Trojan Boat Forum

I have 2 inboard engines, 1 generator, 3 batteries, 1 Guest 1-2-both-off switch. Currently, both engines and house panel are connected to Common terminal, one battery connected to terminal 1 and the other battery to terminal 2 on the switch. The generator is independent and is connected to a separate battery through a Guest on/off switch. Is it possible to change the current configuration, without installing another switch, so at least 1 engine is separate from the house circuit to use it as a starting battery in the event the house battery died? Any suggestions / alternative wiring configurations would be greatly appreciated.

Need a little more information about type of batteries, are the engine/house starting only or is one a deep cycle?
How much house load do you have? Type of boat?
What I have done on my F32 as the house load is part of one engine's wiring is to install a third (deep cycle) battery for my fridge and inverter only.
The other loads of lighting etc on one starting battery is of little concern in the way I boat. My boat has a crossover switch to join both engine starting batteries should one go low. The Genny has it's own battery that is charged by the Genny when it runs. So my three leg charger does engine 1, 2 and house.
I don't need a 1,2, both switch with the crossover.
Downside of my setup is the house battery is not charged by an alternator which does not worry me as my travel days vs anchor days are about 1:4 so I needn't charge my house while running as I'm using the Genny which I run twice a day.

The boat is a 2000 Trojan 400 Express. All 3 batteries are the same deep cycle. House load can be heavy with A/C, fridge, lighting, computers along with radar, chartplotter, vhf. Since the Genny has its own battery, is it possible for me to take either one engine or both engines off the common feed on the 2-1-off-both switch and connect them to the genny Guest on/off switch. Or, if I add a starter battery, can this be connected without adding another switch. Thanks for your input.

I'm confused.... You are talking about 12volt and 120v loads.... Once you are running the engines it is the alternator that handles the 12v load. The Genny handles the a/c 120v loads.
You may be worrying unnecessarily......
Since you have the Genny on its own.... You can always charge the engine/house batteries.
It might be better to invest in a display of your battery voltages to ensure you recharge them before they go below 50% discharge=12.2Volts!

I just wanted to give you run down on how and what we operate. I'm concerned when we're on the hook and the genny fails, which it did on our last over nighter and the batteries had died since we were unaware of the genny failure since it happened in the middle of the night and we slept through the incident. I'm just looking for a solution to avoid the situation from occurring again.

maka lea wrote:I just wanted to give you run down on how and what we operate. I'm concerned when we're on the hook and the genny fails, which it did on our last over nighter and the batteries had died since we were unaware of the genny failure since it happened in the middle of the night and we slept through the incident. I'm just looking for a solution to avoid the situation from occurring again.

Maybe you need some alarms!
Still concerned that part of a night would kill your engine batteries(both?) when presumably most of the 12V load is off as you were asleep.... Which should only affect one engine. This suggests to me you have got weak batteries that only function right when being charged. Have you had them load tested?
You don't use the switch on both do you?
One should have been able to start the non house engine then throw switch to both and start the house engine..... How old are the batteries and are they good quality?
Cheap/low priced batteries are a false economy in my experience. I spent $350 on my house battery in 2007 and it is still doing the job! And I leave it in my boat all winter!

The genset failure should not have caused your batteries to go dead . Unless of course you had lots and lots of your 12 volt stuff on . The fridge may have switch over to 12 volts and the anchor light would be on But that should not kill all your battery's. What else was on ?

I would start with the basics , test all the batteries and make sure they have a good capacity



If your "house loads" include leaving the " lighting, computers along with radar, chartplotter, vhf" on all night while you sleep then you need a VERY large battery bank . And you should have one battery (or more ) that is for starting a engine only , that is completely out of the house circuit .

Leave a radar on can be a battery killer they draw a lot .

Never have the switch on both. The fridge and CO2 detectors were the only things on overnight. I planned on replacing 2 of the 3 batteries before this happened which made me ask my original question. Is it possible to change the current configuration, without installing another switch, so at least 1 engine is separate from the house circuit to use it as a starting battery in the event the house battery died?

The way your describing it with the battery switch on #1 battery #2 would be out of the circuit and when battery #2 is on #1 one would be out of the circuit . So one of the battery soul have been good to go .

So if i am understanding this correctly , it just sounds like bad battery issue .



With that said ,I don't like the idea of both engines sharing the common thermal on this switch . I would have have each engine on its own battery with a on/off switch and use the present switch for the house only ( and as a emergency jump on the all position ). I would have one battery thats a starting battery , the other a duel purpose battery for the house / other engine . Of course a dedicated house bank would be even better in you anchor a lot and use the house battery w/o the gen set going

Could I remove one engine from the 2-1-both-off switch and connect it to the the generators on/off switch to share the genny's separate battery? I will be replacing the two other batteries in the spring. Thanks for all the input, greatly appreciated.

I wouldn't .

I HATE THOSE SWITCHES!!!

I think you're missing something....your question has already been answered though you may not be understanding the logic.

prowlersfish wrote:....with the battery switch on #1 battery #2 would be out of the circuit and when battery #2 is on #1 one would be out of the circuit . So one of the battery soul have been good to go...

It's a matter of load and switch management. As Paul was describing, if you do not leave the switch on "ALL" then one of the batteries/engines would have been isolated and maintained its charge ready to go providing you don't unknowingly have a bunch of stuff hooked up to the other battery somewhere in the circuit. If there is, you need to change that or no amount of switch management will matter and you'll drain both anyway. You already have the ability to do what you're asking. When you get to your anchorage, the switch should be set to the house battery/bank. When you go to start the engines the following day, there are two options; setting the switch to "ALL" will combine the two batteries so you can start off both. The caution is that if one of the batteries is badly drained, the still charged battery will drain into it in the "ALL" position and you may not be able to start off either battery. By switching to the other battery instead that is still charged, you should be able to start both engines depending on how she is wired. Just don't move the switch position while an engine is running unless you are sure it's a "make before break" style of switch. What you need to find out though is how both banks get charged off the alternators if you are switched to either battery #1 or #2. If the alternators are hooked up to the battery side of the switch, then you're fine.

You could change the configuration but you'll need more hardware to do it properly; ideally; one battery per engine and a separate house bank. Each is kept isolated from all others when not being charged. The two engine batteries should have a way to TEMPORARILY connect in case of a dead engine battery. I much prefer a paralleling solenoid controled by a momentary switch at the helm. When your house bank drains, you can't connect to an engine battery, you must charge. A lot of variables to consider, and many different ways to deal with potential problems.

Leave the generator battery alone.

Big D wrote:......providing you don't unknowingly have a bunch of stuff hooked up to the other battery somewhere in the circuit. If there is, you need to change that or no amount of switch management will matter and you'll drain both anyway......

Would I be correct in assuming that you have a bunch of small positive wires hooked up to both batteries? Or are they large battery main cables only? I ask because this is such a common practice. People will hook up accessories directly to the batteries which is a no no, essentially defeating the ability of being able to manage loads through the switch, then wonder why all batteries are dead even though only one was selected.

My view on what the OP has been posting is that the batteries need to be replaced and for some reason he wants to wait till next season, putting those on the boat at risk!!
Another example of poor decision making to save spending $$..... A choice that should never be made on a boat IMHO.