How to handle Voltage drop over 100 ft?

E

eatumup

New member
Ive got 3 singing props running 565 5v ws2811 smart bullet pixels. They are rated at 3A/50 nodes. Im running at 40% brightness.
They are the only thing running off a 300w power supply.

There is injection every 50 pixels.

At the end of the power line (approx 80ft 18awg) the voltage is 4v.

There should be plenty of power here.

Problem is that when all 3 props are going the 3rd in line shows all the signs of low voltage. It wont produce accurate colors, it even dims out. But when it lights up on its own its fine.

Any ideas what might be going on here?

Also, I have a variable 5v Meanwell power supply. Can i up the voltage to something like 5.3 volts to keep the voltage up at the end of the run? Not sure how that would effect the first set of LED's that would likely see just over 5v. The particular bullets i have don't list a voltage range like some do. Looking for thoughts on that too.
 
You could up the output voltage slightly, but check the level at the 1st pixel. Another option would be to use a higher voltage PSU then use buck converters to reduce it to 5V at strategic points.

E.g. my garden lighting distribution runs at 24v to reduce losses, but I drop it to 12v for the spotlights.

Slightly thicker cable may also help. there are online calculators for length / wire size / current / voltage drop
 
Last edited:
+1 for the 24v solution. I use 24v with 5v 3A buck converters at my prop power injection points. Since the current through the wire drops from 50A (or more) to 10A, I get away with using a 16AWG wire and I don't worry about losing 2V over the length of the wire. Also, since the current through the wire is lower, I have less heat generated by the wire, making the system safer.

On the negative side, there is a 20% loss of power at the Mains-to-24v PSU (this is normal) and another 10-15% loss at the buck converters. This means the entire system is a little less efficient. Not that big a deal considering the overall advantages but still something to consider.
 
For the record, another solution: put a power supply much closer to the prop, don't run 5V wire for 80 feet, and properly power inject the additional power supply in. Effectively, you're running 120V AC (US) for the 80 feet instead of 5V and then reducing it to 5V at the last minute. Which is very similar to running 24V DC and then bucking it down to 5V at the last minute, except you're just sticking with the 120V AC (US) you originally started with.

Of course, if your singing props are close to each other, and you mean they each have 565 pixels apiece, that's what using a smart receiver (or dumb) is all about.

To frame the problem from a different angle, if you have 565 pixels, drawing 3A per 50, then you need 33 amps. Your wire resistance needs to be down around 5V/33a = .15 ohms, and that's just for the wire alone. And you're travelling 80 feet. Our cell phones charge at 5.3V, 3A, and we don't use 80-foot USB cables. The resistance in the wire is just too high for that distance and that voltage, and it's not close. 18AWG wire is rated at .63ohms per 100 feet, and 16AWG is not that much better.
 
Thank you all for the suggestions. It sounds like my wire is too thin for that run at that voltage then. I didn't do the wire math. figured it would be fine. lesson learned.. do all the math.
For clarification, all three props combined total the 565 pixels.

The first prop is on i think about a 30 ft run from the psu. the third prop injection attachment to the main lead id say totals about 50ft from the PSU. I measured my footage at the furthest end of the injection wire which is hanging out for other props assuming i sorted this out.

So I need to get with some buck converters or find a way to get more power up on the roof.

Out of curiosity, what would be considered a safe typical over voltage for a 5v pixel? I seem to recall that generally 5v pixels are rated for up to 7volts. I cant seem to find the answer to that one.
 
Just to clarify, all your PI points have both V+ and V- (ground) on them?

Are you power injecting from a backbone or direct from the PSU?

Have you connected a direct power injection point at the very end of the run?
 
The pixels are wiredwatts pixels. I am doing both + and - direct from the psu.

For anyone watching to learn from my mistakes...
I added another run of my 18awg wire today. It definitely got better. I need to replace it with 12awg and i think ill be good. Or ill have to setup another PSU somewhere closer.

Thank you all for your help.
 
Unless you truly are seeing a very low voltage at the end of the 100ft run then pixel problems are more commonly a ground rise issue than a voltage drop issue. I explain this in detail in my 2020 vcs presentation which is on YouTube entitled why do my pixels flicker.

Adding more ground rather than more power will make a bigger difference. Say you were adding a 3 core cable for power injection ? always double the ground.

This is because when power is drawn you see voltage drop over the positive and voltage rise on the negative which you read at the end as a voltage drop but it?s against a different ground. The problem is the data line sees almost no voltage drop because very little current is drawn but is then referenced against the ground that has risen. That makes it hard for the pixel to read the data. Doubling the ground halves the ground rise which may help.


Sent from my iPhone using Tapatalk
 
My solution is never have a problem to start with. Voltage drop is a function of resistance and temperature. I have always oversized DC wiring. The smallest wire I use is 16ga. This is the signal wire from the controller to the prop, whatever it is. This wire will never be longer than 8 meters unless I use an inline F-Amp. All my connections are built by hand using weather-pack connectors. I never used pre-molded cables in my display for the simple reason you cannot be sure what gauge wire is being used. The largest wire in xConnector, Ray-Wu, and others I have seen is usually 18ga. These are nice if you have the time to solder all this together. I appreciate my direct approach, save the burnt fingertips, and many feet of shrink tube.

The largest cable I use is 6ga from the 200-amp 5v, 250-amp 12v, and 50-amp 36v power banks. This power gets sent everywhere needed through junction boxes. I run 5v, 12v, and 36v props. Power injection is liberal. 5v needs twice the injection points as 12v. Since the 36v is only floods, they do well on their own.

Bottom line: larger cables reduce voltage drop. That pretty much sums it all up.

Oh, BTW: 4v at the end of the run? Without a load? Wire is too long and too small.
 
You must log in or register to reply here.
Back
Top