Silvertip
Supreme Mariner
- Joined
- Sep 22, 2003
- Messages
- 28,764
Periodically there is a question that goes like this: I have a 24 volt trolling motor. Can I get 12 volts from this system?"
The answer to that is certainly. Each of the batteries in that system is capable of providing 12 volts if you connect a 12 volt device DIRECTLY to one of the batteries. The following discussion may be hard to get your head around but perhaps the diagrams will help. There is a situation that involves grounding that can bite you if you are not fully aware of how your devices are built the ramifications of how you mount them.
I've provided two diagrams here. The first one shows the way I recommend you wire any 12 volt device in a 24 volts (or 36 or 48 volt system). Note the grounds from the device and BAT 1. They are all at the same potential (interconnected). The ground symbol is added to the diagram to illustrate CHASSIS ground (although the symbol for that is different, most of you should know what the one I show is). Take a motor or radio with a metal shell for example. That motor very likely has the case and the ground wire at the same potential. In this wiring scheme that is not an issue because the negative terminal of the battery AND if by any chance that terminal also is tied in any way to other metal on the boat, it still does not pose any grounding issues. You really need to know if the metal chassis and ground are at the same potential on any 12 volt device. If so, it is a risk. So here is the way I recommend you do this to eliminate the risk.
(Edit: Inserted correct diagram)
Below is a diagram where the same devices are wired to BAT #2. If there are no grounding issues, those devices will work just fine that way. But here the POTENTIAL for disaster is much greater. If, for any reason the metal chassis of any device and the ground lead on that device are common, AND for whatever reason that metal shell OR the ground wire meets the ground buss for this system -- represented by the black line from BAT #1, you just created an instant arc welder. Just look at the dotted lines which point out the direct short. Conditions that can cause this are rare but if they can happen, why provide the opportunity. Wire to BAT #1 to limit that chance. Remember that aluminum hull boats are conductive and are at ground potential via the bolts that secure the engine to the hull. While the starting battery is not tyically part of the 24 volt system, there would not normally be an issue. However, all it takes is the touch of a tool or other metal object between the negative terminal of BAT #1 and the boat hull and NOW they are part of the system. If the radio for example were bolted to the hull, you would be in need for a new one in a heartbeat. I therefore recommend you NOT wire 12 volt accessories this way.
The answer to that is certainly. Each of the batteries in that system is capable of providing 12 volts if you connect a 12 volt device DIRECTLY to one of the batteries. The following discussion may be hard to get your head around but perhaps the diagrams will help. There is a situation that involves grounding that can bite you if you are not fully aware of how your devices are built the ramifications of how you mount them.
I've provided two diagrams here. The first one shows the way I recommend you wire any 12 volt device in a 24 volts (or 36 or 48 volt system). Note the grounds from the device and BAT 1. They are all at the same potential (interconnected). The ground symbol is added to the diagram to illustrate CHASSIS ground (although the symbol for that is different, most of you should know what the one I show is). Take a motor or radio with a metal shell for example. That motor very likely has the case and the ground wire at the same potential. In this wiring scheme that is not an issue because the negative terminal of the battery AND if by any chance that terminal also is tied in any way to other metal on the boat, it still does not pose any grounding issues. You really need to know if the metal chassis and ground are at the same potential on any 12 volt device. If so, it is a risk. So here is the way I recommend you do this to eliminate the risk.
(Edit: Inserted correct diagram)
Below is a diagram where the same devices are wired to BAT #2. If there are no grounding issues, those devices will work just fine that way. But here the POTENTIAL for disaster is much greater. If, for any reason the metal chassis of any device and the ground lead on that device are common, AND for whatever reason that metal shell OR the ground wire meets the ground buss for this system -- represented by the black line from BAT #1, you just created an instant arc welder. Just look at the dotted lines which point out the direct short. Conditions that can cause this are rare but if they can happen, why provide the opportunity. Wire to BAT #1 to limit that chance. Remember that aluminum hull boats are conductive and are at ground potential via the bolts that secure the engine to the hull. While the starting battery is not tyically part of the 24 volt system, there would not normally be an issue. However, all it takes is the touch of a tool or other metal object between the negative terminal of BAT #1 and the boat hull and NOW they are part of the system. If the radio for example were bolted to the hull, you would be in need for a new one in a heartbeat. I therefore recommend you NOT wire 12 volt accessories this way.
