• Get involved.
    We want your input!
    Apply for Membership and join the conversations about everything related to broadcasting.

    After we receive your registration, a moderator will review it. After your registration is approved, you will be permitted to post.
    If you use a disposable or false email address, your registration will be rejected.

    After your membership is approved, please take a minute to tell us a little bit about yourself.
    https://www.radiodiscussions.com/forums/introduce-yourself.1088/

    Thanks in advance and have fun!
    RadioDiscussions Administrators

D.I.Y. Building AC Power Monitor

S

spinjector

I'd like to create a network of AC voltage monitors for our transmitter building, so I know when the main/backup utility feed is up/down. The same is true for the main/backup transfer switch, and the transfer switches for the generator, too.

I need a little advice, since the building is wired for 480 volts.

Essentially what I'm thinking is a simple unregulated DC supply with a very small capacitor, sized just to filter the AC & noise into DC and not really supply much in the way of current.

1) How do I select the proper winding/current/dielectric for the transformer? I'm assuming just a generic AC power transformer from Digikey will do.
2) Are the MOV really necessary? If so what value? I want to protect the Burk of course.
3) Is this even advisable on a 480-volt 3-phase system? Or am I just tempting the creation of metal vapors and smoke?

Thanks.

.............Fuse.....Xformer.........Bridge
277v Leg >ÄÄÄÄ(~)ÄÄÂÄÄÄÄ8 8ÄÄÄÄÄÄÄÂÄÄÄÄÄ¿..ÚÄÄÄÂÄÄÄÄ¿
...................³....8 8.......³...ÚÄÅÄÄÙ.+.³....ÀÄ>
..............MOV1.Ø....8 8..MOV2.Ø...À<X>Ä¿...Ø C1.....To Burk ARC-16 Input
...................³....8 8.......³.....³..³.-.³....ÚÄ>
Neutral..>ÄÄÄÄÄÄÄÄÄÁÄÄÄÄ8 8ÄÄÄÄÄÄÄÁÄÄÄÄÄÙ..ÀÄÄÄÁÄÄÄÄÙ
 
Sorry - I forgot to say I need to select the transformer to scale the AC into the range of the Burk analog input.

I also need to account for the RMS (?) of the change from AC to DC.

The Burk input voltage range escapes me at the moment, and I don't have the math to figure all this out on paper.

I could just fiddle until I find the right transformer, but at 277 volts this is probably inadvisable.
 
spinjector said:
Sorry - I forgot to say I need to select the transformer to scale the AC into the range of the Burk analog input.
I also need to account for the RMS (?) of the change from AC to DC.
The Burk input voltage range escapes me at the moment, and I don't have the math to figure all this out on paper.
I could just fiddle until I find the right transformer, but at 277 volts this is probably inadvisable.
Click to expand...

Once you've transformed the AC to a more reasonable low voltage (and, importantly, isolated it), rectified and filtered it, you can use a simple pot as a voltage divider to set the final DC sample level to be (roughly) in the sweet spot of the Burk's A/D input. Then use an RMS-scaled DVM on the primary as a reference to calibrate the Burk to give the same reading, and all should track very nicely.

This way you don't have to depend upon the AC output of the transformer to be some exact figure.

In addition to an MOV on the AC, I would put an appropriate zener across the Burk's sample input, too, to prevent overload.

Kind Regards,
David
 
Watch out for that 480 volt AC.
I've always heard, "110 and 220 will hurt you, and so will high voltage. But 480 is what kills."

Use good isolation.
 
For 480 volts it is 277 volts to neutral for each phase. I have designed a circuit and PC board for this using small 240 volt input transformers and associated circuitry to provide a 10 V maximum DC sample to GSC3000's. I can send you a parts list and diagram (and sell you the blank circuit board) if interested. Legal disclaimer - this device is not UL listed (but the transformers used are).
 
At my transmitter site I have auxillary contacts on the generator transfer switch wired to a status indicator on the Burk to indicate when on generator. When calling the power company to report the outage they always ask if "all the power is out or only part of your power is out?" To remotely answer that question, I wired a 120Vac (we have 120/208 three phase) from each phase to neutral. These are wired on the utility side of the transfer switch. The NC contacts of each relay are wired to status indicators on the Burk. Usually we only have one phase out and I can tell them which one. Due to lack of metering inputs, I only monitor voltage of one phase with a old unregulated cassette wall power supply plugged into the rack power strip. Its 6 vdc output is wired to the Burk. May not be 100% accrate but seems to be vary close.
 
Doctor_Technical said:
Or... just buy a handful of these cheap critters from your local a/c supply house: http://www.icmcontrols.com/products/product.php?prod_pk=50
Click to expand...
Thanks Doc. Those are cool. I might use one to automate the transfer switch between the Main & Backup power company feeds. The control panel we have on it now is the manual version. $30 for that module is prolly a lot cheaper than a new automatic control panel.

But in the end I do want to actually monitor the voltages, read each leg individually, and log them.
 
David Reaves said:
Once you've transformed the AC to a more reasonable low voltage (and, importantly, isolated it), rectified and filtered it, you can use a simple pot as a voltage divider to set the final DC sample level to be (roughly) in the sweet spot of the Burk's A/D input. Then use an RMS-scaled DVM on the primary as a reference to calibrate the Burk to give the same reading, and all should track very nicely.

In addition to an MOV on the AC, I would put an appropriate zener across the Burk's sample input, too, to prevent overload.
Click to expand...
Dave,

Will-do on the voltage divider and Zener-bypass. Thanks for the input.

But - could you clarify the isolation? The 277v to 12v transformer would perform this function, correct?

And what is an RMS-scaling? I have a nice digital meter that does a lot, even frequency, capacitance, and a couple other functions.
 
gsmith said:
Due to lack of metering inputs, I only monitor voltage of one phase with a old unregulated cassette wall power supply plugged into the rack power strip. Its 6 vdc output is wired to the Burk. May not be 100% accrate but seems to be vary close.
Click to expand...
Yup. That's exactly what I had in mind with my little unregulated circuit project here, but I'd like to monitor all three legs.
 
gsmith said:
At my transmitter site I have auxillary contacts on the generator transfer switch wired to a status indicator on the Burk to indicate when on generator. When calling the power company to report the outage they always ask if "all the power is out or only part of your power is out?" To remotely answer that question, I wired a 120Vac (we have 120/208 three phase) from each phase to neutral. These are wired on the utility side of the transfer switch. The NC contacts of each relay are wired to status indicators on the Burk. Usually we only have one phase out and I can tell them which one. Due to lack of metering inputs, I only monitor voltage of one phase with a old unregulated cassette wall power supply plugged into the rack power strip. Its 6 vdc output is wired to the Burk. May not be 100% accrate but seems to be vary close.
Click to expand...

Here's where I remind folks. I have 2 boxes of unused wall wart power supplies I can't throw out. Most are 12-18v DC and some are 6-9v DC. One multi AC strip, 3 wallwarts, inputs for 3 ph to status on the Burk, Sine, or other such unit.
 
ChiefEngineer said:
Here's where I remind folks. I have 2 boxes of unused wall wart power supplies I can't throw out. Most are 12-18v DC and some are 6-9v DC. One multi AC strip, 3 wallwarts, inputs for 3 ph to status on the Burk, Sine, or other such unit.
Click to expand...
I'd be happy to do that if it weren't 480/277. =-)
 
spinjector said:
David Reaves said:
Once you've transformed the AC to a more reasonable low voltage (and, importantly, isolated it), rectified and filtered it, you can use a simple pot as a voltage divider to set the final DC sample level to be (roughly) in the sweet spot of the Burk's A/D input. Then use an RMS-scaled DVM on the primary as a reference to calibrate the Burk to give the same reading, and all should track very nicely.

In addition to an MOV on the AC, I would put an appropriate zener across the Burk's sample input, too, to prevent overload.
Click to expand...
Dave,

Will-do on the voltage divider and Zener-bypass. Thanks for the input.

But - could you clarify the isolation? The 277v to 12v transformer would perform this function, correct?

And what is an RMS-scaling? I have a nice digital meter that does a lot, even frequency, capacitance, and a couple other functions.
Click to expand...

The transformer performs two functions: one, to reduce the voltage to something a little more manageable to ultimately be sampled by the Burk, and two, to isolate the high voltage and allow the secondary to be referenced to ground or some common voltage reference, as used by the Burk.

The measurement you are interested in is the RMS voltage of the AC. Your reference can be a true-RMS voltmeter, or any voltmeter that is scaled to indicate correctly for the RMS voltage of a sine wave. Most DVMs, even cheap ones, will do one or the other. Since the voltage you are measuring will always be a sine wave (or should be!) then the cheap one will probably suffice.

Keep in mind that you do not want a regulated supply! You want the long-term variations in the voltage to come through, warts and all, to be monitored.

Transformer > rectifier > parallel smoothing capacitor > voltage divider > parallel protection zener > Burk input

Good luck!

Kind Regards,
David
 
spinjector said:
As for the dangers of 480, I keep this in mind whenever I'm within 10 feet of any of those panels:

Arc Flash Demonstration
http://www.youtube.com/watch?v=-Qq7U7tFsvQ
Click to expand...

I did not enjoy this link, nor any of its offered links as I deal with live 480 3-ph constantly.
 
Tom Wells said:
I did not enjoy this link, nor any of its offered links as I deal with live 480 3-ph constantly.
Click to expand...
I'm sorry Tom, I didn't mean for it to be unpleasant. If you work with it every day, I would have thought you'd have seen such a video in a training class of some kind. As I said, I keep that video in mind when I'm working on those panels, to keep me on my toes.
 
Status
This thread has been closed due to inactivity. You can create a new thread to discuss this topic.


Back
Top Bottom