Constant Current Power needed... I'm confused...

[tedoro]

Hi, I have an art project and I have found a hundred bulbs (9-12v 3 watt COB) and I desire to not burn my house down.

https://www.ebay.com/vod/FetchOrder...sId=957416770021&_trksid=p2057872.m2749.l2673

I vaguely understand that these bulbs can continue to pull more current as they heat up, causing problems... so a power supply that caps their consumption is safer than one that would not. I found this...

https://www.amazon.com/dp/B07DWM42M5/?tag=cpf0b6-20

So I would wire up 320 watts worth of bulbs and I should be good?

t

 

[DoctorMemory]

Well, the 3W LEDS are rated for 260-280 mA and to drop 9-12V. You will have to series the LEDs and run 260-280 mA thru the whole string. You cannot parallel the LEDs unless you want major headaches.

The supply offers 700 mA which is too much, you want 260-280. They want you to buy a MSSL200 to set the current lower.

The supply will put out 183-457 VDC depending on the AC voltage fed into it. You will need 12V for each LED; if you feed it with 120VAC it will put out around 244VDC which would allow around 20 LEDs in series. If you want more you'll need another power supply for each new string. That supply is overkill with 700 mA output, you should look for something in the 280-290 mA range. Then see how many LEDs at 12V each can be strung, and then how many power supplies you will need, one for each string.

 

[tedoro]

I am very appreciative that you took the time to respond, especially to a noob like me (I just signed up). I am an artist here in Portland Oregon and often use LED's but honestly, you can do a ton without knowing much, which is me in a nutshell.

I've been testing with these in parallel. I will stop that.

I have 12 strands of eight bulbs, which can easily be 6 strands of 16 bulbs. So let's go with the latter.

First off, is constant current the correct way to handle this... its just what I read somewhere. I am completely willing to take your advice whole heartedly.

I am concerned with heat, and would like to be able to reduce the wattage to reach the sweet spot of good light output and low heat.

So, 16 bulbs would want 192 VDC at 260-280 mA if I am following you. Shoud that be a constant current supply? Do they make them with a voltage adjustment such that you needn't buy a second device?

Again, your help is very appreciated. I will owe you big.

 

[tedoro]

I suppose it would be better for me to shoot for the desired brightness from the design, and forego the adjustability. My testing of these bulbs have shown that when run at 2.5 watts they are bright enough and not hot to the touch. So what power supply would be right for 16 (or eight) strung in parallel?

t

 

[tedoro]

This seems to be as close as I can find... (I barely know what I am doing...)

https://www.amazon.com/dp/B071CJ6M4Q/?tag=cpf0b6-20

for a eight lights strung in series. But its 300ma and likely running it at less than 2.5 watts.

or this is close too...

https://www.amazon.com/dp/B00ZCB2JSS/?tag=cpf0b6-20

 

[JustAnOldFashionedLEDGuy]

Ignore DoctorMemory. He is giving you advice on something he does not understand. The driver you linked will put out 700mA. It will do that if you keep the string voltage in the output voltage range.

If you connect 20, 12V LEDs in series it will output 700ma and the voltage will be around 240v, but probably higher as your LEDs are not rated for that current. The input AC voltage has nothing to do with the output voltage.


You could parallel LEDs with likely not too much issue. Modern LEDs are manufactured to better tolerance. It's not ideal, but usually no issues and many many led products do this. The safer way is normally put parallel 3 together so you get a 700ma rating and the stack those. I would go 4 in parallel, and then stack them to average 175ma per led but some will be higher and some lower. Make sure they are close thermally. Voltage varies with temp. You can put 20 in series and then 4 of those strings in parallel but greater chance of mismatch.

 

[JustAnOldFashionedLEDGuy]

And caution, those DC voltages are high and DC is more dangerous than AC. Treat it with respect.

 

[tedoro]

Ignore DoctorMemory. He is giving you advice on something he does not understand. The driver you linked will put out 700mA. It will do that if you keep the string voltage in the output voltage range.

If you connect 20, 12V LEDs in series it will output 700ma and the voltage will be around 240v, but probably higher as your LEDs are not rated for that current. The input AC voltage has nothing to do with the output voltage.





You could parallel LEDs with likely not too much issue. Modern LEDs are manufactured to better tolerance. It's not ideal, but usually no issues and many many led products do this. The safer way is normally put parallel 3 together so you get a 700ma rating and the stack those. I would go 4 in parallel, and then stack them to average 175ma per led but some will be higher and some lower. Make sure they are close thermally. Voltage varies with temp. You can put 20 in series and then 4 of those strings in parallel but greater chance of mismatch.

Okay. I'm still a bit overwhelmed. Heres the deal. I want to run these 3 watts lights a tad bit less than rated to keep them cool. Numerous strands are needed of 8 bulbs (or 16). I want them very safe. how do I do that? I am finding a bunch of 300ms constant current drivers. Is that too much? (I'm in the US 110v AC) was he right that parallel is not the way to go?

I am using these COB 3 watt led's, but have not chosen the power supply. The world is my oyster... Whats easiest?

 

[tedoro]

Now I'm mostly talking to myself...

What if I used this power supply

https://www.amazon.com/dp/B07MSBK9GV/?tag=cpf0b6-20

and wired up 8 lights in parallel and put the whole thing on a LED dimmer?

Seems expensive, $30 times 12... and the cost of a dimmer that size. But I gotta get this done.

 

[JustAnOldFashionedLEDGuy]

Okay. I'm still a bit overwhelmed. Heres the deal. I want to run these 3 watts lights a tad bit less than rated to keep them cool. Numerous strands are needed of 8 bulbs (or 16). I want them very safe. how do I do that? I am finding a bunch of 300ms constant current drivers. Is that too much? (I'm in the US 110v AC) was he right that parallel is not the way to go?

I am using these COB 3 watt led's, but have not chosen the power supply. The world is my oyster... Whats easiest?

Can you send a link to the LEDs that is not to your order, but their product page or similar?

You want to run 100 of them, or do you want to run less? How to you plan to mount them, i.e. how safe do you need the voltage to be? Generally under 60V is somewhat safe indoors, 30V outdoors where wet is an issue. If you are going over those voltages, then you need to make sure people can't touch them, and that you don't have accidental shorts to metal that someone can touch.

Let's say you are going to go 48V, so that appears to be 4 in series. Let's say you do 0.2A per unit. That would be 25 parallel strings, or you could do 25 in parallel, and then stack those 4 high. You would need a 5A output driver.

For high voltage, let's take your 700mA driver and divide it by 4 = 175mA per string. You have 100 LEDs, divide that by 4 = 25 stacked in series with a voltage around 25 * 12 = 300V, but realistically between 250 and 300V. Best to wire those as sets of 4 in parallel and then stack those sets 25 in series. If you do find 1 out of 4 is noticeably brighter than the other, then you can swap that out for another one. Unfortunately it does not sounds like you have the tools to sort them. You could stack them 25 in series * 1, and have 4 strings. Than add a 50 ohm, 5W resistor in series with each string. That will help balance the strings for voltage differences between the strings.

 

[tedoro]

https://www.ebay.com/itm/311651957952

my apologies

Indoors.

The mounting is all figured out with heat sinks.

100 led's total.... in strands of 8 led's.

I found this driver that looks like an interesting option to run two of my rows with....

https://www.amazon.com/gp/product/B07R7QQ286/?tag=cpf0b6-20

 

[tedoro]

feel no need to utilize the power supply I linked... as I haven't purchased it.

 

[tedoro]

I feel like I would like to have it be a bit smaller, like perhaps having a few power supplies run sections. If I can pull it off without resisters that would be great.

I really appreciate your write up. for the most part, I can follow it.

Tell me, if I used the 20-24Vdc power supply linked below, could I run eight in series, then parallel two series? When will a series strand start to be too long?

https://www.amazon.com/gp/product/B07R7QQ286/?tag=cpf0b6-20

 

[JustAnOldFashionedLEDGuy]

Tell me, if I used the 20-24Vdc power supply linked below, could I run eight in series, then parallel two series? When will a series strand start to be too long?

https://www.amazon.com/gp/product/B07R7QQ286/?tag=cpf0b6-20

Your LEDs are ~9-12V, so with a 24V maximum supply, you can only do 2 in series 2*9-12 = 18-24V. Then 7-8 in parallel = 1500/7-8 = ~200mA each. It will probably work, but I am concerned with any driver that has a narrow operating range like 20-24V. That tells me the design could have some issues.

I would go with something like this:

https://www.digikey.com/product-detail/en/mean-well-usa-inc/LPC-100-1750/1866-3133-ND/7704802

1.75A gives you say 8-10 parallel strings, and 4-5 in series. 4-5 drivers will power everything, but expect some of your 100 units to be "spares". This is <60V, and <100W which is better for safety, but you still need to protect from touch.

If you want to stick below 30V, then maybe this:

https://www.digikey.com/product-detail/en/tridonic-inc/28002153/2538-28002153-ND/12141492

 

[tedoro]

okay, let me look this over

 

[DIWdiver]

A string of 8 of those LEDs near full power is going to be 70-90V. This is above the maximum safe voltage, which depending on who you ask is anywhere from 48-60V. If you really need to do that, you have to take extra precautions to ensure that nothing in your system can short to metal that anyone can touch.

I would much rather you wire that electrically that as two strings of 4 in parallel (which could still be physically arranged as one string). 12 strings of 8 would become 24 strings of 4. To run them near full power, but not quite, let's say 250 mA per string. That adds up to 6A.

So to do it that way would require a supply capable of 48V, 6A, with adjustable current limit.

Other ways to keep the voltage safe is 32 strings of 3 (which maybe doesn't fit your design), for which you'd need 36V, 8A; 48 strings of 2, which requires 24V, 12A.

Personally I think the 48V, 6A is a good compromise that keeps both the voltage and current reasonable.

EDIT: Crossed in the mail. I realize this is a bit late to the party!

 

[DIWdiver]

Yeah, I'd also be leery of a no-name device that costs 1/3 of what a name-brand one does. If it doesn't need to last, maybe take a chance, but if failure is not an option, go with the name brand.

 

[tedoro]

So if I run 3 in parallel and get 36vdc, then run a bunch of those in series, perhaps 5 times, I would get 1.4 amps... is that your thinking? (my apologies if my nomenclature is improper.

I was kinda hoping for the cleanest strand of 8 leds I can do... (this is an art project using these as grow lights for plants on a grid)

 

[tedoro]

A string of 8 of those LEDs near full power is going to be 70-90V. This is above the maximum safe voltage, which depending on who you ask is anywhere from 48-60V. If you really need to do that, you have to take extra precautions to ensure that nothing in your system can short to metal that anyone can touch.

I would much rather you wire that electrically that as two strings of 4 in parallel (which could still be physically arranged as one string). 12 strings of 8 would become 24 strings of 4. To run them near full power, but not quite, let's say 250 mA per string. That adds up to 6A.

So to do it that way would require a supply capable of 48V, 6A, with adjustable current limit.

Other ways to keep the voltage safe is 32 strings of 3 (which maybe doesn't fit your design), for which you'd need 36V, 8A; 48 strings of 2, which requires 24V, 12A.

Personally I think the 48V, 6A is a good compromise that keeps both the voltage and current reasonable.

EDIT: Crossed in the mail. I realize this is a bit late to the party!

Okay, let me think about what you said now.

 

[tedoro]

I would much rather you wire that electrically that as two strings of 4 in parallel (which could still be physically arranged as one string). 12 strings of 8 would become 24 strings of 4. To run them near full power, but not quite, let's say 250 mA per string. That adds up to 6A.

So to do it that way would require a supply capable of 48V, 6A, with adjustable current limit.​

I understand this, or I think I do. Let me put it into my words, to make sure I really do.

I put all the LED's into parallel strands of 4 (48vdc, 250ma). I group two of those strands into series, making my 8 LED strand my design requires (48vdc, 500ma), then put all of those groups in series.... 12 times (48VDC 6000ma)

Is that correct? This seems great!