Battery / charging management

Hi there. I'm sorting out a new (to me) boat and I would like to make some changes to how the DC system is configured so that batteries are charged and isolated properly. What I will have is a group 27 starting battery for each main engine - the only other loads on these are the genset and windlass. There will be a bank of GC batteries to run the DC house loads and a 2 kW inverter. Obviously I would like the system to be configured so that all batteries can receive a charge either from the battery charger if on shore or gen power, or from the engines' alternators while underway, and isolate when not charging.

Functionally I would like the system to operate this way automatically, but still have the ability to manually parallel the two engine starting batteries, manually parallel the house bank to the starting batteries, or manually isolate all three systems when desired or needed.

So my questions are: What is a good ACR that has this functionality - it looks like Blue Sea has something like this that has a remote three position ON-AUTO-OFF rocker but I couldn't find a diagram so I'm not sure if this would work the way I'm thinking. I would have one between the two starting batts and one between the house and engine common from the other switch. Second question is with the system configured thusly, would it be ok to run a single bank charger either hooked up directly to the house bank, or in between the two switches, or would I be better off to run a three bank charger?

The issues I see with each are: With a single bank charger, in the case of a deeply discharged house bank the charger will be in bulk charge mode which would tend to overcharge the starting batteries which should only need a float charge. Even if I run a three bank charger the ACR's, seeing charging voltage will want to parallel the banks anyway. I could run manual switches but then you have to remember to switch between modes or run the risk of drawing down or overcharging the start batteries etc. which then you have the scenario that you're tired after a long day and forget to isolate the system and then in the morning you've run down your starting batteries too and then you're in a jam. So are there other components I could use or configure the system differently to work as described above?

I suppose that if I have a multi bank charger the only cases I would want the engines paralleled into the system is when I'm underway and want the alternators to also be charging the house bank, or in the unlikely scenario that the starting batteries are down and I need to connect to the house bank to start the engines. Is there a "one-way" ACR that would parallel only if there's charging voltage at the engine / alternator side, but not from the house side - if the house bank is charging that means the battery charger is on and charging the start batteries as well. Did I just answer my own question...?

Anyway...I've attached a basic sketch of what I was envisioning. Sorry for the long-winded post but please tell me what I'm missing or how this could be done better. Thanks!

 

My house bank charge setup has an acr wired how the pdf that blue sea has included with its set. My inverter is an inverter charger and only hooked up to the house bank, have a second much smaller charger on the starting side. The smaller charger is only powered up from a circuit energized by shore power or generator. The inverter charger is all internally switched so as long as the shore power cord is hooked up the batteries are charged both running and in my stall with no input from me.

 

You can do a manual system with a pair of A B AB off switches. There are seven different practical ways of wiring 2 of them up depending on exactly how you want them all connected for normal ops, engine starting, and self tending when not aboard. I usually had everything connected together when not aboard and the solar maintaining everything (for months at a time). I isolated the house bank prior to engine starting starting and then could connect the house bank again from either switch if I wanted to charge the house bank from the engine. These are simple and cheap and redundant. In a pinch, you can get everything done with one of the switches if the other one fails and you have to isolate it. You also don't loose the diode voltage drop that happens with many of the ACR setups.

I had posted the seven wiring schematics here, but it vanished when the forum changed software.

Okay, here's one of the seven ways to do it - https://www.boatdesign.net/attachments/boat-electricalsmall-jpg.70325/

 

I don’t like your schematic.

The house bank is the best for the windlass because you never want the windlass to take down the start battery. And the engines can bring the house back up. And the windlass discharge can be high, so why take down a start.

It is not a good practice to ACR the house and the starts, but it is a good practice to ACR the two starts. The likelihood of both starts failing is poor is why.

The starts theoretically never or rarely need charging. If they did get drawn down; you manually charge them with a decent charger.



My boat is a decent setup. Twin engines. House bank is 24v 240AH lifepo4. Two starts are acr’d. The engines have Orions on them, but I’d recommend buck boost over them today. If my starts run low; it is cuz I left the key on, but not an issue for a week or less.

My inverter is a tiny Compact Victron Multiplus 24/2000 or some such. I also have some solar.

The system seems to work okay. I have yet to test it hard. I only allow the Orions a 2 minute cycle on bulk. I am a bit worried about amp draw on the starters. Someone told me to drop the wire gauge down to reduce the current from the alternators. My system has never been hard field tested because it is usually plugged in, so this is the one unknown.. alternators are 32amp only.

 

Thanks for the feedback - food for thought... To elaborate a bit - I had some people out on the boat the other day and after about an hour trip from the marina and putting around for a while, I had an overheat alarm on the stbd engine at which point I shut that one down and started heading (slowly) back toward the slip. After giving the engine about 20 minutes to cool down I attempted to restart it and the voltage would drop way down and that engine wouldn't even turn over. I had my wife stand watch and went down to take a look, and found that ALL of the battery terminal nuts were not much more than finger-tight and one positive cable was barely hanging on. At the end of the day, that was really the only problem. I was able to get the engine started - I think the overheat alarm may have even been a result of this because it ran normal the whole way back.

The boat currently has a group 24 battery to start each engine, and one group 27 deep cycle for the house bank. The cables to the engine are #4 which seems marginal to me (even being gas V8's) and the house bank was low when I got back just from having some lights, water pump and the vacu-flush running for a couple hours. I don't ever want to deal with a dead battery (even though that's not what happened) and so part of my motivation was me being frustrated and wanting to rip everything out and start over. I worked as a diesel mechanic and marine tech for years - so generally speaking all the boats I was around were always broken (LOL) so with my OWN boat I want everything to be tip top shape and well sorted so I can just enjoy it and not have to worry about being surprised by ****. I'm okay with overkilling everything just for peace of mind's sake, but I see the value in the KISS principle.

I looked everything over a little more closely yesterday - there are 1/2/ALL switches that would allow paralleling the main engine batteries manually, and I think there is some sort of ACR between the engine batteries (there is an indicator light on the battery switch panel but I haven't looked at how it's wired yet). There is a 3 bank, 40 amp onboard charger that's hooked to each of the three batteries. I don't think that the house bank is tied to anything to charge from the engines at all. I do have a 5 kW genset as well but it currently won't come up to speed - probably a sticky gov. actuator as it's had very little use but haven't gotten around to fussing with that yet.

As I mentioned I will be installing a 2 kW inverter and installing more house batt capacity. The existing batteries are 4 year old (flooded lead-acid) so will be replacing the starting batteries anyway and looking at the runs to/from the switches it might be as much as 20 feet so I will probably go up in cable size as well. It seems like there should be a way to parallel the house and engines even if it's a manual switch - for emergency purposes, or if I'm underway to have the alternators supply some charge to compensate for small / intermittent DC house loads as described above.

I've always wired a windlass to a start battery with the assumption that you would ALWAYS be running an engine when raising the anchor. I figure if you have no engine you should probably stay put, unless you intend to row...