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Old 17-08-2015, 11:23   #1
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Can I tap into a 12v battery bank from multiple points at the same time?

Hey Cruisers!

Quick basic question: can I tap into a 3 battery 12v bank at more than just one +/- point?

Another way of wording it is if I have 3 12v battery's connected in parallel, can I for example hook up my main DC panel to one battery's poles, my small AC inverter to another battery, and my solar charger/battery charger to the third battery?

If so, will this change power output? Wear on batteries? Current or capacity change? Does this change anything at all or am I just tapping into the circuit from more than one point?

Thanks!
Hank
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Old 17-08-2015, 12:04   #2
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Re: Can I tap into a 12v battery bank from multiple points at the same time?

The best way is to connect the three to the POS of the first and the NEG to the last battery in the bank thereby ensuring a balanced draw and recharge across all three.
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Old 17-08-2015, 12:09   #3
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Re: Can I tap into a 12v battery bank from multiple points at the same time?

As long as the batteries are side by side and connected to each other with minimum length high current wires, it won't make any difference. Electrically they are the same.
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Old 17-08-2015, 12:38   #4
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Re: Can I tap into a 12v battery bank from multiple points at the same time?

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Originally Posted by jwcolby54 View Post
As long as the batteries are side by side and connected to each other with minimum length high current wires, it won't make any difference. Electrically they are the same.
Exactly. Assuming that all cables are well connected and ignoring the very small and for all practical purposes, insignificant resistance and voltage drop between the batteries, if they are in parallel then connecting to one battery positive is exactly the same as connecting to any other battery positive.

I have connected the six 6 Volt batteries in my boat the way suggested by S/V Illusion IE pos at one end of the string, neg at the other. However I have read arguments from some marine electronics guys that do know what they're doing that in the average boat this also makes little difference. Since it costs nothing and doesn't create awkward wiring for me I'll just keep doing it this way, just in case.
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Old 17-08-2015, 12:48   #5
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Re: Can I tap into a 12v battery bank from multiple points at the same time?

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Originally Posted by TenaciousH View Post
Hey Cruisers!

Quick basic question: can I tap into a 3 battery 12v bank at more than just one +/- point?

Another way of wording it is if I have 3 12v battery's connected in parallel, can I for example hook up my main DC panel to one battery's poles, my small AC inverter to another battery, and my solar charger/battery charger to the third battery?

If so, will this change power output? Wear on batteries? Current or capacity change? Does this change anything at all or am I just tapping into the circuit from more than one point?

Thanks!
Hank
That is not a good idea. It will make it difficult/expensive to install proper battery fuses and make it impossible to install a shunt for a battery monitor or ammeter. Make sure the paralleling wire is very fat and connect positive in one end (with a proper MRBF fuse) and negative in the other end of the bank.

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Old 17-08-2015, 13:25   #6
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Re: Can I tap into a 12v battery bank from multiple points at the same time?

Here is a link to a diagram showing the proper way to parallel batteries as others have described.

Battery School | Batteriesnorthwest.com | Connect Your Batteries for Optimum Efficiency

There is another link that details why this is important, even for what seems like very short and fat cables, but I'm having trouble coming up with it.
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Old 17-08-2015, 14:22   #7
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Re: Can I tap into a 12v battery bank from multiple points at the same time?

svlamorocha.
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Please allow me to ask why you would fuse the postive side of a D.C. circuit as this is after the load. Electricity comes out of the negative side of the battery. Would it not be better to fuse on the negative side before the load there by protecting it from a over current event?
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Old 17-08-2015, 14:27   #8
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Re: Can I tap into a 12v battery bank from multiple points at the same time?

I use diffent poles so that the gain and draw are evened out and stuff goes in and out of the bank differently.

for example I have a freezer directly connected to the bank. It uses different poles than the main board. Same with the solar and wind, different poles.


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Old 17-08-2015, 14:28   #9
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Re: Can I tap into a 12v battery bank from multiple points at the same time?

Quote:
Originally Posted by hlev00 View Post
Here is a link to a diagram showing the proper way to parallel batteries as others have described.

Battery School | Batteriesnorthwest.com | Connect Your Batteries for Optimum Efficiency

There is another link that details why this is important, even for what seems like very short and fat cables, but I'm having trouble coming up with it.
Here is a different opinion on battery wiring and the benefit or not of connecting the pos and neg wires to one battery vs opposite batteries in the bank. The whole thread is here.

Batteries in Parallel

It is a common misconception despite being perpetuated and mis-quoted frequently.

Its not that voltage differences do or do not exist during starting, but the fact that they are small in comparison to the internal differences in battery impedance. You are going to all that trouble to save 1/10 volt during starting an
engine when in fact the inherent battery parameters are an order of magnitude larger. If they had not been in parallel and you tested each battery for voltage supplied during starting loads, their voltage would differ much more than the minor drops due to wiring layout.

Within a second after starting is completed, the batteries will all be at the same voltage due to battery to battery current so any imbalance only lasted a few seconds. Each battery contributed energy for the starting function but once completed they all are AT THE SAME VOLTAGE so each had contributed its share of the energy that it could release between the initial voltage prior to starting and the rest voltage after starting.

Eventually you took xyz amp-hours out of the battery bank to start the
engine. The net effect of wiring differences boil down to heating loss which again is insignificant. For maximum efficiency the wiring layout should minimize wiring resistance.

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Old 17-08-2015, 15:45   #10
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Re: Can I tap into a 12v battery bank from multiple points at the same time?

I'm in the habit of isolating my starter batt. for startups - I've often wondered if i'm just wasting my time fiddling with switches - in particular, i often forget to switch the house batteries back on so they get some charge. Are there any potential problems from overloading the starter if all batteries are connected? I know that as the old starter started dying, i gradually had to use more batteries to get a turnover.
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Old 17-08-2015, 15:53   #11
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Re: Can I tap into a 12v battery bank from multiple points at the same time?

OK, someone's gotta say it...
Three posts and you fuse the neg because the juice comes out there???
I guess I had better completely rewire my boat !

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Old 17-08-2015, 16:42   #12
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Re: Can I tap into a 12v battery bank from multiple points at the same time?

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svlamorocha.
New guy just guy just joined the other day.
Please allow me to ask why you would fuse the postive side of a D.C. circuit as this is after the load. Electricity comes out of the negative side of the battery. Would it not be better to fuse on the negative side before the load there by protecting it from a over current event?
While it is true that electrons or electronic energy flows from negative to positive, by historical convention, the positive wire is used to feed individual appliances and the negative wires are all connected together, hence the fuses are in the positive cable.....in effect it doesn't make any difference.
Any current flow is caused by the potential difference and the resistance of the appliance, the direction of flow is immaterial to the fuse...
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Old 17-08-2015, 17:08   #13
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Re: Can I tap into a 12v battery bank from multiple points at the same time?

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Originally Posted by senormechanico View Post
OK, someone's gotta say it...
Three posts and you fuse the neg because the juice comes out there???
I guess I had better completely rewire my boat !

IIRC it's because the boat is in the Southern Hemisphere.
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Old 17-08-2015, 17:17   #14
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Re: Can I tap into a 12v battery bank from multiple points at the same time?

Ok just saying operational readyness of the circuit does not care where the fuse is, but the expensive electronics you are trying to protect might. I know A.C. and D.C. are not exactly the same but it is a simular argument the fuse an A.C. circuit on the neutral leg not an acceptable arragement.
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Old 17-08-2015, 19:04   #15
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Re: Can I tap into a 12v battery bank from multiple points at the same time?

Quote:
Originally Posted by charliehows View Post
I'm in the habit of isolating my starter batt. for startups - I've often wondered if i'm just wasting my time fiddling with switches - in particular, i often forget to switch the house batteries back on so they get some charge. Are there any potential problems from overloading the starter if all batteries are connected? I know that as the old starter started dying, i gradually had to use more batteries to get a turnover.
Putting batteries in the circuit, as long as you keep the system at 12 volts will not hurt the starter in any way. In fact it could be beneficial as more battery capacity connected to the starter you will get less voltage drop.

Instead of trying to remember to switch batteries on and off for starting, charging and to isolate the start batteries so you don't accidentally run them down you need to get a battery charge controller like the Yandina Combiner or Balmar Duocharge.
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