RE: (ET) Min. battery voltage

["Elie, Larry \(L.D.\)" <lelie ford com>]

Cells only reverse under load.  The load may be other cells, but it is 
still 
under load.  That said, I have never seen a battery under load at 5.2 V 
(for 
a "6V", half a "12V") battery reverse.  A battery at only 5 V unloaded, 
and then 
seeing a LARGE load can be reversed, but the load will pull it way under 
5V.  
That's only anecdotal; not a guarantee.  Think load.

Larry Elie


-----Original Message-----
From: elec-trak-bounces cosmos phy tufts edu
[mailto:elec-trak-bounces cosmos phy tufts edu]On Behalf Of Christopher
Zach
Sent: Monday, June 21, 2004 11:57 AM
To: Markus Lorch
Cc: elec-trak cosmos phy tufts edu
Subject: Re: (ET) Min. battery voltage


> I have read several posts and online documentation on the lowest
> save voltage to which a lead acid deep cycle battery may be discharged
> and found values around 10.5V / 80% (for a 12V bat).
> I think this is consistent with what Chris' recent battery monitor
> looks out for. 

Yep.

> The question I have is: Is this the lowest voltage under load or the
> voltage immediately after load is removed? I read somewhere that to 
> measure battery voltage one should let the battery sit for 2 days without
> charging/discharging to get an accurate reading.

Always check voltage while under load. That's when you can get a 
reasonable reading. If you're dropping below 10.5 volts under load, you 
are running the risk of reversing a cell.

> Anyhow, I have one (12V) battery that seems to be not so good, it reaches
> low
> voltages before the others do and when I keep mowing after I see it go to
> 10V it is getting very hot and drops to as low as 6V when you start the
> mower
That is a battery that is reversing. Consider it "toast"

> or start driving. If I stop the current flow it returns to about 11V or 
> so
> almost immediately. So when do I reach 80% depth of discharge, when the
> battery first dips to 10.5V or when it holds 10.5V after load is removed?

When it dips to 10.5, though my guess is it will fall thru to 6 really 
fast after that.

> 
> Also at what voltage do I have to fear cell reversal? the other two 12V
> sections
> in my pack do not dip below 12V when this troublemaker is already below 
> 10V,
> so I
> am concerned about them forcing current through these weak/discharged 
> cells.

10.6 volts.

Chris


> 
> 
> Thanks
> Markus
> 
> 
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> 


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