Power Supply Question for RGBW LED PARs

[partyanimallighting]

Hi all, I'm just throwing this out there seeking some feedback. I have a few 14 x 10 Watt outdoor rated LED PARs that have been really problematic over the years that I've used them. Diodes have died consistently on all eight units and they constantly require repairs via RGBW diode replacement. Most times they do not come back from jobs without at least one failing me. In my opinion the issue is a poor quality diode/diode plate and I decided to resolve the problem once and for all by replacing all the diode plates in the units. Here's where the question/query/inquiry comes in. The 14 x 10 watt plates were all replaced with 18 x 10 watt plates and lens plates and the replacements fit perfectly. However, the 14 x 10 watt utilizes a 28VDC power supply whereas the 18 x 10 watt requires 24VDC. Instead of replacing the eight 28VDC power supplies with the required 24VDC power supplies, I simply reduced the SMPS voltage down to 23.5 ~ 24VDC via the onboard requlating potentiometer and each and every unit now works fine, no blown diodes to date, no overheating issues like in the past. Does anyone see an issue with adjusting the 28VDC voltage feed downwards to 24VDC? Reducing the voltage would send the amperage up slightly but I would think that would be insignificant. The only issue I could foresee is that, if the pot fails or shorts, the output voltage could revert (spike) back to 28VDC and possibly burn out the diodes. Are there any issues I should be aware of?

[DrV]

Reducing the output voltage of the PSU won't increase the current at either the input or the output per se. However, the total power required by the old plates was 140W and the new ones require 180W. Therefore the current drawn by the original plates was 5A (140/28) whereas the new ones require 7.5A (180/24). If your PSU is indeed maintaining 24V under load you may well be stressing that beyond its rating.

Where it gets more complicated is if the LEDs are being driven by a constant current driver rather than just being connected directly across the supply. In this case, if you haven't adjusted that current, then the LEDs will still be being supplied at 5Amax so there'll be no harm done. And if the new LEDs are more efficient than the old ones you may still get an increase in brightness despite the fact that you are running them at less than their rated current.

Do you still have an old one for comparison? If so it would be worth measuring the INPUT current (i.e. the mains supply current) as that will give you an idea of the total power being supplied by the PSU.

[partyanimallighting]

Hi DRV! Thanks for the response. The plates are not connected directly to the SMPS but via a 6 wire harness (R/G/B/W++) feeding the four individual color channels that are driven by the LED PAR motherboards, most of which utilize 9910C LED drivers. The original SMPS installed is 28V 5.3A and as you mentioned I'm now drawing 7.5A at 24V across the 18x10W plate. If it is that the plates are receiving only the maximum 5.3A from the 28VDC SMPS I'm fine with that because their output is sufficiently bright without any pulsing/flicker. The lower current draw will also extend the life of the diodes (am I correct here?). I've already done the plate swap out so I'll have to open up a unit again and take an amperage reading from the SMPS 28V+ to the motherboard with my meter and see what the current draw is like. According to what you've said above, if I'm drawing ONLY the maximum 5.3A from the SMPS I'm fine. If the current draw is higher in my readings then I run the risk of overloading the SMPS. Makes sense or is there anything else to factor in?

 

[DrV]

The driver circuits on the main PCB are constant current drivers so you won't be drawing any more current from the PSU. You could get a VERY rough measurement of the total power being consumed by just measuring the mains current if you have something to measure that safely. It won't be at all accurate but if you can compare the current drawn by an original unit and a modified one you should find it's a little less. It's just a reassurance measurement to set your mind at ease!