PWM LED dimming/flicker in marine environment

Thread Starter

JoshD

Joined Nov 11, 2017
8
Hi,

Could you guys give me some advice on the setup for LED strip lighting on my boat? Please bear in mind that I know a little but not a lot ...

I'm installing an engine on my boat, and so for the first time will have electricity pretty much on tap (hurray!). (For those who are interested the boat is an Essex smack, built 1892, 37' on deck: https://www.dropbox.com/s/thpmlw5pxy8oxey/Wivenhoe finish.jpg?dl=0). It's going to be a 12V installation, probably around 200Ah of lithium battery for domestic use. I've got around 12 circuits planned using LED strip, each circuit is 10W or less, and I wanted to be able to dim them. I reckoned I needed a load of PWM dimmers, and web research showed stuff available at every price point from £2-£100+. Starting at the cheap end I bought some of the £2 dimmers (12v or 24v, 8A, rotary control, loads on eBay), and actually it seems to work fine on my test setup, connected directly to a 12v battery, so I'm not necessarily in a rush to upgrade (unless you guys disagree).

But one thing I did find was that if I started charging the battery with a mains battery charger I got a lot of LED flicker. This is actually quite a realistic scenario as it will be commonplace to be charging the domestic battery either from shore power or from the engine alternator while the lights are in use. This set me thinking that it's probably not a great idea in any case to power my LED circuits direct from the domestic battery---I seem to remember being told that voltage variation kills LED strips. So my question is what sort of voltage controller to use (eg, LM2596, other DC-DC converter, regulator)? should I expect any problems of compatibility with the PWM dimmer? and should the voltage controller be upstream or downstream of the PWM device?

I'm planning to take the innards of the PWM device out and put it into a nicer box (along with an on-off switch), so that box could incorporate also a voltage controller. The rotary control on the PWM seems to be a 0-800ohm pot, and I might take the opportunity to upgrade that as it seems already unimpressive and likely to deteriorate in the marine environment.

Many thanks!

Josh
 

joewales44

Joined Oct 8, 2017
150
i would NOT use strip lights if you plan on using them for a long time. they turn yellow, burn out, and the glue doesn't hold very long.
there are many single LED lights called bolt lights or rock lights that will far outlast strip lights.
some are available with good drivers instead of just a resistor.
i would try to find some with pulse width modulation driver or at least a linear driver.
they sell rock light kits with a separate adjustable driver/dimmer that should work good for your application.
 

Thread Starter

JoshD

Joined Nov 11, 2017
8
i would NOT use strip lights if you plan on using them for a long time. they turn yellow, burn out, and the glue doesn't hold very long.
there are many single LED lights called bolt lights or rock lights that will far outlast strip lights.
some are available with good drivers instead of just a resistor.
i would try to find some with pulse width modulation driver or at least a linear driver.
they sell rock light kits with a separate adjustable driver/dimmer that should work good for your application.
Thanks Joe. One thing I didn't say: although my boat looks a reasonable size, it's actually tiny down below, with your head touching the underside of the deck when you're seated. Led strips are so compact and easy to install that I think they're pretty much the only thing that makes sense. I'm using aluminium extrusions with diffuser covers, which will hold strip into channel if glue fails (but I usually augment with double sided foam tape). I'm using 20mm extrusions with two strips, one very warm white (2500-2700K), the other red, so you can switch between if you need to protect night vision. I'm also using bulkhead lights, so it's not just LED strip.
 

Thread Starter

JoshD

Joined Nov 11, 2017
8
BTW, I have used LED strip for terrestrial applications with no problems. And I'm not using a resistor for dimming, I'm using PWM. The PWM circuit uses a pot for the user to specify the dimming level.
 

philba

Joined Aug 17, 2017
959
You can get sealed strips for wet environments. Not sure the applicable standards for salt water environments but even for interior use, I would look for that.
 

Thread Starter

JoshD

Joined Nov 11, 2017
8
You can get sealed strips for wet environments. Not sure the applicable standards for salt water environments but even for interior use, I would look for that.
Indeed, I'm using IP67 sealed units.

Just to explain, I've bought the strips, the led extrusions they sit in, and the pwm dimmers. My understanding is that PWM dimmers work by dividing time up into slots, perhaps a few milliseconds long, and switch the power off for part of the slot. The eye doesn't see the repeated on/off, but simply sees it as dimmed. It all broadly works and I am happy with it. My key question is about adding voltage stabilisation either before or after the PWM stage: (a) should I? (b) if so, how would I, in a cheap and simple way.

Any advice on that would be much appreciated!
 

philba

Joined Aug 17, 2017
959
It depends on the strips you are using. Do you have their actual specs? Particularly the voltage requirements.

How variable is the voltage on your boat going to be? For a battery bank, it will be in a pretty predictable range. Not sure about your generator/charger circuits. In an automobile, you can go as high as 14+ VDC.
 

Thread Starter

JoshD

Joined Nov 11, 2017
8
It depends on the strips you are using. Do you have their actual specs? Particularly the voltage requirements.

How variable is the voltage on your boat going to be? For a battery bank, it will be in a pretty predictable range. Not sure about your generator/charger circuits. In an automobile, you can go as high as 14+ VDC.
The specification voltage for the strip is 12v. The LEds are 3528, 60/metre, dimmable, drawing 400mA/m, so power consumption is 4.8W/m. I expect to have somewhere in the range 1-2m in each circuit.

Except for extraordinary events, I would see the power supply staying in the range 11-14.5V. It will be at the lower end of this range when either the battery is running low on charge or is feeding the anchor windlass (draws up to 70A); and at the higher end when either the shore power is connected or the engine is on driving the alternator.

There's a particular problem with charging from shore, and possibly with alternator use as well, in that the led's flicker, I guess picking up the 50Hzcycle of the mains, along with what high frequency components come from the alternator.
 

Thread Starter

JoshD

Joined Nov 11, 2017
8
Further research and I think I've answered my own question: it seems like best practice is to add a buck-boost converter. I'm inclined to have a single high capacity (100W+) unit for all the lighting circuits. Incidentally some manufacturers of 12V bulbs include a buck-boost-converter in the bulb electronics----worth looking out for.
 

Thread Starter

JoshD

Joined Nov 11, 2017
8
... except the whole thing I was concerned about in the first place was the terrible interaction you sometimes get between buck-boost and PWM devices. Isn't this why so many dimmable LED steups either don't actually dim, or do so only with unacceptable buzz/flicker?
 

philba

Joined Aug 17, 2017
959
Yeah, buck-boost DC-DC converter is the way to fly on that. It will keep your light string at an even brightness while the voltage is going up and down.

If a string has an integral buck-boost DC-DC converter then PWM would likely interfere with it. It's trying to keep the voltage at 12V and the PWM module is sending a square wave. The DC-DC will try to restore a constant 12V. This is why you put the DC-DC before the PWM module. It's possible that the DC-DC won't like the load swinging between very low and high. A faster PWM cycle may help with that.
 

Thread Starter

JoshD

Joined Nov 11, 2017
8
Thanks philba.

Knowing to put the buck-boost upstream of the PWM will save me some time here (I'd been thinking that it probably had to go the other way round: in the terrestrial world on AC you put the leading- or trailing-edge dimmer, sort of the equivalent of the PWM, upstream of the driver). But I guess what's called for is a certain amount of trial and error in just trying to find a buck-boost and PWM that are compatible. I'm not someone to make my own so I'll be buying in ready-built circuits, so any advice on what to look for when I'm shopping would be great, otherwise it get's both expensive and time consuming. I haven't seen any PWMs that allow the user to speed up the cycle---certainly the £1.70 one I'm playing with doesn't---so if you know of any do let me know.

Josh.
 
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