1,2 Both Switch - When on Both do the 2 batteries even out on charge?

[Ceirwan]

Well they kind of do, why do you think all decent battery chargers drop to a float voltage instead of maintaining 14.4 volts (or 14.7 for non sealed)?

They don't go to all that trouble for nothing, the thing with cars is that no one really notices how healthy the battery is. Most people get in their car, start it up and then drive off, all electrical loads are taken by the alternator, and apart from maybe being sat with the stereo on for a few minutes, literally the only load is to start the car.
The only time people notice when a car battery is not so good as it was is when it becomes hard to start the car, but by that point the battery is almost finished anyway as a modern well maintained car starts very easily.
And when it gets reluctant to start its just a case of replacing, worse case scenario you need a jump start.

 

[ghostlymoron]

Well they kind of do, why do you think all decent battery chargers drop to a float voltage instead of maintaining 14.4 volts (or 14.7 for non sealed)?

They don't go to all that trouble for nothing, the thing with cars is that no one really notices how healthy the battery is. Most people get in their car, start it up and then drive off, all electrical loads are taken by the alternator, and apart from maybe being sat with the stereo on for a few minutes, literally the only load is to start the car.
The only time people notice when a car battery is not so good as it was is when it becomes hard to start the car, but by that point the battery is almost finished anyway as a modern well maintained car starts very easily.
And when it gets reluctant to start its just a case of replacing, worse case scenario you need a jump start.

I've had car batteries that have lasted over ten years and the current one has done seven so far. If being constantly charged at 14v+ were 'bad' for them, they would fail prematurely - that's the only way a battery can fail - and they don't.

 

[shaunksb]

[/FONT][/SIZE]
[/FONT]Service Bank Priority
VSRs and battery combiners must be wired so that the service bank has charging priority. This means all the available charging current is directed to the service battery. All other loads such as an anchor windlass should be wired to the service bank as well. The alternator will then be supplying current immediately to these heavy loads just when they are needed.

Bummer. Just as I thought I was starting to get a handle on this.

Would I have been better not buying a dual sensing vsr so that a depleted house bank woul not pull juice back from my smaller starter battery?

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[shaunksb]

I've had car batteries that have lasted over ten years and the current one has done seven so far. If being constantly charged at 14v+ were 'bad' for them, they would fail prematurely - that's the only way a battery can fail - and they don't.

Yes but with cars we rarely drive them for 12 hours at a time to compare with an overnight charge.

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[sailorman]

Yes but with cars we rarely drive them for 12 hours at a time to compare with an overnight charge.

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OK how about lorries & commercial vans

 

[RichardS]

That's interesting as my system uses twin solenoids which appear to work in this way rather than VSRs and I've always wondered whether my system is less effective because of it, although it seems to work perfectly well.

Basically, I have twin engines each with its own alternator. The house battery bank is connected to one side of both solenoids whilst the starter battery is connected to the other side of it's own solenoid along with the charging output from the alternator from that engine. When the engine is not running the heavy duty contacts in the solenoid are disconnected and the house bank is isolated from both of the starter batteries which are isolated from each other.

When one engine is started the starter battery for that engine begins to charge immediately and the solenoid coil is then activated by the alternator current and the charging current is then directed to the house bank paralled with that engine's starter battery.

When both engines are started, each alternator charges it's own starter battery and both alternators are paralled to charge the house bank.

As far as I can see there is no "voltage sensing" in my system (ignoring the regulator in the alternators) other than the fact that the solenoid "senses" that the alternator is producing an output and closes the heavy duty contacts. If this is, more or less, the same as a VSR, why don't other boats use it?

Richard

I was hoping that Bru might also help me with my question as he explained that "when the sense side of the VSR reached the preset voltage, the batteries will be paralleled until the voltage drops below the preset. Charging and (which most people forget) discharging will then happen across all the batteries as if they are one bank."

Unfortunately Bru seems to have left the thread since I posted my question.

Richard

 

[shaunksb]

OK how about lorries & commercial vans

Ok. Good point, well made...

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[lw395]

I've had car batteries that have lasted over ten years and the current one has done seven so far. If being constantly charged at 14v+ were 'bad' for them, they would fail prematurely - that's the only way a battery can fail - and they don't.

You don't drive your car 24/7 do you?
Your car battery generally gets charged for 1 or 2 hours, rested for a few hours, rinse and repeat ad nauseum.
I destroyed a motorbike battery by floating it at 13.9V for a few months constantly.
It simply dried out.
I was in the telecoms industry for a while, the back up batteries always had two charging voltages (per cell) printed on them. One for float charging, another for cyclic charging. Most marine systems are raising the voltage from recommended cyclic charging in search of fast charging.

 

[pvb]

You don't drive your car 24/7 do you?

Lots of taxis are ordinary cars which get used virtually 24/7, and they don't have premature battery failure.

 

[Bru]

I was hoping that Bru might also help me with my question as he explained that "when the sense side of the VSR reached the preset voltage, the batteries will be paralleled until the voltage drops below the preset. Charging and (which most people forget) discharging will then happen across all the batteries as if they are one bank."

Unfortunately Bru seems to have left the thread since I posted my question.

Richard

Sorry, can you repeat the question? I got distracted by the rugby!

 

[BabaYaga]

Lots of taxis are ordinary cars which get used virtually 24/7, and they don't have premature battery failure.

So is float voltage on a mains charger just an unnecessary precaution then?

 

[GHA]

So is float voltage on a mains charger just an unnecessary precaution then?

Seems little doubt it's a "good thing" for something which may well be left on 24/7. The other point is just how bad is 14.4v for a battery for a good few hours at a time. Looks like not as bad as some would think.

 

[BabaYaga]

The other point is just how bad is 14.4v for a battery for a good few hours at a time. Looks like not as bad as some would think.

Yes agreed, this is the crucial question. And how bad if this pattern is repeated over and over, as could be the case with a starter battery paralleled by a VSR.

Not sure how relevant it is to compare with cars and lorries, though. If I am not mistaken alternators often have thermistors in them, reducing voltage as they run hot.

Also, I would not be surprised if a lorry had a less aggressive charging profile than a typical city car (just speculation).

 

[GHA]

Yes agreed, this is the crucial question. And how bad if this pattern is repeated over and over, as could be the case with a starter battery paralleled by a VSR.

Not sure how relevant it is to compare with cars and lorries, though. If I am not mistaken alternators often have thermistors in them, reducing voltage as they run hot.

Is it any different in a boat compared to a car/truck?

Same stater battery, mostly the same alternators.

 

[BabaYaga]

Is it any different in a boat compared to a car/truck?

Same stater battery, mostly the same alternators.

No and yes, but I think we were comparing car alternator charging for many hours ('virtually 24/7') with mains charging for many hours (repeatedly) or permanently.
A mains charger will be able to hold the voltage at 14,4v steadily, until it drops to float, while a car/lorry alternator might be reduced by the thermistor (possibly, I don't know).

 

[ghostlymoron]

This thread just proves how many ways there are to wire up a boat. Everyone seems to have a different idea how it should be done and different theories on what their priorities are. Maybe we should all go back to first principles and consider what we want the system to achieve. Also I'd be interested to know what modern boat builders supply as standard - they must surely have given it a lot of thought.
I've not been on a brand new boat for ages as I, and most of my cronies, have MOBs. Perhaps I'll review some glossy new boat brochures to see.
By the way, the answer to the original question is - YES (but its not as simple as that).

 

[GHA]

, while a car/lorry alternator might be reduced by the thermistor (possibly, I don't know).

Same alternators so is a boat any different?

 

[lw395]

Lots of taxis are ordinary cars which get used virtually 24/7, and they don't have premature battery failure.

Are you an expert about the battery-buying habits of taxi firms?
A car battery is deemed healthy if it starts when you turn the key.
A taxi is unlikely to be parked for more than a couple of days for its abused battery to self-discharge.

If leaving the battery at 14 point something volts long term was a good idea, we would not be using 3 stage battery chargers.
Ask a battery manufacturer.

 

[GHA]

Y

Are you an expert about the battery-buying habits of taxi firms?
A car battery is deemed healthy if it starts when you turn the key.
A taxi is unlikely to be parked for more than a couple of days for its abused battery to self-discharge.

If leaving the battery at 14 point something volts long term was a good idea, we would not be using 3 stage battery chargers.
Ask a battery manufacturer.

So why aren't car/van starter batteries dying consistently and why would a boat starter battery be any different with the same treatment?

"If leaving the battery at 14 point something volts long term was a good idea, we would not be using 3 stage battery chargers.
Ask a battery manufacturer"
so why aren't the battery manufacturers screaming and shouting about modern alternators putting out ~14.4v

 

[pvb]

Also I'd be interested to know what modern boat builders supply as standard - they must surely have given it a lot of thought.
I've not been on a brand new boat for ages as I, and most of my cronies, have MOBs.

Most new AWBs have two on/off switches (one for engine, one for domestics) and a charge isolator (usually a low-loss device). It's interesting that they have gone this route rather than using VSRs, especially as VSRs are much cheaper (£40 or so vs £160 or so).

The Bavaria I bought a couple of years ago has, as standard equipment, a 115A alternator, two on/off switches, a Quick ECS163 low-loss charge splitter, 4 AGM batteries (1 start, 3 domestic), and a Cristec 40A mains charger. This is not a bad spec, and it's not cheap either, contrary to the popular belief that AWBs are pared to the bone on specs. The batteries, in particular, are pretty good and retail in the UK for around £170 each (although obviously Bavaria wouldn't have paid that).