My DIY COB light wattage keeps changing...?

I have a DIY light that has 10 COBs on it, divided by three on/off switches (three drivers), each with their own dimmer. My temps have been fluctuating, so periodically I'll take out the Watt-O-Meter and check the "at-the-wall" watts. One time it was up to 330, the last time it was at 280. Yes, I checked the dimmers, they are still at max (they are taped over in that position, long story). I'm usually looking at the same time of day, a few hours after the timer has turned them on, so they should be "warmed up".

I built and disassembled, redesigned, and rebuilt lights over about two years, so the drivers are slightly different ages, but I just looked up my notes, and the oldest parts go back to 2015, most are from 2016. Is this just the lifespan of a Meanwell driver? I generally run two grows per winter, now I'm growing autos so they are 20/4 light schedule for about six months (two grows back to back).

330 to 280 is a pretty big watt usage swing, any ideas on what could cause that? Are they just getting tired/old? How do drivers die when they crap out -- fade, pop, fizzle...?

Removing the dimmer completely then measuring the wattage would be my 1st step.

HippieDudeRon said:

Might be the potentiometer going bad. Take it completely off and see if it stays stable.

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Star Dog said:

Removing the dimmer completely then measuring the wattage would be my 1st step.

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Thanks, I'll give that a try tomorrow.

The dimmer is the most likely culprit. But also check the killawatt, they go funny aswell. I remember someone coming on here saying his killawatt would show similar 20% difference between when he touched the light and not.

Wow. It's been a minute (or 5 years) since I worked on a light. I had soldered the dimmer connections, so sadly there was no way to disconnect them that left an easy way to reconnect... so I just snipped them. The subsequent test showed that changed my light from around 300w to a full but stable 400w. I raised the light, luckily I think the plants are done stretching and I have some room up top. Now I'll just need to keep an eye on it for temp changes and leaf burn, see if I need to go any higher, there's about 6" left of vertical travel space, not really that much.

Because of health issues, this is probably my last grow, so at least now I know it should run consistently for the duration. No time or energy to get new potentiometers and attach and test them in the middle of the grow. I'll just ride it out at full blast, it should be OK. There are 8 cobs on at 50w each, everything is well within functional spec, it's just a lot of light for a 2x4. I'm running autos so they are on 20/4, luckily we're mid-winter and the temps are pretty easy to control. The tent keeps my living room warm. It's not an efficient use of light or electricity, but it might be the best I can do for now.

I did a quick search, and the light test images I saw indicated that the PPFD roughly cuts in half every 12 inches of distance... does that sound about right? I'm not sure if that's just for QB's or also for COBs? I was trying to get a sense of how much I'd have to raise a 400w light to mimic a 300w light's output, since that was my target range...?

Thanks again for the advice, @HippieDudeRon @Star Dog @Rocket Soul

Humanrob said:

I have a DIY light that has 10 COBs on it, divided by three on/off switches (three drivers), each with their own dimmer. My temps have been fluctuating, so periodically I'll take out the Watt-O-Meter and check the "at-the-wall" watts. One time it was up to 330, the last time it was at 280. Yes, I checked the dimmers, they are still at max (they are taped over in that position, long story). I'm usually looking at the same time of day, a few hours after the timer has turned them on, so they should be "warmed up".

I built and disassembled, redesigned, and rebuilt lights over about two years, so the drivers are slightly different ages, but I just looked up my notes, and the oldest parts go back to 2015, most are from 2016. Is this just the lifespan of a Meanwell driver? I generally run two grows per winter, now I'm growing autos so they are 20/4 light schedule for about six months (two grows back to back).

330 to 280 is a pretty big watt usage swing, any ideas on what could cause that? Are they just getting tired/old? How do drivers die when they crap out -- fade, pop, fizzle...?

Click to expand...

Are your cobs actively cooled? Heat can cause voltage drop

Boatguy said:

Are your cobs actively cooled? Heat can cause voltage drop

Click to expand...

Passively cooled with clip-on fans blowing cross the heat sinks. Everything is warm, but not hot.

HippieDudeRon said:

What CCT are you running? can get a lux to ppfd conversion factor

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It's been a while since I've thought about let alone talked about lights, so I've forgotten most of what I knew.

If by CCT you're asking the kelvin I'm running, in flower its; (2) 4000k, (2) 3500k, and (4) 3000k. Is that what you were asking?

There are some other supplemental lights in limited use, but that's what's on the fixture. I have no meters for measuring anything other than temps and RH, it's a pretty simple setup (no soil or light testing). Mostly I just estimate, play with it, try to keep it simple, and the plants usually finish well.