One driver with two different led strips?

[Stefan]

Hello guys
Now that the CEN-100-48 driver (more or less "HLG-series"-like, with less cold start current) proved itself with the QB22A strips (these are incredibly bright in the way that I have to use the CEN-75-48 now due to plants' bleaching), I am left with a few strips from two manufacturers, 2 QB22A and 2 EB Gen2 1120 mm strips. The first has a Vf of ~44V and the second 39V.

Can I use the 100-48 driver to wire them all in parallel? I know that these voltages are both in the constant current region of the driver, but will the driver run these together?

Thank you

[de la soil]

I was told by the guys at Photon Phantom designs that small changes in voltage equal big changes in current, and may lead to thermal runaway thus burning the diodes out quicker. I initially inquired them because they say not to run two of their different boards in parallel because of that issue. If you're running them in series, I don't think that it would be an issue because of the constant current. But I'm just a diy guy so you may want an expert opinion, just reiterating what I was told. I'll post the response as well. So parallel with two differing voltages = bad, but in series may not be. Hope this helps

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[r2k]

Can I use the 100-48 driver to wire them all in parallel?

Yes, but....

As mentioned, running two different products will have it's challenges. Here is what I see:

1) It would definitely be better if you could run them in series, but that would mean all strips will need to accept the same amount of current. It also means the power supply must be able to source enough voltage to equal the sum of the two strips.

2) You can run them in parallel but you have to account for the voltage difference. You can do this by inserting regular old silicon diodes in series with the strip that uses less voltage. Each silicon diode will drop about 0.3 to 0.7 volts (see note on this below) when forward biased (ie- make sure you put the diode in with the correct direction) Add more silicon diodes for more voltage drop. You have about 5 volts difference between the two strips, so you would need about 7 diodes in series with the 39 volt strip and connect this in parallel with the 44 volt strip. I would recommend starting with 8 silicon diodes and measuring voltages to see how it all balances out. You might be able to bypass (or remove) one of the seven diodes when it is all working. You must make sure the silicon diodes can deal with the current that the lower voltage strip will consume and that the diodes are all adequately cooled or heat sinked. If the strip draws 1 amp, each diode will drop about 0.7 watts and that will make them get noticeably warm.

---HOWEVER---

You have to watch and consider the behavior of the strips over temperature. These are diodes, but they are not all the same. They behave differently as temperature changes. You can't just assume the strips will remain matched in performance as they warm up. Likewise, the silicon diodes will also not behave the same as the strips. They are all diodes but they have different voltage-vs-current curves and temperature-vs-current curves. I would recommend starting with eight diodes and then carefully measuring voltage drop and current through both strips over a wide range of temperatures. It is better to be safe than find out the hard way.

Putting in the silicon diodes is going to make your power usage less efficient. Current will pass through the diodes and convert to heat with no light output. That's probably OK for you but it is worth noting. Make sure you do a power budget to make sure the supply can source the current, voltage, and power needed.

If I had the parts, this is what I would do. They are probably useless without something like this approach anyway, so might as well try it out. I would really recommend trying to run the strips in series to avoid the extra set of diodes and the uncertainty of something cobbled up.

NOTE :

Regarding diodes, it looks like the plain ol' silicon diodes are not really available any more. I wrote this and then I checked the data sheet and found diodes have changed. The old diodes that drop 0.7 volts are wasteful and inefficient, so they now have lower forward voltages than the old days. These are all Schottky diodes, which mean they have lower forward voltage drops. Here is an example of one you can get on DigiKey:

http://www.onsemi.com/pub/Collateral/MBR340-D.PDF

This will drop 0.45 volts @ 2 amps and 25 DegC, 0.4 volts @ 2 amps and 100 DegC. Instead of 7 or 8, you will need more like 12 or 13 diodes. That's ok, more diodes to spread the heat over and they are about 16 cents each, so you can afford to buy a bunch. You just need to know the current you are going to use in the design and use the data sheet to figure out how many diodes you need.

...but I would still run them in series if I had the choice.
-r2k

[LEDG]

Can I use the 100-48 driver to wire them all in parallel?

Yes, but....

As mentioned, running two different products will have it's challenges. Here is what I see:

1) It would definitely be better if you could run them in series, but that would mean all strips will need to accept the same amount of current. It also means the power supply must be able to source enough voltage to equal the sum of the two strips.

2) You can run them in parallel but you have to account for the voltage difference. You can do this by inserting regular old silicon diodes in series with the strip that uses less voltage. Each silicon diode will drop about 0.3 to 0.7 volts (see note on this below) when forward biased (ie- make sure you put the diode in with the correct direction) Add more silicon diodes for more voltage drop. You have about 5 volts difference between the two strips, so you would need about 7 diodes in series with the 39 volt strip and connect this in parallel with the 44 volt strip. I would recommend starting with 8 silicon diodes and measuring voltages to see how it all balances out. You might be able to bypass (or remove) one of the seven diodes when it is all working. You must make sure the silicon diodes can deal with the current that the lower voltage strip will consume and that the diodes are all adequately cooled or heat sinked. If the strip draws 1 amp, each diode will drop about 0.7 watts and that will make them get noticeably warm.

---HOWEVER---

You have to watch and consider the behavior of the strips over temperature. These are diodes, but they are not all the same. They behave differently as temperature changes. You can't just assume the strips will remain matched in performance as they warm up. Likewise, the silicon diodes will also not behave the same as the strips. They are all diodes but they have different voltage-vs-current curves and temperature-vs-current curves. I would recommend starting with eight diodes and then carefully measuring voltage drop and current through both strips over a wide range of temperatures. It is better to be safe than find out the hard way.

Putting in the silicon diodes is going to make your power usage less efficient. Current will pass through the diodes and convert to heat with no light output. That's probably OK for you but it is worth noting. Make sure you do a power budget to make sure the supply can source the current, voltage, and power needed.

If I had the parts, this is what I would do. They are probably useless without something like this approach anyway, so might as well try it out. I would really recommend trying to run the strips in series to avoid the extra set of diodes and the uncertainty of something cobbled up.

NOTE :

Regarding diodes, it looks like the plain ol' silicon diodes are not really available any more. I wrote this and then I checked the data sheet and found diodes have changed. The old diodes that drop 0.7 volts are wasteful and inefficient, so they now have lower forward voltages than the old days. These are all Schottky diodes, which mean they have lower forward voltage drops. Here is an example of one you can get on DigiKey:

http://www.onsemi.com/pub/Collateral/MBR340-D.PDF

This will drop 0.45 volts @ 2 amps and 25 DegC, 0.4 volts @ 2 amps and 100 DegC. Instead of 7 or 8, you will need more like 12 or 13 diodes. That's ok, more diodes to spread the heat over and they are about 16 cents each, so you can afford to buy a bunch. You just need to know the current you are going to use in the design and use the data sheet to figure out how many diodes you need.

...but I would still run them in series if I had the choice.
-r2k

Nice! Talk about a detailed answer!

[Stefan]

yeap, very good answer! Thanks a lot!

I will quit this idea and order 2 more of each so each brand gets its own driver. More lights, more shelves, more joy