Engine DC Power On/Off Switch - What does it do?

[SkuffedKeel]

Hello everyone,

I'm still learning my first boat and I'm struggling to understand what this Engine DC Power switch does, and whether it should ever be switched to the OFF position. I've gone through the manual but can only seem to find reference to the Main Battery Select switch.

I believe I understand the Main Battery Select, but please correct me if I'm wrong.

When the engine is running or on shore power:

If set to 1 then only the house bank will be charged
If set to 2 then only the starter battery will be charged
If set to both then the house bank and starter battery will be charged

When the engine is not running and I'm not connected to shore power:

If set to 1 then only the house bank will be used to run the accessories
If set to 2 then only the starter battery will be used to run the accessories
If set to both then the house bank and starter battery will be used to run the accessories

If set to both when starting the engine, will both the house bank and starter battery be used to start it?

So, going back to the reason for my post (assuming everything above is correct) would switching the Engine DC Power to off stop the engine/alternator from charging the batteries, and, if this is the case, would the alternator not be damaged if I started the engine with it in the off position?

Thank you in advance!

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[KenKrawford]

I'm assuming you have the factory configuration of two 4D batteries. You can designate either battery (1 or 2) as your house or start battery. I noticed that my batteries were wired backwards at the factory. The best way to check yours is to disconnect the positive cable from the battery you think is the #1 (in your case "House") and then check voltage on the electrical panel meter with the switch in the number 1 position. If you get a reading of around 13vdc then you know the batteries are wired as designated. Otherise you will need to switch the positive cables or rewire the connection on the panel meter.
I agree with your battery assumptions but you don't want to EVER turn either selector switch to OFF with the engine running. You will fry the diodes in the alternator. You cannot start the engine with the Engine DC Power switch in the off position because there isn't any power available to turn the engine over.
Unless you're going to install a third battery as a dedicated starting battery, it is usually suggested that you not continuously use the same battery as the "house" one. This battery is usually subjected to most of the drain on a boat whereas the "start" battery is only used for a few seconds. Some people switch their batteries to "1" on odd numbered days of the calendar and to "2" on even days. This helps equalized the demands of each battery.
I chose a different path on my boat. In installed four 6V golf cart batteries and mades them one large 420 amp hour "house" circuit. I then added a group 26 12vdc battery and wired it as battery #2 and save it as a backup starting battery if the house circuit isn't enough to start then engine. So far, this has never happened.
Sorry for the long, rambling reply.

[SkuffedKeel]

Ken, I appreciate the long reply! Haha.

I should have stated in my original post that I have a dedicated 12 VDC Discover type EV4DA-A, 1190 mca starter battery and 2 x 12 VDC FullRiver type DC210-12, 220 amp hr. batteries for the house, according to the survey.

From what I'm gathering though, the Engine DC Power switch should remain in the on position, unless i'm doing electrical related work on the engine and don't want to get zapped.

[Olivia Mae]

What Ken said. I'll add a couple of things.

Yes, leave the dc switch on any time you think you may need the motor. I leave mine on at anchor, just in case. At the marina, I shut it off, especially when we leave the boat.

Considering your battery configuration. It appears it is set up like I did mine, with one bank set as an emergency start bank (just there in case), although your battery is more than you would actually need for this. So you could run everything, including starting, off the main house bank knowing you have a fully charged emergency battery if needed. That said, you should spend some time tracing how your charging is run to the banks. With mine, I have all charging (solar, engine, and shore power) routed to the house bank. I then use a combiner to charge the emergency start battery from there. That way it is always charged. The way the boat is set up from the factory, the only way to charge both banks at the same time is to set the battery switch to both. You could also switch between your banks and use bank 1 then bank 2 as needed but I don't see the point when the larger house bank is all you'll likely need day to day.

[D&M]

Agree with Olivia Mae,
Always switch off the engine start battery when away from the boat. This shuts off 12 volt power to the pedestal and thus you cannot have the problem of a 12v wire being chafed and putting a constant voltage into the steering chain/rudder and you won't have your rudder fall off! Belt and braces. The switch is in line between the start and house batteries and the starter/alternator if wired as per factory. (From the C terminal of 1,2,all.)

Of note, I installed 2x200 amp lithium batterys for the house and the 1,2,all switch is not connected to the start battery. The start battery connects only to the DC to DC charger which then provides charge current to the house bank three minutes after engine start.

[SkuffedKeel]

Thank you everyone for the great information! Having a place to come to where people know "my" boat is a godsend