Question about low-battery cutoff LBCO for Xantrex/Trace SW series

 Running an SW4048 (4KVA 48V system).

I'm trying to figure out the best values for the LBCO (low battery cut
off) Volts and Delay.

It occurs to me, that if the device is providing no power to any load,
then we have a very slow rate of voltage drop in the battery, due to
self-discharge, and "wasted" power in the inverter ( I believe this
inverter consumes about 16Watts) just sitting there idling (unless one
engages the search mode)

In this 'idle' scenario, the battery will eventually reach the LBCO
voltage, and the delay timer (15minute default) will "expire" before the
battery gets much lower.

However, if I'm really loading the system, the battery will go through
the LBCO voltage and keep going, possible quite a bit lower before the
timer expires.

Granted, one should never design a system where one expects to run up
against the LBCO, but  it does happen in snow storms, etc.

So... what's a reasonable set of values for LBCO/delay? The default is
44V/15Minutes.... The voltage seems excessively low to me.. That's just
11 volts (normalized to 12v system)

Most of the "battery tables" I have show a 12V battery to be 100%
drained at ~11.6 volts..

Comments?

jim22 AT trlp DOT com

  The commercial battery charts we use show nothing of the sort. At 11.6 volts
a 12v battery is about 50-70% charged still. I would have to go to work to
find the actual charts from many manufacturers of flooded lead acid cells.

If you have a heavy load on a fully charged 12V battery is will go to 11.6V
and still be 100% charged. If you have no load on it and read 11.6V is may
be almost dead. I guess this depends on how deep you want to cycle the cells
and how much load the metering is done at.

 Gymy Bob wrote:


Why do we have to check out everything you post? You keep pumping out this
misinformation without regard for it's consequences. Do some research before
you kill somebody with bad advice.

I got suspicious of you when you stated that a circuit breaker became
defective after one TRIP AND NEEDED TO BE REPLACED. When you posted that a
lightning bolt would light up a lightbulb for under ONE second, I became
certain you were a joker.


Some REAL battery discharge states are below. I would think they ALL have
more credibility than you.



=================================
At 11.7 volts, the battery has 20 percent charge left.
At 11.6 volts, the battery has 10 percent charge left.
http://www.solar4power.com/solar-power-battery.html
=================================



LESS than 25 percent charge left:
=================================
                 SG    12 Volt Battery
100% Charged     1.265     12.70
75% Charged     1.239     12.37
50% Charged     1.200     12.06
25% Charged     1.170     11.67
Fully Discharged     1.110     10.5

http://www.solarexpert.com/Pvbatinfo.html
=================================



10 percent remaining at 11.6 volts:
=================================
http://www.poweriseverything.com/impt-info/battery.html
=================================


Less than twenty percent left:
=================================
http://www.capsante.com/Articles/battery_info.htm
=================================


and hundreds of OTHER sites that, not surprisingly, disagree with you again.




mike

 

m II wrote:

Thanks Mike... I have to admit... Bob's numbers rattled me for a bit.

 are some voltages down to 1.2 VDC per cell (7.2V) and 1.75V per cell (10.5V)
stated by Exide with regards to their ratings. These voltages are the
minimum levels under various loads to consider a lead acid battery to still
have valid charge.

There are so many factors involved in this determination. My previous post
stands correct with different loading conditions and temperatures as stated.


http://www.exideworld.com/faq/faq_marine.html