What kind of dimmer to get?

Sorry this is probably a stupid question, but I've bought a dimmer before and it didn't work as intended. So I was wondering if there's a specific kind you should be getting for your grow lights?

I have a Northern grow lights Photon 180w LED and it has a dimmer on the side but it doesn't seem to work properly, if I turn it all the way down it goes to full power and if I turn it the other way it slightly dims and then goes to full power at the other end of the dial as well.

So I was wondering what specifically I should be looking for in a dimmer, to ensure it works properly. (Is it even safe to dim lights like that externally?)

(The last dimmer I bought only worked half the time and would turn off the light and/or intake fan entirely when I tried to dim it)

Connecting the ac power cord to some other dimmer won't work, you need to replace the dimmer (potentiometer) in the light. Can you open it up and post pics of the dimmer and the label on the driver?

Open the casing and replace the potmeter if possible.

1212ham said:

Connecting the ac power cord to some other dimmer won't work, you need to replace the dimmer (potentiometer) in the light. Can you open it up and post pics of the dimmer and the label on the driver?

Click to expand...

Gotcha, here are some pictures, as I can see there are two drivers(?). Meanwell, can't seem to find the exact model when I look it up though, or I'm looking up the wrong thing.

I circled the dimmer in two of the photos. It has two fans as well but they were on the "roof" that I removed. Noctuas, decent!

Rennpappe said:

Open the casing and replace the potmeter if possible.

Click to expand...

I will have to look up how to do that, thanks! I messaged the company that used to make these and asked what they would suggest. The company doesn't exist any more but they merged and became something else. Can't hurt to try.

That looks very promising.
Usually when a potmeter is bad you can turn it left-right-left-right 30 times and that should make a difference. Internally it will be slightly dirty and by turning it you'll clean it.
However when it is really bad you can swap it.

1. get the knob off. If there is no tiny screw in the knob holding it you should be able to pull it off.
2. under the knob is a nut. screw that off.
3. the potmeter is now loose. pull it out from the back.
4. get the wires off. If these are soldered you'll need a soldering iron to unsolder the wires.
5. measure the resistance of the pot with a multimeter from the far left terminal to the far right terminal. This one will likely be 50 k or 25 k ohm. Many pots have the resistance written on them.
6. buy a new pot and solder it in and build the lamp back together.

But first try to clean it by simply rotating the knob!
Good luck

Rennpappe said:

That looks very promising.
Usually when a potmeter is bad you can turn it left-right-left-right 30 times and that should make a difference. Internally it will be slightly dirty and by turning it you'll clean it.
However when it is really bad you can swap it.

1. get the knob off. If there is no tiny screw in the knob holding it you should be able to pull it off.
2. under the knob is a nut. screw that off.
3. the potmeter is now loose. pull it out from the back.
4. get the wires off. If these are soldered you'll need a soldering iron to unsolder the wires.
5. measure the resistance of the pot with a multimeter from the far left terminal to the far right terminal. This one will likely be 50 k or 25 k ohm. Many pots have the resistance written on them.
6. buy a new pot and solder it in and build the lamp back together.
Good luck

Click to expand...

Thanks for the detailed info! I hope it's just dirty, but I appreciate the concrete steps!

Just in case I need to buy a new potmeter, what specifications should it have specifically? I'm not very electrically inclined, I'm more a computers guy Just the ohm? Or is there something else? Because when I check the biggest store in my country the selection is quite large

Most pots have the actual resistance on them like 10K or a 3 digit code in the part number. The 3 digit number is the first two digits then 10 to the power of the third number.

252=2.5k
502=5k
103=10k
104=100k
...ETC

Yes, and the axle (is this the right word for it?) must have a certain diameter for the knob to fit. For example 6 mm is a normal size I believe.
Some axles are long, this one is short.
Also some axles have teeth, you'll see it when you have the knob off.

HandyGringo said:

Gotcha, here are some pictures, as I can see there are two drivers(?). Meanwell, can't seem to find the exact model when I look it up though, or I'm looking up the wrong thing.

I circled the dimmer in two of the photos. It has two fans as well but they were on the "roof" that I removed. Noctuas, decent!



I will have to look up how to do that, thanks! I messaged the company that used to make these and asked what they would suggest. The company doesn't exist any more but they merged and became something else. Can't hurt to try.

Click to expand...

It's probably 50K ohm, linear taper. Don't buy audio taper. It will not damage anything if you get the wrong resistance/ohms.

1212ham said:

It's probably 50K ohm, linear taper. Don't buy audio taper. It will not damage anything if you get the wrong resistance/ohms.

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Op: This is what you need for 2 driver dimming, one driver use 100k ohm. You need to attach both dim+ to the middle tap/hole and dim - to either of the other holes; the side controls which way dims brighter/lower on the dimmer. Since they are usually cheap its a good idea to pick up a few spares, these tend to break down with use and getting dirty .

Rocket Soul said:

both dim+ to the middle tap/hole and dim - to either of the other holes

Click to expand...

In this case there's six wires; two red, two black and two white. The white is possibly a thermistor, wired in parallel, that is glued to one of the heatsinks that when overheating lowers the resistance of the dimming assembly to lower the LED current.

@HandyGringo


This image is provided with many Meanwell drivers. It shows that for dimming two drivers the pot needed is 100k/2 = 50k. But to be sure you'll have to measure the pot or see what's written on it.

Rennpappe said:

In this case there's six wires; two red, two black and two white. The white is possibly a thermistor, wired in parallel, that is glued to one of the heatsinks that when overheating lowers the resistance of the dimming assembly to lower the LED current.

Click to expand...

You dont need to know exactly what is what: just 2 same color wires in the middle tap/hole and 2 other same color wires to either of the other sides. Its easy when you have it in your hands.

I appreciate all the help and all the input! Just a status update, I bought an adapter to measure how much power the light uses, to see if the dimmer works/how much it works.

It's still not completely logical, like it doesn't go from 40 to 100, it goes 40 to 100 to 40 or something like that, but dimming wise it does work. I just assumed the knob was broken since it doesn't seem like logical behaviour. I'm not sure what word I'm looking for. It's not linear or incremental as I'd expect a dial to be.

But I measured it and at full power, it uses about 100w and dimmed as much as I can it goes all the way down to 40w, which is perfect for my use-case. So I don't have to change anything it seems, unless the dimmer breaks entirely.

Thanks again, much appreciated. Now I know what to do if it breaks.

There is a chance that this light was advertised as 180 watt (makes light as a 180 watt lamp) while being 100 watt.
So it's possible that the maximum power draw is actually 100 watt.

To check this, you can cut on each driver one of the dimming wires. The drivers will then try to deliver full power.
When the test is done you can reconnect the wires with two Wago 221:

There are already two Wago's in the lamp so it's not a problem to add some more