Anyone see a problem with the following wiring? I wanted a back-up starter battery, not one only available if I swapped the current battery with the back-up, but one which I could have available "on-line" by merely throwing a switch. So, I bought a switch which has positions for "on" for battery #1, "on" for battery #2, both "on", or both "off"). I wired each of the two batteries, via their postive terminals, to separate posts on the switch: one post to receive each battery's positive wire. The switch's third post("common") is attached to the wire which had run to the positive terminal on the original battery. Also, I wired the two batteries' negative posts together (not through the switch) for the ground, leaving the orignal battery's ground wire in place. I have a photo/diagram of this wiring which I can email anyone for further explanation. (It's a photo, but I don't know how to attach it to this message). Anyone see a problem in this wiring?
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If I understand correctly you
had one battery and now you have added a second one and a battery switch. Setup seems OK but bear in mind that when the the switch is on bat #1 or bat #2 that is the only battery being recharged by the engine and when the switch is on "both" you no longer have two independent batteries but just one larger one. The proper way to use them is to alternate their use on #1 and #2 to keep both charged and one always in reserve. "Both" should be used only for a short time to give an emergency starter boost.
had one battery and now you have added a second one and a battery switch. Setup seems OK but bear in mind that when the the switch is on bat #1 or bat #2 that is the only battery being recharged by the engine and when the switch is on "both" you no longer have two independent batteries but just one larger one. The proper way to use them is to alternate their use on #1 and #2 to keep both charged and one always in reserve. "Both" should be used only for a short time to give an emergency starter boost.
Interesting
Benny, I think Jim already has a house bank. This is an independent starting circuit, using two batteries and a 1-2-A-Off switch of its own. Sounds right. But how will you charge them?
Benny, I think Jim already has a house bank. This is an independent starting circuit, using two batteries and a 1-2-A-Off switch of its own. Sounds right. But how will you charge them?
Benny, not necessarily true
MOST boats have their alternators wired to the C post of the 1-2-B switch, so you'd be right. IF, however, the boat was enhanced, and the alternator output was (correctly) moved to the house bank and a combiner or echo charger (or another switch for emergency battery combination) was added, then that would NOT be the case, because the ONLY connection to the C (B) post would be the output to the DC panel. Because of the newer and improved techniques of wiring boats to maximize energy charging, we should all be careful about how we put what we say, because the "good old days" are (thankfully) over.
MOST boats have their alternators wired to the C post of the 1-2-B switch, so you'd be right. IF, however, the boat was enhanced, and the alternator output was (correctly) moved to the house bank and a combiner or echo charger (or another switch for emergency battery combination) was added, then that would NOT be the case, because the ONLY connection to the C (B) post would be the output to the DC panel. Because of the newer and improved techniques of wiring boats to maximize energy charging, we should all be careful about how we put what we say, because the "good old days" are (thankfully) over.
Issues, and more info need.
Need more info: is there also a house battery, and if so, how is it wired? Assuming there is not, and this is the only battery system on board, there is a serious problem with this topology. First, I don't know what "most boats" have, but wiring the alternator to the common terminal is a mistake, unless the battery selector switch is of the special type that has an alternator field disconnect switch. Without it, if you select "OFF" while the engine is running, you will destroy the alternator rectifying diodes. Without addition equipment, it would be best to connect the alternator output to one of the batteries, say batt. 1; connect the load, starter or all loads, to "COMMON;" and then wire batteries one and two to switch terminals "ONE" and "TWO." In operation one would start the engine by selecting one or two or both, select both while charging; and select one or two or off when the engine is off, depending on whether you are running loads. "BOTH" would be used if the batteries are a matched pair of house batteries, meaning same type, age, and history. If you already have the house battery issue solved and simply want to add a back-up starting battery, I recommend a battery isolator, or automatic charging relay, and then the selector switch you have to connect the batteries to the load (starter plus engine electrics). This way you could always leave the switch set to "ONE" and both batteries would charge when the engine runs. Bear in mind the isolator will introduce a voltage drop that may result in poor charging unless compensated for. Also, if the boat has a single alternator and it is also used to pump up a big house battery via an external charging regulator, you may damage the starting batteries over the long term; however, the isolator might actually help in this case, dropping the usual acceptance mode charging voltage of 14.2 to 14.4 (temperature dependent) that the starting batts would see down by a 1/2 volt or more, pretty close to the usual float level of 13.8, which most batts can stand forever. This all assumes wet cells. Levels are different for AGM and gelled cells. An echo charger, as someone previously suggested, would work well here, too, 'though you'd still need to get it connected to both starting batts somehow. More information about your boat's electrical system, including any other batteries, would help the analysis.
Need more info: is there also a house battery, and if so, how is it wired? Assuming there is not, and this is the only battery system on board, there is a serious problem with this topology. First, I don't know what "most boats" have, but wiring the alternator to the common terminal is a mistake, unless the battery selector switch is of the special type that has an alternator field disconnect switch. Without it, if you select "OFF" while the engine is running, you will destroy the alternator rectifying diodes. Without addition equipment, it would be best to connect the alternator output to one of the batteries, say batt. 1; connect the load, starter or all loads, to "COMMON;" and then wire batteries one and two to switch terminals "ONE" and "TWO." In operation one would start the engine by selecting one or two or both, select both while charging; and select one or two or off when the engine is off, depending on whether you are running loads. "BOTH" would be used if the batteries are a matched pair of house batteries, meaning same type, age, and history. If you already have the house battery issue solved and simply want to add a back-up starting battery, I recommend a battery isolator, or automatic charging relay, and then the selector switch you have to connect the batteries to the load (starter plus engine electrics). This way you could always leave the switch set to "ONE" and both batteries would charge when the engine runs. Bear in mind the isolator will introduce a voltage drop that may result in poor charging unless compensated for. Also, if the boat has a single alternator and it is also used to pump up a big house battery via an external charging regulator, you may damage the starting batteries over the long term; however, the isolator might actually help in this case, dropping the usual acceptance mode charging voltage of 14.2 to 14.4 (temperature dependent) that the starting batts would see down by a 1/2 volt or more, pretty close to the usual float level of 13.8, which most batts can stand forever. This all assumes wet cells. Levels are different for AGM and gelled cells. An echo charger, as someone previously suggested, would work well here, too, 'though you'd still need to get it connected to both starting batts somehow. More information about your boat's electrical system, including any other batteries, would help the analysis.
house battery is present
I do have a house battery (in addition to the two starter batteries) which is separately wired and has its own on/off switch. I never switch either the original starter battery (with its own on/off switch)or the house battery (also with its own on/off switch) to "off" while the motor is running. The two starter batteries are the same brand, etc., except one is one year older than the other. Both of the starter batteries and the house battery are "flooded", wet cells (i.e., none is gel or AGM). To my knowledge, I have one alternator.
I do have a house battery (in addition to the two starter batteries) which is separately wired and has its own on/off switch. I never switch either the original starter battery (with its own on/off switch)or the house battery (also with its own on/off switch) to "off" while the motor is running. The two starter batteries are the same brand, etc., except one is one year older than the other. Both of the starter batteries and the house battery are "flooded", wet cells (i.e., none is gel or AGM). To my knowledge, I have one alternator.
It is just another battery bank
The fact that you use it for starting only is not important. You could also use it to run the reefer in a pinch to keep the beer cold. Just wire it like a second battery bank. You set up is exacly that if I'm reading you right. Just make sure "one of these things doesen't look like the other" doesen't happen.
The fact that you use it for starting only is not important. You could also use it to run the reefer in a pinch to keep the beer cold. Just wire it like a second battery bank. You set up is exacly that if I'm reading you right. Just make sure "one of these things doesen't look like the other" doesen't happen.
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