LED light & salt water/waterproof battery container

[Sean Bartleet]

Hi,

I have made a small LED light consisting of 2 AAA batteries, a switch,
resistor and an LED.

Does anyone know what will happen if this is frequently splashed or even
submerged in salt water?

I know that salt water is conductive. I presume that when submerged current
will short circuit. What will the affects of this be?
Will it drain my battery, does anyone know how quick this will happen? Will
it be like a direct short?
Will I damage the LED?
Will I get corrosion? Could I put a sacrificial anode in my system to direct
the corrosion to a particular point?


The light is to be used as a blacklight for a compass on my sea Kayak. So
when it is rough it is likely that there will be a lot of water frequently
splashing the deck. And if I capsize The whole thin will be submerged.

I have been unable to think of a way to waterproof the light. I considered
encapsulating the whole thing in a ball of silicone, this presents problems
when I need to change the battery. I have tried in vain to get a waterproof
battery holder. There is limited space under my compass, just enough for a
double AAA battery pack placing the battery pack in a film canister will not
work. I need to find out if the problems I will experience will out
waterproofing will outweigh the hassle of re encapsulating the whole thing
in a ball of silicone every time I need to change the battery.

Any suggestions will be welcome.

Sean

 

[default]

Hi,

I have made a small LED light consisting of 2 AAA batteries, a switch,
resistor and an LED.

A UV LED that runs on three volts? They typically take much more -
3.6 to 4.0 so three cells are often used for 4.5 or you could use a
lithium type cells. (3 volts per cell)

Does anyone know what will happen if this is frequently splashed or even
submerged in salt water?

I know that salt water is conductive. I presume that when submerged current
will short circuit. What will the affects of this be?
Will it drain my battery, does anyone know how quick this will happen? Will
it be like a direct short?

It will drain your batteries over a period of hours but the major
problem will be corrosion / electrolysis - use once throw away.

Will I damage the LED?

I may eat the leads away but the led itself is well protected

Will I get corrosion? Could I put a sacrificial anode in my system to direct
the corrosion to a particular point?

Sacrificial anode won't work - the voltages produced by a zinc anode
will be much less than the 3+ volts you have. The zincs only work on
metals when there's no additional source of voltage.

They do make an active system where the anode is an electrode fed by a
battery and electronics that adjusts the voltage to protect the metal
parts - but that's not really going to work for you and is too
complicated.

The light is to be used as a blacklight for a compass on my sea Kayak. So
when it is rough it is likely that there will be a lot of water frequently
splashing the deck. And if I capsize The whole thin will be submerged.

I do a lot of kayaking (going today - winds gusting to 30 perfect
kiteyaking weather)

I also do a lot of underwater electronics work.

The easiest ways to waterproof electronics . . .

For prototypes and for total submersion I like to pot the stuff in
paraffin wax. Once a design is finalized it will get potted in epoxy.
LED's can poke through the surface of the epoxy or polyester resin -
they might be visible through the epoxy or resin, but most resins
don't tolerate UV light and turn yellow or pit when exposed to the
elements day in and day out.

Metal (steel cans) solder sealed with a backfill of mineral oil are
another good technique. Glands (wire-through) connections are via
something called a feedthrough capacitor that can be soldered to the
can and water proofed with some varnish. The oil provides crush
protection, a good dielectric insulator, and helps achieve neutral
buoyancy.

For serious stuff that needs a window I use PVC plumbing pipe and seal
with RTV and/or O rings. Those get backfilled with dry nitrogen and a
coating of varnish on the electronics.

I have been unable to think of a way to waterproof the light. I considered
encapsulating the whole thing in a ball of silicone, this presents problems
when I need to change the battery. I have tried in vain to get a waterproof
battery holder. There is limited space under my compass, just enough for a
double AAA battery pack placing the battery pack in a film canister will not
work. I need to find out if the problems I will experience will out
waterproofing will outweigh the hassle of re encapsulating the whole thing
in a ball of silicone every time I need to change the battery.

Any suggestions will be welcome.

Sean

Best easiest way for someone with limited electronics experience,
would be to pot the circuitry in wax, epoxy, or polyester. Use a
rechargeable battery and pot that too. (use a battery with solder
tabs or solder directly to it - don't use a battery holder) For a
switch you can use a reed switch close to the surface of the potting
compound with a magnet that slides into place to turn the light on.

That still leaves two connections that will be exposed. Use a pair of
brass tabs in the potting compound and coat them with solder. Lead
corrodes slowly in salt water and can easily be replenished with just
the touch of a soldering iron.

The two wires (tabs) will be going to the rechargeable battery and
will cause it to discharge when coated with spray or submerged. That
can easily be remedied with a small silicon diode (one way valve for
electricity).

If you do a lot of electronics, building an inductively coupled
charger would be a neat trick (the way some medical implants are
recharged).

An easy technique is to just buy a small waterproof 3-4 cell
flashlight and modify it to hold a UV LED.

Or . . . give up the idea of UV and use cheap disposable LED pen
lights.

Use chemical light sticks? Not UV but real handy when kayaking on a
dark night with a buddy. My wife and I use them on a string necklace.
When she's in the lead she flips her light to the back and I wear mine
on the front.

Taped to the paddle shafts the movement makes them easier to spot at
a distance or over the swells.

 

[Zak]

If you do a lot of electronics, building an inductively coupled
charger would be a neat trick (the way some medical implants are
recharged).

Electric toothbrushes charge the same way, as you probably are aware.


Thomas

 

[The Alien]

X-No-archive: yes On Sun, 4 Dec 2005 18:11:38 +1000, "Sean Bartleet"

Hi,

I have made a small LED light consisting of 2 AAA batteries, a switch,
resistor and an LED.

Does anyone know what will happen if this is frequently splashed or even
submerged in salt water?

I know that salt water is conductive. I presume that when submerged current
will short circuit. What will the affects of this be?
Will it drain my battery, does anyone know how quick this will happen? Will
it be like a direct short?
Will I damage the LED?
Will I get corrosion? Could I put a sacrificial anode in my system to direct
the corrosion to a particular point?


The light is to be used as a blacklight for a compass on my sea Kayak. So
when it is rough it is likely that there will be a lot of water frequently
splashing the deck. And if I capsize The whole thin will be submerged.

I have been unable to think of a way to waterproof the light. I considered
encapsulating the whole thing in a ball of silicone, this presents problems
when I need to change the battery. I have tried in vain to get a waterproof
battery holder. There is limited space under my compass, just enough for a
double AAA battery pack placing the battery pack in a film canister will not
work. I need to find out if the problems I will experience will out
waterproofing will outweigh the hassle of re encapsulating the whole thing
in a ball of silicone every time I need to change the battery.

Any suggestions will be welcome.

Sean

A cheap water proof $5 LED pen light from Walmart does the trick for
me, but then again, there's no fun in that!


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and after sirname.

 

[default]

Electric toothbrushes charge the same way, as you probably are aware.


Thomas

Wasn't aware. Thanks, will check one out sometime.

 

[quietguy]

I am wondering about how important the light is to your safety. Do you need to
have it working at night? And does it mean you might be paddling to your doom
in the wrong direction if it fails?

If safety is a factor, then some back up might be the way to go - ie a couple of
those $5 pens just in case your other solution(s) fail while you are paddling in
the dark/fog etc



David

 

[Sean Bartleet]

Everyone,

Thanks for the replies, I really appreciate the suggestions.

The LED I have was sold as a Cat No Z 4074 3600med 5mm Ultrabright Red LED.
The specifications state a typical voltage of 1.8, 2.4 max. I am not sure
what a UV LED is.

I will look into the various suggestions made, much appreciated.

Quietguy, I guess that I will have the moon (some of the time) and a
flashlight as backup. I will look into the $5 pens.

Sean


in message

 

[default]

Everyone,

Thanks for the replies, I really appreciate the suggestions.

The LED I have was sold as a Cat No Z 4074 3600med 5mm Ultrabright Red LED.
The specifications state a typical voltage of 1.8, 2.4 max. I am not sure
what a UV LED is.

From your post "The light is to be used as a blacklight for a compass
on my sea Kayak,"

A "BLACKlight" is an Ultra Violet light, Green Blue White and UV
require more voltage than Red.

I thought you had a fluorescent compass card and wanted it to glow
with a UV light . . . I guess you meant "back light?"