Battery size v. Alternator size

[Champagne Murphy]

Here's the thing, alternator puts out in the region of 60-70A. Starter battery is 70A and domestic is 2x100. Split charging controlled by a VSR.
Do I need a bigger alternator?

 

[VicS]

Here's the thing, alternator puts out in the region of 60-70A. Starter battery is 70A and domestic is 2x100. Split charging controlled by a VSR.
Do I need a bigger alternator?

A larger alternator might help to recharge a heavily discharged domestic bank more quickly but depending on the rating of the present one may not make a huge difference

What is the maximum rated output of the present alternator?............what it "puts out" will be limited by what the battery will accept.

You might like to consider some form of advanced regulator but even the improvement by something like that will depend on the voltage at which the current one controls the alternator

 

[pvb]

The starter battery will need almost no charge; the 200Ah domestic bank will struggle to accept much more than 50A most of the time, so your current alternator is fine.

 

[RichardS]

Here's the thing, alternator puts out in the region of 60-70A. Starter battery is 70A and domestic is 2x100. Split charging controlled by a VSR.
Do I need a bigger alternator?

I think you are mis-understanding something here. The starter battery will not be 70A ..... it might be 70Ah but that's a completely different thing. So saying that you have a 70Ah battery plus some other batteries and the alternator is only 70A so it can't be powerful enough is mixing up apples and pears.

As others have said, a 60 - 70 amp alternator should be fine.

Richard

 

[Hoolie]

I remember seeing a rule of thumb, can't think where, that a reasonable charging capability in amps should be at least 10% of the battery capacity in Ah. In your case your alternator at 70 amps is a lot more than 10% of your 270 Ah battery banks. No problem!

 

[VicS]

I remember seeing a rule of thumb, can't think where, that a reasonable charging capability in amps should be at least 10% of the battery capacity in Ah. In your case your alternator at 70 amps is a lot more than 10% of your 270 Ah battery banks. No problem!

I think you might be confusing it with the rule of thumb for a battery charger . 10% is about right there.

 

[sailorman]

fit an adverc :encouragement:

 

[VicS]

fit an adverc :encouragement:

As I said earlier "You might like to consider some form of advanced regulator"
Read more at http://www.ybw.com/forums/showthread.php?453367-Battery-size-v-Alternator-size&p=5655654#post5655654

 

[GHA]

fit an adverc :encouragement:

Depends on what voltage the alternator regulator is set at, if it's not that old then it might be 14 plus already so nothing to be gained. Mine puts out 14.6 at the batteries.

 

[sailorman]

Depends on what voltage the alternator regulator is set at, if it's not that old then it might be 14 plus already so nothing to be gained. Mine puts out 14.6 at the batteries.

Ah but @ what amps are going in normally diddly squat

 

[VicS]

Ah but @ what amps are going in normally diddly squat

If an alternator is already controlled at 14.4volts or more there is nothing to be gained by adding an Adverc, or similar device, because 14.4 volts is the top voltage of its charging cycle except where a diode splitter is reducing the volts delivered to the battery. The OP, however, has a VSR.
You will only get more amps into the battery by increasing the volts.

 

[GHA]

Ah but @ what amps are going in normally diddly squat

Voltage and state of charge of the batteries control what amps are going in, if the voltage is 14.4v at the batteries then there is no way they will know if an adverc is attached or not.

 

[rob2]

The size of the battery bank does have an influence on the choice of charging components, that is to ensure they offer sufficient charge if the batteries are depleted by around 50% capacity. Beyond 50% capacity the batteries will suffer from the deep cycling and lose capacity as a result. You really must consider every aspect of the charge /discharge usage on your individual boat.

The most immediate calculation required is of the actual daily electrical usage, to see what needs to be replaced, and the expected daily input from any/all charging sources. Just as an example, if the boat is mainly used for day sailing without a fridge or running cabin lights all evening, then a solar panel or wind generator running all week will more than likely keep the batteries topped up without any need of alternator input except to put back what it took out of the starter battery!

The other extreme is a live-aboard who is heavily dependent on electrical systems on a daily basis. Although he will obviously use any available charging source to the max, solar, wind, shore power, he is also more likely to have the biggest alternator he can drive and intelligent controller in order to charge at maximum rate when it is in use. Electric motors are the really big loads - fridges and bow thrusters, leaving the lights on probably a close second!

Rob

 

[charles_reed]

fit an adverc :encouragement:

I had an Adverc (well two) for 26 years. For general UK sailing, with short engine runs it was just great. Quickly charged the two (finally 3 domestic batteries) and kept electrics up to scratch.

However as soon as I did some serious motoring the toll on burnt-out alternators mounted.
So I went up from the standard 35 amp Hitachi, first to a Lucas 90 amp one and finally to a Magnetti Marelli 110 amp unit.
This last alternator - in use in the Med, with engine runs of commonly 12+ hours, lasted fine for 8 years and onto a second engine.
After a run of alternator failures (and accompanying replacements) I finally leave the Adverc beast out of circuit and rather than bank on getting 100% of charge into batteries, on motor, settle for 85% and have draped the boat in as many PV panels as I can mount (330 w nominal). If I really want to get a boost charge I just re-connect the external controller.
I'm now running a Bosch 80 amp alternator (designed for diesel Mercs) with a new 110w Magnetti Marelli in reserve (excellent ballast if kept low in the boat).
Being able to pick and choose when to replace an alternator means I don't have to suffer the usual price of €250 - €500 (the boxed MM cost me £140.

So a few points that I've found from bitter experience (I do 2200- 1350 nm doddering around Aegean and Ionian each year).
1. Have as large an output alternator as you can cram in to your engine compartment. It won't charge your batteries any faster but will not melt (as did the standard Hitachi 60 amp that came with the 3YM20)
2. Most marine diesel alternators are cheap and cheerful - and insufficiently cooled for running in 40C ambients.
3. Don't bother with charge boosters - modern alternators have on-board regulators good for 14.5v where 13.5 was the standard 20 years ago.
4. Have as many alternative methods of charging your batteries as you can - PV panels, wind-generators, smart shorepower battery chargers, generating sets, alternator-equipped cycle exercise machines.... as well as your engine alternator.
Modern liveaboard boats have far greater electrical demands than the Pardeys' dream of.
3.

 

[Chris_Robb]

If the alternator is regulated to 14.6V then what happens when the battery is fully charged and where an Adverc/Sterling would then go to float charge (13.5V)? Or are they multi stage chargers in themselves?

 

[VicS]

If the alternator is regulated to 14.6V then what happens when the battery is fully charged and where an Adverc/Sterling would then go to float charge (13.5V)? Or are they multi stage chargers in themselves?

The Sterling, and I assume the Adverc, drops back to the alternator output volts so in effect don't really offer a float stage if the alternator is regulating at above the normal float (13.8v ??) you see with battery chargers.

 

[Chris_Robb]

The Sterling, and I assume the Adverc, drops back to the alternator output volts so in effect don't really offer a float stage if the alternator is regulating at above the normal float (13.8v ??) you see with battery chargers.

Yes - that is in effect what happens - but the question is what happens on a modern alternator set to 14.6V if it does NOT stop charging at that voltage when the batteries are full?

My Prestolite 110 Amp Alternator from Adverc charges at only 13.8V if I disconnect the Sterling. So when the sterling has finished its cycle it switches off - so falling back on the Prestolite which is giving a float voltage.

I cannot quite reconcile the two

 

[GHA]

If the alternator is regulated to 14.6V then what happens when the battery is fully charged and where an Adverc/Sterling would then go to float charge (13.5V)? Or are they multi stage chargers in themselves?

What's more likely is the adverc/sterling drops back to float on a timer before the batteries are actually fully charged, assuming they have full control of the alternator and the internal regulator is disconnected. It is a timer to drop back to float isn't it?
Would a few hours at 14.6 at full charge be that detrimental to a battery? I'd guess that not getting a full charge would be worse.

 

[RAI]

A fully charged wet cell will just bubble away at 14.6 volts, no problem if it gets more water topped up.
Not sure about AGMs, they charge faster, but after that there is a pressure release valve that is not supposed to release if the AGM is properly treated.

 

[pvb]

What's more likely is the adverc/sterling drops back to float on a timer before the batteries are actually fully charged, assuming they have full control of the alternator and the internal regulator is disconnected.

I don't think an Adverc will work with a disconnected alternator regulator, although a Sterling supposedly will.