Bank Wiring Advice

[ALNelson]

Hi everyone. I’m looking for some advice on the setup of battery system on our new-to-us Catalina 400. We have just purchased new batteries and I want to ensure a correct setup prior to their installation. The current system has:

• Two 200 ah AGM batteries, labeled in the battery box as Battery 1 and Battery 2 (soon to be replaced with 210 ah Lifeline AGMs) Two 200 ah AGM batteries, labeled in the battery box as Battery 1 and Battery 2 (soon to be replaced with 210 ah Lifeline AGMs)
• A 95 ah AGM starter battery (soon to be replaced with a 130 ah Lifeline AGM)
• A Xantrex Trucharge2 charger for shore power
• A Victron MPPT 100/50 charger for solar power (570 watts across two panels in parallel)
• A Victron BMV 702 battery monitor (connected to Battery 1 and the starter battery)
• A 1/2/Both battery switch
• A On/Off starter battery switch

I’ve attached a drawing of the current system. Bat 1 goes to 1 on the switch and Bat 2 goes to 2. The Xantrex charger has a positive lead to Bat 1 and Bat 2, and the neg lead goes to the neg on Bat 2. The alternator is wired to the positive on both Bat 1 and Bat 2. The solar charger goes ONLY to Bat 1. The starter battery positive out connects to the starter switch input, AS DOES a lead from the battery switch C output.

From what I can tell, the current wiring in essence makes the entire system one large parallel bank, as the starter battery AND the battery switch output are connected at the starter switch input. If the switch is on B all three batteries are connected, and if 1 or 2 is selected that battery AND the starter battery are in parallel.

If correct, I see a number of issues. One is that the solar can’t charge Bat 2 unless the switch is on B. Another is that the starter battery isn’t isolated from the others, so it can be drawn against the others. A third is that the battery monitor has no way to read Bat 2 (although I presume that if the battery switch is on B it reads the voltage across Bat 1 and 2?).

I presume the prior owner just left the battery switch on B all the time. This gave him — I think — in essence a single parallel bank across Bat 1 and 2 (as the positives are connected via the battery switch and the negatives are connected in parallel via the battery monitor shunt). The shore power and alternator charged all three (Bats 1 and 2 via direct connection and the starter via the battery switch), and the solar charged all three (Bat 1 via the direct connection to Bat 1, Bat 2 and starter via the switch), but with the downside of an inaccurate battery monitor (I’m guessing) and a starter battery that is not really isolated as a cranking battery and as an emergency backup battery.

The conduits are difficult for me to get to without ripping the boat apart, which makes it very difficult for me to run new wires across the system (or take existing wires out). I’m looking for the best, and easiest, way to improve the setup for the new batteries. I’ve read the posts on battery wiring here at length. From what I can tell I can:

Keep it the way it is today. Always operate on both and live with the downsides.

Keep it the way it is today but DISCONNECT the backup / starter battery for use only in an emergency, and connect it for a top off charge from time to time.

New wiring option 1: Leave it the way it is, but run a ACR between Bat 1 / Bat 2 and the starter battery, and keep the battery switch on Both all the time. This way the starter battery would take a charge, would help crank the engine, but would not charge Bat 1 and Bat 2. Given that I can’t easily run new wiring from Bat 1 and Bat 2 to the starter battery could I connect the ACR between the starter C post and the starter switch (to which the starter battery is connected)?

New wiring option 2: Disconnect Bat 2 from the battery switch, and disconnect the Xantrex charger and alternator from Bat 2. Connect the positive posts on Bat 1 and 2 and the keep the negatives connected via the shunt. Use the cable that used to connect Bat 2 to the switch to connect to the ACR and connect the ACR to the starter battery via the input on the starter switch. Connect the output of the starter switch to the 2 post on the battery switch so it can serve as an emergency house battery if needed. My question here is, what do I do with the alternator and charger leads that used to connect to Bat 2? I can’t easily take them out as I don’t have access to the conduits without tearing the boat apart. Or can I just leave them connected to Bat 2 without harm?

I’ve attached images of both options. I’m interested in advice, including any options I may not be seeing. The ultimate fallback is to simply swap out the batteries with the new ones and find a local marine electrician to do the work, but I’d hate to harm those batteries in the interim. I don’t feel comfortable going out today — Bat 1 is pretty toasted, Bat 2 is a bit better, and the starter is in the best shape, but I worry about not being able to crank the battery after a sail, and when there is a heavy load on the system (electronic nav, lights, fans, plus fridge) the voltage can drop low enough that it’s a low-voltage situation. I’d like to be able to use the boat in the event a marine electrician is weeks or months from being able to do the work.

Thanks in advance for your thoughts and patience as I am learning all this as a newish boat owner.

[Stu Jackson]

OEM 1-2-B Switch Wiring History http://c34.org/bbs/index.php/topic,4....html#msg30101


1-2-B Considerations (New 2020 - Rod finally got around to diagramming what I had done in the above link in 2009 )
https://marinehowto.com/1-2-both-bat...onsiderations/

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: http://c34.org/bbs/index.php/topic,6604.0.html

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
http://forums.catalina.sailboatowner...d.php?t=137615

This is a newer primer for boat system wiring design with a thorough diagram: Building a Good Foundation (October 2016)
http://forums.sailboatowners.com/ind.../#post-1332240

The Short Version of the 1-2-B Switch Stuff: http://c34.org/bbs/index.php/topic,5....html#msg38552 This is a link to the Electrical Systems 101 Topic, reply #2


****************************
There are many more pointers in this link including ACRs, which all are from my page:
Electrical Systems 101 http://c34.org/bbs/index.php/topic,5977.0.html

[Kelkara]

The whole thing looks confused, but three things stand out immediately ...

1. The cable from the alternator to BOTH bat1 and bat2 connects these two batteries in parallel permanently ... thereby reducing the 1/2/both switch to a simple on/off, since positions 1, 2, and both will all be "both".

2. You have not shown any negative connection between bat1/bat2 and the starter battery ... I'm pretty sure there will be a connection somewhere.

3. The positive from the start battery is permanently connected to the panel at the 'C' terminal of the 1/2/both switch ... this permanently parallel the starter battery with bat1/bat2 any time the 1/2/both switch is on, and when it is off permanently connects the starter to the panel.


All together this looks just like a very confusing way of having all three batteries permanently in parallel as one bank, with the switches poorly arranged.


*4. There probably should be some fuses, but you may have just omitted them from the diagram for clarity.

My vote is that the whole thing is a mess generated by the previous owners tinkering with the system over the years. If the boat is new to you, you would be well served by rewiring the whole lot so you can start out with a simple well designed system that you can then turn into your own mess over the years of your ownership for the next owner to be baffled by.

Start from a simple two bank system, Use bat1 and bat2 in parallel as one bank and the starter battery as the second bank ... then add the chargers and monitors per the manufacturer's instructions.

start by looking here for advice:
https://marinehowto.com/1-2-both-bat...onsiderations/

[smac999]

the acr must be used in option 2 direct to each battery, you can't go to the swtich outputs.

I would join them into 1 large bank. there is no reason to have 2 house banks. as mented above, unless that alt is going through a battery isolator then you only have one bank now anyways because the alt wires join them.

[SailFastTri]

I thought this thread would be about sending money.

[ALNelson]

Originally Posted by SailFastTri

I thought this thread would be about sending money.

Given that I’m about to hire someone to do this work, I think it its!

[GrowleyMonster]

Wire the two big batteries in parallel and connect to battery switch as 1 or as 2. Wire the engine start battery as the other bank. Connect start cable to battery switch so you can start engine with start battery or in a pinch, start with the house batts. Connect alternator to battery switch so you can charge house, start, or both banks together. Same with shore power battery charger. Same with MPPT controller? Honestly I don't think I am qualified to answer that as I haven't really messed with solar much at all, but my instinct would be to connect the solar charge controller to the battery switch, too.

You COULD have two house banks but since you have identical batteries, and presumably the same date codes on them, it makes sense to just keep them in parallel. When you don't seem to have the voltage or the charge capacity you should have, then just disconnect one and then the other for troubleshooting. If one battery goes North on you, then running the other, with a brand new one in parallel, could be a minor issue. They won't be electrically identical. At that point you could replace BOTH house batts if they are near the end of their normal useful lifespan anyway, or add another battery switch so you can operate off either/or.

There are good reasons to have all of your identical house batteries in parallel. One big one, with any lead acid battery, is called Peukert Effect. When the discharge current in amps is a large fraction of C, or the nominal capacity in amp hours, battery efficiency is significantly reduced. Total watt hours available is reduced. When it is a small fraction of C, efficiency is increased. You get more watt hours out of the charged battery. And less wear and tear on the battery, as well. The most obvious way to reduce discharge current is to reduce the total load by not running as much stuff on the bank. But the other way is to increase total amp hours capacity by parallel connection with more than one battery. So a single parallel bank is more efficient, and particularly so when you have a large load. When you are only powering your running lights and a tablet for navigation and a night light below, maybe a binnacle light, doesn't matter. If you have a bunch of fans, fridge, a floodlight, a watermaker, household appliances running on the inverter, it makes a big difference. Plus it is just simpler, except that you have to manually disconnect to isolate one of your two house batts, to get to the bottom of things. With unsealed FLA, you can just take the specific gravity of each cell to find the bad battery, or measure cell to cell voltage by sticking your test probes right into the electrolyte. Obviously AGMs call for individually testing resting voltage, maybe doing a load test or capacity test, which means isolating them.

But if you did end up with two non identical batteries in the house bank, you could always install a second 1B2 battery switch, fed from and feeding one leg of the original one. It is just that it is common for both identical batteries to age out at about the same age, and so replacing both together is the usual thing.

[ALNelson]

This is all really helpful. Thanks, all. It confirms what I had suspected, and I am going to have a certified electrician work with me to rebuild the 12v charging system wiring from scratch with the two big AGMs in parallel and the starter battery isolated.

One question in the meantime for anyone who might know: In the short term I could achieve that by disconnecting Bat 2 and Bat 2's alternator and charger leads and running a positive cable between Bat 1 and Bat 2. Then they would be in parallel without going through the alternator or battery switch. If I were to do that is there harm in connecting both alt leads to Bat 1 (or both charger leads, for that matter)? I wouldn't want them just hanging out in the battery box obviously but I can't get to the conduits easily enough to remove them.

[GrowleyMonster]

Originally Posted by ALNelson

This is all really helpful. Thanks, all. It confirms what I had suspected, and I am going to have a certified electrician work with me to rebuild the 12v charging system wiring from scratch with the two big AGMs in parallel and the starter battery isolated.

One question in the meantime for anyone who might know: In the short term I could achieve that by disconnecting Bat 2 and Bat 2's alternator and charger leads and running a positive cable between Bat 1 and Bat 2. Then they would be in parallel without going through the alternator or battery switch. If I were to do that is there harm in connecting both alt leads to Bat 1 (or both charger leads, for that matter)? I wouldn't want them just hanging out in the battery box obviously but I can't get to the conduits easily enough to remove them.

Well, if you have two alternators running off your engine, maybe pick the bigger one and use it to charge your new united house bank, and keep the other alternator for a spare. Or use it as a dedicated charge source for your start battery, or a backup start battery or a backup/emergency radio battery. I feel your pain, re wires not connected to anything LOL!

I forgot to mention one thing. You probably already know this so don't think I am talking down to you, but just want to make sure you know that you must never disconnect an alternator completely from the batteries while the engine is spinning it. It is okay to switch from one battery to another with a standard 1-Both-2 battery switch, or switch to Both, but you mustn't switch to OFF while the engine is running, or disconnect the output or sense wires from all loads and batteries. It will probably zap your rectifier diodes, which obviously is a problem. In fact if you ever find that your batteries are going dead flat for no reason, check your alternator rectifier.

[ALNelson]

Thanks. Not talking down to me at all, though I do know to to disconnect the ALT while spinning. I'm making progress getting this system straightened out. It will be some time -- weeks -- before an electrician can rebuild the system from scratch. A big issue was that the starter battery and C post on the switch were connected at the On / Off starter battery switch, so the starter battery was draining into the house. I've separated those. A second problem was that the shunt was wired incorrectly. I've fixed that. The two house bats are now in parallel via the alternator and the negative leads off the shunt, though they still go to post 1 and 2 on the selector switch.

In the short term, could I not just connect them both to post 1 on the selector switch? The two positive cables from both batteries are the same size and length, and the two neg cables from the end of the shunt back to both batteries are the same size and length (though much shorter than the positive runs to the switch). Then I could connect the on / off starter switch to the 2 post on the battery switch, completely isolating the starter battery but still being able to use it to run the panel in an emergency (and to charge it, I would just switch the battery selector to Both). So: BOTH Bat 1 and Bat 2 of the house to post 1 on the switch, and the starter battery to post 2.

[ALNelson]

Correction: I know NOT to disconnect the alternator / turn battery off while spinning ...

[GrowleyMonster]

Originally Posted by ALNelson

Thanks. Not talking down to me at all, though I do know to to disconnect the ALT while spinning. I'm making progress getting this system straightened out. It will be some time -- weeks -- before an electrician can rebuild the system from scratch. A big issue was that the starter battery and C post on the switch were connected at the On / Off starter battery switch, so the starter battery was draining into the house. I've separated those. A second problem was that the shunt was wired incorrectly. I've fixed that. The two house bats are now in parallel via the alternator and the negative leads off the shunt, though they still go to post 1 and 2 on the selector switch.

In the short term, could I not just connect them both to post 1 on the selector switch? The two positive cables from both batteries are the same size and length, and the two neg cables from the end of the shunt back to both batteries are the same size and length (though much shorter than the positive runs to the switch). Then I could connect the on / off starter switch to the 2 post on the battery switch, completely isolating the starter battery but still being able to use it to run the panel in an emergency (and to charge it, I would just switch the battery selector to Both). So: BOTH Bat 1 and Bat 2 of the house to post 1 on the switch, and the starter battery to post 2.

Yes, if I understand you correctly. Either way should have them in parallel. Cable length is a big deal with smaller wire but if you are running at least 2/0 then minor differences in cable length are not a biggie.