Just purchased a back up starting battery which I would like to hook up to the main starting battery for "just in case". I thought of running one cable neg to neg and the other pos to a battery switch then to pos. This way, I could turn on the spare only when needed. By the way, these are totally issolated from the house ones. Anyone know if this is a good way to do it? Thanks, Bob C 30 3634 Windborne Westbrook, CT
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Not quite....
I think what you need to do is hook you the negitive like you said, but then take both positives to a switch, and the common output from the switch would then go to your engine. The problem I see is that unless you keep the switch in the both position once the engine is running, the second battery won't charge. You could get around that by a bank charging combiner, and then you could keep the switch in the "1" position and only bring the second battery on line when you needed it. Hope this helps, Steve
I think what you need to do is hook you the negitive like you said, but then take both positives to a switch, and the common output from the switch would then go to your engine. The problem I see is that unless you keep the switch in the both position once the engine is running, the second battery won't charge. You could get around that by a bank charging combiner, and then you could keep the switch in the "1" position and only bring the second battery on line when you needed it. Hope this helps, Steve
STARTING BATTERY
Bob: I partly agree with Steve but with the following caviat: If you add a "starting" battery in parallel to the existing house batteries, you are simply creating a single battery with greater capacity. Not a bad option but if you want a "get home" battery, you do need to add a switch like Steve memtioned. Not only that, but unless you add some sort of isolator or even combiner, current will flow from one to the other...more fully charged to lesser charged. An isolator with ON/OFF switch will allow you to hold the starting battery in reserve until/unless needed, keep the batteries totally separate but still charge that battery when you are running the engine or using the battery charger. There are several good books about charging systems, including Nigel Calder's "BOATOWNER'S MECHANICAL AND ELECTRICAL MANUAL" (best around) and the "12 Volt Doctor's Practical Handbook." Unless you are an expert on DC power systems (I sure the heck aren't!) I'd highly recommend you refer to them before putting in your starting battery. Good luck! Tim Leighton S/V "Magic" C-400
Bob: I partly agree with Steve but with the following caviat: If you add a "starting" battery in parallel to the existing house batteries, you are simply creating a single battery with greater capacity. Not a bad option but if you want a "get home" battery, you do need to add a switch like Steve memtioned. Not only that, but unless you add some sort of isolator or even combiner, current will flow from one to the other...more fully charged to lesser charged. An isolator with ON/OFF switch will allow you to hold the starting battery in reserve until/unless needed, keep the batteries totally separate but still charge that battery when you are running the engine or using the battery charger. There are several good books about charging systems, including Nigel Calder's "BOATOWNER'S MECHANICAL AND ELECTRICAL MANUAL" (best around) and the "12 Volt Doctor's Practical Handbook." Unless you are an expert on DC power systems (I sure the heck aren't!) I'd highly recommend you refer to them before putting in your starting battery. Good luck! Tim Leighton S/V "Magic" C-400
Starter Battery
I just installed one yesterday. I use the 1-2-both switch. Battery one (house) is two deep cycle 27s wired in parrallel to make one huge bank. Battery 2 (starting) is a 900 cold cranking amps battery. It was very easy to do. When the battery is in the both position, all batteries are charged by the engine. When anchored, simply switch to battery 1 and keep battery two as a backup. Sean
I just installed one yesterday. I use the 1-2-both switch. Battery one (house) is two deep cycle 27s wired in parrallel to make one huge bank. Battery 2 (starting) is a 900 cold cranking amps battery. It was very easy to do. When the battery is in the both position, all batteries are charged by the engine. When anchored, simply switch to battery 1 and keep battery two as a backup. Sean
Third Bank?
Bob It seems to me that your description is that you already have two battery banks, one house and one starting, and that you are adding a third bank. Is that right? If so, you'd need to wire the "extra" backup starting battery so that either one or the other is connected, since you already have the 1-2-Both switch "occupied." But why would you want to do this? If you have space for another battery, why not just add it to the house bank, so that you won't run that bank down, and always save the existing starting bank for your backup? Stu
Bob It seems to me that your description is that you already have two battery banks, one house and one starting, and that you are adding a third bank. Is that right? If so, you'd need to wire the "extra" backup starting battery so that either one or the other is connected, since you already have the 1-2-Both switch "occupied." But why would you want to do this? If you have space for another battery, why not just add it to the house bank, so that you won't run that bank down, and always save the existing starting bank for your backup? Stu
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