[PSUBS-MAILIST] Battery Question

[Sean T. Stevenson via Personal_Submersibles]

As far as battery interconnections are concerned, in the absence of a battery / cell management module, it is next to impossible to ensure that individual battery voltages stay balanced. That said, you can minimize the potential for unbalance by making sure that your parallel batteries are connected cross-string, instead of to the terminals of one battery in the parallel bank. By this, I mean make the positive connection to the first battery in the parallel string, and the negative connection to the last battery in the string.  As far as the series connections go, there is only one way to hook it up, but you can minimize the unbalance by ensuring that every battery is of the same type and capacity, and of the same age (I.e. replace all batteries simultaneously). Also, try not to tap off of a lesser number of batteries if you need a lower voltage for some purpose - instead, use a DC-DC converter powered by the entire string.

As for charging, see if a recommended charge curve is provided by your battery manufacturer, and source an appropriate charger. The specs you listed are straightforward: maximum 2.4 Volts per cell (Implying 14.4 Volts max for a 12V battery) during charge, with nominal charge voltage 2.35 V per cell (14.1 V on a 12V battery. Once charged, the float voltage must drop to 2.25 - 2.3 Volts per cell (13.5V - 13.8V on a 12V battery).  For a 24V system, you would double these values.

The maximum ripple spec has to do with the quality of the rectifier output. A good quality charger will have circuitry to create more pulses per AC cycle and smoothing capacitors on the output side to better approximate a DC output. The ripple is the distance between minimum and maximum peak amplitudes on the "DC" output side.

Sean


On June 17, 2016 4:53:35 AM MDT, James Frankland via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> Hi All
>
>Could anyone give me a hand with a battery charging question.  It
>sounds
>simple enough but I seem to be getting conflicting advice all over the
>place.
>
>How do I charge my battery banks correctly?
>
>I have just spent a lot of money on a brand new set of batteries and I
>don't want to charge them incorrectly.
>
>The batteries are WING ESL 55-12.  AGM
>12v
>55ah
>
>On the sheet it gives charging instruction.
>
>Float 2.25 - 2.30 VPC @ 25deg C
>Cycling 2.35 @ 25deg C
>Max 2.4 VPC Max Ripple 0.05C (A)
>
>This seems straight forward enough for a single battery, but I have
>them
>configured as a bank which seems to be where the issue lies.
>
>2 pairs in parallel, then the 2 pairs joined in series to give 24v.
>
>I will have to charge them as a bank through the 24v output terminals.
>
>I will add the spec sheet of the batteries.  Hope it gets through.
>
>Any advice appreciated.
>
>Regards
>James
>
>
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>
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