Battery charging

[noswellplease]

After looking at the various options for charging batteries using all sorts of high tech battery voltage sensing devices and diode splitters, (which of course can go faulty!) I am coming to the conclusion that as the engine starting battery is permanently connected to the starter and alternator a simple switch (make before break type) that allows the domestic battery to be charged or isolated and indeed put in parallel with the starter battery when needed is the best option for a troublefree set-up?. I will be putting my hand in my pocket soon and would be interested in opinions?

Sailing, another word for spend spend spend!

 

[brianrunyard]

To keep it simple I'd suggest.
An Off-1-Both-2 switch.
Start battery on 1
Service battery on 2

Switch to 1 for starting.
Switch to 2 to charge both batteries.
Switch to 2 when at anchor so that starting battery stays charged.
This is basically what I do, except that both are starting batteries and I alternate:
i'e Start on #1, switch to both to charge, #2 at anchor.
next time out start on #2, charge both, #1 at anchor.

 

[Ruffles]

I have the same set up as BrianR. Common on many boats.

Disadvantage is that the alternator will self destruct if the battery is turned to 'Off' when the engine is running. Not happened to me yet - but this season my son will be three.....

So your idea seems perfectly good to me. Note however that if the service battery were left connected when the engine was started and the started battery were faulty, the full starting current could flow in the service battery cables so make sure they're up to it.

There are products around that will automatically disconnect the service battery when starting the engine and when the batteries are charged. Alternatively a relay can be wired such that it disconnects when the engine is started though this doesn't prevent you flattening the engine battery.

 

[tobble]

This does indeed seem to be the most common option and is therefore well proven to work. It's also about the cheapest way of having two batteries!

It does seem to me, however, that in general, it is a bad idea to have two batteries that do different job connecting in parallel even while charging.

if the levels of charge are different, then the the deader one will fairly quickly draw charge out of the more charged one until they are equal. There are various scenarios where this will be a nusiance (e.g. domestic drains the starter so there's not enough grunt to turn the engine over), and possibly even damaging:

A near-completely dead battery will absorb a lot more charge than it can release, in other words you have to put more energy in than you had to before, in order to store and release the same amount of energy, or more simlply the efficiency decreaces... This could mean that a dead battery rapidy renders a healthy one useless by drawing charge untill it goes below the point of no return...

This is unlikely but it has happened to me! Mainly my fault for not taking proper care of the batteries, but I won't make that mistake again! who was it said "lessons learnt are directly proportional to amount of equipment ruined."?!

 

[gbr9840t]

Keep the service battery disconnected and use a split charge relay powered by the alternator to connect it, like caravans and motorhomes. If your service battery is a proper deep cycle one your alternator will destroy it unless you limit the charge in some way, regardless if you connect it by a relay or switch. You can use the switch in emergency if the main battery is flat. Best of all dig in your pocket and buy a proper 2 battery control unit, I know they are pricy but so are melted batteries. I've got no money but I'm going to buy one anyway.

 

[john_morris_uk]

[ QUOTE ]
If your service battery is a proper deep cycle one your alternator will destroy it unless you limit the charge in some way, regardless if you connect it by a relay or switch. You can use the switch in emergency if the main battery is flat. Best of all dig in your pocket and buy a proper 2 battery control unit, I know they are pricy but so are melted batteries. I've got no money but I'm going to buy one anyway.

[/ QUOTE ]With the greatest respect, this is nonsense.

How exactly are you suggesting an alternator is going to destroy the battery?

Deep cycle batteries are constructed with more robust plates so that they are capable of being discharged and recharged without destroying the battery. (Car starter or cranking batteries have a far lower tolerance to being deeply discharged and have a short lifespan if you deeply discharge them a few times). Whether its a deep cycle or a cold cranking battery is almost irrelevant in the context of whether it will be destoyed by the alternator as in any normal situation it can't happen.

The alternator will not (cannot) put more charge into the battery than it will a) produce and b) the battery will accept. The alternator is limited by its internal design and the temperature and the charging controller.

The alternator would have to be able to produce a HUGE charging current to damage a battery it was charging and the fact that it is a deep cycle battery is irrelevant.

Very flat batteries of any sort initially accept high charging currents as the surface of the plates accept the charge. However very quickly (in the first few minutes) the physics of the battery takes over as it charges. The chemistry needs to penetrate the plates more and more and the charging resistance goes up. I suppose if you have a several hundred amp alternator and a very flat battery and didn't limit the current, something might melt, but this isn't the norm on the average yacht.

How on earth you think a normal boat alternator is going to damage a battery is beyond me.

 

[doug748]

I have two Lucas heavy duty switches (the sort with the Micky Mouse ears on the top). Switch one connects the engine start battery for starting; switch two the domestic. Mostly, of course I start on the dedicated battery, sometimes I switch over to the domestic to give it a charge boost. Of course I am careful to switch one off only after switch 2 is on. For it is said that I will otherwise knacker the alternator, except that I have done it lots of times and it never has. I commented on this to an electrical engineer and he said the damage business was a myth!
If I will be so lucky with my new 60 amp job we will see. Think I will make up a reminder to hang over the switch. I would not be keen to change my simple system however clever the alternative was.

 

[macnorton]

I have done this for many years, and it works fine.
My present 110 marine batterys are 5 years old and started both engines no problem last weekend.
simple to use and you can test either battery by starting the engine with it alone.

 

[ms1]

I have the simple switch as you suggest.
off = charge starter battery only
on = charge both
for normal running I have 'both'
for moored for overnight etc, I switch of to prevent the domestic usage affecting the starter battery.
works a treat.
There are complex electrical engineering issues that suggest that in this format both batteries should be identical, but mine aren't & I have no probs..

 

[capricorn]

I assume you're weighing up options for how to add a seperate domestic battery to a single combined starter/house battery set up as I did.

I did more or less exactly this, except that I used a Voltage Sensed Relay to connect the house battery in parrallel with the starter battery in place of the simple switch.

Switch closes automatically when the volts on the starter battery are high (ie when the engine's running and the alternator's charging) and dissconnects automatically when the engine is off to prevent the domestic load draining the start battery.

No worries with messing around with swiches and risking open circuiting alternators or draining starter batteries, just turn all switches on when I get on the boat and forget about them until it's time to go home.

Big advantage was that I could leave the starter/alternator wiring untouched and just had to rewire the domestic side to use the new dedicated house battery.

I chose a voltage sensed relay over a diode setup as I understand there's a voltage drop across the diodes so your batteries never actually achieve full charge.

Understand your concern that it's another thing to go wrong but it's proved completely reliable. A light on the VSR tells me if the batteries are combined or not and a quick check of the volts on each battery on the panel confirms that it's telling the truth.

 

[gbr9840t]

Sorry I didn't mean to be alarmist. I'm looking at the long term effects of ordinary alternator regulator systems on so called 'leisure' batteries. Panasonic, as an example, state that the MAXIMUM current on their sealed standby batteries (lead acid) is about 45 amps per 100Ah. Diesel engine alternators are usually 55 or 60 amps minimum, sometimes up to 100 amps and have very crude regulators. If your main battery is well charged, as it normally is, any other connected battery can draw off a current proportional to its demands. If you have a good control system this will be sensed and adjusted. I suggest that you look at <http://www.sterling-power.com> and see how complicated it can be. I don't want to replace my batteries every 2 years. My large diesel car engine draws around 350 amps when the temperature is below freezing, and recharges within a few minutes, its 3 years old and perfect because its designed for the job. Choosing a boat battery is perhaps a little more personal.

 

[vyv_cox]

I vote for the simple approach. The rotary Off-1-2-both switch is trouble free and never fails. It only requires that the skipper remembers occasionally to rotate it to ensure batteries are kept up to charge. I have had this type of switch for all of my 20 years of cruising and have yet to have a failure of any battery.

Conversely, the sexy, high-tech split charge relay on my camper van is unreliable and cannot by any stretch of the imagination be described as suitable for my boat. We have endured several occasions when the domestic battery failed after quite limited periods of use.

 

[qetoo]

I prefer to have the alternator normally connected to the domestic battery bank and charge the start battery with an automatic paralleling device. I am presently using a Heart Echo Charge to regulate the charging of the start battery. I also have a smart-charger permanently connected to the domestic battery bank which operates whenever the boat is connected to shore power. I've been operating this way for 11 years now and have had very satisfactory service.

I've posted my wiring diagram at:

http://carlten.tripod.com/Electrical_system/electrical.html

I have installed cut-off switches to shut off the system in case of fire.

 

[Guest]

[ QUOTE ]
Sorry I didn't mean to be alarmist. I'm looking at the long term effects of ordinary alternator regulator systems on so called 'leisure' batteries. Panasonic, as an example, state that the MAXIMUM current on their sealed standby batteries (lead acid) is about 45 amps per 100Ah. Diesel engine alternators are usually 55 or 60 amps minimum, sometimes up to 100 amps and have very crude regulators. If your main battery is well charged, as it normally is, any other connected battery can draw off a current proportional to its demands. If you have a good control system this will be sensed and adjusted. I suggest that you look at <http://www.sterling-power.com> and see how complicated it can be. I don't want to replace my batteries every 2 years. My large diesel car engine draws around 350 amps when the temperature is below freezing, and recharges within a few minutes, its 3 years old and perfect because its designed for the job. Choosing a boat battery is perhaps a little more personal.

[/ QUOTE ]

Sorry but you are now mixing batterys and making a fundamental mistake ... A SLA battery is not a Leisure or cranking battery..... and should be regarded as completely different. Yes they are used in Emerg Start packs- such as I have ... but then you have a special charger specific for it to stop the gassing and re-constituting of electrolyte necessary in a SLA.
A Leisure batter is a thicker plate variant of the standard Lead Acid battery. About the nearest you would get to sealed is Maintenance Free ..... (that's a joke term anyway !!)

Even boosted alternators will charge typical and Leisure Batterys on a boat without problem unless charge ampage / voltage goes too high as I've seen on a few boats with these systems.

For the original post - I would go for the simple change-over switch as thousands upon thousands of boats have and are fairly happy with.
I only have one variation on mine :

I have provision for shore power charging via a bog std car charger and Maplins splitter ... this is permamently connected to both batterys.
Having tried Diode splitters etc. - I soon came to the conclusion to disconnect them and not use ... I went back to the 1-Both-2-Off switch ...

My regime now is ... start on 2 (engine battery HD Diesel Van battery about 80 A/hr) ... chug out of marina and keep charging battery maybe 30 - 40 mins ... then switch to both and charge for remainder of exit of marina "river" .... giving maybe another 20 - 30 mins to both. Stop engine and switch to 1 for services .... ariive off destination and then start on 2 .... once started and run for period to put back start useage .. switch to both again ... or if I think batt 1 needs it .. switch to just batt 1 to charge ... arrive and berth - stop engine and services on batt 1. Of course if 240v available - then charger goes on via splitter.

 

[pvb]

It\'s a common fallacy...

It's a common fallacy that a 60A alternator pumps out 60A, and that a 100A alternator pumps out 100A. The truth is that they only produce what the batteries will absorb. At normal charging voltages, you'd be hard-pressed to put much more than 30-40A into an ordinary 100Ah lead-acid battery (no matter how powerful the alternator), and it would only take that current for a matter of minutes.

Also, as sbc has pointed out, Panasonic standby batteries are not really comparable with deep cycle boat batteries.

 

[jimbaerselman]

Just to clarify a minor point which makes a big difference on recommendations - I assume you're talking mainly weekend sailing in cooler climates, with a re-charge back at the marina in between?

As apart from warm climate cruising with a big fridge consumption and not many shore chargers to put the stuff back in?

For the first, a 1,2, both, off is absolutely fine.

For the latter, you want to re-charge as efficiently as possible with the minimum of engine running time. That's when a splitter diode and a smart regulator (sensing battery voltage when charging) come into their own.

Horses for courses . . .

 

[pvb]

It sounds as if your Trintella has had only one battery up to now, and that you're adding another battery as a domestic battery. If that's the case, your start battery probably already has some sort of on/off isolator switch.

My advice would be to fit a second, simple on/off switch (about £8) for the domestic battery, and then to charge the domestic battery via a VSR (about £50). This is simple and foolproof. The start battery will always be charged, and there's no possibility of inadvertently flattening it.

In contrast, the traditional 1-2-Both switch relies on someone correctly changing its setting every time the engine is turned on and off, and therefore offers lots of scope for getting it wrong and ending up with flat batteries.

If you do decide to use a 1-2-Both switch, be sure to buy a high quality one (which will probably cost £30-35). There are cheaper ones around, but their reliability leaves much to be desired. The small extra cost of using a VSR instead would be well worthwhile.

 

[noswellplease]

Many thanks for all the suggestions there certainly is a lot there to go on. Still not sure which system I will go for but I'm attending the Dublin Boat Show this weekend so I'm sure some smooth talking sale type will talk me into buying his wonderful box of tricks....Russell

 

[pvb]

Never believe sales staff at boat shows!

 

[noswellplease]

The VSR seems to be the way to go without making everything too complicated...thanks Russell