Saturday, August 12, 2017

Capacitor Bank

Since I have a number of DC appliances which are using directly both the 12v & 24v supply rails, it was imperative that I make sure that my DC supplies are as smooth as possible, without any spikes and with the least amount of voltage fluctuations.

A list of appliances which are utilizing directly the DC supply rails can be found here. Loads with motors will generate spikes and back-emf. In my case there is the Reverse Osmosis pump and also In Summer I utilize multiple low voltage pumps to circulate water for the pool.

The below image is displaying the capacitor bank / protection devices installed. 

Actually there are 2 separate circuits, a 12v (top board) and a 24v (bottom board). Both circuits are almost identical except for the components working voltages.
The circuits consist mainly of the following components;
  • Large electrolytic smoothing capacitors. When a huge DC load is switched on, this will starve temporarily the DC lines, i.e. due to a higher current demand, the voltage will go down. These large capacitors will smooth this effect.
  • Smaller electrolytic smoothing capacitors with a low ESR (Equivalent Series Resistance). These capacitor also offer a smooth DC voltage when a huge DC load is switched on. The added benefit of a low ESR is better ripple suspension.
  • Non electrolytic  capacitors. These capacitors offer high frequency suspension on the DC lines. (I have installed 4 Battery Desulphators, 2 per battery bank, and since these work by generating high frequency pulses, I though to be safer if I also compensated for these pulses not to reach my appliances).
  • Multiple voltage varistors. Varistors, also known as voltage dependent resistors work by varying their resistance varies with the voltage. In this case, if the DC voltage for the 12v supply reaches 14v+, the varistor will shunt the supply rail thus preventing the supply rail from reaching excessive voltages. Same for the 24v supply, If the voltage tries to exceed 32v+, the respective varistors will shunt the supply rails.
  • Blocking diodes. These diodes are fitted in reverse order thus they will only conduct and will suppress any back-emfs

Parts List:
  1. C1-C3 --> 100,000uF 63v
  2. C4-C8 --> 470uF 50v Low ESR
  3. C9 - 470nF
  4. C10 - 0.1uF
  5. C11 - C13 --> 100,000uF 25v
  6. C14-C18 --> 470uF 50v Low ESR
  7. C19 - 470nF
  8. C20 - 0.1uF
  9. D1 - Orange LED (24v)
  10. D2 - Yellow LED (12v)
  11. D3, D4 - 7amp Diode
  12. R1 - 1.2K
  13. R2 - 2.2K
  14. VAR1 - VAR5 - 32v Working Voltage Varistors
  15. VAR6 - VAR10 - 14v Working Voltage Varistors

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