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I have two solar panels: SunWize SW-85P; 85W max power, 5.1A, 16.7V.

I have a charge controller: SOLAR BOOST 2000E.

I have four 12V batteries: two Interstate SRM-24 (couple years old), two CarQuest DP27M (new).

I have a fence energizer: Speedrite 3000 w/ 12V DC power adapter.

What is the best arrangement of batteries for this system? Since the batteries are 12V and the fence energizer requires 12V input, I believe that there is no series arrangement of batteries that is possible. However, what parallel arrangement is best? And in particular, which specific battery terminals should be connected to what?

Thanks.

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  • \$\begingroup\$ Any one of your batteries appears sufficient to run your electric fence, unless you want to run for a week or more without sunlight. \$\endgroup\$ – Jack Creasey Sep 22 '18 at 17:04
  • \$\begingroup\$ Wouldn't this depend on how much fence I have connected (and the degree to which it is shorted to ground)? \$\endgroup\$ – Jean-Paul Calderone Sep 24 '18 at 12:07
  • \$\begingroup\$ No it does not depend on the fence configuration (number of wires or any shorts). The fence generator has a fixed energy pulse into the fence, so the current drawn by the unit does not significantly depend on the load. Read the documentation for the unit. \$\endgroup\$ – Jack Creasey Sep 24 '18 at 15:24
  • \$\begingroup\$ Ha ha, documentation. Good one. \$\endgroup\$ – Jean-Paul Calderone Sep 24 '18 at 16:12
  • \$\begingroup\$ Of course!! I looked at this documentation: speedrite.com/sites/default/files/… …...notice on Page 14 all the specs are there including the maximum current requirement of 340mA. \$\endgroup\$ – Jack Creasey Sep 24 '18 at 16:21
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How often would you expect your fence to go off? Do the cows tend to stay clear after sampling or would it be expected that a large number of animals would periodically sample the fence? Measuring your no-load power consumption and clarifying whether the solar panels are the only source of power or a supplement wouldn't hurt if you want the best possible answer.

I have two solar panels: SunWize SW-85P; 85W max power, 5.1A, 16.7V.

I have a charge controller: SOLAR BOOST 2000E.

I have four 12V batteries: two Interstate SRM-24 (couple years old), two CarQuest DP27M (new).

I have a fence energizer: Speedrite 3000 w/ 12V DC power adapter.

What is the best arrangement of batteries for this system? Since the batteries are 12V and the fence energizer requires 12V input, I believe that there is no series arrangement of batteries that is possible. However, what parallel arrangement is best? And in particular, which specific battery terminals should be connected to what?

You may not use those panels in series with that charge controller, nor the batteries, so you will be connecting your panels in parallel + to PV+ and - to PV- and if they will be exposed to differing levels of light (not in the same location or same direction) you should diode protect the panels to prevent them from becoming loads if diodes are not included in them. Whatever batteries you use will be connected in parallel, and that set connected to the charge controller + to BATTERY+ via an inline 30A fuse and - to BATTERY-.

As far as the batteries to use, you must equalize batteries before you parallel them, meaning connect them with a resistance and allow the voltages to equalize before removing the resistance and connecting them with a low resistance connection. After this the batteries can be charged and discharged as a group. If you are going to parallel them they must be matching chemistry, and lead acid are probably the most tolerant to using unmatched batteries, so long as none of the batteries have failed. That said, best results typically come from matched batteries, so it may be worthwhile to have the older pair reconditioned if you intend to have them matched with the new pair.

If there is no additional line voltage charge available, the power of the solar panels will probably matter more than the size of the battery bank, as the battery bank must simply be sufficient to power the load during the time between charges.

As far as the solar panels, really put some thought into their arrangement. You want them to stay cool, to be hit by the brightest, most perpendicular possible light for the longest period of time possible. Having a shadow on part of the panel can be almost as bad as over the whole panel depending on the series/parallel arrangement of cells inside, so take nearby poles, trees, mountains into account. Depending on your longitude and latitude you should be able to find information on the best direction(NESW) and angle to put your panels at. If you end up mounting panels high up, put some thought in at the start about how you will maintain them. If they're on a pole in a forest/clearing, consider if there is anything you need to add to the pole so that when you need to clean the panels you can safely do so with a ladder without having to uninstall or bring down the panels.

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  • \$\begingroup\$ In practice, the fence is always shorted by something. Maybe it's an animal less than 1% of the time but that leaves varying degrees of vegetation the other 99% of the time. \$\endgroup\$ – Jean-Paul Calderone Sep 23 '18 at 17:27
  • \$\begingroup\$ @Jean-PaulCalderone in that case you would be best to measure the actual power consumption of the unit at steady state and also during an incident/rain \$\endgroup\$ – K H Sep 24 '18 at 7:08
  • \$\begingroup\$ Can you elaborate on "connect them with resistance" and discuss which terminals to connect the load to? Thanks for the info so far. \$\endgroup\$ – Jean-Paul Calderone Sep 24 '18 at 9:47
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    \$\begingroup\$ If you parallel two batteries of unequal voltage, a current will flow between them to equalize their output. If you do this with big low resistance battery cable the current could be quite large and damage the battery, so it is better to put a resistor temporarily in the loop to equalize them at a lower current. Charge both batteries to "equal" voltage, then connect their negative terminals then connect their positive terminals with a 50 watt 10 ohm resistor and leave them until you can't measure a voltage across the resistor. Remove resistor and connect positive poles. \$\endgroup\$ – K H Sep 24 '18 at 9:55
  • \$\begingroup\$ @KH You DO NOT need to connect a resistance between the batteries if you connect them in parallel This is an old wives tale. Any battery fully charged has a terminal voltage below that which would be used to charge it at any significant rate. Any battery that is in a discharged state has a much higher source resistance and is therefore self protecting. Connecting a fully charged and a fully discharged battery together will result in current flow, but it will not be a concern. \$\endgroup\$ – Jack Creasey Sep 24 '18 at 15:28

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