I'm making progress on building a portable light for my kayak.

It will use 3 of following chips: 50W, 12V chips.

The battery will have to be portable so I'm planning to wire them in parallel. I calculate 11.25 Ah needed so thinking to get the battery between:

  • 12V, 14Ah
  • 12V, 18Ah
  • 12V, 35Ah

It is just going to depend on weight.

Each light will be in an aluminum housing and only turned on under water.

I've read about the troubles with overworking one LED when in parallel. Can I put a resistor before each of the 3 lights and if so, can someone direct me there?

Also, can I add switches to each light to conserve battery without overworking? That is, only turn on the lights I need?

enter image description here

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    \$\begingroup\$ "Can I put a resistor before each of the 3 lights and if so, can someone direct me there?" yes. it's called series resistor and is kind of required. \$\endgroup\$ May 16, 2021 at 13:59
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    \$\begingroup\$ If these LEDs are designed to operate from 12 V then they aren't just "chips". They might have series resistors built in to them already. You need to provide a link to the manufacturer's datasheet (and not the Amazon or Ebay seller's page). \$\endgroup\$ May 16, 2021 at 14:02
  • \$\begingroup\$ Unfortunately, I don't have a data sheet..hopefully when they arrive this week.. \$\endgroup\$ May 16, 2021 at 17:20
  • \$\begingroup\$ Nice casing bud. I hope it seals well. On the topic of series resistors, using series resistors with high power LEDs sucks. it isn't impossible, but boy does it ever just suck. I would strongly recommend doing what you need to to find current controlled drivers for the lights if they don't have built in resistors, even if you need to use a driver per light. Also if you have a "thrower" type LED like a COB with no lens on it, you probably want more of a broad wash of light than a targeted light cannon, so put some thought into what you use as a diffuser lens. \$\endgroup\$
    – K H
    May 17, 2021 at 1:07
  • \$\begingroup\$ You can lose a lot of light with each layer of lens. For ease of manufacture, you probably want acrylics, so I would recommend a combination of shaped acrylic lens sheet (like the pyramid sheet you see on flourescent lights for example) and flat LED diffuser sheet impregnated with glass microbeads advertised as "Opal" acrylic sheet although that may be specific to a brand. The shaped sheet has high transmissivity by virtue of being clear, and the microbead infused sheet diffuses through its full thickness rather than just having a frosted coating, so also has high transmissivity. \$\endgroup\$
    – K H
    May 17, 2021 at 1:11

2 Answers 2


That kind of COB LEDs have power control chip on board, it has even overheating protection. I am using similar, 50W, 120VAC without any PS, just straight connection. 50W is a lot of heat, you need good heatsink. And yes, you can connect them in parallel, total current will be sum of currents. Switches to each LED will be OK, just choose proper voltage and current.

  • \$\begingroup\$ This isn't a novel concept I'm building as folks use these lights fairly often on the coast...here is an example: afishnsealights.com/collections/batteries/products/… I was looking to build one to my specs and will be mounting the chips to 4in sections of 3/16" aluminum rectangle tube. Should I additionall add heatsink material to the back of the rectangle tube if they will be submerged? \$\endgroup\$ May 16, 2021 at 17:14
  • \$\begingroup\$ Just looking for confirmation as I'm learning here...so all will receive 12v in parallel...I just need to ensure I have enough amps to 1) power them e.g. >11.25ah and 2) enough to run them for the desired amount of time. So for example, 35ah will run them for ~3hrs and 14ah will run them for ~1.24hrs. With the switches in place, it will prevent one chip from taking too much current? i.e. not the same as running all 3 lights on and one being burned out? \$\endgroup\$ May 16, 2021 at 17:23

If it is a chip, it will have a datasheet missing in this question and an equivalent series resistor internally with a tolerance. on the best Samsung high efficacy LEDs, Rs= V+/3V * ~ 30% * 1/Pmax= 12/(10*50W)= 24 mohms +/- x%. So if you understand the tolerance, adding a small series R and to match all LEDs, but they must be at the same temperature. Otherwise you increase R to compensate for -4mV/‘C for each LED in series. But this is a poorman’s way as the battery voltage changes 10% over which the LED’s get continuously dimmer to nearly off, but it is also a good way to extend the battery life.

LEDString’s are completely different with only 3 LEDs per array thus 3x3V LEDs in series and a 3V resistor drop added.

FWIW this is not an answer since the question has no tolerances or specs.

You would need every part to be waterproof , which LEDs in epoxy are not. Something like this in 4A to 5A “ Waterproof DC Buck Converter, Yeeco 8-22V 9V 12V to 1-15V 3V 5V Waterproof DC-DC Step Down Voltage Regulator Converter 45W 3A Adjustable Volt Transformer” from Amazon for each light with a dimmer pot or switch.

  • you may have to also use Aluminum heavy wire non-corrosive
  • \$\begingroup\$ Unfortunately, they have not arrived yet so no data sheet...only the listing: amazon.com/gp/product/B081QBC9MZ/ref=ask_ql_qh_dp_hza \$\endgroup\$ May 16, 2021 at 17:19
  • \$\begingroup\$ You’ll need a 100W heatsink on each one and best to get and 15A adjustable Buck regulator for 14.7V Li Ion and everything must be cool not enclosed and water proof. silicone spray helps but hurts magnetics from capacitance added and also reduces light intensity but electromigration damage to substrate. If you don’t follow my advice run dimmer to avoid thermal runaway selfdestruction.. \$\endgroup\$ May 16, 2021 at 17:40
  • \$\begingroup\$ Stewart...just added a picture...assuming its water proof and staying submerged, do you imagine addition heatsinks needing to be added? \$\endgroup\$ May 16, 2021 at 18:23
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    \$\begingroup\$ As long as both conditions are true. Ok. \$\endgroup\$ May 16, 2021 at 19:49
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    \$\begingroup\$ I’m using high voltage LEDs (56V) but the same power rating. 3/16” box section should be fine. If the heat sink has water-cooling on the back then in some ways thinner is better, but 3/16 is good. \$\endgroup\$
    – Frog
    May 17, 2021 at 6:01

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