DIY LEDs - The write-up

[TheFishMan65]

For those that don't recall the discussion:
XM-L T5 are 260 at 700 ma and 2.9 volts or 128 lumens / watt
XP-G are 139 at 350 ma and 3 volts or 132 lumens / watt

Compare that to the lumen output of the same number of XML at the same current.

I disagree because XMLs are designed to run hotter so IMHO the same current is out. So it make sense the XMLs should have more current (so fewer LEDs for the same output).

Or find out the number of XML needed to to supply the same number of lumens.

but at what current? I picked (I think) the manufacturers recommendation.

Also, keep in mind the the watts consumed by a XML at the same current as the xpg is less

A watt is a watt. XML require less current to reach a voltage (so consume less power/watts) it really boils down to how much light/lumens/PAR/PUR is produced.

While the lumen output of the xml may be the same/ higher/ lower than the xpg, the XML use less energy to do the same amount of work.

That is why I was comparing lumens per watt.

The question is where are most people operating these. If someone calculates I need to run my XPGs at 350 ma to get X lighting then thinks I will save money by buying 1/2 as many XML and doubling the current to double the light. Then they would be wrong. Now it maybe true at 700 and 1400 (I would have to do the math), and probably many other values. I think we need to find out where most people are running the XM-Ls.

 

[TheFishMan65]

From my reading I would guess most people are running XP-Gs around 700ma. So:
139 lumens * 187% / (.700ma * 3.2 volts) = 116 lumens / watt
for a XM-L
2 LEDs * 139 lumens * 187% / 260 lumens = 200% so at 200% the XML current is (I would guess from the chart) 1550 ma and at that current the voltage is 3.1 so
2 * 139 & 187% / (1.55 * 3.1) = 108 lumens per watt
So it appears the trying to save electricity by using 1/2 as many XM-Ls is not going to work. However you can save electricity by using the same number of XM-Ls as XP-Gs (having them produce the same amount of light). Or some other ratio of XP-G to XM-L less than 2 to 1. I guess that might be some math for tomorrow

 

[jcgd]

Okay, I see what you mean now.

I agree, at the same current, XML are more efficient than xpg. Because the increase in lumens isn't linear, the lumen output doesn't increase at the same rate as the current. So would technically need closer to 5/8 the number of XML ruining at twice the current as you would have had with the xpg for the same amount of light.

I've argued two points before, based on what you just pointed out. Use around half the number of XML at just over double the current for lower upfront cost with a bit higher energy cost long term (because xpg are around $4.50 while XML are $6.80 or so) or use the same number of XML as xpg with the same current for higher upfront cost but savings long term in energy consumption.

I haven't done the math, but I would put my money on the first option being cheaper long term. 20% energy savings isn't a whole lot per year on a 300 watt fixture. I think the extra cost of all those extra XML could be more at this point.

Im just guessing.

 

[jkopp36]

Is there something I can put across the dimming circuit on an HLG to keep it from going open as a failsafe in case the control creates an open circuit? Trying to prevent the driver from driving at full power if that happens. I would prefer something that would result in approx. 10K ohms of resistance across the circuit if the controller goes open. I'll be dimming using 1v-10v from an Apex.

 

[kcress]

VACATION !!!!

Whew. Was starting to think you'd gone on vacation to the Outer Banks during the last few days..

 

[TheFishMan65]

No I went the other direction to the Blue Ridge Mountains. As near as I can tell no power loss from the earth quake or hurricane .

jkopp36,
What current do you need to limit the HLG to? I mentioned it somewhere (kcress do you remember?) about adding a parallel resistor to a 100k pot that will keep the voltage down.

 

[jkopp36]

jkopp36,
What current do you need to limit the HLG to? I mentioned it somewhere (kcress do you remember?) about adding a parallel resistor to a 100k pot that will keep the voltage down.

I've got the voltage capped by using a resistor and diode so that it does not go over a certain amount but I'm worried about the possibility of an open circuit which would cause the driver to run at full throttle+ and thought that if I could just put a 10K resistor accross the circuit right at the driver it would be a good failsafe. I'm guessing it's not that simple but that there might be a way using some other components along with it. I'm not even sure what happens to the variable voltage ports on an Apex if it loses power or something so it may not even be that big of a deal but I like redundancy whenever possible. Hopefully that makes sense.

 

[TheFishMan65]

Making up some numbers then. Lets say you need to limit the current to 70% of the HLG output. There are three ways to control the current:
- PWM - not applicable but even in this mode you can't go above 70% for the voltage. Anyone know if they really limit the current or pulse the current? Reading the datasheet it look like it limits the current.
- Resistor only you would need a 70k ohm resistor across the the dimming signals
- Voltage would need to be limited across the dimming signals to 7 volts.

So if you removed your controller you would want a 70k ohm across the dimming signals. So start there. Now the controller can output 10 volts and you need to limit it to 7 volts. Using a resistor you can add a 30k and you can never reach more than 7 volts.

+- Up to 10 volts from the controller
|
30k resistor
|
+ Dimming + to the HLG
|
70k resistor
|
+ Dimming - to the HLG and ground reference of the controller

Your only risk is that the 70k resistor comes loose and I don't see a way to mitigate that risk. I assume you still plan for fuses in your circuits.

 

[jkopp36]

So like this then?:

 

[TheFishMan65]

Sure show off for the crowd with fancy pictures

But, yes that is what I mean. It will also allow for the full range of the controller's dimming. Just change the resistors for whatever percentage you need.

 

[jkopp36]

Sure show off for the crowd with fancy pictures

But, yes that is what I mean. It will also allow for the full range of the controller's dimming. Just change the resistors for whatever percentage you need.

lol - sorry, I've just burned up enough stuff in my time that I wanted to be sure.

Can I just use common resistors available at RS?

Thanks for the info. Good stuff!

 

[TheFishMan65]

There should not be a lot of power so 1/4 resistors should be fine.

 

[brassmonkyballs]

Issue I see is he wants to prevent open circuit causing max output. This solution caps the Max output to whatever resistor you use. If you want to limit it to 10% output in the event of an open circuit this won't work without limiting your output during normal operation. You can always limit it to a higher value as in fishes example of 70% which limits max with your controller and in the event if an open circuit but I thought you already had that figured out.

My suggestion is to try to take advantage of fuse.

 

[jkopp36]

I see your point brass. TBH, I'm not even sure what the output from the Apex does in situations such as power outage, rebooting, etc. I may just run it first and see how it goes. I do have everything fused. I am not as worried about it now after reminding myself that even at full power the drivers shouldn't be putting out enough to really hurt anything short term (742mA on the XPEs and 1300mA on the XPGs at 100%).

 

[jkopp36]

Well, in doing some final testing last night before wrapping up my build I have ran into a bit of a confusing issue. The dimming circuit on my HLG-240-54B seems to be causing some problems but even more confusing is that even at full throttle it should not be able to get anywhere close to 1A on each string but it has popped my 1A fuses twice now on start-up. I'm running 6 strings of 14 XPE RBs with it and it should max out at around 743mA per string. Even at 10% over max it should only be around 810mA so I cannot figure out how it is blowing all 6 fuses. I could see if a string was open or something but even then I'm only at max 972mA and less than 6 of the fuses should have blown. I've also tested each string using a spare ELN and they are all fine. I was feeding the dimming circuit 1.25v with a bench supply I made and plugged the driver in after the dimming circuit was live. The HLG-185 I am using on the XPGs is working perfectly using the same testing method.

Any ideas or thoughts? Very perplexing.

 

[TheFishMan65]

Can you switch the HLG from the XPG or is it different?

What if the bench supply is at 0 volts? Then plug in the HLG and ramp up the bench supply. Maybe (it shouldn't be) the ramp up is required.

If you can get it to run at 1.25 volts what are the current through each string?

It looks like at 700ma the the XP-E runs at about 3.4 volts 54/3.4 or 15.88 LEDs per string. We have heard the ELN can supply more than the stated 1.3 amps at lower voltage (power is probably the same). Maybe the HLG does the same thing. Can you add 1 or 2 more LEDs for testing?

 

[TheFishMan65]

Oops - double post

 

[jkopp36]

The 185 is a 24v.

The lowest my bench supply will go is 1.25v so that's why I started there.

I only had 3 1A pico fuses left so I did not do any more testing last night. I'm going to pickup some inline holders for glass fuses and a bunch of 1A AGC's so it will be easier to switch them out if/when I blow them again.

There is a remote chance I damaged the dimming circuit on the 240. The power supply I used when I first started testing was not regulated and was doing some weird things. That's why I put together the DIY bench supply. I did have the 240 running ok Sunday using a 100K pot but there was a very limited area on the pot to get from approx 10% to full power on the driver - like maybe a 16th of a turn on the pot so something weird is going on. May be a $100 uh-oh but I'll know more tonight hopefully.

BTW - The HLG-185-24B drving the XPGs seems to be working dead on specs but I'll have some hard numbers to post soon. My strings need to be balanced first. There is a fairly substantial difference between the sting with the highest current and the string with the lowest - something in the neighborhood of 750mA vs. 1100mA.

 

[jgwinner]

I found a really great heat sink calculator:

http://www.luxeonstar.com/kb_results.asp?ID=41

== John ==​

 

[rysher]

i'd like to tap on the experience that you guys have here.
is there a big difference in luminous intensity by running an XPE RB @ 625mA compared to running @ 750 mA.
I believe most of the DIY'ers are running theirs at 750mA?