BLUEMOMENT

Our domestic battery is obviously shot and has been patially responsible for the postponement of our intended Atlantic crossing attempt - whether for a week or a year or forever remains to be seen.

Current system is two batteries

1 95AH high CCA lead acid car battery as a dedicated engine start

1 110AH 'deep cycle' leisure battery as the domestic battery (now knackered - it was the engine start battery for 3 years until switched to domestic duties ten weeks ago)

One school of thought is to use two lead acid batteries and swap them regularly between domestic and engine start use, so that both are regularly discharged by a substantial amount, which helps keep them in condition - I was told this by an ex submariner, who used to depend rather heavily on his batteries being in good condition . . .

So - should I just buy another car battery and switch regularly?

or . . .

Another expert has told me that lead acid batteries are just no good,and that I should get gel batteries. He recommends two gel batteries for hte domestic load, with a solar panel - expensive, but maybe I can trade something. He says the gel batteries are a good deal because they are made just across the water in Tenerife.

Bearing in mind we are looking at medium term liveaboard and long passages with 12 hour nights, which option would the panel go for, or is there a third way?

_________________
- Nick

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This is a subject with about as many opinions as punters, but I'll stick my head above the parapet. In my view (and it will no doubt be challenged) I reckon that the ideal solution would be a high CCA starter battery dedicated to engine cranking and a high Ah deep discharge, traction type battery for domestics. The latter is what milk floats (and, I suspect, older submarines) use / used.

A method of cross-connecting in an emergency is desirable, either by using the "both" position on a 3 way + off switch, a wired-in "emergency parallel" switch (better, since a dead battery can be isolated while using the good one to feed both cranking and domestics), or even a jump lead. The latter suggestion will have doom sayers raising images of hydrogen explosions, but since hydrogen is only given off when batteries are charging - and then only once they're almost "full" - you are unlikely to be in this position and simultaneously trying to make an emergency connection to get the engine started. Unlikely, but not impossible - see later.

Charging more than one battery is another can of worms. My view is that the alternator should initially charge only the cranking battery, preferably using a smart regulator. Once that's fully charged a VSR fitted between the batteries closes, and the domestic battery starts to charge too. That way, accidents apart, the cranking battery should always be fully charged - just like a car battery in fact, reinforcing the point that for starting CCA are more important than Ah. Incidentally, I have a strong dislike of "diode splitters": they're inefficient and they cause all sorts of subtle problems, some of which can easily shorten battery life.

Other charging devices, solar, wind, towed, or whatever, should charge only the domestic battery (because the starting battery should already be nearly full, see above) via a regulator to avoid overcharging unless they're really feeble, e.g. a tiny solar array. A slight sophistication is to have your VSR of "twin sensing" type. This costs little, if any, more than the single sensing type and means that when either battery reaches 13.7V, i.e. is well charged, the VSR closes. This could have advantages on a long engine-free passage in counteracting the self discharge of the cranking battery.

It is the above circumstances which make me think of a possible - if unlikely - scenario where hydrogen could be a danger. If the starter battery died when the domestic was being well charged by wind, say, then there might be a risk in making a connection to it. In these circumstances a minute or so of good ventilation should dispose of any risk.

And what if the big domestic battery dies? Well, that's a bit harder. Using the cranking battery will get you by up to a point, but there's then a real risk of losing the ability to start the engine. There's a lot to be said for having a spare battery - which might have its own job to do in normal circumstancies. I have two: one for the windlass, one for the electric outboard; either could be used as a spare domestic in an emergency.

And I also advocate carrying long jump leads: rafting up to another boat to get a jump start isn't daft, but how many carry the wherewithal to do it?

That's gone on a bit, and if posted on "the other place" would undoubtably generate a long and heated thread, but hope it's of some use.

Nick, I've just realised that I hadn't actually directly answered your two questions!

Gel: they're dear, and also have a different charging characteristic (lower voltage) to wet cell batteries, so if you have one of each you could get into trouble if you're not careful.

To replace the knackered domestic battery I would use a conventional lead acid. A traction type would be ideal, a 12V truck battery probably next best, then a "leisure" battery, in each case of as big an Ah capacity as you can get to fit in the space. A very poor last choice would be a car battery: if that's all that's available then, again, get as big as you can manage.

Hi Nick

As Dave says, you are likely to get a different opinion from every poster.

You need to remember that there is nothing very extreme about Fairwinds, the 13.5 Beta (and the Volvo before it) won't take heavy cranking amps, and IIRC you don't have a fridge or watermaker so your domestic draw isn't horrendous.

Gel batteries would need a different charging regime and the hassle and usually greater expense wouldn't be worthwhile. The biggest advantage to you would be that they don't spill, and could be rigged in akward positions if need be.

I don't remember where your batteries are mounted. Both my batteries, and the fuel tank, are under the saloon sole and I found that width and height limited the maximum size of battery that I could fit.

I assume that you have a digital voltmeter, the difference between a half discharged and fully charged battery is only 0.5 V. As long as it's been at least an hour since charging, and there is no load then 11.7V = absolutely flat; 12.2V = 50% (the minimum you should discharge to); 12.7V=fully charged.

I don't think that a lead acid battery can develope a memory. The thing that reduces the capacity and life of the battery is having it sitting without being fully charged. The chemical change between discharge/charge is fully reversible but when sitting discharged, another reaction takes place which isn't reversible.

You could do a capacity check on the battery - connect a known load - say 20 Watts - and check remaining charge every hour for a few hours and multiply up the result.

You should do an analysis of your domestic load to determine the AHrs used between recharges.

I wouldn't be too precious about which type of battery you fit - the more capacity that you can afford and fit in - the better - as long as you have the capacity to recharge it fully.

Check your charging sources - are they giving 14.4V.

Good Luck

Ash

Right . . .

The reason I mentioned gel is because as I understand it they are usually deep cycle and apparently there is a locally made (Tenerife) brand that Andy the German boat fixer here says is highly affordable and guaranteed ten years.

I was thinking of buying two and connecting them up so they are the new domestic battery bank and on position 2 of the 1-2-ALL switch, keeping the current lead acid high cca battery for starting duties only. I am aware that charging requirements are different, but we never use the ALL position on the switch (except in extremis,) so we would never be charging both types of battery at once, except through the wind generator - and we cold disconnect this so it is only charging the domestics if necessary.


If we do this then are there any other snags that either of you can see?

_________________
- Nick

. . . . . . . . .

Ardvec

Will try to do some searches for you. Assume that you've got a fairly slow connection.

Ash

Some more info


2. Basically there are two types of batteries; starting (cranking), and deep cycle (marine/golf cart). The starting battery (SLI starting lights ignition) is designed to deliver quick bursts of energy (such as starting engines) and have a greater plate count. The plates will also be thinner and have somewhat different material composition. The deep cycle battery has less instant energy but greater long-term energy delivery. Deep cycle batteries have thicker plates and can survive a number of discharge cycles. Starting batteries should not be used for deep cycle applications. The so-called Dual Purpose Battery is only a compromise between the 2 types of batteries.

3. Wet Cell (flooded), Gel Cell, and Absorbed Glass Mat (AGM) are various versions of the lead acid battery. The wet cell comes in 2 styles; serviceable, and maintenance free. Both are filled with electrolyte and I prefer one that I can add water to and check the specific gravity of the electrolyte with a hydrometer. The Gel Cell and the AGM batteries are specialty batteries that typically cost twice as much as a premium wet cell. However they store very well and do not tend to sulfate or degrade as easily or as easily as wet cell. There is little chance of a hydrogen gas explosion or corrosion when using these batteries; these are the safest lead acid batteries you can use. Gel Cell and some AGM batteries may require a special charging rate. I personally feel that careful consideration should be given to the AGM battery technology for applications such as Marine, RV, Solar, Audio, Power Sports and Stand-By Power just to name a few. If you don't use or operate your equipment daily; this can lead premature battery failure; or depend on top-notch battery performance then spend the extra money. Gel Cell batteries still are being sold but the AGM batteries are replacing them in most applications. There is a little confusion about AGM batteries because different manufactures call them different names; some of the popular ones are sealed regulated valve, dry cell, non-spillable, and sealed lead acid batteries. In most cases AGM batteries will give greater life span and greater cycle life than a wet cell battery.
SPECIAL NOTE about Gel Batteries: It is very common for individuals to use the term GEL CELL when referring to sealed, maintenance free batteries, much like one would use Kleenex when referring to facial tissue or "Xerox machine" when referring to a copy machine. Be very careful when specifying a battery charger, many times we are told by customer they are requiring a charger for a Gel Cell battery and in fact the battery is not a Gel Cell.

AGM: The Absorbed Glass Matt construction allows the electrolyte to be suspended in close proximity with the plateÕs active material. In theory, this enhances both the discharge and recharge efficiency. Actually, the AGM batteries are a variant of Sealed VRLA batteries. Popular usage high performance engine starting, power sports, deep cycle, solar and storage battery. The AGM batteries we sell are typically good deep cycle batteries and they deliver best life performance if recharged before the battery drops below the 50 percent discharge rate. If these AGM batteries are discharged to a rate of 100 percent the cycle life will be 300 plus cycles and this is true of most AGM batteries rated as deep cycle batteries.

GEL: The gel cell is similar to the AGM style because the electrolyte is suspended, but different because technically the AGM battery is still considered to be a wet cell. The electrolyte in a GEL cell has a silica additive that causes it to set up or stiffen. The recharge voltages on this type of cell are lower than the other styles of lead acid battery. This is probably the most sensitive cell in terms of adverse reactions to over-voltage charging. Gel Batteries are best used in VERY DEEP cycle application and may last a bit longer in hot weather applications. If the incorrect battery charger is used on a Gel Cell battery poor performance and premature failure is certain.

Are the proposed batteries truly Gel type?

Is the controller on the wind generator switchable from lead acid to gel?

Did you fit a smart contoller to the alternator, and is it switchable as above.

If the gels are a good buy, then go for it, and use a charging regime for gels and accept that the starter battery will be slightly undercharged.

I'm sure that there have been some good articles in the yot mags - I'll see what I can find.

Ash

Nick, If you're going to go for gels for the domestic, then I would certainly agree that (emergencies apart) you should avoid parallelling them with the cranking battery. Whether or not you can do this will depend on the configuration of your electrics, in particular the charging arrangements. If alternator, starter and loads are all connected to the common terminal on your 1/2/both switch, with the batteries connected to 1 and 2 respectively and there are no other connections then you should be OK.

If there are other load connections to the common, e.g. a direct feed to the VHF or whatever, you'll still be OK (side rant here: far too many manufacturers' instructions say "take a direct feed from the battery to my kit": if you followed them all you'd have a right rats' nest. A properly organised distribution system is IMHO far better). The thing to watch for is what else is connected to either battery or the 1 or 2 terminal? Extra connections here could potentially mean problems. Connections to individual loads are probably OK (just an odd way to wire them). The biggest problem will come from that spawn of Satan, the diode splitter. You don't have one, do you?

Where is the output of your wind generator connected?

I might be wrong there - further research shows that 3 stage chargers float gels at 13.8V and wets at 13.25V

Ash

This thread has been a right good read and has answered many of my original questions. It's raised some too.

I have just dumped two lead acid 95 Ah cranking batteries.

I'm going to replace them with a cranking battery for the engine and a deep cycle battery for the domestic stuff, which seems to be the way to go, or one of them at any rate.

The little hand book with the boat says to switch the "1,2,both/off" switch to "both" to start the engine. Then when the engine is done with switch to 2, if that's the domestic battery. It also warns not to switch with the engine running.

What I'm not sure about is what happens when it comes to charging. If the domestic battery has had some use and is half or less charged, will there be any problem when I switch to "both" to start the engine?

I don't know that there is anything other than an alternator, will the engine battery get any charge at all before the domestic battery reaches the same state of charge?

Would a smart charger charge both at the same rate even if one needs more charge than the other?

_________________
Chiron: Westerly Centaur.
Cheers Bob.

And another thread is raised from the dead!

I think I would be tempted to first look at your set up and draw a wee diagram showing what is connected to what, since there are a number of ways it can be done. (My post of a couple of years ago mentions some of the variations.)

I have distinct reservations about the "switch to both before starting" advice. As you have already identified, the first thing that will happen is that current will flow from the (hopefully) fully charged cranking battery to the partially discharged domestic battery. It also rather defeats the point of having specialised batteries for each job. Assuming you have the simplest wiring arrangement, i.e. alternator, starter and loads all connected to the common terminal, cranking battery connected to "1", domestic battery connected to "2" then I would recommend the following starting procedure:

1. Switch to "1"
2. Start the engine
3. After a few minutes of running at sufficient revs to charge batteries, switch to "both", then to "2": delay doing this if the engine was difficult to start or it has been some days since batteries were charged, since the idea is to first replace the cranking energy used plus the starting battery's self-discharge.

When you shut down the engine leave on "2". This should ensure you keep your cranking battery fully charged while discharging the domestic.

The key point is remembering to make the switch at the right time: some of us are better at this than others. A properly installed VSR makes the process automatic and saves having to remember. A smart controller can significantly reduce the time taken to charge. A battery monitor can give a very good indication of what's going on, but a simple DVM will be much better than nothing.

I assume, in the above, that your 1-both-2 switch is make before break. It should be, but check with a meter to confirm. If it is in fact break before make then you risk blowing your alternator diodes if you switch with the engine running. In that case I would recommend replacing the switch, or taking the opportunity to overhaul and improve the whole set up. Alternatively, you would have to switch to "both" before starting, then not touch it until the engine is stopped. Which, given the manufacturer's advice, does rather make me wonder...

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Are you resurrecting old batteries or old threads?

I have the setup which you are proposing. A lead acid starter battery and a lead acid 'leisure' battery for the domestics with an off/1/both/2 switch. I decided that 2 would be the domestics. My switch doesn't go round and round - the sequence could only be O/1/B/2/B/1/O. It is designed such that no disconnect when moving between 1 or 2 and Both. I believe that this is all fairly usual.

My technique is to switch to 1 for the first engine start of the day, and leave it there for all the marina manoeuvres. Once motoring in open waters I will switch to either Both or 2 - most commonly 2 - with the engine at more than a tick over, I can hear the alternator load going on as I switch in the domestic battery which will be more discharged than the starter. With the engine off, I will have the switch on position 2. I am happy enough to do 'warm engine' starts on position 2 - i.e. from the domestic battery - after all it's only a 2 cylinder 13.5hp so won't need much.

I once switched from 1 to off for a few seconds with the engine running but didn't seem to harm the alternator - the battery load would have been removed but there would still have been a load from the vhf, depth, etc.

I don't have any smart charging, neither on alternator or mains. I've bought a second-hand Sterling two output mains charger but haven't picked it up yet. My understanding is that this unit share its total output, dependant on the variation in the state of charge.

Ash

Edit - I wrote this before DaveS had posted, but stopped for my dinner before my post - don't have time to amend to suit.

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"This is a sailing Forum"

Thanks men for your replies. And all the previous info too, I decided to go for two different batteries based on that.

On another forum I frequent, folk are encouraged to exhume old threads and add to them instead of re-hashing the same ground lots of times, it seems to work.

I will have to do some circuit testing but I suspect my 4 way switch is not the type I want, ie. one I can operate as Ash does.

It's probably the original fit on a 1979 Westerly. It's the Westerly manual that warns against breaking the diodes if the switch is moved when the engine is running.

This learning curve is steep, but fun.

_________________
Chiron: Westerly Centaur.
Cheers Bob.

Bob, if this is the start of what could develop into something else, it's worth remembering that the off/1/both/2 switch may eventually be used purely for choice of OUTPUT from the batteries.
If you subsequently add splitter diodes (Recommended) it won't matter what you do with the switch while the engine is running.
On that same point, in spite of the Westerly manual, the switch is designed as make-before-break, so will only go into 'diode kill mode' if you turn it to "off" with the engine running.
Have fun,

_________________
Just because you're paranoid
doesn't mean they're not out to get you.