Tuesday 10 August 2010

Boat Battery Maintenance Pt II

Boat Battery Maintenance Pt II

The inside of a battery depends on what kind of battery you have. Boat batteries are normally the lead-acid type and provide a nominal 12-volt potential difference by connecting six galvanic cells in series. Since the cells naturally produce about 2.1 Volts. The actual voltage is roughly 12.6 Volts.

Lead-acid batteries are made up of plates of lead and lead oxide, which are submerged into an electrolyte solution of about 35% sulfuric acid and 65% water. This causes a chemical reaction that releases electrons, allowing them to flow through conductors to produce the required volts and amps.

The Battery bank on a boat typically consists of a number of 12 volt batteries connected in parallel with each other to give a greater ampage capacity whist still providing 12 volts. A typical leisure battery has a rating of one hundred ampere hours. So in this case the three batteries connected together would give a capacity of three hundred ampere hours at 12 volts.

A single 12 volt battery is made up of a number of galvanic cells, each cell being a nominal 2.1 volts. When the cells are connected in series, the cell voltages add together.

In this case the six cells connected together provide a typical single 12 volt battery.

The batteries on a boat are quite expensive to replace and need great care if they are to have a long working life. However, there comes a time when the batteries will have to be replaced or refurbished in some way. If I had to replace all of the batteries on Rosie, I would expect to pay out somewhere in the region of £500 pounds.

So I wondered to myself, is there any way of re-conditioning a battery getting towards the end of it useful life. A process that the average boater could do.

This set me off on a trawl of the T'interwebbie to find out. There is a lot of stuff out there on battery reconditioning. Some of it seems to have some merit on first viewing, and some other is an obvious load of old tosh. I looked at a large number of web sites. However, although using a battery charger with a pulsing system has some merits. I have experienced so Lazarus like recoveries of old batteries from using one. However, never to more than a "subjective 90%ish" of their capacity. So the chemical reconditioning route was the one I favoured the most.

So I had a chat with some of the chemistry boffins at the University where I work, about the subject and several possible solutions were offered. Then out of the blue one of them said that he knew of a way using tetrasodiumethelenediaminetetraaceticacid to do the job. Tetra what? I said.

But I digress....

So it appears that if you have a lead-acid battery that isn’t working properly, you may be able to recondition it. The most common reason for a battery failing is due to the chemical processes which take place in each cell when the battery is not fully charged. Even the slightest discharge condition allows both plates to react slowly with the sulphuric acid electrolyte to form lead ions. In other words batteries have a chemical aging process. It is these lead ions which cause the problems. As they combine with sulphate ions in sulphuric acid to form highly insoluble lead sulphate. When this coats the plates of the battery, it fails to deliver enough power to be of use. The battery may well be serviceable every other way - only the "sulphating" stops the battery from delivering enough power to be of use.

The sulphating can effectively be removed, or prevented, by adding to each cell a chemical called tetrasodium ethylenediaminetetraacetate (often abbreviated to tetrasodium EDTA). Now I asked myself why would the maker of the battery not put this chemical additive in the battery from new? I could not come up with an answer other than to maintain sales levels or that it would not work.

EDTA - ethylenediaminetetraaceticacid or tetrasodium salt to be more specific is the version in which we are interested. This chemical forms co-ordination compounds with many metal ions, including lead ions formed in the discharge cycle of a battery. The compound formed by lead ions and the EDTA ion is not particularly stable in the acid medium of a battery, but when it breaks down again any lead sulphate regenerated tends to drop to the bottom of the cell where it lays harmlessly since it doesn't conduct electricity. Any regenerated EDTA ions are free to continue their work.

Sufficient to treat one 'normal' sized battery - £2.34 including P and P from Courtiestown

Remember -- Only fix the battery cells that need fixing, so test each cell in turn.

First look at this uTube video on re-conditioning by Walt Barrett and listen to the description.
Take note of the tools you will need - voltmeter hydrometer etc. You can get suitable bits from a good car spares shop like Halfords (except for the hydrometer which I found on eBay). Safety goggles, Rubber gloves, Plastic container, Plastic funnel, Distilled water, Battery charger, Drill (for sealed batteries, Tight fitting plastic plugs (for re-sealing batteries), Voltmeter with wire probe (which I already own) etc.

When you have the items needed to check a battery and after you have watched the video you will have a better understanding of what you need to do.

Caveat - I have not tried the above yet, but I will be doing so on an old battery that I have obtained just to do a test. I shall report back later on my results.

An alternative and questionable process I found on the web.

I would treat the worth of this procedure with a very large spoonful of "Epsom" salt, but you could try it on a dead battery.

Lead-acid batteries have a slow decline in performance most often because sulphur accumulates on the lead plates of the battery, blocking electric current flow. You can use a common household chemical, magnesium sulphate (Epsom salts), to recondition a lead-acid battery. If you follow the proper procedure, the magnesium sulphate will remove the sulphur and restore the battery to normal operating condition.

  1. Heat a half a litre of distilled water to about 150 degrees F and add 7 oz. of Epsom salts. Stir until the Epsom salts are completely dissolved. Do not use tap water because it contains chemicals that will contaminate the battery.
  2. Remove the battery caps and carefully drain the liquid from the battery. If you have a sealed (low-maintenance) battery, find the access points (also called shadow plugs) and use a drill to open them. Insert a funnel and pour enough of the Epsom salts solution in to refill the cell. Repeat until you fill each cell.
  3. Replace the battery caps. Use plastic plugs to close up the drill holes in a sealed battery.
  4. Shake the battery vigorously for a minute to make sure the solution works its way through each cell.
  5. Place the battery on a charger and allow it to charge slowly for 24 hours.
  6. To completely recondition a lead acid battery, you may need to charge it to capacity several times over the next few days.

Part I

Part III


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