Wind, solar, alternator and 3 battery banks

[zoidberg]

Slightly different to another nearby thread, but maybe there's enough to make a difference to the answers.

Elderly sailboat, new engine with 75Ah alternator. All batteries will be AGM.
One 50Ah/825CCA battery to be fitted just ahead of the engine, in bespoke box.
Two groups of batteries to be fitted under P &S quarter berths, for house/services. Each group of two or three having rated capacity >150Ah. Cables run distance from engine/electrics bay not more than 1.5metre, each.

Two pairs of modest ( 10Ah and 20Ah ) PV panels, with individual controllers, capable of being connected either 1. each pair to one of the groups respectively or 2, both pairs via a 4-input controller. These pairs could be connected in series to provide nominal 24V at controller.
One robust Canadian wind generator, capable of being connected via 4-input controller.
There is a demounted Plastimo '1-Both-2-Off' rotary switch.

'Lecky usage frugal. All LED lights. VHF, navtex, small GPS, Yeoman Sport, NASA baro/wind, depth, car radio/CD, Autohelm, notebook PC, h/h VHF charger. No radar, fridge or thruster.

How best can I connect all these such that the two groups of house/services batteries can be separately selected and charged up? What devices are recommended, and where?

 

[temptress]

Why do you want 3 banks? I would have one dedicated engine start battery and connect al the others into one large domestic bank. I understand there are 2 separate domestic battery boxes but these can be connected together using larger cables to reduce voltage drop and get one larger bank.

I ask again why 3 banks?

 

[zoidberg]

I ask again why 3 banks?

Primarily, the physical topography of the cabin - 'Two groups of batteries to be fitted under P &S quarter berths'. There's room under each q'berth for 2 or 3 batteries. These are physically separated by the walkway down the centre of the cabin. Cables linking the Port group to the Starboard group must pass under the floors or under the engine, or laterally clipped across the top of the engine space. That's where the 'lecky control panels, harness connector and busbars are optimally sited, so it makes sense to have an On-Off/Isolator switch ( plural? ) thereabouts. Besides, I'm advised there's an optimum relationship between the charging alternator max. output and the capacity of the services/house/domestic battery bank....

Having 2 such switched banks Port and Starboard for services purposes, plus a dedicated engine start battery, seems analogous to having 1 bank for services and a further one for bow thruster.....

 

[jac]

Primarily, the physical topography of the cabin - 'Two groups of batteries to be fitted under P &S quarter berths'. There's room under each q'berth for 2 or 3 batteries. These are physically separated by the walkway down the centre of the cabin. Cables linking the Port group to the Starboard group must pass under the floors or under the engine, or laterally clipped across the top of the engine space. That's where the 'lecky control panels, harness connector and busbars are optimally sited, so it makes sense to have an On-Off/Isolator switch ( plural? ) thereabouts. Besides, I'm advised there's an optimum relationship between the charging alternator max. output and the capacity of the services/house/domestic battery bank....

Having 2 such switched banks Port and Starboard for services purposes, plus a dedicated engine start battery, seems analogous to having 1 bank for services and a further one for bow thruster.....

There is a big difference though. Assuming a 60ah discharge before recharging, under your twin domestics arrangement you will take 40% out of the batteries. Under the single large bank option you will only take 20% which is much kinder to he batteries.

A large bank can also absorb a given charge must faster.

Finally the charging is better. By having a single bank, no need for split charging be that via VSRs or whatever. Simply the whole output can be dumped into the bank with no need to juggle. With 30W of charging - that will keep a 300Ah bank nicely topped up and avoid self discharge. It will also make a useful contribution to replacing a weekends use over a week but will not make you independent.

 

[lw395]

Conversely, it's quicker to recharge one bank from 80% than both banks from 90%, if charging current is limited.

 

[pvb]

Besides, I'm advised there's an optimum relationship between the charging alternator max. output and the capacity of the services/house/domestic battery bank....

You can usefully disregard that advice. Wire the whole lot as a single bank. As jac pointed out, it'll be better for the batteries, and they'll recharge faster. There's no downside.

 

[zoidberg]

OK. You've convinced me, thanks. 'One big battery bank for services'. ( one ring to rule them all.... )

Each individual battery with it's own fuse? I have several manual On/Off switches. Would it make any sense to have one of these on every individual battery?

I have a used Plastimo rotary 1-Both-2-Off switch, and am aware that some on here consider them 'Devil Spawn', although I don't quite understand why. What, please, are the pros/contras re using this and what is a 'better way'?

 

[pvb]

OK. You've convinced me, thanks. 'One big battery bank for services'. ( one ring to rule them all.... )

Each individual battery with it's own fuse? I have several manual On/Off switches. Would it make any sense to have one of these on every individual battery?

I have a used Plastimo rotary 1-Both-2-Off switch, and am aware that some on here consider them 'Devil Spawn', although I don't quite understand why. What, please, are the pros/contras re using this and what is a 'better way'?

You don't need a fuse on each battery. You don't need an on/off switch on each battery.

The risk with a 1-2-Both switch is that, if you or someone else inadvertently sets it wrongly, you could end up with a flat starter battery. The better way is to separate the start battery completely, with its own on/off switch, and to separate the house bank, with its own on/off switch. You then need to arrange for the alternator current to feed both banks when the engine's running, which you can do by connecting the banks with a VSR, or by using a diode splitter (low-loss versions are available). The end result is that you'll always have a fully charged starter battery, and you'll never need to fiddle with the 1-2-Both switch. Just arrive at the boat, switch the two on/off switches on, enjoy the boat, switch the two on/off switches off, go home.

 

[PaulRainbow]

Each individual battery with it's own fuse?

No, pointless. If you fuse the banks you fuse at the battery where the load cable is connected.

I have several manual On/Off switches. Would it make any sense to have one of these on every individual battery?

No sense at all.

I have a used Plastimo rotary 1-Both-2-Off switch, and am aware that some on here consider them 'Devil Spawn', although I don't quite understand why. What, please, are the pros/contras re using this and what is a 'better way'?

First you want to fit a switch to every battery, now you want to fit a 12B switch, rather contradictory ?

Connect the domestic bank to the domestic circuits via an isolator switch, suitably rated for the loads of your highest bank. Connect the engine battery to the engine with a second switch. Fit a third switch for emergency use.

There are more than enough threads on here discussing the "best way", no need to make this into another one. Try here : http://www.ybw.com/forums/showthread.php?493683-Another-one-bites-the-dust

 

[zoidberg]

First you want to fit a switch to every battery, now you want to fit a 12B switch, rather contradictory ?

Actually, I don't want to fit any switches. I was thinking of asking you to do it, together with the other 'lecky work.... but that not going to happen, now.

 

[zoidberg]

Thanks, 'pvb'.

I'm getting there. Painfully....

 

[PaulRainbow]

Actually, I don't want to fit any switches. I was thinking of asking you to do it, together with the other 'lecky work.... but that not going to happen, now.

You asked some questions, i gave you the correct answers (same as PVB actually). Sorry if you don't like my answers, i'll be sure to spend some of my time freely helping you next time you need some help though

 

[GrahamM376]

Conversely, it's quicker to recharge one bank from 80% than both banks from 90%, if charging current is limited.

Correct but the downside is quicker and deeper cycling of individual bank compared to both connected together = smaller discharge = longer battery life.

 

[lw395]

Correct but the downside is quicker and deeper cycling of individual bank compared to both connected together = smaller discharge = longer battery life.

You'll probably only get the longer battery life if you have ample charging current to swiftly bring the batteries back to fully charged.

Some people have made splitting the house bank into two switchable banks work well for them as it means they can renew half the batteries at one time instead of all of them.
It suits some people to know that not all of their batteries are getting old.

 

[monkfish24]

I've just changed my DC supply lay out from having two separate house batteries to just one. I had the same issue as you.

I had one start battery then a 3 way changeover switch where position 1 was meant to be the start battery, then you'd change to position 2, which was meant recharge the start battery and one of the house batteries, position 3 then was to recharge the two house batteries. That on its own always meant the switch change always got forgotten about so usually the engine got started and ran, shut down, sailed all day before we realised late in the day that we hadn't switched over. Luckily for us we never had a flat battery.

This then got complicated because number three battery only supplied the pumps, via a 12-24v converter because the pumps are 24v !?!

I have now removed battery number three, moved the house battery into the engine bay where I can add more batteries in parallel and will be fitting as large a solar panel as will fit on the hatch and coach roof. The engine start battery is directly connected to the engine. The house battery is only connected to the domestics. I will then fit three isolator switches, two in the cabin to isolate the two batteries from their respective loads and a hidden parallel switch in the engine bay for emergency use.

This is the most common method because it's simple and works. I understand you have a complication with location but it is definitely worth looking into moving all your batteries into one bank and ensuring your charging system is matched to suit/your battery capacity suits the charging abilities.