Questions about wiring LEDs and a fan

vance.110

New member
I could use a little or a lot of help with wiring a DIY light for a upflow algae scrubber being housed inside of an unused overflow in a 72G bow front. I feel comfortable with the lights (6x 3W Cree Reds and 2x 3W Ultra Blues) wired in series with the blues in parallel to reduce their output all running off of 1 Rapid Led Nano dimmable driver. My questions is about adding the pot. RapidLed no longer sells the driver with the pot attached so I'll have to do it myself. I'm confused about adding the power supply along with the pot. The driver specs say no additional ac power cord is needed, but the pot says a 10V ac adapter is needed to work with the driver... Will I then have 2 power cords running, one for the driver and another for the pot? Or will I not use the original cord that comes with the driver?

Also, would it be possible to run a small fan off of the same power supply? I only have about 2.5" between the tank and the back wall to make this fit and I wanted to put them in a 3d printed box to minimize light spilling all over the wall, and I'm worried the LEDs will overheat. I've bought 28mm individual aluminum heatsinks for each of the lights and was going to add ventilation to the box but thought adding a fan may work better. But running a second (or third) power cord sure seems like overkill for 24 watts of light.

I know I could buy a grow light for a lot less hassle, but there is no fun in that and I'm also working in a small 7x8" space and buying something off the shelf in that size that has decent LEDs is going to be next to impossible.
 

frankv702

New member
Which driver are you using? If it’s a mean well eln series driver, you’ll need a 10v reference on the pot so you will have two separate power cords for the one fixture. You may be able to run a fan off of the driver but you’d probably be better off using the 10v source for the pot to power the fan because if you do it through the output of your driver for the leds, you’ll be taking power away from them.

If you can’t find a 10v power supply lying around, you can use a 12v power supply and hook a 10v zener diode in reverse to it or create a voltage divider. That’ll regulate the voltage to 10v. You can also run a parallel wire off of the output to power the fan. Just make sure you get a 10v or under fan. Use a voltage use some resistors to get the current you need. The pot only needs about 50mA of current. A lot of the 10v AC/DC adapters are over 500mA so you’ll have plenty of excess to run a fan off of.
 

vance.110

New member

frankv702

New member
You can use that fan and driver, you’ll need a 12v power adapter and some components though to hook it all up but it would be pretty straight forward. If you want to do it, I can draw you a diagram of what you’d need to do to get it wired up correctly.

Basically you’ll need to wire the 12v source directly from the power adapter to the fan, have a parallel wire going to a small circui with a couple of resistors for a voltage divider to drag the voltage down to 10v going to the pot.

How important is it for you to have the lights dimming? You can use a cheap meanwell driver and wire up your fan and lights to the one driver so you just have one power cord.

Simple answer, yes you can make all of that work with the exception of your power adapter but it will take some diy simple circuit making.
 

vance.110

New member
Frank thank you for all of your input. I ended up ordering the 10v power adaptor for the pot. Having the ability to dim the lights was high on my priority list because I don’t have much room behind the take to create distance to lessen intensity. I know I could use a number of different diffusers but since this is going on my dads tank I want to make adjustments as easy as possible for him.
I also ended up ordering a couple of 12v pc fans from amazon. From other threads it looks like I can run the 12v fans off of the 10v power supply they’ll just run a little slower and hopefully quieter. Do I connect those in series to the pot?
Finally the leds I bought are from amazon
https://www.amazon.com/gp/aw/d/B00MN79YW8
I know they aren’t Cree or some of the other higher end brands but For my purpose I think they’ll be sufficient.
 

oreo57

Active member
looks like I can run the 12v fans off of the 10v power supply they’ll just run a little slower and hopefully quieter. Do I connect those in series to the pot?
Finally the leds I bought are from amazon
https://www.amazon.com/gp/aw/d/B00MN79YW8
I know they aren’t Cree or some of the other higher end brands but For my purpose I think they’ll be sufficient.

no, parallel..

If you find that a fan promptly starts up at a given lower voltage, then you should feel free to use that lower voltage.
Your fan will operate. It will make less noise. It will waste less power. It will last longer. Because it turns slower it will shift less air and it will have less back pressure.
You can't model an inductive load as a fixed resistance, especially a brushless DC motor. Some will actually drop in current as the voltage increases.
This is what I was alluding to orig. but apparently.. it depends...;)
Nothing to worry about except roughly adding # of parallel fans and current draw up..
The dim circuit prob. draws little current..

9-36V and 700mA.. IF it's the driver I saw soo. keep your series strings in that voltage range (volts add in series , the reason you don't run series fans btw..)

2.2V~2.6V DC
notice the range.. 5 (or possibly 4 at that current) is minimum per string..13 max of that part. diode..
Keep in mind cheap diodes are notoriously out of spec...;)
 
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frankv702

New member
Yes wire the fans in parallel. Keep in mind your power adapter is 500mA. So you have to see what current your fans need to make sure you have enough current being supplied to them. Your driver doesn’t need much current at all as it’s just a 0-10v reference for dimming but your fans are going to require a certain amount of current. Each time you branch off on a parallel circuit, your going to split current without resistors.

For example, you have 10v 500mA power supply you need to use for both the 0-10v reference and 2 fans. You’ll have 3 separate branches with 10v each splitting up that 500mA. You can use resistors to control the current you need in each branch. If you use a 200 ohm resistor on the parallel branch going to the pot, that’ll drag the current down to 50 mA on that branch and split up the remaining 450mA between two fans supplying them both with approximately 225mA. Just make sure you’re meeting the minimum requirements needed for the fan.

Also, with the leds you linked, they have a max forward voltage of 2.6v. Hook one up to a new 9v battery and test the voltage drop across it with a volt meter then notate it. then hook your meter up in series with the led and put it on the current setting to measure your current.

If you’re using 8 of those leds, total voltage drop is 20.8 volts (multiply the number of leds by the voltage you notated when measuring with your meter) out of your 36v available from your driver. This will allow you to hook up your 12v fan in series to your led string if you’re using only one fan. You’ll be supplying your fan with 12v but you’ll need to make sure your fan can handle 700mA of current. Depending on the particular fan, this option may also slow down and speed up the fan as you adjust the light intensity.
 

vance.110

New member
The max input current on the fans is 50mA so I'm assuming I would need to add resistors to each branch for the fans and the pot.
 

frankv702

New member
The fan you linked to rapid led is the one you’re using? How many are you planning on running?

The issue you’re going to run into now with a max input of 50mA for the fans is that your power adapter is 500mA. Current going into the parallel circuit will equal current going out. So you’ll need to put most of the current through the pot or create a current divider to allow only the amounts of current you need in each parallel branch.

What I would do is mount the leds to the heat sink, wire them up to the driver and light them up This will operate them at 100%. See how hot they get and then decide if you even need a fan. If they get too hot to touch, that’s too hot and you’ll need a fan. If they get warm to the touch but you can still leave your finger on them, they’ll be fine without a fan. Or even look for a bigger heat sink. I’ve used the below heat sinks up to 20 watts without needing a fan. You’ll be running a little less than 15 watts so it should be plenty if it’ll fit for your application.

https://www.amazon.com/dp/B01B6DLG3...olid=27ST5S1BWMKXD&psc=0&ref_=lv_ov_lig_dp_it
 

oreo57

Active member
AFAICT there is no need to "control" the current to the fans..or in any of that circuit.
You don't know what the power draw of the dim circuit is either btw, w/out measuring it..

As I understand this the current is "pulled" based on the part, not pushed..
and the pull is minimal i.e 50mA for fans prob. sub mA for dim circuit..

Resistor doesn't hurt per se.. but w/ a few brushless DC fans of the same model/type I'd just say it's not necessary..
If you had multiple fans pulling large-ish different current then "may be"

please note this is on my more limited knowledge base.

Can't see ever hooking up a fan in series w/ current controlled LED's or any for that matter.

Voltages to the string changes w/ temperature ect...your fan would fluctuate in voltage.
Even the Chinese don't do this.. ;)
It is a unique concept.

BTW 50mA seems low ..
 
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frankv702

New member
Absolutely there’s a reason to control current going into a device. If you hook a 500mA power source to a 50mA rated fan, the fan isn’t just going to operate at the 50mA. Current going in is going to equal current going out. So that 500mA current is going to go through that 50mA fan and overdrive it. Same with the leds. If you have a 1400mA driver and a 700mA led and hook them up without reducing that 1409mA, that led will last about 10 seconds before it blows from having more current flowing through it. When you load a circuit, it will have a voltage drop across it but not a current drop. Current going into that load will remain the same Coming out of that load.

Voltages to the string of leds isn’t going to raise or drop significantly to make a difference if you ran a 12v fan n in series In this particular example. A load is a load regardless of what component it is. As long as you stay within the specs of that component, it’s fine.

The Chinese also use 54 leds on a cheap pcb they pass off as a heat sink with two fans that are absolutely essential to get any type of life out of the leds.
 

vance.110

New member
FAN Specification
Size 40x40x10 mm
Mounting hole spacing 32x32 mm
Connector 3-pin
Bearing SSO2
Blade Geometry A-Series with Flow Acceleration Channels
Frame Technology AAO (Advanced Acoustic Optimisation)
Rotational Speed (+/- 10%) 4500 RPM
Rotational Speed with L.N.A. (+/- 10%) 3700 RPM
Airflow 8,2 m³/h
Airflow with L.N.A. 6,6 m³/h
Acoustical Noise 17,9 dB(A)
Acoustical Noise with L.N.A. 12,9 dB(A)
Static Pressure 1,78 mm H₂O
Static Pressure with L.N.A. 1,21 mm H₂O
Max. Input Power 0,6 W
Max. Input Current 0,05 A
Voltage 12 V
MTTF > 150.000 h
 

oreo57

Active member
FAN Specification
Size 40x40x10 mm
Mounting hole spacing 32x32 mm
Connector 3-pin
Bearing SSO2
Blade Geometry A-Series with Flow Acceleration Channels
Frame Technology AAO (Advanced Acoustic Optimisation)
Rotational Speed (+/- 10%) 4500 RPM
Rotational Speed with L.N.A. (+/- 10%) 3700 RPM
Airflow 8,2 m³/h
Airflow with L.N.A. 6,6 m³/h
Acoustical Noise 17,9 dB(A)
Acoustical Noise with L.N.A. 12,9 dB(A)
Static Pressure 1,78 mm H₂O
Static Pressure with L.N.A. 1,21 mm H₂O
Max. Input Power 0,6 W
Max. Input Current 0,05 A
Voltage 12 V
MTTF > 150.000 h

well I stand corrected.. I just happened to be replacing a computer power supply fan ATM and it was rated at 10x that 450mA...
OPP's 90mm fan on my end..
 
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