w1ntersun Posted May 4, 2013 Share Posted May 4, 2013 I will try to explain this as simply as possible You have 4 x 100 amp batteries connected in parallel You connect an invertor that draws 100 amps to the end battery. Forgetting losses resistance etc. What is the current drawn in each of the linking cable between batteries and what fuse size should be put in Richard Link to comment Share on other sites More sharing options...
Tracker Posted May 4, 2013 Share Posted May 4, 2013 Not an expert answer I'm afraid, but I would use at least 150 amp rated starter or welding cable to link all four batteries, preferably with crimped terminals, and I would draw the inverter power from the positive of no 1 battery and the negative from no 4 battery so that all four work equally. Site the inverter as close as is a sensible location to the batteries as power loss in a 13 amp ac cable is a lot less than in 12 vold dc cables. Switch the inverter off when not in use as many of them take 12 to 24 watts just on standby and will flatten your batteries if left on. Link to comment Share on other sites More sharing options...
w1ntersun Posted May 4, 2013 Author Share Posted May 4, 2013 Hi, Thanks for the answer but its a hypertheticle question. A school science teacher said it dosn't matter where you connect the invertor and that the current is equal on all cables. Richard Link to comment Share on other sites More sharing options...
Tracker Posted May 4, 2013 Share Posted May 4, 2013 w1ntersun - 2013-05-04 10:59 AM Hi, Thanks for the answer but its a hypertheticle question. A school science teacher said it dosn't matter where you connect the invertor and that the current is equal on all cables. Richard I'm don't have enough knowledge to say he/she is wrong but would you trust a hypothetical teacher to wire up your van! Link to comment Share on other sites More sharing options...
crinklystarfish Posted May 4, 2013 Share Posted May 4, 2013 Think of the 4 batteries as made up of 6 parallel cells each (which they are), so in effect the bank is 24 cells. All should become clear... Link to comment Share on other sites More sharing options...
hallii Posted May 4, 2013 Share Posted May 4, 2013 The current in a circuit will always be the same. So if connected as "Tracker" suggests there will be a circuit and the current will be equal at any point within it. If both connections were made at say, battery 1 then the other batteries are not part of the circuit so different currents would be found depending where the measurement is taken. It's because cables have resistance, no matter how thick they are, so will affect the current/voltage. Even if connected properly each battery will not be exactly the same as it's neighbour so will have a slightly different output under load. Tricky stuff this electrickery! H Link to comment Share on other sites More sharing options...
sshortcircuit Posted May 4, 2013 Share Posted May 4, 2013 The fuse must be rated under the current carrying capacity of the cable Link to comment Share on other sites More sharing options...
Andy_C Posted May 4, 2013 Share Posted May 4, 2013 w1ntersun - 2013-05-04 10:59 AM Hi, Thanks for the answer but its a hypertheticle question. A school science teacher said it dosn't matter where you connect the invertor and that the current is equal on all cables. Richard I think he's wrong. The current will be equal in all of the battery linking cables only if each battery's +ve terminal was taken to a single +ve connection point, each -ve terminal was taken to a single -ve connection point, and the inverter was connected to those single connection points. Ignoring differences between batteries, battery internal resistance, resistance in cable and connections, etc, each battery would be supplying 1/4 of the current drawn by the inverter. So for a 100A load each battery would supply 25A. For a parallel connected battery bank, connected in the way you describe, with the load connected to battery 4, the current in the connecting cables would be: 1 > 2 = 25A, 2 > 3 = 50A, 3 > 4 = 75A, 4 > Load = 100A The trouble is this doesn't happen in real life! See: http://www.smartgauge.co.uk/batt_con.html Andy Link to comment Share on other sites More sharing options...
Tracker Posted May 4, 2013 Share Posted May 4, 2013 Andy_C - 2013-05-04 12:53 PM The trouble is this doesn't happen in real life! See: http://www.smartgauge.co.uk/batt_con.html Andy Method two for two batteries and method three for three batteries was how I was shown to do it by an experienced auto electrician some years ago - and I see no reason not to follow those methods. Link to comment Share on other sites More sharing options...
w1ntersun Posted May 4, 2013 Author Share Posted May 4, 2013 Hi, Thanks Andy thats exactly the link and answer I was looking for Richard Link to comment Share on other sites More sharing options...
Airstream Posted May 5, 2013 Share Posted May 5, 2013 Hi, Andy C's answer is 100% correct the rest 100% wrong Ray Link to comment Share on other sites More sharing options...
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