DC-DC converters and pixels.. getting your feet wet?

[BundyRoy]

I apologise if this has been covered earlier, but can a convertor be damaged if the supply voltage is not high enough or does it just stop working if the supply voltage is too low.

 

[David_AVD]

Damage to the converter due to under voltage is unlikely, but the output may be unstable once the input voltage drops too low.

 

[multicast]

I apologise if this has been covered earlier, but can a convertor be damaged if the supply voltage is not high enough or does it just stop working if the supply voltage is too low.

Many converters will have an UVLO.. ( under voltage lock out ). The main reason for that is to stop the current getting too high. For example,, If you had a convertors who's output was 5V and an input range of 24-48V, at 24V, you'll roughly have twice the input current that you would at 48V. If you took that down to 12V, it would be 4x.. You get to a point where the currents are too big, and you can damage things..


If it goes under voltage, they generally will just stop, until the input voltage goes back over the threshold.


Not all converters do this, but any worth their salt will.

 

[plasmadrive]

I finally connected my six new mini trees with 50 each WS2811 pixels on each. They each have a converter for the 5vdc supply. I feed them all from a single 24vdc supply. I am using the 20 gauge white 4 core cables from Ray. (had a bunch left over)

At full white on six trees including losses in the cables and the current to drive the controller, I am getting a calculated 85.4% efficiency. I am use .06Amp per pixel at 5vdc as my bench mark for the LEDs. I am pretty sure that is not right on the money but perhaps close since the drive chips themselves do take a minor amount of power.

It takes a total of 4.3 amps @24vdc for the entire lot of six. I do know that I am dropping about 8vdc across cables and connectors from the supply to the input of the last converter. That means each successive converter will draw a bit more current because the voltage feeding it will be less due to the drop.

I have even color temp (as much as possible from these pixels) from first pixel to last since I am feeding 5vdc right at each tree, both front and back of the strings. Looks like I will be able to run all 12 trees (total made) from one 24vdc 10 amp supply. I am happy with that..
I have even color temp (as much as possible from these pixels) from first pixel to last since I am feeding 5vdc right at each tree, both front and back of the strings. Looks like I will be able to run all 12 trees from one 24vdc 10 amp supply. I am happy with that..

 

[BundyRoy]

Just had a thought about these DC-DC convertors. Say you get a short (water ingress) into your lights downstream of the convertor. Can you have the fuse back at the power supply and the short gets "passed" through the convertor to blow the fuse or do you need a separate fuse on the positive wire downstream of the convertor. I'm guessing you need it on the downstream side of the convertor as they are effectively two separate circuits but just wanted to check.

 

[multicast]

Just had a thought about these DC-DC convertors. Say you get a short (water ingress) into your lights downstream of the convertor. Can you have the fuse back at the power supply and the short gets "passed" through the convertor to blow the fuse or do you need a separate fuse on the positive wire downstream of the convertor. I'm guessing you need it on the downstream side of the convertor as they are effectively two separate circuits but just wanted to check.

you need to current protection in both locations. however, you'll find that Many DC/DC converters will shut down in over current situations, very very rapidly. ( due to the topology of how they are set up )

 

[plasmadrive]

Just had a thought about these DC-DC convertors. Say you get a short (water ingress) into your lights downstream of the convertor. Can you have the fuse back at the power supply and the short gets "passed" through the convertor to blow the fuse or do you need a separate fuse on the positive wire downstream of the convertor. I'm guessing you need it on the downstream side of the convertor as they are effectively two separate circuits but just wanted to check.

The converters I use have short circuit and over current protect inherent. The main 24v supply I use to drive them all also have both of those to protect itself. I use large enough buss wire ( #14) on the Plasma Icicles that it will sustain the full current capability of the main supply without issue. On the mini pixel trees I do supply a smaller fuse to protect the smaller gauge cables that I run the 24v thru.

 

[nzlongfellow]

I finally connected my six new mini trees with 50 each WS2811 pixels on each. They each have a converter for the 5vdc supply. I feed them all from a single 24vdc supply. I am using the 20 gauge white 4 core cables from Ray. (had a bunch left over)

At full white on six trees including losses in the cables and the current to drive the controller, I am getting a calculated 85.4% efficiency. I am use .06Amp per pixel at 5vdc as my bench mark for the LEDs. I am pretty sure that is not right on the money but perhaps close since the drive chips themselves do take a minor amount of power.

It takes a total of 4.3 amps @24vdc for the entire lot of six. I do know that I am dropping about 8vdc across cables and connectors from the supply to the input of the last converter. That means each successive converter will draw a bit more current because the voltage feeding it will be less due to the drop.

I have even color temp (as much as possible from these pixels) from first pixel to last since I am feeding 5vdc right at each tree, both front and back of the strings. Looks like I will be able to run all 12 trees (total made) from one 24vdc 10 amp supply. I am happy with that..
I have even color temp (as much as possible from these pixels) from first pixel to last since I am feeding 5vdc right at each tree, both front and back of the strings. Looks like I will be able to run all 12 trees from one 24vdc 10 amp supply. I am happy with that..

Plasmadrive Just ordered 30 DC-DC units like yours. Could you please include a sketch of the wiring you did as I have 24 mini trees with 50 pixels I am wiring up next.

 

[plasmadrive]

I finally connected my six new mini trees with 50 each WS2811 pixels on each. They each have a converter for the 5vdc supply. I feed them all from a single 24vdc supply. I am using the 20 gauge white 4 core cables from Ray. (had a bunch left over)

At full white on six trees including losses in the cables and the current to drive the controller, I am getting a calculated 85.4% efficiency. I am use .06Amp per pixel at 5vdc as my bench mark for the LEDs. I am pretty sure that is not right on the money but perhaps close since the drive chips themselves do take a minor amount of power.

It takes a total of 4.3 amps @24vdc for the entire lot of six. I do know that I am dropping about 8vdc across cables and connectors from the supply to the input of the last converter. That means each successive converter will draw a bit more current because the voltage feeding it will be less due to the drop.

I have even color temp (as much as possible from these pixels) from first pixel to last since I am feeding 5vdc right at each tree, both front and back of the strings. Looks like I will be able to run all 12 trees (total made) from one 24vdc 10 amp supply. I am happy with that..
I have even color temp (as much as possible from these pixels) from first pixel to last since I am feeding 5vdc right at each tree, both front and back of the strings. Looks like I will be able to run all 12 trees from one 24vdc 10 amp supply. I am happy with that..

Plasmadrive Just ordered 30 DC-DC units like yours. Could you please include a sketch of the wiring you did as I have 24 mini trees with 50 pixels I am wiring up next.

When you asked me this I realized I did it all out of my head and didn't have a sketch.. so I made one.. I need to keep on top of those.. LOL

 

[nzlongfellow]

That's how I thought it would be and thanks. Any chance of a pic or two of how you set them up/ mounted them on your mini trees. Pics do wonders. Cheers.

 

[plasmadrive]

That's how I thought it would be and thanks. Any chance of a pic or two of how you set them up/ mounted them on your mini trees. Pics do wonders. Cheers.

Not rocket science.. I used zip ties.. : Don't have any pics of the wiring stuff.. sorry.. I did mine as a 3/4 round and not a full 360 deg setup..