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Inverter dumps the battery at 10.6V?

B

Bedraggled

Jan 1, 1970
0
Ok. I'm looking confused right about now.
I am reading that the lead acid battery is considered
totally discharged at a specific gravity of around 1.13...
which several tables indicate will occur at around 11.8V.

? I have two small inverters (400W and 150W)
that I use for emergency lighting...
both disconnect the battery at well under 11.8 V.
(one of them disconnects at 10.5 or sok the 400W inverter
drops the battery at 10.0V ) [??!]

Overdischarging of the battery is damaging to its plates.
I would expect that the battery disconnect voltage would
be at or above 11.8V...not well below that point.
Are these inverters badly designed?...not taking proper care
of the battery...? ..some piece of the puzzle I am not seeing..

or am I even more confused than I think I am?

*stares at data sheet....(staring is not helping...sigh)

*puts message into bottle, casts the bottle into the cyber sea.

*plays with the crabs on the beach.
 
B

Bedraggled

Jan 1, 1970
0
Ron Rosenfeld said:
Probably that those voltages are measured with the battery at rest -- i.e.
no charging or discharging for at least three hours.

Under load, there can be a considerable drop in battery voltage.

Having said that, those cutoff voltages seem a bit on the low side to me.
I would probably use 11.0V for a 12V system, but I might change that
depending on the particulars of the system and my experience with the
batteries.


--ron


**************
Just ran an experiment and ran the inverter hard for a few hours.
The "heads up, I'm about to disconnect the battery" alarm went off
at 10.8V.
I turned all the loads off...let the battery sit for about 20 minutes..
....battery voltage now at 11.8 volts. Right at the "advertised"
"battery is discharged " voltage.

It does seem that the battery disconnect voltage is trying to
account for the fact that the load is pulling the battery voltage down.

at any rate...the majic seems to be working.

[I did not allow the test to continue to the cutoff voltage [10.0 V]
No sense in slapping the SLI battery (not a "deep cycle" type) that hard
if I don't have to. Will consider the disconnect as more of a "fuse" than
a normal operating mode.

thanks for the input..
A single clue can solve a puzzle!
 
B

Bill Kaszeta / Photovoltaic Resources

Jan 1, 1970
0
Most lead-acid batteries are rated for capacity at a specific rate
and final voltage, usually a discharge over 8 hours to a final
voltage of 1.75 volts per cell (10.5 volts for a 12-volt battery).

While the batteries can be discharged to this voltage, it is
only for a limited number of times. Battery life is greatly
extended if the depth of discharge is limited. For a typical
golf cart traction battery:
300 cycles to 100% discharge (10.5 volts)
600 cycles to 80% (about 11.6 volts)
1000 cycles to 50% (do not have the data at home)
etc.

A lot depends on the quality of the battery, but the relative
cycle life follows the above.


Bill Kaszeta
Photovoltaic Resources Int'l
Tempe Arizona USA
[email protected]
 
M

m II

Jan 1, 1970
0
Bill said:
Most lead-acid batteries are rated for capacity at a specific rate
and final voltage, usually a discharge over 8 hours to a final
voltage of 1.75 volts per cell (10.5 volts for a 12-volt battery).

While the batteries can be discharged to this voltage, it is
only for a limited number of times. Battery life is greatly
extended if the depth of discharge is limited. For a typical
golf cart traction battery:
300 cycles to 100% discharge (10.5 volts)
600 cycles to 80% (about 11.6 volts)
1000 cycles to 50% (do not have the data at home)
etc.

A lot depends on the quality of the battery, but the relative
cycle life follows the above.


So, where do your think the bast battery bang for the buck lies? There
has to be a 'sweet spot' where the total cost for the usage obtained is
the best.

I get the feeling that three hundred dollars per two volt cell may not
be the best deal, even though they last the longest. Are the best deals
in the middle range somewhere?



mike
 
Bill Kaszeta / Photovoltaic Resources said:
...Battery life is greatly extended if the depth of discharge is limited.
For a typical golf cart traction battery:
300 cycles to 100% discharge (10.5 volts)

Say 300x100Ahx12V = 360 kWh over its lifetime.
600 cycles to 80% (about 11.6 volts)

And 600x0.8x100Ahx12V = 576 kWh over its lifetime?
1000 cycles to 50% (do not have the data at home)

And 1000x0.5x100Ahx12V = 600 kWh over its lifetime?
...the relative cycle life follows the above.

Trojan data seem to go in the other direction. Deeper discharges
allow a battery to store more total energy ("LEU") over its lifetime.

Nick
 
B

Bill Kaszeta / Photovoltaic Resources

Jan 1, 1970
0
So, where do your think the bast battery bang for the buck lies? There
has to be a 'sweet spot' where the total cost for the usage obtained is
the best.

I get the feeling that three hundred dollars per two volt cell may not
be the best deal, even though they last the longest. Are the best deals
in the middle range somewhere?



mike
There are no simple answers to this question because all situations
are different. One has to consider first cost, life vs depth-of-discharge,
related labor costs, disposal/recycling costs, and reliability. Deeply
discharged systems are more likely to fail than systems with shallow
discharges and failure may have a high cost.

A lot depends on the scale of the system. Systems that can use up to 5
parallel golf cart batteries may have the lowest cost per kW-Hr stored,
but may have a higher failure rate than larger cells (such as fork lift
batteries).

if you want a lot of battery technical (but not product) data, try:

http://www.azsolarcenter.com/technology/technical/batteries.html
Bill Kaszeta
Photovoltaic Resources Int'l
Tempe Arizona USA
[email protected]
 
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