Had a bit of time on my hands this afternoon so I reviewed all the comments from everyone and then designed a fully automatic switching system for 3 batteries (one engine battery, two house batteries) for 12 / 24 volt operation and allowing ALL batteries to be combined for engine starting and battery charging. Note: This assumes you have a real charging system, not a stator low amperage system. It will still combine the batteries for starting purposes but stator output is very limited for charging.
I've tried to design the system to be extremely safe and have used Sealed Solenoids there by meeting ABYC and USCG requirements for "ignition protected". These solenoids are sold by many Marine distributors and you can buy them from your favorite distributor but I've found a cheaper source. For those that feel the desire to check the specs. on them I will also provide a link to it. Note: Solenoids should be mounted vertically with the coil terminals on top as shown in the diagram.
If you are the nervous type or just like going to the back of the boat to switch things around you can replace Solenoid 3 (S3) with an off the shelf Perko style On/Off switch. Simply remove the coil wiring and connect the load leads to the Perko switch.
A bit about safety, many had issues with using solenoids and/or relays to do the switching asking "what if" this or that fails. If you study the diagram you will see that S3 can NOT energize (completing the circuit to tie the batteries together) unless both S1 and S2 have changed state. Turning on the ignition switch of the boat powers the solenoid coils of S1 and S2 and only after they change state does S3 have coil voltage applied. That happens in the blink of an eye time wise, unless there is a fault. Additionally note there is a fuse between House batteries and the rest for the circuit. Should a space born meteor fall from the sky and destroy a solenoid and melt all the wiring into a molten mess, the fuses would blow and break the circuit. I spec. a 200 Amp Fuse based on using three batteries during engine cranking. This is a ANL ignition protected fuse that has a time delay for current "in rush". (Made by Blu Sea - Sold by many)
Additionally I have included a Buck Booster to supply 12 volts to lights, fish finder, etc. that draws it's power from the house batteries and / or the alternator when the engine is running. It's advantage is that it places it's load on BOTH house batteries regardless of being in 12 volt or 24 volt mode AND prevents uneven discharge and wear associated with tapping a single battery. The booster can handle 8 amps continuous and 10 amps "surge". I know some might consider that over kill and for those folks it can be taken out of the circuit and simply tap House battery 2 for 12 volt supply. Do NOT tap House battery 1 for this purpose!
I welcome any and all comments and if it meets with everyone's approval I'd like to see this post made a "sticky" instead of having to go look for it each time it's needed.
Just in case Photbucket goes away I'm including the drawing as an attachment.
I've tried to design the system to be extremely safe and have used Sealed Solenoids there by meeting ABYC and USCG requirements for "ignition protected". These solenoids are sold by many Marine distributors and you can buy them from your favorite distributor but I've found a cheaper source. For those that feel the desire to check the specs. on them I will also provide a link to it. Note: Solenoids should be mounted vertically with the coil terminals on top as shown in the diagram.
If you are the nervous type or just like going to the back of the boat to switch things around you can replace Solenoid 3 (S3) with an off the shelf Perko style On/Off switch. Simply remove the coil wiring and connect the load leads to the Perko switch.
A bit about safety, many had issues with using solenoids and/or relays to do the switching asking "what if" this or that fails. If you study the diagram you will see that S3 can NOT energize (completing the circuit to tie the batteries together) unless both S1 and S2 have changed state. Turning on the ignition switch of the boat powers the solenoid coils of S1 and S2 and only after they change state does S3 have coil voltage applied. That happens in the blink of an eye time wise, unless there is a fault. Additionally note there is a fuse between House batteries and the rest for the circuit. Should a space born meteor fall from the sky and destroy a solenoid and melt all the wiring into a molten mess, the fuses would blow and break the circuit. I spec. a 200 Amp Fuse based on using three batteries during engine cranking. This is a ANL ignition protected fuse that has a time delay for current "in rush". (Made by Blu Sea - Sold by many)
Additionally I have included a Buck Booster to supply 12 volts to lights, fish finder, etc. that draws it's power from the house batteries and / or the alternator when the engine is running. It's advantage is that it places it's load on BOTH house batteries regardless of being in 12 volt or 24 volt mode AND prevents uneven discharge and wear associated with tapping a single battery. The booster can handle 8 amps continuous and 10 amps "surge". I know some might consider that over kill and for those folks it can be taken out of the circuit and simply tap House battery 2 for 12 volt supply. Do NOT tap House battery 1 for this purpose!
I welcome any and all comments and if it meets with everyone's approval I'd like to see this post made a "sticky" instead of having to go look for it each time it's needed.
Just in case Photbucket goes away I'm including the drawing as an attachment.
