Thinking of building my own 7500lm worklight

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Cuprani
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Thinking of building my own 7500lm worklight

I wan’t to have a new floodlight / construction light for DIY work around the house and garden.
It must be powerful enough for (inside) paint jobs at night.
It must be portable, but not for travel.
And it must be a cheap.

I have owned a couple of different flood lights with claims of 20W to 100W which just aren’t bright enough. Even the more expensive ones from the tool shop are not what I expected.

Now I’m thinking of building my own.
I wanted to share my thoughts before I start building it.
Maybe you guys have got some great ideas because I never really build anything like this.

I have a large 3D printer available and I still have some stuff in my garage (which makes it possible to build cheap, with probably some overkill parts).

Battery
I have an 1000 Wh 4P20S 26650 li-ion battery left from my ebike.
It has a couple of bad cells, but I will dismount is to make my own battery packs of 4P(arallel) and 3S(series) (10,8V nominal power and 12,6V fully charged).
That is 12 × 26650 cells in total, and I want to make 2 or 3 packs.
3600mAh for one cell, so 14400 mAh in total for 1 battery pack
Capable of about 80 Amps continues (because I will never use any over 10 Amps, heat will never be the problem in case of the battery)
This way the battery pack will be 104mm x 78mm and 650mm high (+ some packaging), and will weigh about 1 KG

Light
I also have an unused 12V led-strip of 5 meters. (120 leds/m SMD 3528)
I will use this for my first test build, but I want to buy a more powerful led strip for my final build.

Was thinking of a 5 meter SMD 3528 led strip.
240 leds/m
1500lm/m
20W/m
4000k
12V

Housing
I will wrap this around an aluminium tube with a diameter of 150 mm.
The tube will be about 120 mm high (at least) for the 5m led strip to fit.
This tube is very light weight and will spread the heat of the led strip a little.

The tube will sit an a 3D printed base plate.
And I will slide over a 200mm polycarbonate satin finished tube for defusing and softening the light.

I want to design a round housing for the battery pack that will fit inside the aluminium tube.
The top will also be 3D printed, and I will mount a Battery Management System and dimmer in the top.

Total height will be around 20 cm.
Total weight about 2 KG
I’ll make a hook on top
I’ll put a nut under it inside the housing to be able to mount it on a tri-pod

Thoughts..
Will this work?
Do I need any cooling for the led strip?
Any other suggestions? Better led strips to use? Or other design features to make it better?

Edited by: Cuprani on 10/16/2020 - 15:45
Robin Dobbie
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Yup, buying LEDs based on wattage is not a way to get what you want. You could have one like that’s low-CRI, pegged at 100 watts and outputting 6000 lumens. And another one that’s high-CRI, drawing about 60 watts and outputting over 10,000 lumens, but with the capability of handling about 200 watts and still maintaining some decent efficiency for a total of almost 28,000 lumens. If you have a decent heatsink.

COBs that do that are* about $20(compared to the $4 ebay pieces of shit)
heatsinks that handle that are about $45
drivers that handle that are about $10(plus a few more for a fan, I’ve found)

Cuprani
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Of course you could always go bigger and better, but then it won’t be cheap anymore.
Any suggestions on other type of LED strip that could do the job better and won’t cost me a lot?

And I will use a 12V DC powersuply so I don’t think I need a led driver.
I could use a voltage stabaliser I supose.

If heat would be a problem I could mount a fan insite the aluminium tube and vent the air from the bottom to the top, but I don’t know if that would be enough.

Robin Dobbie
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I dunno, that’s still pretty cheap.

You could go with a last-gen COB and an OEM PC CPU heatsink and still come out better than what you’re proposing.

Stock intel and AMD heatsinks are like $10
COBs that crank out 9000 high-CRI lumens with as little as 60W are $13(although, could handle 130W for 16,000 lumens if you spent $25 on a heatsink)
Got to have a constant current driver. Not an option. That’s one of the problems with the light strips. Sure you can get away without a driver because the strips are peppered with current limiting resistors. But you’re pissing away efficiency. When you were told you would get 1500lm from 20w I don’t believe it. That’s 75lm per watt but I believe it would end up being closer to 50 at temperature. I could be wrong, but I would bet money that’s what they do.

Cuprani
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I still have 2 stock CPU coolers at home from PC upgrades so that won’t be a problem.

But what kind of cob leds must I look for? What kind of brands, types, specifications? Do you have a link or site to start from?

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Cuprani
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Thanks, but those aren’t nearly around the $13 that Robin mentioned.

Robin Dobbie
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So you’re in the netherlands, I’m more familiar with digikey. but I did find something good.

L2C5-40801812F2300

https://www.avnet.com/shop/emea/products/lumileds/l2c5-40801812f2300-307...

Here’s my search strategy

Digikey search strategy

Robin Dobbie
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Digikey.nl might work for you as well.

Cuprani
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Many thanks!
Can I use this kind of driver to power them with my batteries?

€ 4,09 | 400W DC-DC Step-Up Boost Converter 8.5-50V To 10-60V 15A Constant Power Module Led Driver Voltage Charger Power
https://a.aliexpress.com/_BOwoEh

This is a constant current driver I supose. How do I regulate the power (amps) of these things?

Robin Dobbie
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Yes.

Keep in mind when they say:

“(please enhance heat dissipation if more than 8A)”

Bless their hearts, but what they really meant to say was:

“(please enhance heat dissipation if more than 2.5A)”

There is a diode and other components on that unit that reach ridonkulously high temperatures without active cooling. And in my experience, they start doing undesirable things above 2.5A after a few minutes of passive cooling. So they either need their own fan, or to be positioned such that they catch a breeze from the primary heatsink fan on your LED.

Coming from a 12V power source like you mentioned, to get 60W that’s 5A(60/12=5). Unless my input voltage was at least 30V, I would want to make sure that’s getting active cooling. So on batteries that would be your cut-off voltage for a 10S configuration.

Another consideration with these units is inrush current. I can not start them at full power, on their own, successfully, especially on power supplies with fuses or inrush protection. They can also have problems on high-drain cells because these units can even blow their own fuse. When you fist turn them on, those capacitors will fill up and appear almost like a dead short to your power supply. I can usually get them to do OK if I start them at a low output then ramp to the desired output. You can use an SPST POT to be the power switch and to ensure that when the switch is turned on, the output is automatically at minimum.

Another option is an inrush current limiting thermistor. These are great because they’re cheap and automatic. But if someone plays with the light, turning it off, then back on within like a minute, the thermistor will not have had time to cool down and raise its internal resistance and inrush protection back to the levels you need, and then you’re back to blowing all the fuses again.

Yokiamy
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Interesting, i’d like to know what you come up with!

Robin Dobbie
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Another thought. Given that this is a worklight and could be left unattended, and you’re using cells, you might consider the 1200W boost converter. You don’t need that much power. But for one thing you might be able to get away with passive cooling. Most importantly, however, those converters have a low-voltage cut off trimpot so if you forget to monitor your cell voltage, you don’t accidentally over-discharge. You can dial in 30 volts and if the combined voltage of all your cells falls below that, it shuts off. Really something to think about.

Cuprani
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I will use a battery management system for my batteries for sure for equal balanced dicharge and safe cut off of the cells.

Will look into de SPST Pot as well.

I’m looking at design options now as I want to be able to use it outside as well. It doesn’t have to be waterproof but must be able to work in mild rain.

Robin Dobbie
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For the emitter I’ve seen people just make sure they don’t destroy the insulation on the wire up to the leads, then they hot glue the exposed solder joint. For the converter there are a few options from spray clear coat to epoxy to fingernail polish. I like the thought of potting compound as well. You just dip the whole thing. Not sure how that affects thermals with this. You could just position all the electronics under a cover. I have a lot of experimentation I needed to have already been doing, I’ve just been lazy. And poor. I realize in the experimentation I may lose a few trying to find out what works. So I’ve been using what I have strictly in good weather(indoors), at the moment.

I’ve been on the lookout for a weatherproof SPST potentiometer. If anyone knows of one I’d be interested. My thoughts on this right now are I need to find a rubber sealed bearing with an ID(Inner Diameter) the same or similar(larger) as the OD of the pot shaft. Should be easy enough to seal up any slight play, there. This is probably what I’d do regardless because regular industrial, water-proof switches start getting pricey, fast.

There are IP52 and IP67 fans, now. I’ve got an IP67 Noctua, but it’s 140mm and was about $30 on its own. The 120mm version isn’t much less. Not sure it sounds like you want to add that expense. Maybe just keep everything covered and be weary in heavy rain with wind.

Cuprani
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I did a quick and dirty sketch. Measuring isn’t accurate.
I couldn’t let loose the idea of a lantern type of light. But maybe I should, and go for something entirely different.
But this way the it will be rain proof.

I think this design will be good for lightning up an entire room when placed in the center of the room.
The “glass” in this design will be the satin finished poly-carbonate from above. This emits 85% of the light and gives it a soft tone.
I’ll hope this will give less hard shadows.

The bottom part will probably be square instead of round because that will make it more easy to install the necessary buttons or displays.
The frame will be made out of 4 large M8 bolt threads where I can mount all the parts and can carry the weight.
Of course this will not be a slick and smooth design, but I don’t care, it only has to be functional.

Cuprani
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I bought some stuff and I found some stuff.
Now waiting for delivery witch will probably take a month (with China shipping).

COB
“ Samsung SPHWHAHDNM251ZR3D2”:https://www.arrow.com/en/products/sphwhahdnm251zr3d2/samsung-electronics
CRI80 at 5000k
13196lm at 1,62A 52V

Driver
1200 watt DC DC CC CV buck converter

Display with amp meter

BMS for the battery

And I’ve found myself a heatsink laying on the shelf.
A Thermalake Big Typhoon.

Cuprani
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Total BOM so far: 25 euro Party

I should be able to have 1,5 hour battery time at low power mode (1,62A), taking in account an 85% efficiency of the driver and 80% use of the total battery capacity.
With 2 or 3 battery packs that will be enough for me.
I will use a 200 Watt laptop charger when I need to use the light for a longer period of time.

At high power mode (turbo mode) I must limit the battery power to 20 Amps because of the limits of this driver.
I could build an 4S4P battery to eliminate this, but this would add 400 grams to the design…
The battery already weighs an 1200 gram in 3S4P.
With 4S4P that will be 1600 gram.. Shocked I think I don’t want that and just limit the power output to 20Amps..

Robin Dobbie
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I might lubricate or even just replace the fan on that old Thermaltake. A seized fan means a dead LED. Look for dual-ball bearings. Otherwise that’s a fantastic sink!

You really want higher input voltages. At 20A, you’d need a dedicated 20A switch. Still a good idea to start fully-dimmed. I don’t remember if I linked to how to set up the dimming. When he’s talking about the trimmer, he’s referring to the CC or constant current trimmer.

Laptop PSUs are often over-rated. I might limit to 60% of whatever they’re rated if you’re using it for hours. Don’t even think about stuffing it in that housing where there’s no airflow! lol

Those boost converters will definitely need active cooling above a few amps. Take a look at the 30A boost converter and see what they’ve done to it. It’s essentially the same thing, but with an extra little heatsink and a little fan.

For my boosts, I ordered extra 5×20mm fuses and in-line holders. They’ve definitely come in handy. Really nice to swap fuses without having to bust out a soldering iron. I got 5×20mm because they’re really cheap in those assorted packs and I have a lot of other stuff that uses that size.