I'm thinking of doing a small-scale Solar off-grid setup 1-2 80 Watt panels with a 12v 40Ah Deep Cycle battery. I have questions for those parts in another thread, but for now, my question is about understanding what to look for in a battery controller. Kindly see the example on this link.

I will copy paste the specs written:

  1. Technical date SMR05
  2. Nominal voltage 12V/24V, automatic recognition
  3. Max solar current or load current 5A
  4. Over charge voltage14.6V/29.2V
  5. Over charge release voltage 14.0V/28.0V
  6. Over voltage protection 15.6V/31.2V
  7. Load disconnect voltage 10.5/21V
  8. Load reconnect voltage 11.5V/23V
  9. Over voltage protection 15.6V/31.2V
  10. Lighting hours 0-18hours
  11. Night/day detect 3.0-7.5V/6.0-15.0V
  12. Battery type Liquid,Gel
  13. Max solar voltage 55V
  14. Max battery voltage 40V

Kindly correct me on my understanding of this specs:

  1. Model
  2. The battery to be putted can either be a 12 volt or 24 volt?
  3. the solar panel's current can not exceed 5A (Solar panel in Parallel should not total over 5A)?
  4. 14.6V for 12V is the indicator that the battery is 100% charge?
  5. 14.0V is the time where the controller will pass the excess energy to the Load?
  6. Protection for the battery.
  7. If the controller detect the drop of v taken from the panel is at 10.5, the load part will be disabled? Or if the voltage drops at 10.5 the controller will not charge the battery?
  8. Battery will charge at 11.5V? or the Load (excess energy) will be re-activated?
  9. ??
  10. ??
  11. ??
  12. ??
  13. ??
  14. ??

2 Answers 2

  1. Yes
  2. Yes
  3. Yes, plus the maximum current sent to charge the batteries is also 5 A.
  4. The charger will cut out charging at 14.6V to avoid overcharging the battery, and...
  5. ... Will start up again once the battery voltage has dropped back to 14.0 V
  6. Will disconnect the load if the battery goes above this (in case someone's done something stupid and is trying to feed power back in to the controller's output)
  7. Will disconnect the load if battery voltage goes below this (to prevent the battery being completely discharged)...
  8. ...and will reconnect again once it rises above this value
  9. Copy of 6.
  10. Not sure.
  11. My guess is that it only turns on the output when the solar voltage drops below this - presumably so that lights are turned on when it gets dark.
  12. Two different types of lead-acid battery. "gel" are safer because the acid electrolyte doesn't spill if the battery is dropped/knocked over.
  13. Max voltage of solar panels. Going over this is liable to damage the controller.
  14. Max voltage of batteries. Going over this is liable to damage the controller.

Looks like a David Smith has them all except number 10 which is a feature in some solar controllers where they allow you to connect a load (usually 12 volt lighting) directly to the solar controller. Number 3 tells you that the solar panel can't be over 5 amps, but also if you connect a load to the solar controller it can't draw more than 5 amps either. So number 10 says that it can automatically turn on and off the lights that you have connected to the solar battery controller. Not only can it turn the lights on an off, but you can set the number of hours (0-18) that the lights or other load will be on. I don't know a lot of people who use that feature but it can be useful.

If you plan to use that feature, then you want #7 to be adjustable so that you can set it to disconnect the load before the battery is 100% discharged, or you will ruin your battery quite quickly. 10.5 volts is essentially 100% DEAD for lead acid.

  • \$\begingroup\$ from what I understand, the Load is where the controller sends the excess power from the solar panel. does the Load also acts as a passthru in case there is no power from the panels? \$\endgroup\$
    – Mr A
    Mar 24, 2015 at 4:12
  • \$\begingroup\$ @MrA - I can't speak for your specific model, but the three solar battery controllers that I use all have the 'load' function. The load option functions the same on all of them. It provides a limited amount of current at 12 volts as long as the battery is above the voltage as specified in number 7. If the voltage goes below the specified voltage it cuts off the current until the batterry's voltage raises back up to what is specified in #8. It will provide current at 12 volts regardless of what the solar panel is doing as it takes the current directly from the battery. \$\endgroup\$
    – Filek
    Mar 24, 2015 at 7:50

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