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Unread 07/20/2011, 05:53 PM   #1
Jocko
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parallel string and ballast question

Hey all. In my quest to avoid having an army of ELN-60's, I considered high voltage and high current. High voltage scares me so I started reading up on parallel strings.

My big idea is to use a 2.8A ballast and then split that out into 4 strings of 8 emitters each. The logic goes that if one string went out and there was an inrush of current into the other 3, that would not result in enough current to blow them. (They would be XP-E's.)

-Is there any flaw in my logic? I'm sort of assuming 8 would give me enough wiggle room to balance the strings. Not sure if that's wishful thinking.

I did have one question about ballasts. A drawback to my plan is it is VERY hard to find a suitable ballast in stock anywhere. The closest thing I've found that I can actually order is the Inventronics EUC-075S280DT. That's a 75W, 2.8A unit. The problem is that it is only 27V. This leads to my 2nd question:

-8 XP-E's would be about 27.2-28V total. Does anybody know what would happen if I tried to run 28V of emitters in each string?

It doesn't seem like that would be enough to trigger the over-voltage feature but I don't know enough of the theory of ballasts to know exactly what the impact of the extra volt would be on the operation of it.

Any help is most appreciated! Thanks!


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Unread 07/20/2011, 08:40 PM   #2
kcress
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More info please.

Total number of LEDs is 32?

You can run 24 or 26 on one ELN60-48 at 650mA+. Why not just run two ELN60s and call it a day. You could run up to 24 RB on one ELN and up to 14 Whites on the other.

You can buy ELN60s pretty much at your local 7-eleven. LOL

Then follow my build or jpcusa's build for the parallel and commissioning process.


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Unread 07/21/2011, 07:45 AM   #3
Jocko
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Yes the total number of LEDs on the ballast would be 32. 4 strings of 8 each. 50/50 mix of blue and RB.

So you are saying two strings on an ELN? I guess as long as there are fuses it would be safe? That would still leave me needing 4 ELNs since there's a total of 64 in the entire setup.

I'd like to avoid the ELNs if possible, but I guess that could be a fallback plan. Although I'd rather have them be able to get up to 700mA since they'll be going up against 32 T6 XM-L's. Yes, I enjoy making life more difficult for myself. Heh.

-Does anybody have any thoughts on my question of 28V out of a 27V ballast?

Thanks!


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Unread 07/21/2011, 01:56 PM   #4
kcress
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It would be a gamble to run that many LEDs in series on that driver. It might work it might not. It might work on a cold day and not work on a hot day. It all depends on the actual Vf of the LEDs you end up with. You are also not leaving any voltage for the resistors that you should be including in parallel strings. They need about a volt unless you use 0.1 ohm resistors and always remember to multiply your current readings by 10.


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Unread 07/21/2011, 03:08 PM   #5
Jimmy54
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I have 64 RBs (8x8) running from a HLG 185-30B @ 750/760mA - and 40 T6 XM-L CWs (4x10)from a HLG-150-36B @ 1000mA
I am going to add 20 more XP-E blue LEDs to be able to get the color more to my liking (and 10 more in reserve just in case it isn't enough)

Dailing down the current-output on the XM-Ls to enhance the blue color, works a little bit for the color but not for the par values, which I haven't measured yet but that's clearly visbile with the naked eye.
In other words; the ratio 32 RBs - 32 XM-Ls isn't such a good idea, unless you like a 10.000 - maybe 12.000K look.

I wouldn't use a 27Vdc driver to run LEDs from which use 28 - probably 27.5 volts in a string.
The driver needs a few "walk around volts" to play with to keep the current at the value the LEDs need.
Squeezing all the volts out, might stress the driver too much.
Hope it all make sense.


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Last edited by Jimmy54; 07/21/2011 at 03:59 PM.
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Unread 07/22/2011, 06:54 AM   #6
Jocko
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Oh yeah I had my eye on the HLGs. Where did you manage to get your's?? I've had a heck of a time finding any in stock anywhere!

Thanks!


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Unread 07/22/2011, 09:03 AM   #7
Jimmy54
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Pretending I had a company I was able to get them straight from Taiwan (China Republic) had to pay $100,- shippingcosts though,
but all in all a lot more cheaper than in Holland.
Now they are bugging me with E-mails to buy more, much more, and I can't seem to get rid of it.
I guess thats the price I have to pay for being sombody else for a couple of days.


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Unread 07/22/2011, 02:44 PM   #8
Jocko
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Thanks man. You inspired me. I just searched again and found a single HLG-150H-54B in stock and ordered it. ($7 shipping )

That should let me do 4 x 15 at 700mA which is close enough. I think I can live without 4 XP-E's. That should be including the resistor voltage (thank kcress for reminding me about that).

As for my XL-M's, I can get an Inventronics driver or two. Pricey, but they'll get the job done.


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