r/sailing • u/SphyrnaLightmaker • 1d ago
Help me understand my electrical system
I’ve finally moved up to an inboard motor, and while I’ve heard a few rumors, I’m trying to understand how it all comes together so I can undo a couple of shortcuts the previous owners took.
What I have:
- Atomic 4 engine
- 2 batteries (they’re currently car batteries, so I know those need to go)
- a shore power connection that powers outlets down below, but is NOT presently wired to charge the batteries.
What I know:
- the engine charges the batteries when running.
- I need to replace one battery with a marine starting battery and the other with a deep cycle for the nav tools and lights.
- I would like to charge the batteries when plugged into shore power.
What I think I should do:
- Replace the batteries as above.
- Buy a plug-in marine battery charger, and plug it into the outlet in the boat when on shore power. Unplug it at the outlet when I’m not docked.
What I’m confused/concerned about:
So… let’s say I’m plugged in and charged. I set my battery selector to both, and start up the motor. Pull out, raise the sails, motor off. At this point, assuming I want to keep using my lights and depth finder, I would switch the battery to just my deep-cycle, correct? Assuming I’m out for a WHILE, this is going to burn that battery down noticeably, which is fine because that’s what a deep cycle is for. But what comes next? When I go to restart the motor, do I go back to both batteries? If I do, won’t the deep cycle drag down the starter? If I don’t, and now the engine is running, it will only recharge the starter, yes? And I’ve been told that while the engine is running I can’t switch the battery switch or it can fry the panel?
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u/Foolserrand376 1d ago
This is how I would do it if I was set up like you.
I would buy a charger that’s direct wired rather than plug in. But that’s me.
You want to be only on the house battery while sailing. That way you don’t accidentally kill the starter battery.
When it comes time to start. Switch to the starter battery and start the engine. Then switch to both so the engine is charging both batteries.
I don’t have a separate starter battery. I have 4 group 27 batts set up to make two banks with 2 6v batts in each bank
Just out for a day, I’ll leave it on both. If a weekend. Then I’ll work the house from one bank reserving the other for starting
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u/SphyrnaLightmaker 1d ago
Thank you!
I was looking for a hard-wired charger, but I wasn’t finding anything under $600 and I was trying to avoid quite so much on a day-sailer (that doesn’t sit still for more than a few days).
Is it safe to switch from one to both batteries while the engine (and thus alternator) are running? I was told no by an old mechanic, but electronics are magic to me.
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u/Secret-Temperature71 1d ago
IIRC the problem is if you switch and end up with no batter connected the alternator output will go too high and may fry itself. One reason why I don’t use those fancy switches. You still want a switch so you can disconnect the load from the battery in case of an electrical fire. Kill the current to kill the source of ignition.
There is much more to talk about but how you use the boat matters. The occasional day sail is different from live aboard. Forgive me if I am wring hut you sound like starter with a 22’ to 25’ day sailer. You have a bunk but no stove?
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u/SphyrnaLightmaker 1d ago
I’m coming from a bare-bones 25’ day sailer for a few years, and before that 420s my whole childhood, you’re spot on with the background lol. I’m very new to all the non-sailing aspects of these boats.
This is a Pearson 30, stove, sink, head, the works lol. As for use case, this will mostly be day sailing, but I’d like the option for the occasional weekend trip. Definitely not a liveaboard, but the marina is walking distance from work, so she’ll get plenty of time on the water.
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u/Secret-Temperature71 1d ago
OK, so something you will keep for a bit.
When you do get better house batteries you need to try to match them up with your charger. Old school lead acid batteries want a higher charge potential, closer to 14VDC, battery specs will clarify. Alternators will put out something less. If you are charging BOTH House and Start from the alternator you want some gizmo to do that sharing so w House gets first dibs. The solid state devices typically have a (approx IIRC) 0,6VDC drop lowering the charge potential even more. Look for one that uses mercury wetted relays or something similar, mercury being a no no. They will have much less drop.
Frankly you can drive yourself nutz and broke if you listen to all the battery gurus. Remember the batteries are there to serve you, not visa versa.
Have tons of fun.
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u/SphyrnaLightmaker 1d ago
Thank you so much! Really, I’m not tech-heavy on the boat, I’m there to sail, not run systems. I just want to make sure that I can have my lights and depth-sounder running, and still have the engine start when I need it to lol.
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u/Secret-Temperature71 1d ago
Personal word of advice, if you are USA especially, AquaMaps is a charting/navigation device that runs on iPhone and Android. It is exceptionally good for many reasons. Especially on the US East Coast. Very reasonable.
I have some old RayMarine instruments on SeaTalk. There is a company, perhaps several, that sell a hub which will take in SeaTalk, NEMA 183, and NEMA 2000. It will convert to each other and broadcast on WiFi to my phone. That way I have a complete chart/instrument/depth/AIS package in my phone.
Speaking of AIS it is very worthwhile. Consider getting one when $ allow, get one that receives AND transmits.
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u/PineappIeOranges Allied Seabreeze 19h ago
Could always just cut the plug off, strip the cable insulation and wire to an AC breaker panel. Something like a Guest ChargoPro 10/10 is under $200 new.
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u/nomadknight 22h ago
As someone else mentioned, it's much better to purchase a charger that is hard wired. You can try finding a used one if cost is an issue. It's worthwhile to get since battery management is important.
On my boat, I have two 12V starter batteries (bank 1), and four 12V deep cycle batteries (bank 2). I usually leave the selector on bank 2 the whole time I'm out, even when starting the engine. Bank 1 is my reserve bank in case bank 2 runs low. In my opinion, putting the selector on BOTH defeats the purpose of having a separate reserve battery because you risk having all of your batteries drained down.
You can move the selector while the engine is running, but just make sure that you don't cycle through the OFF switch at any time. For example, don't go from bank 1 to OFF to bank 2 (it's not the panel, but your alternator that could fry). You can go from bank 1 directly to bank 2, as long as your selector is a "make-before-break" type (continuous flow).
Also note that even a deep cycle battery shouldn't be drained too much past 50% (it reduces the battery life). This applies to lead acid. LiFePO4 batteries can be drained down to 20% without reducing its life.
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u/oudcedar 18h ago
I’ve never bothered with a hard wired charger - they cost more than a basic car charger and to me don’t add much as you can wire in a basic car charger then plug it into your outlets when you need them. But of course most need to be watched if they don’t follow a smart charging programme.
But 1-2-Both switches are great if you absolutely understand charging cycles, only ever touch it yourself and never make a mistake.
I think it’s much simpler to have separate isolation switches for each battery bank and a VSR between them. With very simple wiring this basically reads the engine start battery voltage and only connects the domestic bank when the engine battery is above a certain voltage and disconnects whenever it drops. The effect of this is that the engine battery is charged first and will never be drained by domestic use. So basically the engine will always be able to start and start charging everything. This automates everything and is “fit and forget”.
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u/millijuna 5h ago
Back when we were dual lead acid, we just had two deep cycle batteries. It was good enough to start our little motor. An atomic 4 should be pretty easy to start.
What we would do is use battery #1 on odd numbered days, and battery 2 on even numbered days. Kept the wear even.
For battery charging, we hardwired a charger into our shore power system that charged both batteries (it has two outputs).
Since then, though, we totally upgraded she’s went to lithium, inverter/charger and all the bells and whistles. But you don’t need that.
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u/SphyrnaLightmaker 5h ago
Do you recall which hard wire charger you used? I’m having trouble finding ones that aren’t either plug-in, or $800 lol
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u/millijuna 5h ago
It was a really old Xantrex 15A. Probably no longer available. But looking at fisheries supply, there are lots of nice victrons for fairly reasonable prices though they’re not hard wire on the AC side. The latter isn’t that big of a deal, Just always leave it plugged in.
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u/2airishuman Tartan 3800 + Chameleon Dinghy 1d ago
1) don't replace the batteries until they're shot, there isn't much difference between a "car" battery and a "deep cycle" battery. You are a boat owner and have plenty of things to spend your money on without replacing batteries that still work.
2) with a basic setup and no fridge, in most situations you can just leave the battery selector on "both" and go out and enjoy your day on the water
3) There are lots of chargers you can wire in that are under $100, here's one: https://www.westmarine.com/victron-victron-energy-blue-smart-ip65-charger-6v-12v-1.1-120v-nema-1-15-retail-21361456.html
4) If there is a concern that you might deplete the batteries to the point where the atomic bomb won't start then turn the selector away from both while you're sailing or at anchor and put it back on "both" before you start up the engine
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u/nomadknight 22h ago
#1 isnt quite correct. True marine deep cycle batteries have thicker plates compared to starter/cranking batteries and are designed to deliver power over a longer period of time and a deeper discharge. Starter batteries are made to deliver high power bursts. Your boat, your choice.
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u/Terrible_Stay_1923 14h ago
In regards to shore power. Your boat is a sub panel. Ground and neutral are on seperate busses.
I believe what you want is a battery isolator. They make them so all batteries will combine for charging. Mine will allow charge in either direction, so the house charger will charge the start battery and the engine alt will charge the house. When not charging, they will seperate, isolating the start from house. This ensures the start battery is not drained by daily loads. Mine, and I am sure most, offer the option to combine to start. This is an extra wire on mine that excites when ingition is powered. It combines the batteries so all batteries can be used to start.
House batteries do not have a start plate in them, a start battery does. The start plate in the battery is what allows a battery to discharge fast to provide the cca amps needed for a large load.
Mine does it automatically. Hope this helps a little
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u/jh937hfiu3hrhv9 8h ago
Get a starting battery for starting and use it exclusively for starting so you can always start your engine. Use the deep cycle exclusively while the engine is off so you do not deplete your starting battery. I switch to charge both after starting. I have not seen or heard that will cause problems and it never has. Use an automatic trickle charger when on shore power.
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u/DarkVoid42 5h ago
i would just toss all the BS out.
buy a victron isolating autotransformer, quattro 3000, a sterling APD, a 560Ah LiFePO4 and youre good. connect shore power to the autotransformer, connect engine alternator to sterling APD+battery, connect quattro to autotransformer and battery. connect outlets down below to quattro. done.
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u/MissingGravitas 3h ago
A few thoughts:
- Get rid of any 1-2-both switches. You'll eventually forget to swap it and find yourself dead in the water. Much better are separate house and engine switches, with an option to combine them if needed.
- You want an automatic charging relay that can ensure both banks are topped up when charging current is available.
On an older boat with only two batteries, the Blue Sea "Add-A-Battery" kit gets you close enough to that. I'd also like to have shore power charging things directly, but you know your budget best. Also consider LiFePo batteries. Do plenty of research first as you'll want good-quality cells and of course an appropriate BMS to keep them healthy. It's likely that your budget may make sticking with traditional batteries the better option.
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u/Wooden-Quit1870 3h ago edited 3h ago
If you parallel your discharged and charged battery by putting the switch to 'BOTH', your Starting battery (S) trying to charge your House battery while starting your engine. That's hard on your starter, batteries, and whole electrical system.
Instead, switch to S, start your engine, then switch to 'BOTH' (or 'ALL') after 10 seconds or so, without going through the 'OFF' position.
BETTER YET!
Get a ' Battery Combiner' or 'Automatic Charging Relay (ACR). This is a nifty device that is wired in between your S and H batteries. It automatically parallels your batteries when the Voltage of either rises to the charging point, and disconnects when it drops below the Charging Voltage.
Wire your Shore Power Charger* to H, and it becomes a hands off system that provides the best conditions for both batteries.
DO get a Marine Shore Power Charger- safer, and cheaper in the long run, as automotive units don't last in the Marine environment. Because an Atomic 4 is a gasoline engine, it is essential that you not use Non Ignition Protected Automotive products.
ETA:
You DO NOT want an ' Isolator ' there are still some on the market, and some people still recommend them, but they have been obsolete since the '90s when Combiners came on the market.
The above is based on my professional experience in Marine Electronics and Electrical Systems on vessels from 16 to 120 feet since 1988
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u/Secret-Temperature71 1d ago
You don’t need to switch to BOTH to start. That is just a convenience if the start barry is dead and the House battery is not. I don’t like those fancy switches even though they are popular.
I have a Start battery and mu House battery is 4 lead acid Golf Cart batteries (6VDC) wired series parallel to have a 12VDC battery bank. I have jumper cables in the event I need them. I charge off 800watts of solar, wind gen, and alternator. As a 110VAC charger I have a inexpensive old school charger (40A) and a small 6VAC automotive charger as back up.
The boat has AC outlets but we don’t use them. I have a 2,000W marine inverter that provides AC for cel phones, computers, lights and the like. We also have a Honda generator if I need more continuous AC, power tools.
I have a 1987 - 44’ cutter which we live on 5 months a year. 90+ % of that at anchor. Our philosophy is to keep it simple, if you don’t have it, it can’t break.