1 year later: Inside the Mars Hydro 300w (60x5w) LED light

It’s been just over a year since I started using the Mars Hydro 300 watt grow light. Taking a look inside it clearly needed a quick disassembly…

Mars Hydro 300W melted blue LED's

A few LED’s were visibly melted/burned. To be specific, 4 of the blue ones towards the center. I’m not sure if there’s something different about *those* particular 4 (compared to the other blues in this unit), but needless to say, these ones were toast. Before anyone asks, I did check to make sure there had been thermal paste behind them, and there was.

Mars Hydro 300W melted blue LED's - closeup Mars Hydro 300W melted blue LED's - closeup #2

I ended up replacing them with a few cheap white LED’s that I had kicking around, along with some fresh thermal paste.

As to other internals, I found out where the fruitflies had started going once my fly tape was full:

Mars Hydro 300W - fried fruit flies, yum!

Air compressor took care of things there. I was tempted to replace the thermal paste behind the heatsink (5 screws to detach heatsink from PCB), but the existing thermal paste had it glued on pretty good so I decided to leave things be.

Looking at the fan and drivers…

Mars Hydro 300W - fan and drivers

This had stayed pretty clean and dust wasn’t an issue. I gave it a quick shot with compressed air afterwards since I had it open anyway.

With the new LED’s soldered in, I plugged it in and was up and running….

…except for 1 other white LED that I’d missed.

Mars Hydro 300W - blue led's replaced - 1 more to go!

I pulled it apart later and swapped out that final LED. All was now well!

Thoughts After 1 Year of Ownership

This grow light’s seen various degrees of usage over the last year. Periods of running 24/7, periods of sporadic use on a timer, and periods where it hasn’t been in use at all.

I’m a bit disappointed that 5 LEDs went. It’s generally been well ventilated (ambient temps of 18-24 degrees C), and I really wouldn’t have expected LEDs to start dying. If Mars Hydro cheaped out somewhere, I’d guess it was in the LED brand/quality.

I do really like the rest of the unit itself though. The fan is fairly quiet, I haven’t had a power supply (LED driver) die yet (despite losing a few other drivers in other systems), the thing has a heatsink against the PCB, bypass diodes are used to keep the good LEDs running when an LED dies, and some of the “little things” are there too (bushings to electrically isolate PCB from screws that go into unit, cables nicely zip tied, ample thermal paste used, easy disassembly, etc).


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  1. Mine have burned out in the same place (but 8 in the center on a mars 600) and I have been researching what LEDs I should replace them with, its good to know I can use any colour thanks for your post.

    • Hey Dan, just to follow up a bit:

      The drivers do have a voltage range and different LEDs are driven by different voltages to reach the desired current – you have a bit of flexibility when it comes to swapping in LEDs of a different color but only to a point. Red 1W/3W LEDs tend to use around 2.2v each, and white/blue 1W/3W LEDs tend to use around 3.4v each. If for example you replaced *all* your leds with reds, the voltage might be too low for the driver’s range in which case it’s possible the driver might overdrive them and start blowing LEDs. Going the opposite route, if you replaced *all* your leds with a combination of blue & white the required voltage might be too high for the driver – in this case LEDs might start strobing or the driver might blow.

      The easiest way to minimize any potential issues is to replace reds with reds, and consider blue/white to be the same (replace blue/white with either blue or white).

      The other option is to look at the driver voltage range, and then add up the voltages of all your LEDS on that circuit – so if 1 of the drivers is running on it’s circuit… say… 25 reds, 5 blue, and 7 white, add up (25×2.2v) + (5×3.4v) + (7×3.4v) = 95.8 volts. As long as that falls within the voltage range printed on the driver you’re good – if it’s getting near the minimum/maximum of the driver’s voltage range you may want to adjust (swap to some reds to push down the voltage, or swap to some blues/whites to push the voltage up).

      All that said, if you’re just replacing a few LEDs, most drivers have enough tolerance that you can probably swap in whatever colors you want and get away with it. If you get to the point where you’re replacing a *lot* of LEDs though, the color is going to start to matter a lot more and you may have to do a bit of math to ensure you’re not trying to force the driver to operate outside of it’s range.

  2. Hi, I would like the unit to be used to emulate sunlight for solar cells testing. I did read somewhere that IR and UV can be turned on and off but I can not find documentation to prove that. I do not nead the IR hear, only the broad spectrum light.

    Can you tell me if that’s possible with the mars hydro 300 ?


    • I don’t believe this Mars Hydro has the dedicated UV/IR LEDs.

      In various LED units that do have them, if they aren’t hooked up to a physical switch the ideal option is generally to replace the LED with another (generally replace UV with either blue or white and IR with red to keep voltages similar).

      The less ideal option is to flat out remove/desolder them. If there’s a bypass diode the other LEDs will still come on. If there isn’t a bypass diode, you could solder a bridge in the line. Downside here, particularly if the unit happened to have a *lot* of LEDs is that this could push the voltage outside the range of the CC driver. Or if a CV driver is being used it’ll dump a lot more current through the existing LEDs and/or might overrun the driver.

  3. I want to reverse the fan direction to blow out the top, suggestions?

    • It might be a pretty straightforward fan flip on this unit, but I don’t recall for sure. Pull the 2 screws, flip the fan, re-attach. If it *doesn’t* reattach when reversed (which I’ve had on some units), you may have to do some modding but it’s rare that you’ll run into an issue that a drill won’t solve. Good luck!

  4. Any idea what the wave length of the yellow leds are on the Mars 300? Thanks

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