join Date: Jun 2008
Posts: 121
#24

### Re: 277VAC Output

04/23/2012 11:31 PM

I see ur point Johny, but the power supply rating which the transformer is going to power up is rated as folows

AC input = 100-277VAC/2.1A , DC Output 5A- 7.6A (adj) 22 -27V.If

If i were to take a 240/36V,2A transformer and configure like what u have drawn up, would that be able to power up my modular power supply for at least 24 hours?

Thanks.

Regards

moomoo

__________________
"Shallow men believe in luck. Strong men believe in cause and effect." -- Ralph Waldo Emerson
Power-User

Join Date: Aug 2008
Location: Melbourne, Australia
Posts: 476
#25

### Re: 277VAC Output

04/23/2012 11:38 PM

The AC input current being a single figure is for the lowest input voltage - 100 VAC. Going by the DC output rating, about 250 VA should cover it nicely so a 1 Amp secondary rating would be sufficient - 2 Amps is fine as well.

__________________
johny451
Power-User

Join Date: Jun 2008
Posts: 121
#31

### Re: 277VAC Output

04/24/2012 3:29 AM

Thanks Johny for ur valuble inputs.

__________________
"Shallow men believe in luck. Strong men believe in cause and effect." -- Ralph Waldo Emerson
Power-User

Join Date: Dec 2007
Posts: 143
#37

### Re: 277VAC Output

04/24/2012 7:43 AM

YES...just do it-I have done this for other voltages numerous times.

Guru

Join Date: May 2006
Location: Placerville, CA (38° 45N, 120° 47'W)
Posts: 4717
#27

### Re: 277VAC Output

04/24/2012 12:31 AM

This is the buck/boost transformer that someone else mentioned earlier. Although your drawing does show boost configuration, you should have mentioned that swapping the two leads of the secondary will change it from boost to buck or vice-versa.

Many transformers do not indicate which lead of a winding is the start, so connect the two windings in series, and measure the output voltage. If it is higher than the supply voltage, you have it in boost connection; you're done. If it is lower, then it is in buck connection; reverse the two secondary leads.

I agree that 1 Amp is adequate for the job. 250 Watts or 0.25 kW.

BTW, if you can't easily find a 32V transformer, a 24-28V one would be close enough.

__________________
Teaching is a great experience, but there is no better teacher than experience.
Power-User

Join Date: Jun 2008
Posts: 121
#30

### Re: 277VAC Output

04/24/2012 3:18 AM

thank u warner, ur point noted!

__________________
"Shallow men believe in luck. Strong men believe in cause and effect." -- Ralph Waldo Emerson
Commentator

Join Date: Nov 2008
Posts: 80
#26

### Re: 277VAC Output

04/24/2012 12:05 AM

Find a multi tap ballast for a discharge light,that has taps for 240 and 277 volt at least 150 Watt, connect the line to the 240 tap and common and the load to to the 277 and common. Cap off the high voltage going to the lamp. I do this to test 347 volt fixtures using 110 line.

Anonymous Poster #1
#28

### Re: 277VAC Output

04/24/2012 3:06 AM

It is batter to purchase autotransformer of capacity 300w & 0 to 300v. it will solve

D.D.Kulkarni

Power-User

Join Date: Jun 2008
Posts: 121
#29

### Re: 277VAC Output

04/24/2012 3:16 AM

Well true!, but i want a cheaper method. Here it much cheaper to fabricate than to buy from RS!

Moomoo

__________________
"Shallow men believe in luck. Strong men believe in cause and effect." -- Ralph Waldo Emerson
Off Topic (Score 5)
Power-User

Join Date: Jun 2008
Posts: 121
#32

### Re: 277VAC Output

04/24/2012 3:32 AM

Thanks to all who participated. I hve asked my local supplier to build in the tranfomer unit.

Thanks once again.

__________________
"Shallow men believe in luck. Strong men believe in cause and effect." -- Ralph Waldo Emerson
Associate

Join Date: Sep 2010
Posts: 45
#33

### Re: 277VAC Output

04/24/2012 4:07 AM

Hi,

I think there is no need to have customer made transformer/an autotransfomer.what is important here check the frequency of your device if is compartible with utility power supply.This device, can run at this voltage(240V) without any problem.Always the device(s) designers specify the min&max voltage where the device can operate within.So, I am sure this 277V is the upper limit(max) where the device can accept operation.

Power-User

Join Date: Jun 2008
Posts: 121
#34

### Re: 277VAC Output

04/24/2012 5:16 AM

Thobias, this device is for use in a 277vac line voltage, not 250 line voltage that is used in most countries ruled by GB during days of the raj and thereafter.

__________________
"Shallow men believe in luck. Strong men believe in cause and effect." -- Ralph Waldo Emerson
Interested in this topic? By joining CR4 you can "subscribe" to