|
| Author |
Message |
Skip
|
# Posted: 26 Dec 2010 01:06pm
Reply
I am putting together a 12 V battery bank for a new solar system. I am wiring two 12 V deep cycle batteries together in parallel. Looking at example diagrams from other systems, some show connecting the controller to the positive and negative terminals on the same battery. Others show connecting to the positive terminal on one battery, then the negative terminal on the other battery. Which way is best, and why? THANKS! Skip
|
|
SE Ohio
Member
|
# Posted: 26 Dec 2010 01:28pm
Reply
Please let me know if I'm not reading this correctly. Assuming that the two batteries are wired in parallel (12 V jumpered to 12 V + and 12V - jumpered to 12V -) with sufficient-sized and short-length jumper wires, it should not matter which battery + and - connections are used. If you think the jumpers are a bit small and provide a voltage drop, then attach to + of one 12v battery and - of the other.
You can check this with a volt meter/DMM (DC setting) and check the voltage at each point while the batteries are connected. (MAKE SURE YOU ARE NOT ON AMP SETTING OR YOU WILL DAMAGE THE DMM) You should read the same voltage in each location. If not, check/tighten the connections and try again. Still not the same? you may need to increase the battery-to-battery jumper wire size.
|
|
Skip
Member
|
# Posted: 26 Dec 2010 02:10pm
Reply
SE Ohio: Attached is an image showing the two different wiring options I have found.
In both cases, the two batteries are wired in parallel (positive to positive and negative to negative), with sufficient-sized and short- length jumper wires.
So, if I'm understanding you correctly, either wiring option should work fine (as long as the jumpers are short and of sufficient gauge). Correct?
Thanks for the help! I'm on a steep learning-curve re: electrical.
|
|
maine_island
Member
|
# Posted: 26 Dec 2010 02:16pm
Reply
a diagonal connection is optimal.
if you could wire the batteries in parallel with zero resistance superconductive wire, there would be no difference.
however any practical wire, no matter how stout, will have some resistance, so it is just slightly better to attach the load to different batteries - rather than the same one - because that will better balance the charge and discharge between the two batteries.
this is a second-order effect. it will also work if you attach the load to the same battery. however the battery you attach to will then be called on to supply more power than the other one, which is, in effect, isolated from the load by two very low value resistors - comprised of the two battery leads forming the parallel connection.
the optimal wiring completely balances the arrangement as each battery is attached to the load with only one resistor.
|
|
MtnDon
Member
|
# Posted: 26 Dec 2010 02:45pm - Edited by: MtnDon
Reply
maine_island has it. Diagram 1 is the better way of the two choices presented.
However, the best method would be to use two 6 volt batteries in series eliminating the parallel connections altogether.
You can usually find 6 volt batteries with an amp-hour rating that is about double that of the 12 volt batteries and end up with an equivalent total amp-hour capacity to two 12 volt in parallel.
|
|
Skip
Member
|
# Posted: 26 Dec 2010 03:00pm
Reply
Many thanks to both maine-island and MtnDon!
I was originally considering 6 volt golf cart batteries, but found a hot deal on two commercial-application 12 volt deep cycle batteries.
|
|
SE Ohio
Member
|
# Posted: 26 Dec 2010 04:51pm
Reply
Skip,
Yes, theoretically there is a slight difference in the wiring configuration due to the resistance of the jumpers, but in actual practice it is doubtful you would ever notice the difference. Thus the various wiring diagrams you have seen. If you do happen to take measurements with a DMM, please post your results here.
|
|
Skip
Member
|
# Posted: 26 Dec 2010 05:14pm
Reply
SE Ohio: Will do, and many thanks to you as well!
|
|
|
Skip
Member
|
# Posted: 26 Dec 2010 05:34pm
Reply
One other question: is it OK to put a lead acid battery bank inside the cabin? I understand that lead acid batteries emit hydrogen when charging, so was planning on building an insulated & vented battery box for outside.
|
|
MtnDon
Member
|
# Posted: 26 Dec 2010 05:42pm
Reply
Inside only if the box is acid proof, or lined with acid proof material and is vented from the highest point in the box to the exterior.
The bubbles seen when a battery is charging is hydrogen and oxygen gases. Hydrogen is very light and rises readily to the highest point. The hydrogen is very flammable, explosive.
|
|
Rob_O
|
# Posted: 26 Dec 2010 07:28pm
Reply
Quoting: Skip I was originally considering 6 volt golf cart batteries, but found a hot deal on two commercial-application 12 volt deep cycle batteries.
Like you, I was going to use golf cart batteries but got a great price on factory blem 12V AGM batteries from one of the local car audio guys. I'll be using 4 of them so they will be rotated every month
|
|
PlicketyCat
Member
|
# Posted: 28 Dec 2010 08:36pm - Edited by: PlicketyCat
Reply
We have sealed lead acid batteries inside on a corrosion-proof mat (just in case one cracks). SLAs don't "leak" hydrogen while charging like normal lead acid batteries do, but we still vent the bank box and it's as far from any ignition source as we can feasibly make it... just for safety. Our new system will have AGM, and they are even better/safer than SLAs. I wouldn't want to risk an unsealed lead acid inside the house, way too many opportunities for catastrophe.
Electrical is hubby's domain, but he concurs with maine_island... in any system with two or more batteries, you want to connect the + from the "first" battery and the - from the "last" battery to make sure you even out the load. In our case, we have twelve 12v SLAs wired in 24v -- 6 parallel rows of serial pairs. Left-to-right and top-to-bottom, battery 1 is the + connection and battery 12 is the - connection. All connections are 0000 copper cable, overkill for the short length of run, but almost zero resistance and certainly won't overheat.
|
|
Youngster
Member
|
# Posted: 25 Feb 2011 10:33pm
Reply
Here are some interesting battery bank articles:
http://www.windsun.com/Batteries/Battery_FAQ.htm
http://www.freesunpower.com/battery_designer.php
http://www.sunwindproducts.com/LearningCenter/BatteryBlunders.html
I like MtnDon's battery bank setup:
http://www.small-cabin.com/forum/6_621_0.html#msg4907
|
|
|
