Battery charging maze

[zoidberg]

I'm looking to optimise a battery-charging setup, with all-new components, in my modest-sized sailboat.

My engine has a new 'simple' 70A alternator. I understand this provides 14.4VDC.
I have 3 all-AGM batteries - Start, Service/Port Berth, Service/Starboard Berth. These require 14.7VDC for optimum charging.
I have acquired a Victron Argofet 100-3 preferential isolator https://www.asap-supplies.com/products/victron-argo-fet-battery-isolator-for-3-batteries
I also have a CTEK D250SA charger ctek-d250sa-dual-battery-charger
I have several solar panels, outputs from 8A to 40A, and will want to mount/utilise some of these for trickle/maintenance charging.
I want to provide 14.7VDC to maintain the AGM batteries optimally. This can be provided via the CTEK device by a simple connection.

How can this assembly be made to work?

In the words of the old Irish quip "Well, if I was going there, sor, I wouldn't start from here...."

Might the simplest answer involve a 'non-simple/smart' alternator.....?

 

[PaulRainbow]

I'm looking to optimise a battery-charging setup, with all-new components, in my modest-sized sailboat.

My engine has a new 'simple' 70A alternator. I understand this provides 14.4VDC.
I have 3 all-AGM batteries - Start, Service/Port Berth, Service/Starboard Berth. These require 14.7VDC for optimum charging.
I have acquired a Victron Argofet 100-3 preferential isolator https://www.asap-supplies.com/products/victron-argo-fet-battery-isolator-for-3-batteries
I also have a CTEK D250SA charger ctek-d250sa-dual-battery-charger
I have several solar panels, outputs from 8A to 40A, and will want to mount/utilise some of these for trickle/maintenance charging.
I want to provide 14.7VDC to maintain the AGM batteries optimally. This can be provided via the CTEK device by a simple connection.

How can this assembly be made to work?

In the words of the old Irish quip "Well, if I was going there, sor, I wouldn't start from here...."

Might the simplest answer involve a 'non-simple/smart' alternator.....?

How much engine charging so you intend to do ?

Are the port/starboard domestic banks wired in parallel, or individually selectable.

 

[William_H]

I would not get so hung up about needing 14.7 volts for battery charging from engine. The quoted 14.7 volts will give max practical charge rate to bring batteries eventually up to full charge. But as Paul says you may mostly rely on the mains charger where 240v power is available to keep batteries charged. So only on those occasions when you are living on board and away from mains will you rely on engine charge. Engine charge will not give max charge current at 14.4v and will not fully charge batteries but will give a decent bit of charge with a limited engine run time.
I am guessing that solar will not be a major contributor to battery charging if you are living on board away from 240v mains. I presume "40A " is a mistake that being 2000w of solar not easily fitted on a boat. Plus of course only good in sunshine.
So IMHO set up argo fet to provide charge from engine to all 3 batteries. Set up mains charger to charge all 3 batteries at 14.7v either hard wired in parallel or via a charge splitter. (possibly the same argofet)
Then setup solar panels to charge batteries individually or parallel as seems right. Typically a small panel top engine battery with cheap controller and large solar to domestic batteries in parallel hard wired or with individual panels and controllers or one dual output controller.
Re Paul's question Are the port/starboard domestic banks wired in parallel, or individually selectable. it would probably be ideal to have switching like 1.2.both for the 2 domestic batteries but usually run them on both for charge and discharge. You might deem it desirable to quarantine one bank while discharging the other. But seems unnecessary to me. Much depends on your actual voyage style and requirements. ol'will

 

[zoidberg]

How much engine charging so you intend to do ?

Are the port/starboard domestic banks wired in parallel, or individually selectable.

In response to Paul..... and also to give some context to Ol'Will

The boat will live on trot moorings in the Tamar at Plymouth, and I should be able to glean some PV charge on the days the boat is unattended. It's a 40-ish minute run under engine down river and out into the sound..... and similar coming back, of course. I don't intend to spend many days/nights in a marina berth where I could plug into 240VAC and, for those occasions, a length of cable with a 16A 2-gang socket will permit the use of the CTEK MXS 5 mains charger which currently does the job of keeping my 'spare' AGMs topped up at home.

The P and S domestic banks are individually selectable. The Start battery is close adjacent to the Port bank and an 'emergency' link could be arranged. All 3 are within 1.5m of the engine/alternator.

I expect my use of 'lecky on board to be frugal by contemporary standards, and anticipate being able to recharge daily consumption via PV means. I have reason for having the two domestic banks electrically separate, besides the physical layout below favouring the P/S split.

I'll be able to mount two ( at least ) modest PC panels on the quarter-rails. Their outputs could be parallel-fed into a charger device such as the CTEK D250SA or Victron Argofet, or fed separately to the P and S battery banks. MPPT controllers could/would be utilised.

It may prove practicable, and desirable, to feed the PV output through the CTEK device ( with its own MPPT device ) which can feed 14.7VDC into the Vicron unit, for differential distribution to the 3 battery banks S, P and St.

It may also be simpler to replace the existing 'simple' alternator with another which can be set to output 14.7VDC - and store the existing unit.

I also have a paraffin Tilley lamp I could use as 'last reversionary', should all my backups of backups fail.....

 

[PhillM]

I think you need to start at the other end, how much are you likely to use in each sailing period and how do you ideally want to put it back. That will determine the total battery size needed.

For example in my case of at sea (and with an outboard no engine charging, I would use half of my battery capacity in 24 hours and only be able to put back at max 20%. In theory my range is 48 hours. If I want longer range I either need to add another battery or (in my case) more solar.

 

[Refueler]

My first thought on reading ... 14.4v ...... think you'll find that is a very conservative figure ...

The 14.7v you also quote ... your alternator will be fine ... think you worry too much.

OK - so on a trot mooring ..... and not too often connect to shore ... sounds like Solar Panel needed ...

To make easier to mount sufficient Solar .. being a 'modest boat' ... I would be inclined to split the required wattage into smaller panels instead of one big one. Maybe bungee fix onto boom ??? Then you can take down when you use boat ...

 

[PaulRainbow]

Don't worry about the alternator, it will be fine as it is. Connect it to the Argofet and the batteries.

Do not use the port and starboard batteries individually, keep them in parallel. They will discharge less, cycle less and accept more charge than using them individually. If they are already individually selectable, select both only only isolate one if it fails.

Fit an emergency switch between the load side of the engine isolator and domestic isolator.

Fit as much solar as you can, with a decent controller. How about a panel or two on the guard rails, that fold up/down ?

 

[Refueler]

Solar controllers .. I have dual and single output as well as USB charging ... so as I and Paul suggest - get some Solar to look after things out on the trot.

As Paul says - fit as much wattage Solar as you can .. you NEVER have too much !!

I have a small maintenance panel on the pushpit rail ... it clips on using plastic pipe clips .. with tie-wrap to make sure they don't unclip by accident ... but easy enough to unclip / unplug when not needed. If you do similar - don't forget - Solar panel connects LAST and disconnects FIRST from controller ... not the batterys !

 

[BabaYaga]

I have 3 all-AGM batteries - Start, Service/Port Berth, Service/Starboard Berth. These require 14.7VDC for optimum charging.

Is this what the battery manufacturer states, and if so, does it say optimum in what sense?
Asking as I also have in my house bank three AGM batteries with an absorption voltage indication of 14.7–14.88 V.
However, I have seen no warning of damage to the batteries by using a lower absorption voltage, like 14.4 V.
So my understanding of this is that raising the voltage to 14.88 max is just an option that can be taken in order to speed up charging a bit without damage to the batteries.
If the same applies to your batteries, questions you might ask yourself are how much faster does the charging get by using 14.7 instead of 14.4 V and how valuable is this charging time gain, given how you are using your boat?

 

[Refueler]

Is this what the battery manufacturer states, and if so, does it say optimum in what sense?
Asking as I also have in my house bank three AGM batteries with an absorption voltage indication of 14.7–14.88 V.
However, I have seen no warning of damage to the batteries by using a lower absorption voltage, like 14.4 V.
So my understanding of this is that raising the voltage to 14.88 max is just an option that can be taken in order to speed up charging a bit without damage to the batteries.
If the same applies to your batteries, questions you might ask yourself are how much faster does the charging get by using 14.7 instead of 14.4 V and how valuable is this charging time gain, given how you are using your boat?

Charging doesn't actually increase markedly by having 14.7 vs 14.4 ... charging time is based more on amps in that situation.. actually watts. If the source can pump out the amps at that voltage - then yes.

 

[BabaYaga]

Charging doesn't actually increase markedly by having 14.7 vs 14.4 ... charging time is based more on amps in that situation.. actually watts. If the source can pump out the amps at that voltage - then yes.

I see two ways in which a higher voltage set point might reduce the charging time, from a given state of charge to fully charged:
1. It will extend the bulk phase, meaning that a larger proportion of the energy that is going into the battery will be delivered unrestricted by regulation. During bulk the charging is restricted only by what the source can deliver and by what the battery will accept.
2. The higher voltage held during absorption (14.7 compared to 14.4) should in theory make the battery willing to accept a higher current. On the other hand, the SOC will be higher (because of 1.) when the bulk phase begins, making the battery less willing to accept current. So this second way may not be so significant in reducing time.

 

[B27]

Charging doesn't actually increase markedly by having 14.7 vs 14.4 ... charging time is based more on amps in that situation.. actually watts. If the source can pump out the amps at that voltage - then yes.

A lot of the time a charging source will be current limited, but if you've got a plain lead/acid battery, you might be putting 50% more current into it if you set the volts to 14.7 instead of 14.4.

It will vary with the exact chemistry of the battery, e.g. calcium alloyed into the lead.

The battery may also be gassing madly and warming up a bit.
High charging voltage like 14.7 are common in industrial applications, like a battery forklift which works double shifts in a factory. May not be optimum for a house battery in a boat. A lot of stop/start cars may charge at quite high voltages when going downhill or braking. Yet they still get long life with no topping up.

You need to read the whole of the charge profile, if it says charge at 14.7V, it may have quite a high current threshold for switching to float voltage, or even a multi-stage profile where it switches to a lower voltage for a while.

Lead/Acid batteries take time to charge, the alternator is good for shoving a whack of charge in, but basically rubbish for full charging a battery, unless you motor far too much. Most alternators on boat engines also drop well below 14.4V if you draw even half their rated current. There are still lots of boat engines around with alternators more like 14.2 or even 14.0Volts, because that's a good number for charging the start battery on a mini-excavator which runs 8 hour shifts, or indeed a small fishing boat which runs its motor all day and isn't running a fridge overnight.
Cars have mostly moved on.

 

[Refueler]

One error so many people make is to think any charging regime actually hits 100% full charge. Its actually impossible as its the case of infinite input to battery - IF any charger was capable ..
The best one can hope is in the high 97+ % ...

Why ? The amp rate in diminishes as the batterys resistance to charge increases ...

Now some bod is going to argue .. but its fact.

Anyway - back to OP's question ... IMHO - he should just get on and stop worrying about 14.7 vs 14.4 ...