Battery Configuration

[sailinglegend]

Originally Posted by alexandlorna

.....As far as I am aware though all power from the twin alternators is combined and then supplied where require by the splitter unit....

Do yourself a favour and measure the battery voltage on each bank when the twin alternators are charging. If they go via a splitter with a 0.7 volt drop on each leg then all your batteries are being murdered. Even if you do have battery voltage sense cables they can only monitor one bank. A recipe for disaster.

I would hope your AGMs do look fine after 2.5 years, but they won't last unless you get them back to 100% very often. That could take 20 hours of motoring up and down your river every few days.

[alexandlorna]

Cable size for Vetus BT is 95 mm2 for 8-11 metre run , however we would have been right on the limit .
In Britain very few would go for such runs , most opting for smaller charge cable with battery very near the bows

[sailinglegend]

Originally Posted by alexandlorna

Cable size for Vetus BT is 95 mm2 for 8-11 metre run , however we would have been right on the limit ....

The bowthruster batteries could still be at the bow - the charging cables could be as large as you can fit, just accept a voltage drop, but only when charging in Boost mode.

[Pete7]

Originally Posted by sailinglegend

Do yourself a favour and measure the battery voltage on each bank when the twin alternators are charging. If they go via a splitter with a 0.7 volt drop on each leg then all your batteries are being murdered. Even if you do have battery voltage sense cables they can only monitor one bank. A recipe for disaster.

Indeed, Charlie have a look at VSRs in place of the splitter and have a search on here.

Power Store

Pete

[alexandlorna]

SailingLegend

So can i assume then that this fancy splitter thing is not the zero volt drop ( or almost so ) wonder I was told it was ?
I have had Sterling unit before ,not sure of the make of this one .
I get voltages at the batts of 13.8 -14 volts engine running , how does this compare with what you would expect ?

[sailinglegend]

Originally Posted by alexandlorna

.... I get voltages at the batts of 13.8 -14 volts engine running , how does this compare with what you would expect ?

At these voltages they will never charge properly. Please search this forum to find hundreds if not thousands of postings on this issue.

Batteries need to reach their gassing voltage of 14.4v or more to charge properly - to help de-sulfate the plates and avoid stratification. When up to about 90% charged a multi-stage regulator will drop them down to a Float voltage of 13.2 -13.8 volts to finish the charge - this can take another 20 hours or more with a large number of batteries to charge.

[Pete7]

Alex,

Have a read of this:

http://www.sterling-power.com/images...edcharging.pdf

[alexandlorna]

Thanks Sailing Legend
This has given me some issues to think over .
I don't want to make major changes to the system , however it would seem these voltage issues need to be addressed
Would some sort of intelligent battery to battery charger solve the bowthruster charge issue re voltage and full charging or should I simply fit another shore power charger alongside existing for this ?
As for the other banks would intelligent charge regulators on alternators help or am I barking up the wrong tree?

Alex

[alexandlorna]

Originally Posted by Pete7

Alex,

Have a read of this:

http://www.sterling-power.com/images...edcharging.pdf

Thanks , this explains it rather well

[nigel1]

While all the battery experts are here, I have a somewhat similar situation, but want to combine two banks into one.
Original from factory was a house bank and a starter battery.
Previous owner had a bow thrust fitted, and the installers fitted an independent battery bank forward for the BT.

Present set up is
1 x 125Ah 12V Start Battery
2 x 200Ah House Battery
2 x 125Ah 12V Bow Thrust battery

After 4 years ownership, I reckon the BT see's about 5 minutes use per years, and then in only 1 to 2 seconds bursts of use.

To me, that 250AH up forward is wasted, and I would rather include that in the house bank.
When the time comes, I want to replace the house and BT banks with Trojan T105, two forward, 4 aft.
Ideally would have all 6 in one place, but no space available aft for the BT batteries.

Can I safely parallel connect the BT bank and the house bank (using suitable sized cable)
Second question:
The 3 banks are independently charged by alternator and battery charger. The alternator goes through a Sterling zero loss splitter, and the sterling battery charger has 3 outputs.
If I can combine the BT and house banks, is it OK to leave the charging set up as it is, with a charge output to the aft batteries, and a charge output to the forward batteries, in effect, one bank but with two charge in puts, but to different battery posts.
Welcome any suggestions.

Oh, and regarding large cable's, in the UK, 95mm cable is very expensive, but using 2 x 50mm cable is a lot cheaper.

[mitiempo]

Lets assume a run (there and back) of 60 feet. Let us also assume an alternator of 80 amps without any voltage drop splitters. Alternator output 14.4 volts.

With the engine running and all batteries aft in one bank (except for the separate start battery) and 95mm cabling (between 3/0 and 4/0 Awg) the voltage forward for thruster and windlass will be about 13.8 volts. This works well for both thruster and windlass.

Now if we place batteries forward the wire size required to charge them at a proper voltage will be larger. If the forward batteries are charged by alternator alone they, as posted, will never be fully charged. Even the 20 hours of motoring suggested might not do this. Voltage is pressure and it is just too low. I would expect a short life for the forward Agm bank.

Also not using the Victron to charge the forward Agm batteries is a mistake. The difference between flooded vs Agm requirements is very small, and Agm batteries are happy at the same setting. But with the voltage drop you get charging over such a long run it really makes no difference anyway as the output voltage at the alternator or Victron will be lower forward anyway.

I try to size charging cables for zero voltage drop. It charges much faster and is easy to achieve with a short run, often impossible with a run to the bow. Electronics issues shouldn't occur if the engine is running when thruster or windlass are in use as the alternator is at maximum output at this time.

[alexandlorna]

Originally Posted by mitiempo

Lets assume a run (there and back) of 60 feet. Let us also assume an alternator of 80 amps without any voltage drop splitters. Alternator output 14.4 volts.

With the engine running and all batteries aft in one bank (except for the separate start battery) and 95mm cabling (between 3/0 and 4/0 Awg) the voltage forward for thruster and windlass will be about 13.8 volts. This works well for both thruster and windlass.

Now if we place batteries forward the wire size required to charge them at a proper voltage will be larger. If the forward batteries are charged by alternator alone they, as posted, will never be fully charged. Even the 20 hours of motoring suggested might not do this. Voltage is pressure and it is just too low. I would expect a short life for the forward Agm bank.

Also not using the Victron to charge the forward Agm batteries is a mistake. The difference between flooded vs Agm requirements is very small, and Agm batteries are happy at the same setting. But with the voltage drop you get charging over such a long run it really makes no difference anyway as the output voltage at the alternator or Victron will be lower forward anyway.

I try to size charging cables for zero voltage drop. It charges much faster and is easy to achieve with a short run, often impossible with a run to the bow. Electronics issues shouldn't occur if the engine is running when thruster or windlass are in use as the alternator is at maximum output at this time.

Thanks , so it would be a big improvement to charge the forward batts by an intelligent charger from shore power or would a Sterling batt to batt charger unit be better as this seems to , also boost the voltage at the forward bank?
I may utilise a spare single output unit I have

[mitiempo]

If you have access to shore power regularly - keep the boat at a marina - yes an intelligent charger would be a plus. Voltage drop could still be a problem though - you want 14.4 at the batteries ideally. A small charger installed forward is probably the easiest solution, a complicated system getting a little more complicated.

[sailinglegend]

Originally Posted by alexandlorna

....I don't want to make major changes to the system , however it would seem these voltage issues need to be addressed...

I am always dumbfounded by people who ask for help and then say they can't be bothered to make any changes.

On a boat one small change to something can mean a major re-working of other systems. You have to make the choice between following best practice, or living with a bad installation that will ultimately mean your batteries will die prematurely. One bank killed early - and then the next one will soon die too. The cost and the effort of correcting the problems will always be worth it in the long run.

Sorry to have a go at you but if you know you have a problem - fix it.

[Charliemciver]

Hi, thanks for all comments so far.

I prb should have made 3 points clearer in my original post:

1) the two bow thruster batteries are currently at the front of the boat (rest at the back-ish). The previous owner didn't have them wired to the domestic bank (though it was clearly intended. not sure why. there is evidence of something going quite wrong and it being dismantled, and hence no charging currently). There is substantial cabling that goes between the front and the back of the boat already to make this join, so reconnecting it is easy. Bizarrely the switch gear for the windlass is mid-ship with the intended battery at the back. Moving the switch gear forward and sharing the 2 bow thruster batteries for the windlass is doable relatively easily - I have no idea why they put the windlass battery at the back. It only makes sense to me if they needed the capacity of a 3rd battery on the bow thruster /windlass. Which in the UK seems less likely than the med, say.

2) I currently have a 115A alternator so it can charge reasonably hard.

3) I was proposing 3 banks (not 4) - ie starter x 1, domestic x 3, and then a combined windlass/bow thruster set x2

Maybe I can ask a few more questions to help clarify what I am learning from this and maybe my questions expose my understanding which may need 'adjusting'


People have criticised AGM batteries because they don't like a 'hard charge' from the alternator (ie when Alex uses on bow thruster and only engine charges). So this would be the case when out at sea for a few days and after some hard domestic use and we fire the engine up.... So should I discern from this that AGM is only good if you back in port super regularly and hooked up to the shore-power so the fancy charger used?

People seem to worry about using sealed marine batteries for starter use.... Not enough CCA vs a basic flooded lead acid I guess. Yet I hear a Diesel engine is a light start load and hence doesn't need much charging ? So why is sealed marine battery with lower CCA bad here? Surely if the load isn't bad, marine battery is better as the CCA will be lower but adequate and the overall capacity (RC?) is higher which will give you a longer ability to start?

Re golf car batteries - what are they inside? I don't need war and peace - short explanation is fine.

Really appreciate everyone's comments.

I'll look into SWR meter - I've just fitted AIS with an antenna sharer and have a ham radio background too, so this is familiar turf. I have my SWR meter ready to test my own system this week

Merry Xmas everyone. Blowing a gale here in south UK today!