Battery disconnect switch

[Oysterr51]

My friend has a sailboat with an electrical switch and he asked me to help with the connections. We are both new to this... The switch has three connections, and four positions. Off, 1, 2, 1&2. <br /><br />I am thinking that it will be for batteries, and disconnects. The boat is a 24 foot sailboat, and has presently only one deep discharge battery onboard. He has a Nissan electric start 8 HP (I think 8) that can also charge the battery. The electric start pushbutton is built into the motor, so I imagine the battery power to start, and the battery charging power from the motor generator come through the same heavy duty wire. (What size wire should it be?)<br /><br />Shore power presently is separated from the batteries, and is only connected if a battery charger is plugged into a 110 plug.<br /><br />With only one battery, how should the disconnect switch be wired? With two batteries, how should it be wired?<br /><br />I am the electrician, so I understand the process, but am not sure how it needs to be hooked up. <br /><br />Thanks so much, Mike

 

[DJ]

Re: Battery disconnect switch

The only thing a battery disconnect switch does is break one leg of a circuit. Whether you wire it to break the positive or negative circuit is up to you.<br /><br />In other words, as an example, you have a negative battery cable going to one side of the switch and continue that cable on the other side. Thus, you allow the switch to connect or break the circuit.<br /><br />The wire for the outboard should be about 6 or 8 guage.

 

[Oysterr51]

Re: Battery disconnect switch

OK, thanks for that. I think what we should do then is keep all the positive loads including the positive line to the motor connected to terminal 1, and then run positive from one battery to 2, and positive from the other battery to 3. <br /><br />This will then allow him to charge or discharge either battery or both or completely isolate either battery as required.<br /><br />What he wanted to be able to do is to have essential things like sounder/GPS and VHF radio always available, and other loads like water pumps and interior lights disconnected, but I am thinking that he should just have a panel of fused on/off switches for these different loads.<br /><br />Does that sound correct?

 

[DJ]

Re: Battery disconnect switch

Without knowing how your switch connects internally, I can't answer your question as to what posts to put them on. However, you have the right idea.<br /><br />If #1 connects to # 2 internally, your idea is correct. You are simply breaking the positive circuit.<br /> <br />Be aware that you probably should not switch the positions while the engine is running. Some switches have alternator protection and some do not.

 

[--GQ--]

Re: Battery disconnect switch

Originally posted by MikeDD:<br />[QB] OK, thanks for that. I think what we should do then is keep all the positive loads including the positive line to the motor connected to terminal 1, and then run positive from one battery to 2, and positive from the other battery to 3. <br /><br /><br />OK now I am confused. You have a selector switch with 4 positions: OFF, 1, 2, 1&2. You can not add on a third battery with this configuration unless you parallel two together. In which case defeats the purpose of having three batteries.<br /><br />With the selector switch on position 1 means the power is being provided by battery 1. position 2 means power is supplied by battery 2. When the selector switch is on position 1&2, the power is being supplied from battery 1 and 2. Which means they are connected in parallel via the selector switch. A third battery is not possible<br /><br />Again can you be more specific on what your friend have in mind. Does he want a specific battery for all the accessories and the second battery for all others?

 

[--GQ--]

Re: Battery disconnect switch

 

[Silvertip]

Re: Battery disconnect switch

Please do not switch ground on a boat! You don't do it in house wiring and it should not be done in a boat either. The COM (common) terminal on the switch should feed all of the loads including the positive cable that leads to the engine start solenoid. The engine negative cable connects from the engine block to the negative terminal on either of the batteries. Additionally, both batteries must have their negative terminals tied together as this is the "System Ground". The positive terminal on each battery connects to BAT 1 and BAT 2. Obviously if you have only one battery, you can pick which terminal to use. If there is no battery connected to BAT-2 that position is empty and you have no lights, no engine start, no charging. The way this works is in the OFF position all loads are disconnected from any of the batteries. In the BAT 1 position, BAT 1 is the source. In the BAT 2 position it serves as the source. in the BOTH position both batteries are paralleled and both serve the loads. Here is how you should operate the switch. Storage/docked = OFF. Start = BAT 1, BAT-2 or BOTH. Engine Run = BOTH (for charging). At anchor = switch from BOTH to BAT-1 or BAT-2 to prevent both batteries from being discharged. CAUTION: DO NOT switch positions with the engine running UNLESS this switch is a "make-before-break" design. Doing so will fry the rectifier in the engine in a heartbeat. Additionally, the 8 HP engine does not have sufficient output to replenish one much less two batteries in a short run at moderate throttle. It's output is rated at wide open throttle and it would take hours to recharge both batteries if they were deeply discharged. It very likely has a 6A alternator or in that ballpark. A couple more items to consider. The 12V output from the shore power should connect directly to the batteries or they would not charge with the switch OFF. Bilge pumps should also be wired directly to one battery. Wire sizes used to connect the switch to the batteries must be no smaller than the battery cables feeding the starter on the engine.

 

[DJ]

Re: Battery disconnect switch

So, you want to take wiring advice from a guy that goes by the name "Upinsmoke"? Just kidding, I couldn't help it.<br /><br />Actually his explanation/advice was very good, as usual.

 

[Silvertip]

Re: Battery disconnect switch

I thought about "Neverblewafuse" as a user name but that would be a lie so why not tell the truth and have some fun. Anyone who has ever messed with electricity and says they never made smoke or sparks in the process is a liar or not been on the job long enough to screw up. You would have loved to see my Dads electrical tester. It was the stub of one finger lost in a childhood accident which is another story. He'd stick that stub in a light socket, radio, or whatever didn't work. Apparently the nerve endings in that short finger allowed him to sense the presence of electricity but not at full force. He was good for anything up to 110V AC. It was great to hunt with him. Approaching a fence in farm country was always a challenge. Was it electrified or not? Hey Dad - stick your finger on the fence! Sorry for getting off-topic. You folks aren't the only ones to rib me about the name. Humor is good for the soul.