Lamp powered by salt & water??? - Page 1
Forum section: electronics / general

author: vk6zgo
author_rank: Super Contributor
timestamp: August 21, 2015, 06:58:18 am
content: I found this accidentally:-https://theoldreader.com/profile/5143057654cf8202f2000283?page=16Supposedly,it is some kind of battery.The lady says:"You just dissolve two teaspoons of salt in a glass of water,pour it "on" (I think they mean "in") the lamp,& you have light for 8 hours"."I verra much doobt it,lassie!"

author: Psi
author_rank: Super Contributor
timestamp: August 21, 2015, 07:23:34 am
content: Hard to say how bright that is because the camera exposure can make it look brighter.But you can definitely power an LED from a salt battery.

author: Unknown
author_rank: Unknown
timestamp: August 21, 2015, 07:44:17 am
content: Water-activated batteries have been a thing for a very long time (I nearly ended up making one as part of a college project).

author: TheAmmoniacal
author_rank: Unknown
timestamp: August 21, 2015, 07:52:52 am
content: Sure this isn't a normal zinc-copper type of battery lamp?

author: coppice
author_rank: Super Contributor
timestamp: August 21, 2015, 07:59:31 am
content: If you've never heard of these you haven't properly listened to the safety demonstration on a plane.Every life jacket contains this type of battery. Its a great choice for the application, as its completely inactive until the salt water flows in. Its shelf (or seat bottom) life is, therefore, very long.

author: TheAmmoniacal
author_rank: Unknown
timestamp: August 21, 2015, 08:28:15 am
content: I don't think this product (by SALt) is a water-activated battery at all, but simply two dissimilar metals separated by a membrane. As they state “Using SALt lamp 8 hours a day every day will give you an anode lifespan of 6 months.”, implying that the anode will corrode/be used up. I'd bet on a 3-cell ~ 3.3 V battery powering one LED. Their pictures are all taken in the dark, so there's no real sense of the brightness.But seeing you can get 180 AA batteries for $35, that's a better solution in my book. They even sell water activated batteries with unlimited shelf life:http://www.lazada.com.ph/water-activited-15v-aa-eco-battery-2pcs-blue-347136.htmlhttp://www.lazada.com.ph/kingever-extra-heavy-duty-aa-battery-40pcs-489304.html

author: Delta
author_rank: Super Contributor
timestamp: August 21, 2015, 10:13:00 am
content: 35 (US?) Dollars for a lamp that lasts only 6 months will not appeal to the third world...Another nice sounding product, but completely impractical.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 21, 2015, 10:37:09 am
content: They don't really say anything specific about the seawater activated light during the aircraft safety talk--------they just say you have a light which will automatically go on.What I am seriously dubious about is the life they claim.Actually,I didn't even notice the link that goes to the SALT site before,so I hadn't seen the anode life claim---I was thinking about the "8 hours" claim.Simple cells suffer from"polarisation",where hydrogen accumulates at the cathode,reducing the efficiency of the cell.This limits their operating life and is normally countered by the addition of so-called "depolarisers".Even assuming their claims are correct, a single LED is not anywhere as satisfactory as a light source as even the most basic of kerosene lamps.When I was a child,we lived without Mains power.We had a "Mantle" type lamp from the "Aladdin" company,which closely approached the light output of a 75watt incandescent lamp,It didn't use a lot of kerosene-----a 10 gallon drum would last us for weeks.We also had normal "wick-type" lamps which were not nearly as bright,but allowed us to carry out normal activities by their illumination.

author: coppice
author_rank: Super Contributor
timestamp: August 21, 2015, 10:47:28 am
content: Quote from: vk6zgo on August 21, 2015, 10:37:09 amHad you previously assumed it was by magic, rather than a water activated battery?

author: amyk
author_rank: Super Contributor
timestamp: August 21, 2015, 01:15:53 pm
content: Mike's teardown of a radiosonde contains a water-activated battery teardown too:(Seek to 14:30.)

author: Zero999
author_rank: Super Contributor
timestamp: August 21, 2015, 06:23:17 pm
content: Quote from: TheAmmoniacal on August 21, 2015, 08:28:15 amThat's exactly what a water activated battery is.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 22, 2015, 03:01:36 am
content: Quote from: coppice on August 21, 2015, 10:47:28 amMy point was that the "safety talk" doesn't say anything about how the lamp works,so your assertion is not valid.There are a lot of ways it could be automatic,other than water-activation.As it happens, Ididknow,from another source, that they are "water activated",but that,in itself,doesn't imply they use water as an electrolyte,neither does it validate your original comment..

author: vk6zgo
author_rank: Super Contributor
timestamp: August 22, 2015, 03:41:06 am
content: Quote from: Hero999 on August 21, 2015, 06:23:17 pmNot quite,---Mike's video shows exactly what at least one type of water activated battery is like.It is made up of conventional primary cells,except that the electrolyte is dry,& doesn't become active untilfreshwater is added.There is no question of the water doing anything other than to wet the existing electrolyte.A similar idea was used in the "dry-charged" secondary batteries which used to be available,which came as a "package deal" with the electrolyte in a separate container.Add that & you had a "ready to use" battery.They also had a long shelf life..

author: AG6QR
author_rank: Frequent Contributor
timestamp: August 22, 2015, 05:12:45 am
content: It's not powered by salt and water. The source of power, the energy input, is in the refining process used to make the dissimilar metals that make up the electrodes. A chemical reaction at the electrodes is what produces the electricity, consuming the electrodes in the process. This is like any other battery. At science fairs and such, you may see a "lemon battery", or "potato battery", or some other battery using an unconventional electrolyte. But they always use two dissimilar metals, and it's those metals, not the electrolyte, that provide the source of energy.Salt and water are cheap and plentiful. The electrolyte in a battery generally isn't the expensive and energy-intensive part. It's misleading to say the battery is powered by its electrolyte, because that makes it sound like, when the battery dies, all we have to do is add more cheap salt and water to make it work again. That's not the case. When this battery dies, what's needed are replacement electrodes. And the energy required to refine the electrodes is much greater than the energy output of the battery.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 22, 2015, 06:52:43 am
content: I used the phrase "powered by salt & water" because that was the description in the linked article.A simple cell could use a strip of copper & one of zinc.If we had to produce them in that size from the basic ore,they would be costly,but both metals are used in huge quantities throughout industry.The cost of constructing electrodes for practical cells is a lot higher,as you pointed out.Secondary cells have quite mechanically complex electrodes,with lead oxide paste pressed into a lead/antimony lattice.The electrolyte is a vital part of the cell---I could leave my copper & zinc strips in a container without an electrolyte till the cows come home,with nary a microamp generated.A perusal of various books,plus the Internet,yields no other reference to salt water as an electrolyte.If it were viable,the early pioneers of primary cells would have tried it.My general rule is,"if it doesn't sting your skin,it isn't a viable electrolyte!"

author: SeanB
author_rank: Super Contributor
timestamp: August 22, 2015, 08:56:47 am
content: I took a few apart, from scrapped lifeboats. The common electrodes are a zinc strip and a magnesium strip, separated by a small mesh. Wired up to a 2V 300mA bulb on the top of the life raft, and they sat in a small green plastic housing you dropped over the side into the sea water, which filled it via 2 small holes on the top and the bottom of the cell. They would light on brackish water, but in pure tap water nothing. They just had to run that little lamp for 48 hours minimum when dropped into a bucket of sea water.

author: Zero999
author_rank: Super Contributor
timestamp: August 22, 2015, 09:06:58 am
content: Quote from: SeanB on August 22, 2015, 08:56:47 amI wonder if the modern version uses an LED and Joule thief? That would certainly be brighter, last for longer and not require such a big battery.

author: PeterL
author_rank: Regular Contributor
timestamp: August 22, 2015, 10:23:26 am
content: Slightly related:There is a project going on in the Netherlands where there are creating energy from freshwater that flow's into the salty sea:http://www.fujifilmmembranes.com/blue-energy-technologyThey put some membrane's into our famous 'afsluitdijk' for this, which makes a nice seperation of fresh and salt water.https://www.google.nl/maps/place/Afsluitdijk/@52.9639321,5.3761719,9.79z/data=!4m2!3m1!1s0x47c8c5fe78ac4fb7:0x86222e093977e29e

author: SeanB
author_rank: Super Contributor
timestamp: August 22, 2015, 11:20:04 am
content: Quote from: Hero999 on August 22, 2015, 09:06:58 amDoubt it, the salt water battery is just as thick as 2 AAA cells and around twice as long. Simple enough, and with a lamp that is simple and robust as well, plus you can test it easily. Changing to a LED would require a recertification for the entire survival unit, along with having to stock 2 different spare parts in the 10 year phase out. Simpler to just leave it as is, as with a single person life raft in a survival pack if rescue does not come in 48 hours you likely are not going to survive in any case.

author: Zero999
author_rank: Super Contributor
timestamp: August 22, 2015, 12:39:35 pm
content: Quote from: SeanB on August 22, 2015, 11:20:04 amAre you sure? To light a 300mA bulb for 48 hours, you need a 14.4Ah battery which would be quite large, especially with such a simple battery chemistry.

author: SeanB
author_rank: Super Contributor
timestamp: August 22, 2015, 01:41:12 pm
content: Didn't say it is bright, just something that glows with power. In reality they only work 12 hours with reasonable brightness in salt water, then grow dimmer and dimmer with time. More a physiological aise, as the brilliant orange raft, the dye cartridge are the major visibility items, as a night adjusted eye probably will miss it in the dark unless there is overcast and no moon over a dead calm sea to drown it out.