Batteries fully charged?

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Batteries fully charged?

Postby xeastern on Sat Jun 25, 2016 3:38 am

Am installing a FN-DC and am wondering if to comply with the instructions relative to "fully charged", means at the end of an absorb cycle or when the battery bank shows a voltage which is defined by the manufacture as indicating 0 depth of discharge. In my case the difference amounts to approximately six volts.
Thanks for any info.

xeastern
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Re: Batteries fully charged?

Postby SandyP on Sat Jun 25, 2016 4:38 am

xeastern wrote:Am installing a FN-DC and am wondering if to comply with the instructions relative to "fully charged", means at the end of an absorb cycle or when the battery bank shows a voltage which is defined by the manufacture as indicating 0 depth of discharge. In my case the difference amounts to approximately six volts.
Thanks for any info.

xeastern


With SLA batteries I would be looking at what the charging amps going into the battery bank are to determine if you are at/close to fully charged. Generally the end of the absorb charging stage is terminated either by a timer or an "end amps" setting which is 1-2% of the battery banks amp capacity. So, in your case, make sure the charging amps during the absorb stage has decreased to ~1-2% (and this is not due to poor PV conditions) and the battery bank should be close to full.

I presume the 6V difference is that between your absorb charging voltage and the float voltage?
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Re: Batteries fully charged?

Postby xeastern on Sat Jun 25, 2016 6:20 am

Thanks for the reply. I guess what I'm asking is whether or not the manufacturers zero depth of discharge voltage is considered fully charged? The six volt difference mentioned is actually between zero depth of discharge and end of absorb, not the diff between float and absorb. But, like you say, I suppose the best indication would be observing the amp levels and not the voltages. Thanks again....will follow your suggestion.

xeastern
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Posts: 3
Joined: Sat Apr 13, 2013 7:42 pm
Location: St Croix US Virgin Islands
My RE system: 27 Hyundai HiS-S248MG
FP2-10
Hub10
Mate2
FN-DC
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8 6V SunExtender PVX 4050HT AGM's

Re: Batteries fully charged?

Postby xeastern on Sat Jun 25, 2016 6:29 am

Sorry, in reading the literature more closely, the six volt difference would indeed be between float and absorb since the the listed voltage for zero depth of discharge does indeed fall in the range listed for float. Sorry for the confusion!

xeastern
xeastern
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Posts: 3
Joined: Sat Apr 13, 2013 7:42 pm
Location: St Croix US Virgin Islands
My RE system: 27 Hyundai HiS-S248MG
FP2-10
Hub10
Mate2
FN-DC
2 FM80
8 6V SunExtender PVX 4050HT AGM's

Re: Batteries fully charged?

Postby Vic on Sat Jun 25, 2016 1:24 pm

Hi xeastern,

Generally, voltage readings are not a very good way to determine the State Of Charge (SOC) of a battery.

As SandyP mentioned, the Return current or amps is the best measure, for VRLA batteries. Since you mentioned the FNDC, assume that your system has a Shunt in the negative lead of the battery-to-system connection.

Many SLA battery manufacturers specify the Return Amps, or Finishing current. Often for Sealed batteries, this current is quite small, or sometimes stated as a rate-of-change in this current over a period of time.

For VRLA batteries, Resting voltage IS a good measure of SOC, when it is corrected for battery temperature. But on most systems this Resting period of 6 - 12 hours with NO charge and NO discharge is difficult to achieve.

You might look at the SunExtender site for guidance of just what the finishing current, End Amps, or whatever they happen to call it, is.

FWIW, Vic
4/20/08: 18 Shell SQ 175-106 Vmpp, Stacked 5548 SW+, 1350 AH Surrette 4KS25's, MX-60, Kubota SQ-3250 25 KVA Polyphase Diesel genset. Thanks OutBack for this Forum + the great Support and Service.
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