New Battery systems => Saltwater cells => Topic started by: Mungo on July 26, 2013, 01:41:37 AM

Title: Large Salt water battery ideas and questions
Post by: Mungo on July 26, 2013, 01:41:37 AM
So here is the basic project:  My wife and I have been working on a moderately large houseboat which we intend to move aboard early next year.  A large portion of the  motivation is reducing and taking control of our energy usage.  Accordingly, the original idea was to utilize solar charged deep cycle batteries with a generator backup to drive a paddle (stern) wheel and to provide general power to the vessel.  But recently I've come across information on large salt water cells, and the prospect of using one or two pretty large battery wells to provide power, replacing the electrodes and flushing out the electrolyte with new seawater as needed has become interesting.  So here's the concept we're playing with, and I'd love any ideas, comments, or information the community could provide:

As an aside I should say I am aware of much of the youtube content on such matters, as well as of the Enviro-Gen 12 emergency battery system.

The area I have to play with would create two battery wells, each 16" X 12" X 30", divided into cells (probably 15 from the information I've been able to glean regarding salt water batteries).  The flooded plates would measure at least 12X10", copper and zinc.  Now I'm sure that there is some formula somewhere that would show how much current and voltage such a cell would create, but I've been unable to find said.  It would be possible to create a continuous isolated flow of electrolyte through the batteries.  The salt content would run between 20 and 30 PPT, but that could be amended to a higher concentration.

The motor we were considering creates about 5 hp from 12 volts, geared down 225/1 and series wound.  (I got this idea from some folks building small electric sternwheelers using wench motors as they are already 12 volt and include reliable planetary gearing.)  The batteries would also need to run a modicum of marine electronics and some LED lighting.

Ideas?  Comments?  Anyone able to calculate the likely output?

M

Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on July 30, 2013, 07:17:50 PM
To add a bit of additional information, Seawater has a specific gravity of about 1.028 (though it varies depending on the place measured).
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on July 30, 2013, 10:54:05 PM
you might want to try magnesium plates instead of zinc and graphite instead of copper.it will pack much more power and last longer.
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on July 30, 2013, 11:26:06 PM
probably an excellent idea.  Im a little concerned, though, about availability.  This is rather on the lines of a "big dumb battery" concept.  Any idea for good sources for magnesium and graphite plates?
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on July 31, 2013, 02:54:33 AM
printing plates,old used ones from any print shop should do fine.otherwize aluminum might be a less better but easier option,parts of a ladder perhaps or thick foil roll.graphite can be cut to size plates by order from industrial suppliers of graphite products.do tests on small scale first by removing carbon rods from zinc batteries(non-alkaline ones,cheapo,s,its safe)and rinse and then heat the rods on your stove hotplate or over flame to evaporate all wax binder inside the rod and then it becomes non-waterproof and excellent for tests as a cathode(+).
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on July 31, 2013, 02:57:35 AM
i forgot,welding suppliers sell large carbon arc-rods by the dozen..
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on July 31, 2013, 06:03:50 AM
oooOOoooh I had forgotten about welding rods.  Thanks...also arclight rods are probably still available.
Title: Re: Large Salt water battery ideas and questions
Post by: conradelektro on July 31, 2013, 09:59:19 AM
I did many experiments with salt water batteries.

Copper, aluminium, steel and carbon just do not give enough power to make it worth while. The reaction also stops pretty soon due to deposits on the surface of the metals.

Magnesium works better, but is expensive and kind of dangerous in larger quantities (fire hazard, toxic reactions). Also, a magnesium salt water battery (with carbon as the other pole) does in no way compare to a standard 12 V battery, it just can not come near it regarding the power output.

There is a reason why salt water batteries are not used, they do not work well.

The best option on a boat:

Fife to ten 100 Ah 12 V batteries charged by solar cells and a small wind generator. That really works.

http://www.emarineinc.com/pages/Wind-Generator-vs-Solar-Panels-Which-is-Better-For-Your-Boat.html (http://www.emarineinc.com/pages/Wind-Generator-vs-Solar-Panels-Which-is-Better-For-Your-Boat.html)

Title: Re: Large Salt water battery ideas and questions
Post by: profitis on July 31, 2013, 01:46:20 PM
@conrad,there is no reason why a saltbat wont be practical if its done using right materials.just gota test on smal-scale until you get it right.if its porous carbon then it will function as an air electrode and pull more power.aluminum responds well to chloride ion activity.
Title: Re: Large Salt water battery ideas and questions
Post by: Poit on July 31, 2013, 02:42:19 PM
What you want is a bank of Nickel-iron batteries... will live longer than you!

http://en.wikipedia.org/wiki/Nickel%E2%80%93iron_battery
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on July 31, 2013, 04:39:41 PM
Here's my problem with some of the suggestions thus far, at least for this project (and I do thank you all for the input, it has really caused me to think):  :o I'm well aware I could make this happen using conventional deep cycle batteries and a solar or wind charging input and a generator backup.  That's expensive and relies on a lot of outside materials and devices, but it would work just fine.  My question was whether or not a large "dumb" battery, using fairly inexpensive, common ingredients could be made to work for this, given that the power requirements are limited (ie: no refrigeration, no ac, and only occasional use of a series wound dc motor for power, the rest being led lightiing and a modicum of marine electronics).  I would like to avoid things that are exotic or highly toxic, even if those elements were more effective.

The vessel we're working on is a 42X12 houseboat, and can certainly take quite a bit of weight as long as it's along the centerline.

So given that, what would be required to make this project work, and how might I best do a testbed to find that one out.?

Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on July 31, 2013, 04:46:17 PM
I did many experiments with salt water batteries.

Copper, aluminium, steel and carbon just do not give enough power to make it worth while. The reaction also stops pretty soon due to deposits on the surface of the metals.

Magnesium works better, but is expensive and kind of dangerous in larger quantities (fire hazard, toxic reactions). Also, a magnesium salt water battery (with carbon as the other pole) does in no way compare to a standard 12 V battery, it just can not come near it regarding the power output.

Thanks for the comment, Conrad.  A couple of questions:  What is"pretty soon"?  With no generator to mess with and no other batteries to service, I've no problem doing maint. on this system every 5-10 hours or so if all i'm doing is wiping off a few plates and changing out the electrolyte.  I'm not demanding lithium cell convenience here, nor it's performance.  If this thing is the size of a kitchen table and takes a daily regimen of low level maint. to keep it running, that's fine.

Title: Re: Large Salt water battery ideas and questions
Post by: SeaMonkey on August 12, 2013, 08:39:34 AM
Salt Water Cells using Carbon and Aluminum
do work reasonably well but generate quite
a lot of hydrogen as the chemical reaction
takes place.  Once assembled they like to be
used full time; if they sit idle the aluminum
is slowly eaten away and wasted.

The hydrogen isn't necessarily a hazard but
it does cause "polarization" in the cells which
reduces their electrical output until the bubbles
are swished away from the positive plates.

You may want to try a small scale version of your
battery on a tabletop using small jars to contain
the cells.  You'll probably need to make the salt
solution somewhat more concentrated than sea
water to get the power you are seeking from a
rather small set of cells.

In any case let us know what you discover as you
experiment.
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 12, 2013, 04:38:14 PM
SeaMonkey I actually just completed such an experiment, and was able to pull three volts + from six cells, lighting an LED for several hours.  The hydrogen buildup you described was noted, and did indeed affect output (all I had to do was shake the cathode a little and the cell output would bounce back up).  I ran the salt solution at 1.030 sg , a bit above ocean water in concentration (btw for anyone doing this, one great cheap hydrometer solution is to hit a pet store that deals in tropical fish.  Hydrometers for measuring salt concentration in aquariums can be had for \$8-12.)

I ran the experiment with both copper and carbon cathodes, and with both zinc and aluminum anodes.  The best reaction I got was with the copper/zinc arrangement, but I suspect that the quality of my electrodes had a great deal to do with that.  I'm having trouble finding a decent carbon electrode at an affordable price (here suggestions, especially for the final project, would b appreciated).  Copper and Zinc are much more readily available, especially in clad form.  The aluminum came from a can, sanded free of its coatings, but rather thin.  In general, I was getting .6-.73 volts from each cell, though the metallurgical purity of ALL of my electrodes is, to say the least, suspect.  I did not, at this stage, attempt to measure current, but the cells did light a 3V white led to full luminance for several hours.

As this is technically an aluminium-air or zinc-air battery, its likely that production finally stopped when the O2 in the solution was exhausted.  Vigorous stirring or the addition of a little hydrogen peroxide kicked the battery back to life (oddly, I remember an old Gilligan's Island in which the Professor did just this to charge their radio batteries, probably with galvanized nails and pennies
; the stirring thing I mean, not the peroxide).

Which brings me to some potential solutions, and I'd love to hear what folks thought of them.  A larger cathode, certainly, would make for less impact of the hydrogen bubbles, but two other options occurred to me.  One was to attach some kind of vibrator to the cathode rack which would steadily or periodically shake the hydrogen bubbles free.  The second, which might kill two birds with one stone, might be to place an airstone in each cell (the bubblers you see in aquariums).  The bubble stream could act to dislodge the hydrogen bubbles on the cathode, and would also serve to oxygenate the electrolyte.  Such air pumps consume tiny amounts of energy(about 2-3 watts at 110V), and other, non electrical means could be used to pump air into this system.

The next, pragmatic phase of this experiment will be to actually build a battery of cells at near full size (probably, given the voltage produced, around 20 cells)to produce 12v dc, and place a load on the system (Im contemplating an inverter and a small electric fan (35w ), along with any shaker or air pump used).  Your suggestions for electrode materials and where to find them would be most helpful, bearing in mind the parameters of the original experiment:  Common materials, easily accessed and replaced, and inexpensive. This whole contraption will have to wait until my next check as it is :)

I thank you all in advance for your comments and suggestions.  This board has been an immense education for me, and I wanted you all to know you were appreciated :)

Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 12, 2013, 07:19:54 PM
and while Im on this subject, what might be methods for increasing the current in this setup?  I know just increasing electrode size (or running another battery of cells in parallel) would work, but I was curious what other methods might offer themselves?
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 12, 2013, 07:53:46 PM
what you want to do is make your cathode more oxygen-catalytic to depolarize H2 gas as much as possible so etched copper would probably serve best.you want to increase surface area of the copper by soaking or splashing some hydrochloric acid on exposure to air for a few minutes before thorough rinsing.you want to etch it to roughen surface area. Copper undergoes a double reaction in seawater exposed to air under these circumstances..Cu + Cl- + O +2H+ = CuCl(precipitates on the copper)+H2O.Then CuCl acts as depolarizer 2CuCl + Zn= ZnCl2 +2Cu.copper is regenerated,acting as cyclic catalyst for O2 consumption
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 12, 2013, 09:36:23 PM
what you want to do is make your cathode more oxygen-catalytic to depolarize H2 gas as much as possible so etched copper would probably serve best.
Thanks Pofitis.  Would scoring or abrading the copper work as well, or would etching be preferable?
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 13, 2013, 12:00:43 AM
etching defnitly better @mungo.much more surface area.use dilute nitric,or conc hydrochloric acids(swimpool acid).test it smallscale first.
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 13, 2013, 01:37:17 AM
Ill try that.  Any feedback on the airstone idea?
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 13, 2013, 06:42:56 PM
aha,the airstone idea is nt necessary if you have sufficient porosity.  porous carbon will work but you,re going to have to order carbon slices with emphasis on porousity which is available in different degrees from industrials. you might want to try making your own lead-acid cells simply by passing current between 2 lead plates in sulfuric acid solution.this will give a more power and smoother voltage but you will have to recharge when flat.
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 13, 2013, 08:37:05 PM
I find the porosity thing interesting.  Certainly etching the cathode would help, but going with an industrially produced cathode which had to be ordered or utilizing sulphuric acid as an electrolyte rather defeats the purpose of the experiment, which was to create a big dumb battery out of commonly available materials with low toxicity.  My other thought regarding the airstone was that it would keep the electrolyte oxygenated, and perhaps stop the voltage die off I experienced in the small model.  Thoughts?  Does the anode need to be etched as well (aluminum seems to be the top contender here, though zincs used to protect crab traps are widely available in the Chesapeake.)
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 14, 2013, 07:26:15 PM
definitely @mungo.an etching of the aluminum or zinc with hydrochloric acid beforehand will shoot up the power density.a shaking of the air electrode will be energy consuming but it will help yes but we want to try avoid putting in energy to gain efficiency.if you situate the cathode half-submerged in the seawater it may help absorbtion of air from the atmosphere and self-discharge of the clinging H2 bubbles.try putting the copper plate side-longways half-submerged.try a copper plate that is 2wice as big as the zinc plate for surface area.try folding up a giant copper plate into squigglies(like a roofing) to cram huge area into small space,half-submerged.
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 14, 2013, 07:32:38 PM
try pressing your electrodes between sponge-soaked salt water @mungo.make sure that the sponge is not overly soaked,just a tiny bit seawater will do as you want it to be an almost 'dry cell'.this should alow maximum air access via pores.try newspaper,try fabric,fibreglass as your saltwater sponge.
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 14, 2013, 09:06:17 PM
try pressing your electrodes between sponge-soaked salt water @mungo.make sure that the sponge is not overly soaked,just a tiny bit seawater will do as you want it to be an almost 'dry cell'.this should alow maximum air access via pores.try newspaper,try fabric,fibreglass as your saltwater sponge.

could capillary action from a well of electrolyte be used to keep the sponge medium damp, or would that be too much?
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 14, 2013, 10:36:37 PM
it certainly could.you just have to work out the right sponge.it will be obviously wetter on the base but at least the top will be exposed to more air.the correct way to do this is to actualy have the zinc completely submerged under seawater and just the copper standing aloft against the sponge.we want minimum air exposure to anode and maximum air on cathode.
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 14, 2013, 10:44:24 PM
you could also use a cramped up bundle of copper wire half-submerged in seawater or pressed against sponge for maximum air exposure.make sure that the wire bundle is all electricaly connected in a straight line before bundling and make sure that the insulator coating is all burned off the wire completely beforehand.
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 14, 2013, 11:37:57 PM
how about a bundle of copper pipe, riveted together with copper rivets and etched, half submerged, as you said, and twice the size of the aluminum anode? :) this is fun, and instructive :D

Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 15, 2013, 12:10:25 AM
now a plan is coming 2gether yes indeed.try find pipes that are pencil-thin and bundle them.we want maximum copper/air/electrolyte exposure.pipes slightly pressed onto a sponge or towel will allow air to creep at an angle.
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 15, 2013, 12:28:31 AM
try doing a spot-test using bundled wire half-submerged and tell us if you get improved result @mungo.im realy curious if the theory will match practicality.use normal appliance cord wire,throw it into a fire to charcolize its rubber coat and simply bash off the charcoal pieces,they will fall off like glass,scrap dealers do this all the time
Title: Re: Large Salt water battery ideas and questions
Post by: SeaMonkey on August 15, 2013, 07:36:31 AM
Experimenting with chemical voltaic cells such
as the Saltwater Battery can be great fun and
an enormous learning experience;  but when
one realizes how little energy they're capable
of producing for all the work that goes into them

These types of Voltaic Cells are great for emergency
use to energize low powered devices for a short
time, but when more substantial power is required
the ubiquitous lead-acid battery with a suitable
charging/desulfation device (solar or wind powered
or both) is hard to beat.
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 15, 2013, 01:06:14 PM
it all boils down to the electron-sucking power of the cathode @sea monkey,thats why the lead-acid system is so good with its solid oxidizer PbO2,an extremely powerful oxidizing agent in acid solution:E=1.6v (ph1). Air in seawater: E=0.8v (ph8).hydrogen ion in seawater: E=0.4v (ph8)(2H+ + 2e- = H2 bubbles).also theres no gases involved with the lead-acid system thus minimal polarization of  electrodes but if mungo can get the air cathode art worked out we may see real improvements.
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 15, 2013, 04:04:33 PM
SeaMonkey is your objection to these batteries power density or is it that the hydrogen envelopment of the cathode ultimately shuts down production?  My application is rather specific, my energy needs fairly low, and I really don't care if I have to have 30 cells or if i wind up with two batteries ten times the size of a lead acid to do the same work.

So here's my thinking at the moment:  The next prototype will be a near full sized mockup, using narrow gauge copper tubing bundles as the cathode and bundles of aluminum box beam as the anode.  Both will be etched in muriatic acid beforehand to increase surface area.  The Anode will be completely submerged, the cathode about half so.  I'm going to prep to do the airstone idea to oxygenate the electrolyte and hopefully clear some of the H2 off of the cathode.  I will also prep some absorbent medium and try bundling that with the cathode to see how that works.  If that functions, Ill connect that through and inverter to a load and see how long that runs, how the electrodes perform, and what kind of changes we see in the electrodes and the electrolyte. (using a 1.030 sg salt solution).  I know this thing will produce the voltage, but Im curious what kind of current I can produce with it.  Ideas?  Suggestions?
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 15, 2013, 04:11:06 PM
I am curious about a couple of my initial test results:  The voltage output of the aluminum anode was less than that of the zinc (okay, galvanized mild steel), and due to their electrochemical potential, shouldn't that have been the other way 'round?

Im also curious if a cathode of plates set very close together, angled slightly so that the gap was slightly wider at the top than the bottom, might force the hydrogen bubbles upward as they formed, clearing the plates and creating a mild current (fluid, not electrical) between them.  As we're talking microns here Im not sure I have the toys to do it, but it's an interesting idea.
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 15, 2013, 04:14:26 PM
but if mungo can get the air cathode art worked out we may see real improvements.

I was really liking this phrase until I realized you probably meant "air cathode PART" :) Maybe Art might actually be a better term :o
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 15, 2013, 04:49:29 PM
tis indeed an artform to get batteries into practical gear.ive been doing it for years although my research has centred more around concentration cells and finding ways to maintain their concentration gradients with no expenditure of energy(ive had plenty success here believe it or not).if you used smooth aluminum it wouldve formed a slow-dissolving aluminum hydroxide layer and that would hamper voltage so its important to etch aluminum and get that surface area.zinc on the other hand tends to dissolve more smoothly into saltwater as zinc chloride but you are going to have to renew the saltwater at some stage because its ph will gradualy become alkaline as galvanic reaction proceeds and start precipitating zinc hydroxide on its surface.you must remember that many aluminum and zinc objects are alloys thus their rates of reaction will differ,its just a matter of trial and error to get the right anode.the cathode is the tough part because we want those H2 bubbles to self-discharge on contact with air on the cathode surface: H2 + O= H2O,your copper acting as catalyst
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 15, 2013, 05:07:51 PM
if you adjust the ph of your saltwater by adding some muriatic acid you should get better results.if you adjust the ph to extreme alkaline by throwing in caustic soda or washing soda even better,then it becomes a classic zinc-air system and H2 bubbles will cling less hard due to wetting ability of alkali.throw in some caustic soda and see what happens.take caustic soda supply with you on the boat trip.
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 15, 2013, 05:10:48 PM
So the trick becomes how to bring more air to the cathode surface ....hmmmm...of course, since this is to be a marine application, there will be a constant degree of low level agitation of the electrolyte solution, which will probably help a bit.  I wonder if I could mechanically amplify that to move the cathode a bit from time to time.

I always tend toward the mechanical, but then, thats how my head works.

Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 15, 2013, 05:11:50 PM
if you adjust the ph of your saltwater by adding some muriatic acid you should get better results.if you adjust the ph to extreme alkaline by throwing in caustic soda or washing soda even better,then it becomes a classic zinc-air system and H2 bubbles will cling less hard due to wetting ability of alkali.

so basically Im throwing in soap to break down the surface tension....
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 15, 2013, 05:16:35 PM
yes but dont throw in soap as it will form scum on the anode.throw in caustic soda,it will dissolve zinc hydroxide.
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 15, 2013, 05:29:26 PM
caustic soda will drasticly increase power output of aluminum anodes also,dont throw in too much.
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 15, 2013, 06:26:23 PM

yes but dont throw in soap as it will form scum on the anode.throw in caustic soda,it will dissolve zinc hydroxide.
I meant that metaphorically, but I take your meaning.  ;)
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 15, 2013, 06:37:21 PM
Anyone have any idea how much of a problem the O2 content of the electrolyte might be?  Is surface absorption of atmospheric O2 adequate, or will it eventually be exhausted by the anode?
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 15, 2013, 06:49:14 PM
if you use caustic soda you may just be able to not even worry about air anymore @mungo because of the drastic increased wetting ability at the cathode,the H2 bubbles should seperate at a steady enough pace to give steady current.your copper pipes must stand totaly upright to allow bouyency to lift bubbles up and away.the voltage will be around 1.1-1.5 in this setup and should be quite stable.play with raising and lowering the copper to half-submerged and fully submerged to see if power improves.
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 15, 2013, 07:05:53 PM
these tests may have to go youtube in the future ???
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 15, 2013, 07:05:55 PM
dont use brass as your cathode.brass is 40% zinc.use pure copper
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 15, 2013, 07:08:04 PM
lol yes..it will be of great value for survival skills to watchers
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 15, 2013, 07:20:42 PM
dont use brass as your cathode.brass is 40% zinc.use pure copper
Will probably wind up using either plumbing copper or ground pipe stuff.  It's readily available and not so heavily alloyed .
Title: Re: Large Salt water battery ideas and questions
Post by: SeaMonkey on August 15, 2013, 08:39:30 PM
Quote from: Mungo
SeaMonkey is your objection to these batteries power density or is it...

Not an objection really, since these kinds
of voltaic cells do have their place;  I'd think
of it as more of a preference.  I do have a
supply of materials for when I may need
them.

Chemical cells of the primary variety require
a lot of work in fabrication and maintenance
to keep them "humming."  Eventually it grows
tiring.  And there is the never ending need for
suitable metals to replace the electrodes as
they are either eaten away chemically or
otherwise deteriorate.

Once one has learned how they work and
how much it takes to keep them functional
the fun slips away and it becomes work.

Re-chargeables are just so much easier
to make use of and with proper care will
last many, many years.  I've come to really
appreciate low maintenance sources which
don't require too much work and attention
and have the oomph to handle most tasks.

As we get on up in years we tend to gravitate
to the easier ways of doing things... ;)
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 16, 2013, 12:46:12 AM
:o
okay, just did a little experiment. 8oz salt water at 1.038 sg.  Aluminum anode immersed and copper cathode immersed: .44 volts.  Aluminum anode immersed and copper cathode essentially floating on the surface on a cloth hammock, .78 VOLTS!  Yeow.
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 16, 2013, 01:03:59 AM
Here's the two shots, one with the electrode immersed, one with it suspended on a wet cloth at the top of the electrolyte.  Now, how do I adapt this to something more permanent..... :-\
Title: Re: Large Salt water battery ideas and questions
Post by: SeaMonkey on August 16, 2013, 03:45:23 AM
Aren't electro-chemical experiments fun!(?)

Surprising too.

Here's one man's solution (https://simple.wikipedia.org/wiki/Voltaic_pile) from long ago.
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 17, 2013, 06:43:06 PM
are those 2 shots with caustic soda added?
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 18, 2013, 12:34:42 AM
no.  I added a small amount of bicarbonate of soda to make it a bit more alkyline, but no caustic soda.

New battery test monday on a larger cell.

Any suggestions on the best way to check current on a .6 watt or so cell, what kind of load, etc etc.?
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 18, 2013, 03:30:15 PM
i would suggest to make cells in series and to put caustic soda in there @mungo.caustic soda will attack your anode much better and produce more potent power.baking soda is too mild alkaline.an electric toy motor is a exelent way to chek power levels as it will work under its recomended voltage and draw large currents.
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 19, 2013, 02:28:27 AM
will try the motor idea....Im hoping radio shack may have some, not sure where else around here might unless I buy some cheap toy and cannibalize it.
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 19, 2013, 10:00:37 PM
Okay here's some shots of the new cell
The cathode is a series of 1/4" copper tubes, lightly sanded and bound around a polyester wick.  The anode is a bundle of aluminum tubes.

The solution in the cell tank is 1.030 sg sea salt.  The cathode lies on top of the tank lid with the wick down in the electrolyte solution.  The anode is, of course, below, fully immersed in the electrolyte.  The additional red lead on the cathode is me beginning to set up a load test and is not connected to anything in this shot.

Voltage started at .58/watt, but climbed almost immediately to .75 watt and stabilized.  Using a small dc motor as load, amps read as 5.23 on the 20mA range.  More in a bit as soon as I determine how stable this is.

After this has run for a bit, I will try, as per suggestions, some caustic soda in the mix.

More in a bit.
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 19, 2013, 10:46:40 PM
amazing the difference on air exposure makes.now watch what happens when you throw some(not too much)NaOH.
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 19, 2013, 10:49:14 PM
:(  Have to go buy some first :)

Not at all sure what Im seeing with the amps.  The voltage is insufficient to power the little motor, so its mostly acting as a resistor.

Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 19, 2013, 10:58:39 PM
its the aluminum oxide layer hampering the voltage,you have to throw caustic @mungo.put two or 3 cells in series to get a motor going.you can also scrape loudspeaker wires on there to 'hear' the power ratings,the more power the louder the scratch sounds
Title: Re: Large Salt water battery ideas and questions
Post by: Mungo on August 20, 2013, 12:02:10 AM
well. humpf.  Added the  :o caustic soda and the voltage actually DROPPED to .70.  Hmmmm  ....anyone care to speculate A) why and b) how much amperage this thing could actually pull per cell?
Title: Re: Large Salt water battery ideas and questions
Post by: profitis on August 20, 2013, 02:07:53 AM
add more @mungo.how much did you add.if you had a milliampmeter attatched you would now see drastic increase of current despite voltage drop.ie.total power density way way up
Title: Re: Large Salt water battery ideas and questions
Post by: tom42 on July 25, 2014, 10:18:51 PM
Wouldn't a shunt-wound or stepper motor be inherently more efficient than a series motor? .Brush life is also a concern
Title: Re: Large Salt water battery ideas and questions
Post by: Paul-R on July 26, 2014, 03:59:46 PM
... with a generator backup to drive a paddle (stern) wheel
They can be very inefficient.

A propeller specified for the chosen RPM and the speed you will prefer to travel at might well be much better.
Title: Re: Large Salt water battery ideas and questions
Post by: tom42 on July 28, 2014, 11:17:01 PM
What are the waste products of a magnesium/salt/carbon(?)  battery? Isn't hydrogen one of them? How is its explosive nature handled?
Title: Re: Large Salt water battery ideas and questions
Post by: MarkE on July 28, 2014, 11:33:23 PM
They do emit H2 gas like a lot of batteries do.  It is not a problem unless you are making a big cell and/or the cell is in a highly confined place.    The other waste product is basically milk of magnesia.