Simple explanation on boat charging systems?

[chrisbitz]

I have an inboard engine, and 2 batteries, and a switch labeled off, 1, and both.

I'm guessing that the correct setup/routine is this:

• Most times, keep switch on 1, engine running or not.
• Overnight, keep switch on 1, flatten battery 1 with heater and tv etc.
• in the morning, battery 1 is flat and wont start engine, so switch to both, and spare battery will start engine, and charge both.

Is that all correct?

My only question is, when the switch is on 1, are both batteries charging, or is it likely only battery 1 is being charged?
should I always switch to both when engine is running?

With a multimeter, is it possible to test if both batteries are being charged, or do I need a shunt or something to measure amps?

thanks for any help!

 

[David2452]

As a fairly general rule: A battery isolator switch isolates the battery so your assumption is correct, you could also switch simply to # 2 to start and then to both in order to charge, but you need to make sure the switch is a make before break type or alternator damage could result. You can use a multi meter as a guide to see if the battery is being charged, check at rest voltage and then with the engine running and you should see the difference in voltage, it will not tell you how many amps obviously but at least confirm some sort of charge.

 

[chrisbitz]

I forgot to ask - supposing I flatten a battery, how long should the engine be run to charge it up?
I think it's a 70 amp alternator. Would it be something like 30 minutes, or more like 3 hours?

Will the engine charge at idle speed, or does it need to be revving at a particular speed to start charging?

Many thanks!

 

[nigelmercier]

[1] My only question is, when the switch is on 1, are both batteries charging, or is it likely only battery 1 is being charged?

[2] Should I always switch to both when engine is running?

[3] With a multimeter, is it possible to test if both batteries are being charged ... ?

[1] It is likely that you are only charging battery 1.
[2] Yes.
[3] A digital multimeter, yes. Attach to battery terminals, if charging it will show more than 12.8V. Better to check what the voltage is before starting though.

 

[macd]

Presumably you have two banks of batteries (which could each comprise just one battery), one being starter and the other domestic. For a full answer we'd need to know which battery "1" and "2" connect to. You imply it's the starter battery. Is that correct?

If the switch is set to "1", that battery is in circuit: i.e. it can be charged by the engine and equally discharged by anything you happen to have switched on.
Ditto for the other bank if switched to "2".
On "both", both banks of batteries are in circuit. You would normally only select this once the engine is running and charging. Some people start the engine on the dedicated starter battery, then switch to both to charge both banks; a few start the engine on "both". On no account run the engine with the rotary switch on "off": you could fry your alternator.

Assuming the engine starts easily, the starter battery gets an easy life if used correctly. But it is self-evidently important, so look after it. It's unwise (in my view) to use it to power domestic kit. Your boat's just fine if it can't watch TV, but it could get you into a pickle if its engine won't start.

Do not flatten any of your batteries: it will drastically shorten their working life.

Yes, you can check your batteries with a multimeter, but they should be 'rested' -- i.e. with no charge or discharge -- for at least an hour before you conduct the test. Simply put the +/- probes on the terminals. In rough figures, 12.6 to 12.7V is around 100% charged, down to 11.8V or a less for flat. Ideally, their resting voltage should not go below around 12.2 to 12.3V. Note that if your alternator has a standard car-type regulator, your batteries will never reach more than 80-85% of full charge.
A more accurate method is to use a hydrometer, but this only practical with open lead-acid batteries.

 

[David2452]

Depends what you mean by charge, 30 minutes might be enough to restart a willing motor but even 3 hours is unlikely to fully charge a flat battery of 70ah, though it would be well "up" by then. The alternator will charge at a fast tickover but the more revs the higher the output. A word on flat batteries, don't allow it as it will seriously reduce their life. As a rule of thumb only take about 35ah from a 70ah lead acid battery.

 

[nigelmercier]

I forgot to ask - supposing I flatten a battery, how long should the engine be run to charge it up?
I think it's a 70 amp alternator. Would it be something like 30 minutes, or more like 3 hours?..

Probably at least 10 hours. Get a mains charger:

http://www.amazon.co.uk/exec/obidos/ASIN/B002Q5D6JO/dolcetto-21

 

[alahol2]

I have an inboard engine, and 2 batteries, and a switch labeled off, 1, and both.

A more normal switch of that type would have Off - Bat 1 - Both - Bat 2.
If that's true (and even if it's not) you need to know which battery is which ie start battery on bat 1 / domestic on bat 2 (or both). Or vice versa.

 

[Deleted member 36384]

I have an inboard engine, and 2 batteries, and a switch labeled off, 1, and both.

I'm guessing that the correct setup/routine is this:

• Most times, keep switch on 1, engine running or not.
• Overnight, keep switch on 1, flatten battery 1 with heater and tv etc.
• in the morning, battery 1 is flat and wont start engine, so switch to both, and spare battery will start engine, and charge both.

Is that all correct?

My only question is, when the switch is on 1, are both batteries charging, or is it likely only battery 1 is being charged?
should I always switch to both when engine is running?

With a multimeter, is it possible to test if both batteries are being charged, or do I need a shunt or something to measure amps?

thanks for any help!

Please download this book http://www.dawncraftowners.com/12volthandbook.pdf I have been reviewing this book for a couple of weeks now and it is making things on the electrical front very understandable. The book has been written for folks who know nothing about the subject and the writer is excellent at describing his stuff. It will explain the answer to your questions very well. I bought the latest edition from Amazon but this one is still good enough. Even the make before break switches, how to test alternators with multimeters, its all there, just a click away.

Good luck,

BlowingOldBoots

 

[William_H]

It is likely that your 2 batteries are similar. ie so called leisure batteries designed both for engine start and for deep discharge when using lights etc.
As said it is most likely that both batteries will only be charged when you use "both" position.
It is very desirable that you start the engiene at least occasionally on each of the batteries alone. The common failure mode of batteries is that they will not start the engine even when apparently fully charged. If you always start on both this may occur without you knowing so when you do need a back up battery it will let you down.

You can mostly start on "both" being mindful of above or switch to both after then engine starts. This latter is vital (probably the only way) to get both batteries charged. (topped up)
A Voltage sensing relay bewteen the 2 batteries could always automatically ensure charge of both batteries regardless of switch position. (except off). But you can do the same thing manually using both position.
As said a few minutes charging will often get a flat battery up to good enough to start the engine. But a near full charge will probably take 20 hours or more of engine run.
NB charging one battery at a time will not get more into that battery than charging 2 at a time. so always charge on both.
As said us a multimeter on 20v DC switch position to check voltage at the terminals of both batteries when engine is charging.

Battery engine charging current is a result of many factors each limting the charge current. The most significant is actual charge state of the battery. The higher the internal voltage of the battery the less current the battery takes. This means that usually a battery charge current will start high and reduce withina few minutes to relatively small current hence it takes a long time to fully charge a battery. Indeed you could say it will never fully charge.
The alternator has a regulator which throttles back the field current so the output voltage if the battery is really flat so taking lots of current then the regulator gives full current to the field so alternator runs at its full power which then is limited by the alternator RPM so engine speed. So sometimes more engine revs can give more charge current.

So we get to the so called smart charge regulators for alternator (or for mains battery charger) which increases the charge voltage so forcing more current into the battery until it thinks battery is charged when it reduces voltage. This can halve or better the total charge time for battery charging to a useful amount. (and actually acheive eventually full charge) Fitting one of these is a big step however and you may be satisfied with the regulator you have. (just like a car regulator).

To help you understand what is going on however an installed amp meter can help a lot. It will confirm that batteries are being charged and then show you when charge current has diminished to the point where further engine run for charging is not really productive. A multimeter (volt meter can also help) good luck olewill

 

[westernman]

As said it is most likely that both batteries will only be charged when you use "both" position.

A common (I think usual as well) arrangement is that the chargers go through a diode splitter and are connected directly to the batteries so they will all be charged even with the switch in the off position.

 

[Momac]

On my boat there are two batteries and two seperate isolator switches.
One battery is for engine starting only and the other is for everything else.

There is also an additional switch to connect both batteries together. This is used only if the starter battery should be flat and it brings the domestic battery into use to assist with engine starting. I have never needed to try that.


It sounds like the switch you have is for normal engine starting position 1 .
And the 'both' position is for connecting the two batteries together in case of emergency if the starter battery should have insufficient power .

If I am correct you should presumably have a seperate isolator switch for the domestic battery ?

On my boat the battery does not charge from the shore powered charger if the isolator swich is off.

Never switch an isolator switch on or off with the engine running.


.

 

[Quandary]

Impressed with Old Boots manual, I may even begin to understand boat electrics now. Thanks for the link
When I had a boat with a 1-both-2 switch and two batteries (Sigma 38 and before that Sigma 33) I would start the engine on 'both' and keep it there until the engine was stopped when I switched to '1'. Each new season I reversed the selection so that 'domestic' became 'engine' for a year. I can not recall any problems over the 20 odd years we did this and battery life usually was in the 6-8 year bracket.
Perhaps it was too simple to be right but I still do not know what was wrong?