12v battery question

[muldoon]

I have acquired over the last few weeks 2 12 volt marine batteries for free - both of them being in rather poor shape.  Based on verbal descriptions they have both sat for years unused.  No one has any idea what the state of them before going unused is.  One is what I would call a normal size, the other small - like a trolling boat motor.  Anyway, after filling the cells I put them each on a charger to find they will charge to 12v but seem to drain off fairly quickly under load.  I also have another project underway with a few led lights that I plan to use the 12volt battery for.  The fixture has 3 2watt luxeon led bulbs or a 6watt draw between 6v and 18v.  It works, and running the lights with a multimeter on the battery shows the drainage is quite fast.  about 3 hours on one battery, 2-3 hours on the other.  

I want to run both batteries in parellel to increase amp hours of storage while keeping the voltage at 12v.  My questions are:

1) What size wire will I need to use to join the batteries together.  The light project uses all 12gague wire because that is what I had.  I wasnt sure that tieing the batteries with this was kosher - even with a low draw?  

2) Assuming using small wire is acceptable if the amps being drawn were so low, is there anything about putting the charger on one of the batteries that would then subsequently make the wire need to be bigger?  Ie - in runstate the draw is 6w, but if I put a charger on them - wouldn't the amperage across the batteries be much higher?  

How should I approach this?  get a new or bigger battery?  buy heavy duty cables?  manually swapping the battery is not desirable as this is for night hunting and once setup it really cant be messed with too much.  

btw - the cheaper the better on this one.  Also, I'm loving labor day project weekend. 

[glenn kangiser]

These will likely be a tough case to make usable, muldoon.  They will be sulfated and per your description that diagnosis fits.

I have been playing around with desulfating the big battery bank I got and while I had some success, they were pulling my other bank down so I pulled them offline until I get time to play with them more.

I have a source for Xtreme chargers which desulfate also.  I don't know how long it would take to do this size battery (small compared to my battery pack) - I would expect a few weeks minimum- IF they are restorable.  The small chargers are not too expensive but not as effective as the big one.

Once the batteries go dead, sulfate crystals build up on the plates stopping them from working.  There is a chemical way to clean them using EDTA ( a pretty safe chemical- it is in some of your food) but it is a bit of work and success is not guaranteed.

Here is a description of what happens and how to attempt repair with EDTA.  EDTA is one of the only known ways to chemically help the batteries even though there are lots of snake oils out there.  


http://eduhosting.org/classes/windgens/fixbatts.html

One guy said in the report linked below, I think that he would not mess with the batteries if they do not hold 10.5 volts.

Desulfators work but take time and one big enough to do it faster is expensive.

Welders work if monitored closely but can be dangerous if you do it wrong blowing up the battery, and they can warp the plates.

Also a PDF with info and results on EDTA use - I downloaded it.

http://www.otherpower.com/images/scimages/74/de_sulfating_batteries.pdf


An equalizing charge may help to take some of the sulfation off but most automotive chargers won't do that.


The lights won't draw enough to need bigger wire but charging would if the batteries get better.  I'd use 12 volt battery cables, even if light ones.

I found a good source for EDTA - it arrived here today and I ordered it the first I think.

http://cgi.ebay.com/EDTA-Tetrasodium-Hydrate-98-One-Pound_W0QQitemZ370253981910QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item5634db68d6&_trksid=p3911.c0.m14

[harry51]

One sign that a battery is badly sulphated is if one or both of the ends of the case is bulged. The crystals that form on the plates force them apart, making them push on the battery case from the inside, causing a noticeable bulge.

G/L!

Harry

[muldoon]

Thanks for the comments, the large battery I had was charged on my charger on Monday night, it read 12.15v on Tuesday morning when I went to work; today it read 5.somethingV when I started.  By the rationale above needing to hold 10+V, I am going to say it's just dead and gone.  As for the other, I didnt even bother with it further.  I picked up a new smaller deep cycle marine battery tonight from (of all places) walmart - its a 23 amp hour and cost a whopping 21 dollars.  I charged it for 2 hours and the green led on the charger said it was done, metered it out at 12.6something.  The lights have been on for 4+ hours and the multimeter now shows 11.95volts.  I ran the numbers through my calculator and 23 amp hours should hold the 6watt/12volt load for between 20-25 hours until the battery is at 50%.  I think this is it, case closed. 

Thanks again for answering my questions Glenn and Harry.  I appreciate the feedback, and I'm going to bookmark those battery links for future notes. 

[glenn kangiser]

No problem, muldoon.

When I was about 16 I knew an old German fellow who would remove the tar from around the cells, pull them out individually and separate the plates from the spacers and manually clean them then put them back together, seal them back up with tar, fill them with acid and they would work again.

Today's cases are all plastic and not repairable other than what you can do from the outside but it is still interesting to know that a battery is not all that complex.

Mr. Percy also used an acetylene generator to run his torch.  A hopper dropped calcium carbide in water - pressure built in a few seconds and he was able to cut steel paying only for an oxygen tank - and the carbide.  The generator was a rather large scary looking thing that I think would blow up if not used properly. According to the following it was safe/

http://ublib.buffalo.edu/libraries/exhibits/panam/sel/acetylenebook.html

[MountainDon]

Even though my comments are way late, having been up at the cabin since Friday, I do have a couple things to add.

I was going to say that the best thing about these batteries would be their core value against the purchase of a new battery or batteries.

Nobody addressed the question of wire/cable size between the batteries. With the load being low a small wire would suffice for load purposes. In this case then the interconnect wires/cables would be sized by the maximum input current from the battery charger.

Second, connecting two vastly different capacity batteries in parallel is a bad idea. It's not even a good idea in series. They will not recharge properly for one thing. Similar problems will be apparent when discharging.

Let it be noted that not all batteries that have the words RV/Marine in their name are deep cycle. Some are cranking batteries, better compared to the standard automotive cranking battery.

Even though the label may state "Deep Cycle" some deep cyc;e batteries are better than others. RV/Marine batteries labeled as deep cycle, generally have thinner plates than Golf Cart batteries that are deep cycle types. RV/Marine deep cycle batteries do have plates that are thicker than the cranking battery. This is good. But thicker plates translates into more years of service when other factors of use and care are the same.

It is generally better to achieve the goal of "x" number of amp hours capacity by stringing batteries in series, rather than parallel. For example, two twelve volt batteries in parallel with a rating of 105 amp hours each will produce 12 volts with a total capacity of 210 amp hours. Two 6 volt batteries in series with a rating of 210 amp hours each, will produce the same 12 volts with a rating of 210 amp hours.  However the batteries in series will likely give a more satisfactory (longer) service life. Part o the reason will be the haevier plates in the GC 6 volt batteries. Part of the reason will be in the manner batteries interact in series vs parallel.

One last thing even if a battery is balled as deep cycle that does not mean it will perform happily if subjected to being repeatedly deeply discharged. A deep cycle battery will react to the deep discharging better than a regular automotive cranking battery. However, deep discharges take their toll is decreased srvice life. For good battery longevity the discharge should never be more than 50% of rated capacity. Even better would be to limit the discharge to 25% or less.

If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD (Depth o Discharge). If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%. To complicate things, very shallow discharges can be detrimental to battery life as well. Best is ti aim for somewhere between 10 to 20% DOD, as a regular thing. The occasional deeper dischrge is not a big deal. It is the constant draing down to low states of charge that is bad.

[NM_Shooter]

Those batteries are toast... don't waste your time.

You can't really get a good impression of the health of the battery based just on the voltage alone.  However, if a battery is consistently falling below 10V after being charged and not used, it is not just a case of sulfate.  That battery also has at least one failed (shorted) cell. 

By charging it with 14V or whatever charge source you have, you can temporarily overcharge the remaining cells which puts additional wear on them and ruins the battery further.

Also.. batteries have an internal resistance (impedance) that slowly increases with the age of the battery.  Think of is as a resistor in series with the battery.  As you charge it, or discharge it, the battery temperature will increase, and it limits the amount of power that you can get out of the battery. 

Unfortunately those batteries are only good for core deposits now.  Save yourself heartache and recycle them.

Use the heaviest gauge wire you can find to tie your batteries in parallel.  Auto shops sell battery cables that are terminated with copper ties on each end.

-f-