smithj108
New member
NO !!!!! .... Let me try and break this down:
Problem: a single driver to power multiple unbalanced strings by the use of load resistors in order to achieve current balance.
I highlighted the words "driver" and "load resistors" because they are at the core of your current (and "current") problems. A power supply deemed driver is basically a very very smart power supply. Load resistor are typically needed in "dumb" or voltage driven power supplies, so I fear by mixing of the two your are asking for issues. In your case this Mean Well is double smart in that it can drive to a specified current or a specified voltage - do not try to drive both! I know.... many who are, although it works for them, are theoretically operating these devices inappropriately - that said, yes, I can successfully hammer a nail in with a pipe wrench.
Now for some context. Best-case scenario: if you had one string or several balanced strings (ie same type & # of LEDs), then you would opt to run your Mean Well in "current regulation mode" ONLY. Hookup your DVM in series with the LED string, turn down the voltage POT all the way, then turn up the current POT until you measure the ideal operating LED current desired. Notice, no load resistors required - because the driver will self-vary voltages to maintain the set current (even if an LED shorts/dies)! This is the "ideal" way to drive LEDs. So note to self - consider independent drivers for different LED types (voltages), & do not mix on the same string (yes, seen it done - don't recommend it)!
However, let's leave our "ideal" world, your situation is unbalanced strings. Therefore, we can't use the current POT on your driver because it tries to regulate the sum of the current (all strings as one) attached. You are on the right track however - run the Mean Well in Voltage regulation mode - but ONLY in voltage regulation mode! That means turn the current POT all the way down, then turn the voltage POT up until you reach a desired voltage. Do this without any strings attached and connect your DVM measuring across the (+) & (-) terminals. Note: you "may" however need a small load attached, because the driver may detect an "open" circuit thus shutting itself off.
Now that the driver is in voltage-mode, we can now employ load resistors to isolate each string from affecting the others. We need some simple ohms law calculations for your load resistors to achieve "current balancing". Tip: in order to minimize stress on these load resistors we'll want to max out the total number of LEDs in each string to just under the max set voltage output of the driver. Here's how "I" would configure each string said our driver was set to constant 47V :
String 1 (2.9v LEDs):
(+)-->|-->|-->|-->|-->|-->|-->|-->|-->|-->|-->|-->|-->|-->|-->|-->|---/\/\/\/---(-)
(16) LEDs & (1) 1 ohm resistor {5-10 watts}
String 2 (3.1v LEDs):
(+)-->|-->|-->|-->|-->|-->|-->|-->|-->|-->|-->|-->|-->|-->|-->|-------/\/\/\/---(-)
(15) LEDs & (1) 1 ohm resistor {5-10 watts}
Now, the above two string calculations are good "on paper". The reality is that you won't hit the current specs exactly (but close). DO NOT try and muck with the current POT on the driver in order to tweak it in! Remember, you are in "voltage regulation" mode now, so the ONLY correct way to tweak current in each individual string is to alter the load resistors.
One caveat, I have not personally worked with that model Mean Well driver, BUT the datasheet clearly show it has the features I've described above.
Internet loses context, so please don't take my typing style as condescending. I see that you are a bit frustrated, and if you adhere to what I've written, you'll get out of this jam you are in (albeit your LEDs are not irreversibly damaged). I'd be happy to clarify any of this if you need - best of luck!
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