Voltage stabilization

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hillbilly1

Senior Member
Location
North Georgia mountains
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Owner/electrical contractor
One of my old coworkers called today, they are having issues with excessive voltage drop for a parking lot camera system. The poles are 277, but because of too small of wire, the end poles are at 237 volts! Lights are multi volt LED, so they don’t care, but the transformer at each pole feeding the cameras drops to 103 volts. Lots of buried j-boxes, so pulling in the correct wire is not a good option. Buck/boost transformers are not a good option either, because with the lights (individually photocell controlled now) off, voltage would be too high. Searched for something electronic like multi volt LED drivers do, but haven’t found anything usable yet. Don’t know the actual load yet, but shouldn’t be much. Each control cabinet has 12 volt and 48 volt power supplies, and to keep from violating the UL listed cabinet, don’t really want to do away with their power supplies. Surely somebody makes a converter that will regulate the voltage automatically.
 
zbang said:
Simply boosting what goes into the 12/48v sources might be the ticket (most of those are rated for 120-250v, give or take, so feeding one 175v won't be a problem).
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I am having him check on that with the camera vendor, I thought so too, but they seem to be having issues with the low voltage, so they may be the old fashion magnetic converters.
 
Agree with @zbang first step is to find out the rated power input range of the existing DC power supplies.

You are absolutely correct, in general a boost transformer is a bad idea for voltage drop problems, because when the load changes the voltage also changes, and could become excessive. However if the DC power supplies have a sufficient voltage range, then boosting would be fine.

If they are rated for the higher voltage, you might replace the existing 277:120V transformers with 277:240V transformers, rather than adding boost transformers to the existing transformers. Hell the existing transformers might have dual voltage secondary windings, and you just need to reconnect for 240V.

Voltage regulating transformers are available, however they are hefty and expensive. I'd replace the DC supplies before going down that route. (You mention not wanting to replace the supplies for listing reasons, but bringing in a regulating transformer would be a huge hassle.)

-Jon
 
If it wasn’t for the listed control panel, I wouldn’t have as much concern over changing the power supplies. That particular customer he is doing that for is real picky, it must have been a DC they had taken over. Can’t believe the engineer had #10 specified for that distance with about 12 heads per circuit, unless it was a design/build, and the electrical contractor screwed up.
 
I get the concern about changing the power supplies.

If the supplies require 120V input, and their voltage range is tight, then here is an example of a 'constant voltage transformer'; there are similar devices available for higher or lower power levels and other voltages. As you can see from the prices and size...if you can avoid them you probably want to.


Here is a link to a how these devices work. Unfortunately the company in this link is out of business:

What is a Constant Voltage Transformer - an introduction to the perfect sine wave

What is a Constant Voltage Transformer - an introduction to the perfect sine wave
www.aelgroup.co.uk www.aelgroup.co.uk

Hopefully the existing power supplies work over a wide input voltage range, and the only thing you will need to do is change the step down transformers to work in the required input voltage range.

-Jon
 
Having a senior moment here, but those voltage regulating transformers with an L-C circuit. We talked about them a few months ago in regards to a battery charger
 
winnie said:
If the supplies require 120V input, and their voltage range is tight, then here is an example of a 'constant voltage transformer'; there are similar devices available for higher or lower power levels and other voltages. As you can see from the prices and size...if you can avoid them you probably want to.
...
Hopefully the existing power supplies work over a wide input voltage range, and the only thing you will need to do is change the step down transformers to work in the required input voltage range.
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Another disadvantage of ferroresonant transformers in the OP's situation is that they have relatively poor efficiencies, which is going to add some more load current.
 
Look, we all know that the right answer is to rip everything out and install properly sized wire. The OP explained why that isn't a good option, but once the price of other options is known it might become more feasible.

The next option is to somehow get the load to tolerate the excessive input voltage variation.

If the existing DC power supplies can tolerate a large input voltage variation, then it is a simple matter to use boost transformers or change the existing 277:120V transformers to get the supply voltage range into something the existing DC supplies can work with.

If the existing DC power supplies require a tight voltage range on the input, then the choice is replacing those supplies or regulating the AC input. The OP has stated that they don't want to change the existing DC supplies for listing reasons.

I personally would not have a problem swapping DC supplies but don't know the totality of constraints involved.

The final option is simply replacing the entire camera system, which might be cheaper that installing constant voltage transformers.
 
winnie said:
Look, we all know that the right answer is to rip everything out and install properly sized wire. The OP explained why that isn't a good option, but once the price of other options is known it might become more feasible.

The next option is to somehow get the load to tolerate the excessive input voltage variation.

If the existing DC power supplies can tolerate a large input voltage variation, then it is a simple matter to use boost transformers or change the existing 277:120V transformers to get the supply voltage range into something the existing DC supplies can work with.

If the existing DC power supplies require a tight voltage range on the input, then the choice is replacing those supplies or regulating the AC input. The OP has stated that they don't want to change the existing DC supplies for listing reasons.

I personally would not have a problem swapping DC supplies but don't know the totality of constraints involved.

The final option is simply replacing the entire camera system, which might be cheaper that installing constant voltage transformers.
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That’s what I told him, it would be better to install the correct wire, but he seemed to indicate it would be very difficult. I think they quoted it wrong, and that’s why they are him-hawing around. The customer they are doing it for has plenty of money. Not my employer, so all I can do is give suggestions!
 
Is this just on a single circuit? 40 volts drop on a 277 V circuit seems pretty excessive, especially since the lighting is LED. Have you measured the current? Perhaps a high-resistance connection somewhere or bad breaker?
 
David Castor said:
Is this just on a single circuit? 40 volts drop on a 277 V circuit seems pretty excessive, especially since the lighting is LED. Have you measured the current? Perhaps a high-resistance connection somewhere or bad breaker?
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From the number of heads he said was there, probably around a 15 amp load. He said it was a long way back to the panel, and since it’s a distribution center, it probably is. #10 wire all the way. Haven’t heard back from him to see what they decided.
 
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