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Old 21-10-2007, 12:17   #1
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Electrical Study Hall:

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Old 27-10-2007, 13:41   #2
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Old 27-10-2007, 13:44   #3
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Old 21-11-2007, 22:35   #4
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Batteries
There are three classes of batteries.
Deep Cycle
These Batteries are built with fewer large heavy plates. They are not good at producing sudden High discharges of current, which is required for Starting applications. They are better at producing the slower steady discharge required in house use for powering lighting and inverters etc. A good design tends to have a large gap between the bottom of the plates and the base of the casing, to allow sediment to collect without shorting the plates.
The main concern for as users, is that this type of battery can withstand deep cycling many times greater than starting batteries can. In the order of maybe 1500 deep discharge/charge cycles

Starting
These are built with many more lighter plates. This creates a larger plate surface area, giving the ability to produce high surge demands of current for starter motor operation. These batteries do not like deep discharging and will accept only as little as maybe 30 deep discharge cycles before they fail.
And a combination of both.
These can be found in a couple of designs. Either a mid size plate design or a twin design of both deep cycle and a smaller starting section joined on to the end. Pretty much self explanetry. It is a compromise and will suffice in small vessels where use is not high and room critical.

Combination Starting/deepcycle.
These can come in a range of forms. Either a seperated cell design, one end being a deepcycle and a smaller end being a start. OK on small boats with perhaps a light duty outboard where high starting current is not a major issue. That should allued to the fact that the reserve capacities of these batteries are not huge, but they do suit a market.
Or...a cell desing that fits between the two seperate Deepcycle and start designs. These are a compromise and not really suited to larger vessel systems. But once again, they do suit a particular market.

Battery Designs
Flooded Lead Acid (FLA)
These have Plates submerged in an liquid Electrolyte of Sulfuric Acid.
Advantages: They tend to be the lowest cost/Ahr, or stated a different way, “the best bang for your buck” type battery. A little more robust at being badly treated in regards to charging, thus less expensive charging methods can be used. They tend to be the better at deep discharge duty and tend to have the highest number of discharge cycle rates, providing the 50% minimum cycle rule is employed.
Disadvantages:
These require regular inspection to assure the battery is topped off, so as the plates do not dry out. They can spill Acid and thus can only be installed upright. They can be more quickly damaged if left discharged. They are not as robust in regards to Vibration as Gell and AGM . They have a higher discharge rate and require constant maintenance charging to keep them in good condition.

Gel Cell
The plates of these batteries are submerged in a thick Gel type paste of Sulfuric Acid.
Advantages:
They have the distinced advantage of being able to be placed in any orientation, having no liquid that can leak out. They are also very good at withstanding high vibration environments. If charged correctly, they do not vent much in the way of Gas. This also means that some of these batteries can come totally sealed, or at the very least, have a relief vent in case of pressure build up.
They have a very low self discharge rate.
Disadvantages:
More expensive than FLA. As the Gel dylutes the Acid, the battery has to be made in a way that makes it larger and heavier. So although these batteries are nuggity, don't let that fool you into thinking it is more powerful. The electrolyte can not be replaced, although in saying that, it should never need to be. It requires special charging needs and can be damaged or even become dangerous if charged over 14.2V. Thus unregulated chargers should not be used.
Can require a special charger to bring them up out of a very deep discharge.

AGM
These have a glass mat with the Acid absorbed into it, sandwiched between the plates.
Advantages:
These are also considered “maintenance free”, having no user replaceable electrolyte. Thus they can also be installed in a variety of angles, but not upside down. They do have the distinct advantage of being able to be used for both Starting and deep cycle duties, although once again a compromise and most likely at the detriment of their over all life span. However, They are also made in all three specialised types as Start, Deepcycle and Dual, which. Good shock resistance and very low gas release when charged properly. They have a very low self discharge rate.
Disadvantages:
These tend to be the most expensive batteries. They also tend to be the heaviest/Ahr. Once again, you can not replace Electrolyte, but also once again, you should never need too.

A few common rules for Batteries:
Never mix old batteries with new in the same bank. The older battery will pull the new one down to it’s poor operational level.

And even more importantly, never mix different types of batteries (FLA, Gel, AGM) either in the same bank. Thus also different types should not be charged by the same charger. Unless the charger is truly special and can charge each bank to their own specific needs.

For FLA batteries, *never* charge with a current exceeding 25% of the banks total Ahr rating. eg 100Ahr = 25A.
A sufficient current to charge the batteries efficiently is also required and for FLA batteries, a current of 20% is ideal.
*Never*= with new technology in charging equipment these days, that rule may not necessarily apply as "never" anymore. If proper monitoring, especially in temperature is carried out, much higher charge acceptance can be had. So alwasy ensure your charger is capable of monitoring the battery and like in any application, read the manual!

AGM/Gel, are able to safely handle a current rate of 25% and with newer technology and revised information, some of these batteries can handle much much higher. With good temperature monitoring, some manufacturers state their batteries can be charged at 100% of the rating.

Regularly check the levels of FLA batteries. Always fill with distilled water only and fill to the level indicator only. Do not overfill.

The rule of thumb of a 50% discharge applies to all battery types. This 50% mark determines the best over all life expectancy in relation to the overall cost of the battery. As soon as a battery begins to discharge, it also begins to degrade. The further it is discharged, the less life expectancy it has.

You can never fully charge a battery with a standard automotive charger. To fully recharge a battery, it must go through two stages. First is the bulk charge. The second is the Absorption charge and then the battery can be placed into long term trickle charge. However, even on trickle charge, the batteries capacity maybe still be reducing and cycling the batteries charge once a week is good exercise for the battery.
New generation MPPT charging devices do this differently again and do not use the two distinct charge stages.

Battery State chart:
Voltage---state of charge--specific gravity
12.75 -----100% -------------1.265
12.70 -------95% -------------1.257
12.65 -------90%--------------1.249
12.60 -------85%--------------1.241
12.55 -------80%--------------1.233
12.50 -------75%--------------1.225
12.45 ------ 70%--------------1.218
12.40 -------65%--------------1.211
12.35 -------60%--------------1.204
12.30 -------55%--------------1.197
12.25 -------50%--------------1.190
12.20 -------45%--------------1.184
12.00 -------25%--------------1.155
11.75 -------00%--------------1.120


The following is from our Resident Battery Guru Rick.
It can be used in conjunction with above rules, but I would suggest you need to have a reasonable knowledge of electrical and batteries to use these suggestions.

Flooded start-only start batteries can fail with ONE deep discharge. Because one instance of this may not result in a failure is no justification to think that it will survive another cycle or that another battery will survive one. The old addage that if you want your car to start reliably and the battery has been run down by leaving the radio or lights on then replace the battery!

All lead-acid deep-discharge batteries can be charged at any voltage as long as the resulting current falls within the Amp-hour law (even this may be exceeded for short periods of time). The Amp-hour law places any particular charge voltage limit (other than float voltages) or and particular charge current limit into the category of myth, not fact. The idea that one may not have the equipment to charge a battery using the Amp-hour law does not mean that one cannot still use a monitor and adjust the charge current to fall within the Amp-hour law limits with confidence and safety.

There are caveats that allow mixing batteries within a bank safely, i.e. one CAN mix AGM and GEl batteries. In general, one CAN mix old batteries and new ones. With good charging systems that cyclically bring upper limit acceptance voltages for sufficient times even old batteries will demonstrate a "Best" internal resistance and state of capacity even though those values have been degraded over time. With good treatment these old batteries will not "pull-down" a new one placed in parallel. In fact, they have been shown to track both during charge as well as discharge. Tracking means that they proportionally contribute charge current according to their derated specifications and they charge accept proportionally as well.

The caveat for mixing battery types has more to do with their full state of charge specific gravity (this is how one can mix various agm brands and gel brands by calculating their internal specific gravities using their rated full charge open circuit volgages at the same temperature) than with their different other manufactured internals.

The problems normally associated with mixing different battery types and aging are large when they have been subjected to cyclical charge cycles with low acceptance voltages over time and when they have been subjected to mechanical deterioration like shock and vibration (even had AGM troubles with this but it is more of a problem, of course, with flooded batteries). Sitting for long periods of time in a state of deep discharge will statistically offer a better chance of a shorted cell when attempting to recover the battery and, therefore, a battery with such a history should never be placed into service with new ones in parallel.
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Old 22-12-2007, 01:46   #5
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Zinc Anodes
(I would firstly like to acknowledge the work of Gord for finding this info in the first place.)
Anodes are one of those items that make you cry. You pay good money to watch something disolve away. But it is an essential item and not having one will most likely result in another item of significantly more value, dissolving away in an even shorter period of time. Gord posted some valuable technical info he has gleaned from the Net. So I thought it would good value to all of us to lock that info in here in our study hall.

A voltaic cell is created whenever dissimilar metals, connected in some way, are immersed in a conductive fluid. The voltage created depends on the relative positions of the two metals in the galvanic series. Since the dissimilar metals create an electromotive force, a voltage, we can gauge the adequacy of the protective zinc by measuring the galvanic voltage.

The most common method is to use a "half-silver chloride cell." The resulting cell consists of a piece of pure silver, connected by a copper wire to a sensitive voltmeter and then with another copper wire to a probe that can be used to make electrical contact with various pieces of underwater metal. The Silver/Silver Chloride (or Ag/AgCl) reference electrode is the reference electrode of choice, because it’s easily and cheaply prepared. It is stable, and quite robust. It is sometimes referred to as "SSCE" (Silver/Silver Chloride Electrode) but that abbreviation can be confused with the Sodium Saturated Calomel Electrode.

Almost any digital voltmeter can be used to take the measurements. Analog voltmeters that can read voltages as low as 1/1000 of a volt (one millivolt, or mv) can also be used, except an analog meter will give you a very low reading (if any at all) in fresh water.

To use the voltmeter to check on the adequacy of the sacrificial zinc, one lead wire is connected to the silver electrode and immersed in the water in which the boat is floating.
The other wire from the voltmeter is connected to a piece of metal in the boat that is in contact with the seawater (the prop shaft, for example).

The amount of zinc required to protect other underwater metals varies with the type of metal involved. To make a metal last forever, simply lower its relative voltage 225-250 mV by means of a sacrificial metal (zinc).

Voltage Ranges vs Silver/Silver Chloride Reference Electrode

Bronze: 500 - 700 mV
< 500 mV Bz is eroding - Add zinc, > 700 mV Bz overprotected - Remove zinc

Steel: 750 - 950 mV

Aluminum: 800 - 1050 mV

Lover milli-Voltages indicate metal erosion - ADD Zinc.
Higher mill-Voltages indicate over-protection - Remove Zinc.

Voltage Ranges vs a Saturated Calomel Electrode:
http://www.ocean.udel.edu/mas/masnotes/corrosion.pdf
Attached Thumbnails

Galvanic Series of Metals in Sea Water from the least noble to the most noble and their potential voltage (note: the table is not complete).

Corrosion Potential in mV
Magnesium and Magnesium Alloys -1600 to -1630
Zinc: -980 to -1030
Aluminum: - 760 to -1000
Mild Steel: -600 to 710
Copper; -300 to -570
Brass: -300 to -400
Lead: -190 to -250
18-8 S/S Type 304: -50 to -100
18-8 S/S Type 316: 0 to -100
Graphite: +200 to +300

In order to have proper protection, each metal in the grounding circuit's should have a reading at least -200 mV below its stated potential range of corrosion.


Example: a brass through hull should give a reading of no more than -500 to -600mV (-300 + -200 = - 500 mV) to have proper protection in the grounding system.
Another way of looking at it is that the zinc should be absorbing the electrolysis given its corrosion potential at -980 to -1030 and hence will functions as the anodic agent in the current flow between all the equipment connected in that series of grounding. If the voltage at the brass through-hull is -300 to -400, that means that it is functioning as a potential "sacrificial" anode.

The voltage on all underwater hardware connected to the bonding system should be the same (IF NOT, there are problems in the wiring or connections)

See also:

Marine Metals Reference by Michael Kasten
http://www.kastenmarine.com/mbqMetRef.pdf
and
Corrosion, Zincs, & Bonding ~ by Michael Kasten
http://www.kastenmarine.com/mbqCref.pdf

Excerpted from “The Future for Sacrificial Anodes” ~ by Bob Crundwell
Goto:http://www.jcse.org/Volume4/Preprints/V4Preprint2.pdf

The calculation of the weight of anode alloy required to protect a structure is given by a simple calculation:

W = (A x C x L) ÷ Z

Where:
W = Weight in Kg
A = Area to be protected in M2
C = Polarisation Maintenance Current Density in Amperes / M2
L = System life in Hours
Z = Anode current capacity in Ampere Hours per Kg
The individual components of this equation, with the exception of design life, are known but only approximately*.

* It is a brave designer that claims to know the true surface area of the structure. Dimensional tolerances of rolled sections of the sizes from which offshore structures are made are known quite accurately but it is surprising what bits get left out of the calculation let alone any correction for surface irregularity (one authority quoted the difference to be a factor of x2).
* Maintenance current density is variously quoted at figures between 0.140 A/M2 and 0.040 A/M2 for the same location, a factor of almost 4 times.
* Anode current capacities for Al-Zn-In alloys are variously quoted between 2550 Ahrs/Kg & 2750 Ahrs/Kg In general the lower figure is on the basis of long term field tests and the higher figure is on the basis of short term lab tests.


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Old 02-04-2008, 00:28   #6
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Old 02-04-2008, 00:30   #7
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Old 21-08-2008, 04:36   #8
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Fluke Tutorials

Some EXCELLENT On-Line Troubleshooting Tutorials from Fluke:

“Beat the Book" - Testing Electrical Systems with a Digital Multimeter:
http://assets.fluke.com/appnotes/aut...e/beatbook.pdf

Troubleshooting Marine Engine Electrical Systems
http://assets.fluke.com/appnotes/ele...r/B0270b_u.pdf

Troubleshooting Outboard Motor Magneto Ignitions
http://assets.fluke.com/appnotes/ele...r/B0271b_u.pdf

Diagnosing voltage drop: electrical automotive troubleshooting
http://us.fluke.com/usen/support/appnotes/default?category=AP_AUTO(FlukeProducts)&parent=APP _FPM(FlukeProducts)#

Testing Corrosion Protection Systems

http://www.fluke.com/Application_Not...r/B0269b_u.pdf
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