Scrubber build

I didn’t mean my response toncome off that way, please accept my apologies

I was in a hurry, was between basketball games in an all day tournament so I was just getting my thoughts out quickly. In re-reading that I can see how that kinda came off jerk like

 

Absolutely, no problem! I tend to worry when a discussion goes sideways - it's always good to have expertise so I was hoping I didn't push you away, I welcome any new information and perspectives, but I have to remember that when I write something technical that it's not in a way that could be taken with a snooty tone...hard to do but I've been guilty of it

You're right here, it is an odd approach. I searched around quite a bit before I first tried this and I couldn't find a single instance where anyone had tried this method. The reason I wanted to do it was that my original scrubber (Rev 1) had 6x 660nm Reds and one 455nm Blue in a series, with the reds in a rectangle pattern and the blue in the middle, one of these arrays on each side. I made about 30 of these units and it became immediately clear that there was a issue where the growth was zero in the middle and filled in around the edges first, then eventually filled in the middle, but it took a long time. What I realized was that I had uncovered the issue of photosaturation (or photoinhibition, depending on how you look at it) in front of the blues - the intensity was too much. My first solution was to place a small chip of a diffuser in front of each LED, another was to place a very small piece of black electrical on the acrylic panel in front of the LED, both worked OK but that was a work-around.

That's when I thought about running 2 in parallel to cut down the intensity. The caveat to this working is twofold - 1) they pair of LEDs must be very closely matched (so, from a supplier that properly bins the LEDs) and 2) each LED could run fine if the other one blows and opens it's half of the circuit.

The goal was really to avoid having to use multiple drivers. Another way to go about it could have been to use 1W Royal Blues, but the development $$ isn't really going into lower-power LEDs, so I nixed that. That was further nixed when I went to violets which are less of a "stable" platform, so I had to go with the best possible LED I could find, and I settled on the 3W SemiLED Hyper-violet. So the technique of the parallel-pair-in-series is not one I use anymore really, but it still works for this specific application.

Interestingly enough, I have yet to see anyone else even try this, anywhere else. It seems to me that if you wanted to DIY a display tank fixture and throw in some odd colors but have them be very much supplemental, the way to do it and save $$ by not using extra drivers would be to occasionally throw in a parallel pair. If they aren't matched then you might have one drawing more current than the other, especially if they are cheapo grab-bag LEDs.

Absolutely, and what I've seen done really early in DIY display tank fixture builds (to save $$ because drivers were more expensive and of less variety) was to take multiple "electrically matched" strings (which usually meant using a high power resistor here or there) and put them in parallel & connected to a high-current driver (like 3000mA for 3 strings of Cree RBs) and then put quick-blow fuses on them so that if one LED in a string opened up the circuit, the other fuses would blow and save the other LEDs from getting hit with overcurrent.

That's not what I had done on my Rev 1 and not what I recommended anyone do, that's something I consider a more advanced technique - the parallel pair within a series doesn't have the same problem because you can take one LED of the pair out and it just gets the normal current vs half-current, it's more of a DIY cost saving measure and very specific I think to algae scrubbers, where the Royal Blues have much more intensity than the Deep Reds at the same current. This is probably why you don't see it being used/recommended anywhere else.

This is definitely an interesting topic that I really haven't seen discussed much. I'm going to reach out and see what I can find out actually. Rapid LED carries this one AA Battery LED Tester and they say "Safe to use for testing individual LEDs (except for total spectrum UV and arrays)", I thought Steve's carried one but they might not list it. My thought is that "safe" means you're not going to die lol....

So @LED T back to the OT of the thread (or the recent issue) what do you think might be the problem @Tim had? From what I can see, it looks like he originally was running the red and violets in a simple series chain on a LPC-35-700 driver. This should work like clockwork. Suddenly, the array goes dim like it's not getting the full current to all the LEDs. One the fixture that didn't blow from the 9V test mistake, he took the violet LEDs out of the wiring string and the result was that the reds all fired just fine. This would indicate to me that there was an issue with the violets. The issue seems to be that there was some kind of damage to one or both of them that resulted in at least one of them only being able to "allow" a reduced current to pass through it, in effect, acting as a current choke point of some kind, which of course resulted in all the LEDs experiencing a lower current and thus only lighting dimly.

I've seen LEDs fry and open-circuit so that nothing fires, and I've seen LED fry and close-circuit so that the rest of the chain still fires, but I haven't seen one cause a current-choke like it appears @Tim saw.

 

He posted a video of it happening on a cold fixture where the LEDs flash brightly a few times then go dim, did you see that one?

Here it is, it's a few pages back. This is one where he re-wired the 2 violets so they are in parallel and connected to the new driver - which is I believe the LPC-20-700, so this one would have the 30V drop limit vs the 48V limit of the LPC-35-700

To me there are one of two things going on here:

1) too much voltage drop, this could be indicated by the quick flashing of the LEDs followed by the dim running, but this doesn't seem quite right to me. However I am not familiar with the over-voltage response on this Meanwell.

2) both violets have damage so the current path goes through one with short success, then the other, then both, and then they both shut down. Kind of a strange sequence of start-up, but it's just a theory that fits the video.

That's the first fixture, here is the second. This is all series and I think on an LPC-35-700. In this you can see the closest violet is bright, but the far one is not. I'm not sure if this is a photo effect or what but it does seem like an issue with the violet.

Also these are SemiLED Violets, so they're not low-end. At least I don't think they are.

Also worth noting that both of these fixtures were coated in a 2-part silicone to keep them from getting wet.

 

Yes, this would be a good idea I think. If you're getting good growth at a given intensity, and you have measureable nutrients and/or are still feeding the same, same livestock, etc - then you can usually extend the hours without any issues. You might even go longer, 20-22 hours/day

 

I'm not quite following this part of your post. I get that when you bench-test a single shorted LED, that's like hooking the 2 terminals of a power supply together, so your instantaneous current is going to be high.

But, if you have 10 LED in a string and one is shorted, how would you have a high instantaneous current because of that one LED? I'm scraping some rust off my brain from my EE classes 25+ years ago here...and I haven't really thought about this lately from a technical perspective...and I'm not talking about the whole p-n junction level of technical stuff here. I'm just thinking of a more simple answer. Take just 2 LEDs, both working fine, and put them on a power supply (one that works for 1-4 LEDs in this case). Now take the shorted LED and put that in series with the other 2. What has changed? If the 3rd LED is shorted, I would think that would in effect just act like it wasn't there. I must be missing something

 

Yes, I see how that could do it, but wouldn’t the short to ground in this instance be to the heat sink? Then there would have to be a path back to the driver for the LEDs to continue to operate the way they were in the video.

 

Im not an electronics expert by any means. But I’m an electrical engineer by education so I’m not stupid, but to be quite honest, that’s kind of how you’re treating me here and I don’t get that. I don’t practice circuits and such on a daily basis but I can understand the technical explanation when it’s presented.

What you seem to be referring to with the high power blowouts is a situation when you have a power source that is higher, like a piece of equipment or controls connected to a 20A or 50A breaker, etc. Now something connected to a circuit like that can experience a much higher instantaneous power before the breaker trips, in the kA range.

But in the example here, if the driver has not had an internal failure, then the output current is fixed at 700mA, so any kind of short to ground that you’re describing, that’s where I’m not following the explanation.

If you’re suggesting that the driver indeed is the source of the issue, that’s a different story. I don’t know if @Tim has verified that the issue actually was the driver

 

I’m just trying to figure out the technical explanation for Tim’s problem to try to help him out.

The reason I changed this forum over from supporting my customers to being open to all algae scrubbers is to help anyone with any issue, without the restrictions of some other forums.

The forum is meant to be a place where everyone helps each other out, even if it’s not that busy and it’s mostly users of my product...that’s still what it’s here for. So I welcome your help if you’re willing to offer it.

I don’t always have all the answers, but I’m usually pretty good at finding people who can provide them.