[UPDATED] How to overcome the voltage drop of a DC circuit down a long wire.

Thread Starter

-Ty-

Joined Feb 5, 2017
83
Hey all,

[Edited to include extra information]

I'm working on a project where I'm making some LED light panels for photography. The large panels make use of TWO 5050 white LED strips, equaling a 12.37A load at 12VDC.

I'm using two brandless LED power supplies, which output 12.25V on average. THESE POWER SUPPLIES CANNOT BE CHANGED. I've spent over $130 on them, as per the recommendation of other forum users in the AAC forums. They are international shipments and can't be returned. The power supplies are here to stay.

Because these are brandless ebay parts, no real datasheets are available for either the power supplies, or the LED strips.

The tricky thing is that the power supplies have to lie on the ground, with a wire reaching up the tripods that will be holding the panels. The power supplies are far too heavy to be mounted to the panels directly. This means a wire will have to supply 12VDC at 12A a fairly considerable distance: a MINIMUM of 11 feet (to be able to reach the panel when the tripod is fully extended), to a maximum of 20 feet (for extra photographic convenience.)

Using a simple online calculator, I've calculated that using an 18AWG cable that's 20ft long, under a 12A load, I can expect a 4.83 V DROP at the load!?! Even with a 14AWG cable (which I can't find at the lengths I need) will still result in a 2.0V drop.

I'd be losing a third of my power... That won't do at all, so what's a possible solution?

[Redacted]

Discussion in the thread has revolved around either using a heavy-gauge wire, like a 10/4, or using a DC-DC boost converter to up the voltage that's being sent down the line. I'm leaning towards the thicker cable route.

NEW INFO:

Now that I've gotten one of the panels fully soldered and working, I've been able to take some direct measurements of the working system:

Power Supply (200W) Output voltage with no load, at source: 12.20V
Power Supply output voltage when connected and powering the full 12.37A load, AT SOURCE (<1ft wire): 11.98V
Power Supply output voltage at end of LED array, wired in parallel: 11.86V
Current through panel at full brightness: 12.37A (Might rise as LEDs heat up, but couldnt tell. My multimeter, rated for 20A current testing, was beeping at me so i decided to call it off after about 10 seconds.)

Thanks!
-Ty
 
Last edited:

bertus

Joined Apr 5, 2008
21,258
Hello,

How far are the led panels apart?
Could you go with the mains near the ledpanels and have the led driver near the panels?
The current of the mains is way lower, so less voltage drop.

Bertus
 

Thread Starter

-Ty-

Joined Feb 5, 2017
83
Hello,

How far are the led panels apart?
Could you go with the mains near the ledpanels and have the led driver near the panels?
The current of the mains is way lower, so less voltage drop.

Bertus
Unfortunately, the LED power supplies are far, far too heavy to mount on the panels. The entire assembly would topple under its own weight, when fully extended. The tripods that hold the panels can reach a maximum of 10ft, so I need at least a 10ft segment of wire between the power supply output and the panels, so that the power supply can sit on the ground.
 

Thread Starter

-Ty-

Joined Feb 5, 2017
83
Use copper wire. Use a current source, not a voltage source for LEDs.
Can't, [Redacted], the power supplies are already bought, and are only available in the form i need as constant-voltage supplies.
 
Last edited:

Thread Starter

-Ty-

Joined Feb 5, 2017
83
You could double up the supply wires (or triple up) to reduce the drop by dividing the current between multiple wires.

Hmm, an interesting idea. THIS power supply, which feeds the 12A load, actually comes with three outputs.... i could buddy them up at the source, but I would then need a six-conductor wire at a large gauge to reach the load, and I have never see such a cable. THIS smaller supply, though, which feeds a 6A load, only has one output wire.
 

Thread Starter

-Ty-

Joined Feb 5, 2017
83
Then buy an adjustable DC supply.
Again, can't. These ones are already bought, and apart from the output voltage, fit all of my other requirements. I need to work with what I have now.

I don't mean to be curt, but simply throwing out what I have and starting from scratch, while it would work, isn't exactly the kind of "solution" I'm looking for.
 

Thread Starter

-Ty-

Joined Feb 5, 2017
83
What do the three outputs do?
Are they all connected together?
I assume internally, there aren't separate power delivery rails, but instead, all three output wires are connected to the same rail, and it's simply providing three output wires for the convenience of being able to power three separate circuits.

I could buddy them up so there are three +'ve output wires and three -'ve output wires, but then I would need a large-gauge 6-conductor wire to get everything to the panel, wouldn't I?
 

Thread Starter

-Ty-

Joined Feb 5, 2017
83
So the only thing you can buy is a boost converter?
Yes.
As long as the extra cost and the wiring it into you present setup is not a problem.

Well, I've spent about $132 on the four power supplies I currently have, and I'm unable to return them since they're international shipments. If i were to buy new power supplies, I would be forking out another 150 or so...

On the other hand, DC-DC boost converters can be had for around 10-20$ each. Granted, I would need four, bringing me to 40-80 bucks, but still. I can't think of any other options that are cost-effective.
 

Thread Starter

-Ty-

Joined Feb 5, 2017
83
Good high current power supplies have +SENSE and -SENSE inputs.
You run two wires from the load back to the +SENSE and -SENSE inputs.
Oh how i wish my supplies had that kind of functionality :(

Unfortunately, mine are static 12.25V outputs, no sense inputs.
 
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