Electrical.

[wheels 543]

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.

__________________

[wheels 543]

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/appnot ... keProducts)&parent=APP _FPM(FlukeProducts)#

 

Testing Corrosion Protection Systems

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

[wheels 543]

This article was written by a good friend of mine and I would like to acknlowdge his expertise and the time taken to produce it. Rick is probably one of the best in battery technology. He was also the designer of the early Xantrex/Heart Battery chargers and inverters.

 

Evaluating 12vdc Flooded-Cell Batteries

Evaluating a 12 Volt flooded-cell battery of unknown history and quality

 

To do this you would need to fully charge the battery (making sure that a full 14.4V or more is reached during acceptance charging @ or around 25 C). You would then measure each cell separately, obviously the total has meaning as well yet it is the VARIATION in cell-to-cell readings that reveals the need for equalization or evidence of permanent sulphatation (sulphation is not permanent, sulphatation is).

 

The three things to determine: 1. That the battery is fully charged, and if so that it does not need equalization or that equalization does not yield a reversal of sulphation cell-to-cell. 2. The approximate Amp-hour rating. 3. The battery internal cell resistance.

 

The internal resistance is a very important and little acknowledged attribute of any battery, lead-acid or otherwise. It is the internal resistance multiplied by a heavy load current which results in a “voltage burden” to your system and directly increases losses in the energy stored by the battery that you cannot use.

 

Notice that the fully charged terminal voltage is not on the list because it will be sufficiently high (about 12.7V without surface charge) when the other conditions are met. Surface charge may be removed by applying around a 5% of the Amp-hour rating in Amps and noting the terminal voltage. It will linearly decrease until it becomes constant. Remove the load at that time. Note that most nominal 12V flooded-cell batteries have a specific gravity that results in a 12.66 Volt terminal reading yet many of you notice readings of 12.8Volts or so....this is due to a lingering surface charge after the application of a charge voltage. Similarly many gel-cell and AGM batteries exhibit terminal voltages of 13 Volts or so even though the readings drop to 12.9 Volts (AGM and gell-cell batteries have higher specific gravities than do most flooded-cell batteries and, therefore, the terminal voltage is higher. Terminal voltage, Vt = 6(0.85 + SG) where SG is the specific gravity of the electrolyte for a 12 Volt lead-acid battery (yes, this also includes AGM and gell-cell batteries).

 

Note that state-of-charge means little to you. It is state of capacity that is important and must be inferred from a relatively simple test. Given two batteries in separate boxes that do not allow you to inspect other than terminal voltage: They both read 12.65 Volts. Which one has a greater capacity? One cannot know. What good does it do to have a degraded start battery that exhibits a so-called full state of charge. One day it will easily start the engine. The next day it will not because it may have degraded from a 1 Amp-hour state of capacity to a 3/4 Amp-hour in one day's use and may not start the engine. To be sure, that same battery began as a 75 Amp-hour battery and for 6 years always started the engine. One day the final denouement occurs to one's dismay.

 

Because it is hard on the life of any lead-acid battery to fully discharge it in order to make an attempt to determine capacity it is not advised to do so unless one has many batteries available to waste before choosing a similar one that has not been discharged. What WILL be revealing, though, is to discharge the battery at the theoretical 20 hour rate for an hour (at least 1/2 hour), let the battery recover for at least an hour and measure the standing voltage and use a "look-up" table to determine approximate state-of-charge and using simple algebra calculate the capacity from that information. At the end of the hour observe the terminal voltage under load and then the voltage immediately after the load is removed. Note the current just before removing the load. Calculate the internal resistance by dividing the difference in voltage by the difference in current (as an example for a 180 Amp-hour rated battery the current difference will be 180 divided by 20 minus zero...zero because after removing the load the current should be zero). For this test note as well the initial change in voltage from no load to the 20 hour rated load applied. Calculate that initial resistance as well making sure that initially there is no surface charge on the battery which will make the results lower (better) than the actual value.

 

So, the 20 hour rated current is 9 Amps in this example. Using this test you will notice that the terminal voltage drops linearly for awhile then settles down to a constant value. I would expect that voltage to be approximately 12.5X Volts or better for a flooded-cell 180 Amp-hour “real” battery.

 

The approximate capacity, C = (measured test Amp-hours)/(1-decimalSOC), where the decimalSOC is the decimal value (0 to 1) of the state of charge shown by a chart showing state of charge versus voltage. Now to be more accurate one should divide C by 20 to get the 20 hour capacity current discharge rating and repeat the test at that current to recalculate a refined value of C. **I've corrected my original mistake in this formula caught by cal40john as seen in his improved description in the following entry at 23:56, thanks to John!

 

Obviously the use of an accurate battery monitor is almost essential in making such tests.

 

AGM and gel-cell batteries require similar tests yet require slightly different observations and tests. More on that later.

[rigger 47]

Lithium Batteries seem to be another or the list,

 

SA link 1

 

 

SA link 2

[wheels 543]

Some tables that could be of help

[wheels 543]

Continued

[Guest]

Shunts.

 

Anyone know at what sort of Amperage you should fit shunt if you want to run a basic ammeter in a 12V system?

 

It appears Ammeters over 30amps look to have them pretty much fitted as standard.

 

Below that does anyone have any ideas?

 

Want to fit a Ammeter to D1's Micro Eco dwelling just so she can see how fast her toys are killing the batteries.

 

Had a suss of a well known brand name volt/ammeter with shunt. At 700 odd notes someone's taking the piss. Got a Volt and Ammeter (separate but matching units) for 35 each and a smallish shunt is about the same.

 

Gawd... I hope this is the right thread and I haven't cocked up big scary Wheels Tech talk system/plan

[wheels 543]

Nah that brings up a good discussion KM.

There is no real "point" as such. First of all, a shunt is used for measuring Current. Voltage is measured across the positive and negative. All meters, Voltage and Current are measuring Voltage. The shunt creates the voltage across it as the current flows through it. Some smaller current meters that can connect direct into line has the shunt built internally. But they tend to handle a max of about 30A. Pluse they are terribly inaccurate. The more modern day Digital read outs are far more accurrate.

A shunt works because all conductors are not perfect and thus have a resistance to the electrical current. If you measure at a point A and a point B in a conductor, you will measure a voltage. A perfect conductor would show no voltage between the two points. As rare earth materials and bulk lots of liquid nitrogen are not something we poor boaties can afford to carry, we have to stick to copper. The voltage that can be measured is the elecrical current that is not efficiently "fitting" down the wire at the point. It takes the simpler route through our measuring device.

A shunt is just a piece of Brass usually that is of a size that can handle the current of the cables carrying it, without having too large a drop in our precious power across it. It will conduct close to all the power the circuit will handle, but there is a very very small voltage not flowing through it that the very sensitive digital meter circuit can sense. So the result is a very accurate reading of current with very little loss in our power to do so.

Now that's one part of what they do. You can have a simple meter, but some of the expensive units do more than just that. Cheap is cheap for a reason. Although why they are as expensive as they are beats me. Anyway's, the more expensive units can do a simple calculation and work out how much power you have used from the battery. They are simple adding machines in a way. Even more expensive ones, use very very complex algorythims for working that out, because batteries don't give up the juce in a simple way. Then the very very very expensive units do some real jump through firey hoop type tricks and can work out very accurate details and control charging and controll the chargers they can plug into and so on. The Link system on my charger/inverter was $2.5K. But the info it tells me is quite eye opening and trust me, if you think your batteries are being charged properly with a cheap charger, you are very much wrong. Even worse when being charged from the Alt.

I don't know how much, but Cruzpro have a current metre.

 

KM, I will PM you. I might have something I can help you with.

[wheels 543]

Oh yeah one poor persons meter. You can make a fairly accurate digital meter yourself, but it does require some mucking around. Digital Multi metres are a dime a dozen these days. Also makes you wonder why the boat ones are so expensive. As i said above, the meter is just reading the voltage (PD or Potential Difference) across the shunt. Well you can easily make a shunt with a bit of brass. Easily bought as a Buss Bar. The meter simple gets connected with a lead to each end of the shunt. Run a load and then select a voltage, starting with a high one and selecting down till you get a usable reading. Only issue with this is that the reading may not..most likely not relevant to a current. So you need to have a current meter to then log the reading and plot it. So the voltage shown means what the current is. Some meters allow an adjustment for accuracy inside them. You can then get the thing calibrated to a V that equals a Current. So a 2mV reading could be considered 2A or 20A for say.

Messy yes, but cheap.

[Guest ynot]

I found digital ammeters from a auction site in aus $ 80.00 landed with shunt of appropiate rating ebay ???? something like that or whatever they have in aus.

 

the unit seems to work fine

[Guest]

Charging question.

 

If I have 4 x 6V deep cycles and have joined then all up to make a 12V bank, can I just put a std battery charger on the end and charge that 'bank' just like you would a single 12V battery?

 

I'm thinking Yes but at the same time remembering the number of times I've electrocuted myself, it's been a fair few, so thought it safer to ask.

 

While here, would the same answer apply to 2 x 6V joined into a 12V bank?

 

And - batteries to big switch, as is used on boats, then to a big fuse before heading off to the distribution board be the right call? The key bit being the 'big fuse'. If I should have one any idea what size and before or after the master switch?

 

Someone said batteries could spike up to BIG if something goes bad.

 

The set-up -

4 x 220 Amp hr deep cycles turned into 12V bank. Input via 140W solar panels (currently only 40W but is set up to go up to 140W, which we see as max ever needed). Output usually quite low to drive 10 max LED lights, 72W 12V flat screen, radio, iPlod and stuff 14yo girlie like. Also has inverter to power 2x 240 power plugs, probably for hair-dryers and shite like that. All wiring is std household in 1.5mm for the lighting circuits and 2.5mm for the power circuits, both the 12 and 240V.

 

Batteries to BIG wires to std sort of boat panel with each circuit on a 15Amp breaker. From there 2 x lighting, 2 x 12V power curcuits come out. Plus 1 separate 12V circuit to bathroom which will have a couple of lights and a 1.5W fan running off it. The fan sucks the stinky out of composting loo and pumps it into the atmosphere so the world warms up and we can do the Simrad in shorts and T shirts only.

 

The 2 x 240V power plugs have 1 x 2.5mm wire each which runs back into the battery box itself to a waterproof plug and switch. The plan being we can plug inverter into that or if we need to, an extension lead. Opps, I should drop a fuse into those shouldn't I, damn forgot that. What a dick!

 

The idea of using std household wire is that if someone ever wants it all 240V all they have to do is change the end fittings rather than a total rewire. And voltage drop, max seen 0.2V = nice

[wheels 543]

If I have 4 x 6V deep cycles and have joined then all up to make a 12V bank, can I just put a std battery charger on the end and charge that 'bank' just like you would a single 12V battery?

Yes and Yes.

If I should have one any idea what size and before or after the master switch?

It doesn't really matter too much. The key point to remember is that the Fuse protects the cable. However, if you can afford to go this way, get a Circuit breaker. And the circuit breaker doubles as the switch. Now lets say with everything switched on, you can draw down 50A. So you want a circuit breaker that can handle 50A plus some. An 80A breaker would be a good choice. But the cable has to be able to handle 80A in a dead short without turning into a heater element, which is bad. The problem with a fuse is you have to have a very high rupture capacity. Otherwise they lose lots of heat across them and heat is wasted precious energy. A circuit breaker loses nothing till it trips.

Batteries do not spike. But they will turn a cable into a mess in real short time should you get a short.

The rest sounds good.

[Guest]

Sweet, I'm knot building a big bomb, that's nice

 

That makes sense. Circuit breaker to stop toasty wires = done

[wheels 543]

This is what can go wrong when you do not have a circuit breaker.

[wheels 543]

This is 75mm2 cable and it ran right around a largish engine room. It was either cable tied or inside conduit and was a very tidy installation. The fault started with one cable that ran to the Starter motor. The motor developed a fault that resulted in a dead short to earth for that supply cable. That cable heated and melted itself through all the conduits and ties, resulting in cutting through yet more cables and shorting. In the end, the cables now so hot and having all the insulation melted off them, melted right down through plastic waterlines and drain lines and finally came to rest on the Steel Fuel line running around the engien room. This line was connected to the Engine via flexible lines that had internal steel braid. The braid super heated up to the point where it was boling the Diesel and squirting diesel fumes out in jets all the way along the line. There were three possible scenarios of outcome to this accident. One was that the fumes could have ignited and exploded. The second was that the hot cable could have melted through a skin fitting and it's hose below and the boat could have sunk. Actually there was a Fourth. The batteries being in a hard short situation were boiling and super hot and ready to explode. Thankfully, the third scenario happened, in the the owner, by risking his life, managed to get to the battery bank with a large pair of cutters and cut through the cable right at the posts.

Actually, I will go a little further with this story. The smoke was toxic and choking and so thick that visibility was almost Zero. The Engine room hatch was also a huge Solid Teak Floor panel that weighs a lot. As the skipper climbed down into the thick smoke, he bumbed the piece of timber holding the floor up and the teak hatch crashed down on his head and a catch split his head resulting in blood pouring down his face and eyes and glasses making him almost completely blind. So very very fortunate that he was not knocked unconcious as the smoke would have killed him had he taken a breath. He managed to stay concious, cut the cable and climb back out all holding one breath and then got out of the boat. After the smoke cleared, he confirmed all connections had been severed, the fuel line turned off and the seacock was safe. He then managed to drive all the way back home to a wife that was shocked and looked after him.

Should he have done what he did?? probably not. Very easy to say when it is not you and it is in hind sight. The Skipper paniced about the 1/2mill boat berthed beside him and that fact that he might lose his pride and joy, even though it was insured. He figured he had to do something.

[smithy09 50]

Interesting Post Wheels. What is the usual circuit diagram in a 12V installation? I know there is usually heavy cable going from the battery directly to the starter motor to avoid voltage drop when the key is turned and solenoid kicks in, but is there usually an MCB in that line from the battery? Or a big fuse capable of protecting the cable? This would have to be reasonably heavy duty to carry the starter motor current... I haven't looked closely at boat circuits but would be interested to know how these are usually wired up! 75mm cable is good for about 250A, so you would need a big fuse in there!

[wheels 543]

Yes you would normaly have a start bank and House bank. The start bank has one heavey cable running to the Starter. It is often very hard to fuse the starter cable because the loads can vary from say a real cold morning start and normal warm starts. And because start currents are short duration, the cables are often not as big as they would need to be for continuos loads. A starter that would normally draw a current of 200-300A could actually draw twice that for a short time till the engine gets ticking over. So you need a huges breaker and Breakers capable of handling start currents are expensive.

In this situation and this was the original layout, the cables ran from the Start battery, all the way around the engine room to the isolator switch and then back to the starter. There was so much excess cable, that after I rewired all this and removed all that melted crap, I had enough spare cable to wire the entire system and not have to buy any new cable. The battery banks are now up out of the engine room and in under seating in the Pilot house and the Isolator switched are right by the batteries and easy to access without having to lift or acces any compartment. They are right in view. The House bank has a 100A isolator/breaker and the Start has just the Isolator and the cable now runs straight down to the starter and is protected from both itself and from ever coming against anything else, should a short ever occur. The House cable runs to the main distro board and branches out form there. A 25A cable runs upto the pilot house to a second switchboard which has all the instruments/electronics, wipers, local lighting etc. The main board below has everything else.

[smithy09 50]

So the Starter cable is still not protected! I had never really considered this circuit before, but it is a problem to protect isn't it? Theoretically the same fault could occur again couldn't it? You have only protected the cable from burning anything else, but you could still have the fault, high current and burning cable, as well as potentially exploding batteries! Do current designs all rely on the starter never shorting like this did? Also, what happened to the solenoid relay? That is only meant to come in when the key is turned isn't it? Did it weld shut?

[wheels 543]

Yep it is common not to have a fuse. Although on small motors, it is quite possible to have a circuit breaker. You require a good size cable and a breaker that can protect the cable, yet still remain engaged for all starting situations.

In big engines, yes it is difficult to protect, apart from having the cable as short in length and direct run to the starter as possible. My engine is a 354Cubic inch Diesel and so is on the larger size for Sailboat motors. But small fry when you are talking about big mother engines in launches. By the way, I had 1800CCA of start battery. That's enough to do some nice welding with

Even if you have a section of the cook straight cable connected between battery and starter, the current the starter draws is huge. Even a little engine could draw 100+ Amps. The smallest of voltage drop across the cable results in huge power loss and power loss in cable is seen as heat.

But it is also a rare event. The situation I...err....this fella had was the terminal lug had a dead short to the Starter motor body. Once again, not a common thing to have happen. But this Moron had just rebuilt the Starter. He had bench tested it and it worked sweet. I....errr... I mean, the Moron still can't work out how that terminal shorted and passed the bench test. Anyway, the starter was not engaged. All that happened was that after I...errr...he connected everything uo, he simply turned the Isolator switch to on and went about a quick clean up and then I reached for the engine key and tunred it. Nothing happended. I went down stairs to the DC panel as there is a small breaker there for the start solinoid circuit and I thought maybe I tripped it. I looked at the DC panel and was shocked and puzzled as to why the Volts were reading about 4V and counting down toward Zero. I scratched my head and was trying to work out what was going on when I smelt a faint burning smell. Having just finished electrical work I immediately figured I had a problem back down in the engine room, and shot up stairs and without even a thought, I opened the hatch and an enormous cloud of smoke billowed out. That was a major shock, I simply didn't expect to be greeted with that much smoke. I couldn't see the isolators, but I knew where they were and reached down and found the thing by brail and turned the engine Isolator off. I turned the engine room extractor fan on, which thankfully was running off the house bank and then thinking that was all safe, got out of the boat and allowed about 10Min for the smoke to clear. I then went back to look at the damage and it was at this point that I saw the fuel hoses blowing the jets of fumes and realised my troubles were not over.

[Guest]

In the AM I'm picking up some big battery cable...knot sure what size but they say 'more then plenty' and with that is a circuit breaker rated some Amps less than the wire is rated too. Switch now outta there and will be replaced with said breaker.

 

And circuit breaker fitted just after waterproof switch (which is inside battery box anyway) in the 240 volts side so just an added extra layer of protection if the inverter craps out or someone goes too silly if we are plugged into the mains at the time. The safer than sorry theory.