Which battery charger configuration?

[Sea Dog]

I'm reconfiguring my electrical power systems from a Mastervolt Combi Inverter/Charger to a stand alone Victron inverter alongside separate battery charging kit. Since my batteries are always full or close to full when I connect to a shore supply, I've about settled on a Victron Blue Smart 12v 30a IP22 charger, which does all the clever stuff from a maintenance point of view, as being quite adequate for my long-established and well-proven needs. As well as the extra seasonal input of solar (coming soon), I figure that, in the unlikely event that I should ever need need a higher current to more rapidly charge my domestic bank from a more heavily depleted state, my 175 amp domestic alternator has that covered.

So, here's where I'm prevaricating: Presently, I have a twin charger output from my Mastervolt unit, the second being a 4 or 5 amp dedicated supply to both of my starter and thruster (Shhh!)  batteries.

Should I now choose the Victron 30(3) triple output charger and wire both my domestic bank and the starter bank to one of those each?  (I know that all 3 outputs share the same 30a max charging load, but I'm unable to ascertain whether there's any kind of clever load sharing going on or if there's simply 3 linked outputs). Or, alternatively, should I get the (slightly) cheaper single 30a output version and dedicate it to my domestic bank and use a separate 5a smart charger for the starter battery? I know both would work, but I'm still deliberating a wee bit about how much of an issue is presented by the triple output option if, say, one bank needs bulk charge whilst the other only needs float. 

I have no real cost motivation here as I already have a 5a Ctek smart charger which has proven recently that it can quite happily maintain the 400ah domestic bank, so has no trouble keeping the starter battery smiling. I could either continue to use that as required or perhaps I'd buy another similar unit to install permanently for that purpose which, with the small saving from buying a cheaper single output charger, won't break the bank. It would bring a bit of additional flexibility too, I suppose. 

So, my choice will, I hope, be based primarily on engineering best practice. One 30(3) charger doing both jobs keeps things simple; two separate chargers perhaps provides a more tailored solution for each set of batteries.  Maybe there's a better way to go that I've overlooked.  What does the panel think?

 

Note.  I ought to add that I have considered my 12v DC load when on shore supply and I'm pretty content that the 30a unit is more than adequate. 

Edited October 15, 2017 by Sea Dog
12v DC load note.

[Boredrider]

As you have three banks, and three sources of charge (Solar, Alternator, and charger) I would consider fitting two voltage sensing relays, which will connect the banks together when any source of charge is available.  A more expensive way of doing it would be a Smartguage, Smartbank and two relays - which we have had on our boat for the last four years, and found to be most effective.

[Sea Dog]

Thanks Bonerider. I'm pretty content with my current charging sources and regimes - they're pretty well proven now to suit my usage profile well and, with the Victron BMV I fitted a while back informing my knowledge of the voltages and currents I should be seeing, I am confident in my battery and charge monitoring. All I'm really looking for here is whether to replace the dual charger output of my Mastervolt Combi with the triple output Victron smart charger or the single output and a second smaller one. Plus, of course, a sanity check of my musings in case I've got so close up that I've missed something, so I'm grateful for your input.

[Alan de Enfield]

44 minutes ago, Sea Dog said:

Should I now choose the Victron 30(3) triple output charger and wire both my domestic bank and the starter bank to one of those each?  (I know that all 3 outputs share the same 30a max charging load

I was under the impression that with my Victron 50a charger that the output of 50a excluded the 'starter battery trickle charger'

From the manual:

The full charging current of the Phoenix Charger is divided in two main outputs.

An extra output with limited charge capacity is available to charge a starter battery.

[Sea Dog]

40 minutes ago, Alan de Enfield said:

I was under the impression that with my Victron 50a charger that the output of 50a excluded the 'starter battery trickle charger'

 

Yeah, I think that's not an unusual configuration Alan. That's how my Mastervolt Combi did the job and how the Victron Combis I looked at do it, but not the Victron IP22 range it seems - and I've both asked and downloaded the manual. If it did, this would be a 'no brainer' and I'd just connect the starter battery to that smaller output. Instead, it has 3 outputs sharing the overall 30a capacity, but I haven't been able to ascertain exactly how it's shared. 

[Sea Dog]

Bump!

[nicknorman]

The Victron manual is pretty pants, which is one reason why I don’t much like their products! Anyway, back to basics - why do you need to keep the starter and BT batteries on charge? Unless you don’t use the boat’s engine for many, many months and/or the starter battery is knackered, it shouldn’t really need to. I suppose the BT battery might need recharging if you have used it shortly before you shut down, but I don’t know your BT usage pattern.

So, are you sure you need to trickle charge the non-domestic batteries?

if you really do, then my best guess is that all 3 outputs are pretty much connected together, so you might as well just connect them to the 3 batteries. The slight downside is that if you take a lot of domestic current you will trip the charger into bulk mode which will raise the voltage not just for the domestic batteries but also for the starter and BT batteries which would otherwise rather be on float. I guess that only matters if it happens a lot. A separate small charger for the other batteries would thus be marginally better, but set against that perfection is the extra cost and complexity. There is no “right answer” I suspect.

30A is certainly an adequate output to run normal domestic needs, as you say.

[cuthound]

My boat has a Victron Combi supplying the domestic batteries and thevstsrter battery from its secondary output, plus a dedicated smaller Victron charger for the BT battery. 

It works well.

[Sea Dog]

2 hours ago, cuthound said:

 

3 hours ago, nicknorman said:

...So, are you sure you need to trickle charge the non-domestic batteries?...

 

2 hours ago, cuthound said:

...plus a dedicated smaller Victron charger for the BT battery...

Thanks fellas!  Your posts have helped my thought processes and have steered me back to my original intent.  This was to have the domestic bank under maintenance charge (and thus also a shore supply for the 12V dc load) on the single 30 amp output intelligent charger I referred to. Alongside that, I had planned to charge my start thrust batteries only as required.  I have a Ctek charger that will do that happily, so I'd just bought a Ctek 'comfort indicator' panel/connector which gives a 3 led traffic light state of charge indication to facilitate that.

I got a bit seduced there by the idea of the multi output taking care of both as the Mastervolt did. You're right though Nick, the start thrust batteries will be quite happy if left isolated for the length of the periods I'm away from the boat, and I have the Ctek to simply plug in to the quick connection to charge or maintain them if/when required. Easy enough to connect that permanently if necessary too.

So, unless anyone else comes in with something I've missed, there's my intent. I'll be ordering the single output job for the domestic bank shortly.

Thanks again to all for your input.

Edited October 16, 2017 by Sea Dog
Remove double quote

[cuthound]

12 minutes ago, Sea Dog said:

You're right though Nick, the start thrust batteries will be quite happy if left isolated for the length of the periods I'm away from the boat, and I have the Ctek to simply plug in to the quick connection to charge or maintain them if/when required. Easy enough to connect that permanently if necessary too.

If they are lead acid batteries, they will begin to sulphate if left unattended.

This will take longer if they are fully charged before being left uncharged than if they are left partially discharged, but it will happen. This is because lead acid batteries self discharge at a rate of 4-5% per month.

[Sea Dog]

2 hours ago, cuthound said:

If they are lead acid batteries, they will begin to sulphate if left unattended.

This will take longer if they are fully charged before being left uncharged than if they are left partially discharged, but it will happen. This is because lead acid batteries self discharge at a rate of 4-5% per month.

Thanks CH. I won't be leaving them less than fully charged and I seldom leave the boat unattended in excess of a month. If I do though, that's a compelling argument for plugging in the Ctek, as well as the domestic bank. Frankly, since it's there, the Ctek could just as easily be left connected whenever I'm on a shore supply - as you do, clearly. Thanks for taking the time to add that note.