Led Grow Light

Wendy

Joined Mar 24, 2008
23,415
Thanks again for the help I checked the voltage across the resistors it was around 1.22v. I have a couple more questions though. The 25v I can use does that include the 1.22 from the resistors or do I use 25v in leds? One string of leds that I set up have 25.20v is anything over 25 a no no? One more question kinda two parts on the PS there is a hook up for a fan but there is no power at the pins do you know what turns the power on to the fan? I would like to run a small fan for the power supply off of the hook up for the fan on the PS. My last question would be I would like to run one or two fans to cool the light what fans would you recommend and how would I wire them in. Thanks again for the help.
We are getting into concepts beyond 1st year electronics. While we're not going to make you into an electronic tech you will have a practical understanding of a lot of concepts. A good thing, no?

OK, the LM317 data sheet actually says it will output 1.25V ± .05V. So 1.22V is good. It does have some practical ramifications however. It will affect the real current flowing though the LEDs.

We are also going to have start drawing real schematics of what you are using, to prevent misunderstandings. You are going to have to try your hand at it to some extent. You don't have to do this on a computer screen, you can hand draw it and either take a picture of it or scan it in using a flat bed scanner.

I am beginning to loose track do to number of entries in this thread, and length of time between them. This is another reason to pin down the exact schematics we are talking about.

I am assuming you are following the concepts I'm explaining so far, but I don't know if you are unless you can give me some definite feedback.

So you have 0.7A through the LEDs, with a 25.2V regulated power supply. Lets pin down every chain you have, numbers of LEDs and their colors.

****************************

You are wanting to add a fan, per earlier recommendations. If I read you correctly your power supply is 25V. You can do this three ways.

  1. You can buy a small 5V or 12V wall wart (whatever the fan uses) to provide the power.
  2. You can put the fans in series with your existing power supply (probably the cheapest option, but not necessarily the best).
  3. You can build a voltage regulator to tap off the existing power supply for the fans (LM317s are programmable).

Computer fans are cheap, it is usually what I go for. If you can't find a local source (such as Fry's or a local computer store) I can point you to other online sources. You should not spend much over $3 each over them, though $5 is acceptable. If you have a choice look for ones marked as having ball bearings, they last longer. Fans are also noisy, no way around it.

************************************

It sounds like we are at the end game for your project. A lot of what I was explaining above is the measure twice cut once principle. Better to go over something several times than to burn out any expensive components. :D
 

Thread Starter

TomatoMan

Joined Oct 16, 2011
39
Thanks for the fast reply Mr Marsden. My power supply is 28v. I am using the schematic that you posted in post #77 of this thread. I am using the LM317 with 7 resistors to bring it to .7A. The 25V I was refering to was what you said I would need to use so the LM317 would have 3V. As far as what colors of leds and numbers will vary. I am setting up the strings with combinations of red blue and white measuring the volts as I go trying to reach the 25V goal. The string would be different to some in the numders and colors of leds. One string I did that came out to 25.20V was 4 blue 3 red and 2 white. So seeing that I am building off you schematic in post 77 should I still draw mine out? If so to figure out the right number of leds should I subtract the 1.22v the resistors are using to reach the 25V goal so the LM317 on has to take care of 3V or do 25V just in leds? With your help I know alot more than when I started but still need to learn alot more LOL. Thanks again
 

Wendy

Joined Mar 24, 2008
23,415
I'm about to step out the door, so I'll keep this short for now.

I think we are at the point where you need to draw what you have (or are planning to have). You have the concepts down, you just need what we used to call a check print.

At some point I would like actual pictures if it is practical. Might spot some problems, but mostly I'm nosy.

I just bought some power LEDs for a project I'm working on. I'll show you mine if you show me yours (if you have already done this please refresh my memtory).
 

Thread Starter

TomatoMan

Joined Oct 16, 2011
39
Here are a couple pics for you. This is the small light I am building the large heatsink will be placed on the back of sheet metal. The resistors I have mounted to teh board with the LM317. I have a clip on heatsink for the LM317. On this small light I will only have two strings of leds so I will mount two LM317s with the resistors on teh same board. On my big light I will mount 4 per board breaking the copper strip through teh middle of the board. So on the question about using up 25volts to keep the work load of the LM317 to a minimum will the 25volts be all leds or leds plus the 1.22 volts from the resistors added together. The heatsink compund looks like a mess but that will be cleaned up. Tried post picks direct but did not work so here is direct links. http://www.flickr.com/photos/75483205@N05/6787626443/ http://www.flickr.com/photos/75483205@N05/6787625239/
 

Wendy

Joined Mar 24, 2008
23,415
This site has local hosting, or you can attach pictures as I am doing here.

Here is how I did one a while back. I haven't figured out how to do my new ones.



I used an old 286 CPU heatsink, you don't need much for one or two.
 

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Thread Starter

TomatoMan

Joined Oct 16, 2011
39
I have a large heat sink that I bought at the scrap yard for pretty cheap. I bought a couple large heatsink maybe 8"x4" and 3 a little smaller for the grand total of 3 bucks. So as far as the resistor set up and how I am setting up the leds do you see any issues? Also what should I do run 25v in leds or 23.75 in leds. What would be best for the LM317? Also if I go over by say .25V will that screw things up? What is better being say 1.75 short or .25 over? Thanks again
 

Wendy

Joined Mar 24, 2008
23,415
The only concern I have with your setup is the lack of heatsinking for the LM317. If you get the LED close enough to the limit it will not be needed though, but carefully (really carefully) check to see if the LM317 is getting hot. I have branded mirror image part numbers into my skin before when I part gets above boiling hot and I didn't know it.

http://www.bgmicro.com/to-220sliponheatsink.aspx
 

faharris

Joined Jan 9, 2012
1
I just discovered this thread and forum. Fantastic !

I like tomatoes more than most people, so I'll have to get lighting like this before spring.

Bill_Marsden - What circuit design software do you use to get such pretty schematics and PC board layouts ? I might have to get some for myself.

Thanks !

Chip Harris
 

Wendy

Joined Mar 24, 2008
23,415
You can get my templates that I have made from my blog.

Bill's Index

Introduction and PaintCAD

It is an ongoing work in progress, as I add changes I upload them now and again. Basically the templates get you going, but the drawing is the work you put in. You can us MS Paint, or whatever graphics program you like.
 

Thread Starter

TomatoMan

Joined Oct 16, 2011
39
Thanks for the reply Mr Marsden. I do have the heatsinks for the LM317s they slide on over the top. I left the heatsink off for the photo. I started laying out where I would like each color led for my big light tonight but stopped till I no teh answer to this last question. The only question left is if I need to leave 3 volts for the LM317 and my PS is 28 volts can I use the 25volts in leds or do I have to minus the volts used by the resitors from the 25volt total. So is it 3v lm317 2.22 for resistors and then 22.78 in leds? Well one more question now that I typed this out one more came up. Say the total would be .30v over would taking that .30v from the LM317 be bad? Thanks again.
 

Wendy

Joined Mar 24, 2008
23,415
If you get the 1.25V across the resistors programming the LM317 it is doing its job. That is basically what is important. That and keeping parts cool.

As you can see there is other interest in this project. If you would take some pictures after you are finished I would like to collaborate with you and enter a Completed Projects entry.
 

Thread Starter

TomatoMan

Joined Oct 16, 2011
39
Sounds good about doing up some pics for the completed projects section. So if I am reading it right I can use a full 25volts just in leds. The 1.22 that the resitors use does not come from that total. One more quick question my PS is an open case do they sell covers for them or is it something I will need to bend up? I have looked around a bit but did not see what I needed.
 

Wendy

Joined Mar 24, 2008
23,415
Show me the PSU (power supply unit). As a general rule you want to cover the high voltage parts, you never know who will be touching what (especially with kids). I would also put a switch on it. If the PSU doesn't have a fuse I would add a breaker or fuse. The LED section is pretty safe, all low voltages. Heat is a potential problem though.

Did we get you settled on the fans?
 

Thread Starter

TomatoMan

Joined Oct 16, 2011
39
Here is a PDF link to my PSU http://datasheet.octopart.com/MSMP25028F-Elpac-Power-Systems-datasheet-9804550.pdf bottom of the page has the pic of the one I have. What is crazy some web sites list the unit for 185.00 but the site I bought it from was only 25.00 or so. I think I would like to use this power supply to supply two fans I guess 12 volt fans would be the best bet correct? If you look at the data sheet there is a two pin hook up for a fan but there is no power at the pins any idea how it would get power switched to it? I was measuring some combinations of leds colors I would like to use one strip came up to 23.40 and the LM317 wasvery hot. If I added one more red led I would be a little less than half a volt over 25 volts would this mess up the LM317 doing it's job? Thanks again I see the light at the end of the tunnel LOl.
 

Wendy

Joined Mar 24, 2008
23,415
Something is messed up about the .pdf. It shows the picture, then crashes with the message "insufficient data for image".

Could you show the seller and their listing please?

About the base design, you can stick two 12V fans in series, with largish caps across them. I don't really like that solution, if one fan goes out it could take the second out, but as long as both are working then it would be OK.

Throw in a couple of diodes in series to absorb excess voltage and you should be good to go. I assume this is the main power supply unit for the LEDs though, correct? If this is the case we may add a fuse for the fans to see if we can protect everything. As for the caps, I'm thinking of a couple of 470µF 50V types. Watch out! They will be polarity sensitive.
 

Wendy

Joined Mar 24, 2008
23,415
Thanks Bertus, that did the trick.

I like the base unit. If it exposed as shown in the picture you probably could use something covering the innards, either a small piece of plastic or hardware cloth (or both). The air needs to be allowed to circulate freely though.

The initial picture showed a plastic case with a HP power cord. That would have been too much to hope for though.
 

Thread Starter

TomatoMan

Joined Oct 16, 2011
39
Hello again I have a new dilema. Even when the PS switched off I am getting 18 volts at the positve terminal. I completed all 7 rows of leds and was doing the 8th and last one when it happend. I did nothing different so unsure what went wrong. I was about to order my fans and power supply for the fans. I desided to go with a PS just for the fans to play it safe. So any ideas why all of a sudden I am getting the power even when switched off? I was not using a switch I was just jumping across the switch terminals to turn unit on. I had to order a 6 pin plug to wire a switch the correct way. Thanks agian.
 

jaclement

Joined Apr 15, 2009
35
Leds will produces a voltage when exposed to light. With an open circuit, and a series string you might get 18 volts. Measure the string in darkness.
 
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