On-board Battery Charger with Generator and Engines Running

[Mikwallace]

The other day I took the boat out for a 1 hour exercise because it was a beautiful day. As I was cruising along it occurred to me that with both engines running at about 2400 rpm the alternators are putting out sufficient amperage to provide adequate charging to the battery bank that’s selected. However, I don’t believe the opposite battery bank (selector position 1 versus 2) is being charged by the engine alternators. Only the battery bank that’s selected.

So here’s the question:

Should I turn off the On-board battery charger, if the generator and engines are running to prevent both Alternator and battery charger operating simultaneously?

Maybe I’m overthinking this? But it’s all still new to me!

[Midnightsun]

However, I don’t believe the opposite battery bank (selector position 1 versus 2) is being charged by the engine alternators. Only the battery bank that’s selected.

This is normally how it works on boats with 1/2/both selector switches unless there is some type of ACR or battery combiner installed somewhere which will connect as required. Regardless, no need to shut down the on board charger in any condition.

[Viper]

The only time you'd need to shut down your charger when another charging source is operating is if your charger acts up in the presence of a conflicting charge. This can happen in some cheap smart chargers. You'll know there's a problem when status lights start blinking erratically and the charger's output stops.

Which batteries get charged while the engines are running really depends on how she's wired. Some were wired such that they only charge the bank the battery selector switch is set to while others were set up with devices such as ACRs, combiners, isolators, etc., allowing all banks to be charged by both alternators regardless of the selector switch position. The key is that the banks remain isolated from each other when not combined for charging purposes.

Follow the large charge wire (usually orange) from the alternator, if it goes to the starter, it will charge the battery/bank that the selector switch is set to. If the charge wire leads away from the engine, it's likely heading to a charge distribution device. A lot of builds used a battery isolator back then; a rectangular metal box with cooling fins, and terminal posts. They allow one or both alternators to charge all the banks but the diodes act as a check valve and prevent electricity from flowing in the opposite direction thereby isolating each bank.

[bud37]

Source of the post Should I turn off the On-board battery charger, if the generator and engines are running to prevent both Alternator and battery charger operating simultaneously?

If that is a concern for you, simply shut off the charger and move the switch to both....that way the engines will take care of the bank charging while underway......engine alternator systems are designed for this type of service.

[Viper]

Just make sure you remember to turn the switch back to your house bank once you reach your destination. If you don't and you're on the hook for a couple of days for example, you may not be able to start your engines to get back home. Forgetting to move the switch from the ALL/BOTH position is one of the number one causes for emergency calls on the water. This is why I don't like the use of a battery selector switch in battery wiring setups. It's just one more thing that you need to manage/remember while you're out trying to relax.

[Midnightsun]

All my previous boats had these 1/2/all/off selector switches which if not used correctly, lead to no start issues or low house bank just because one forgets as Viper described. I was a little flustered when I got Midnight Sun because you cannot combine anything, only on/off switches. After a few years with this system I can now see this is the best way of doing things. Everything is automatic, you can never inadvertently run down starting batteries no matter how hard you try which are always full.

[bud37]

Lets face it, that is what the generator is for imo.....all these automatic devices can fail with out warning, we have had some threads addressing just that....only takes a few seconds to operate a few switches, no different than turning the key to start/stop engines, undo lines, power chords etc.

I just think there is nothing wrong with hands on and being aware of how you operate your boat....considering that your life may depend on the correct operation.

That said, I do like all that electronic stuff to do this for you, just not for me for the reasons given above....+ cost.

[Viper]

Source of the post ....only takes a few seconds to operate a few switches,....

Therein lies the problem. The fact of the matter is that people forget to do just that. Considering it's such an issue and that there are other more reliable ways of accomplishing the same thing without having to remember anything, I fail to see why OEMs are still on the path of using selector switches. I can tell you that 95% of boats that I go on at their slip still have their switches on ALL/BOTH. Of coarse they'll also have their chargers on. This combination is a good way to fry your batteries and it really does make having a multi bank charger pointless.

[Phrancus]

Just a reminder: don't switch while the engines are running unless you are sure that the wiring is so that the alternator is always connected to some battery bank.

The voltage regulator will supply enough regulated power when running some rpm's but when it drops to idle, the battery is supposed to work like a temporary source of power to keep it running. Not all (most not) regulators/alternators are designed to not fail when there is nothing to regulate. Not sure how it works when your battery fails while running the engine though.

Anyway, don't go flicking that main switch with the engines running untill you are sure that it's not going to break expensive things.

[Viper]

Unless it's a very old switch or one not designed for marine applications, selector switches should have writing on them warning you not to change positions with the engines running. Having said that, the newer designs that came out as of maybe 20 years ago incorporate a "make before break" contact sweep that allows you to switch positions with the engines running. In these, there is never a break in electrical flow. You should first confirm the type of switch you have so you know how to operate it properly.