Re: (ET) Some Battery advice

["David Roden" <etpost drmm net>]

On 7 Sep 2005 at 8:14, ThompsonG DFO-MPO GC CA wrote:

> First, in one of my tractors one of the batteries is showing 2 volts 
> less than
> the other 5 ...

This usually means that battery has a weak or shorted cell.

> after a night
> on a 6V charger it is up to about 6.3V, the rests of the pack are around 
> 6.0.

Test that battery with a load before using it, to see how many amp hours 
it 
can deliver before the voltage drops to around 4 volts (indicating the 
weak 
cell is at zero volts).  It's fairly likely that the battery (or rather 
that 
cell) will have only a few amp hours of capacity.  If you continue to draw 
current after that, you'll reverse the cell, which will drastically weaken 
it (indeed that has probably already happened at least once).

A long, slow equalization charge on that one battery (a couple days to as 
much as a couple weeks at 2-4 amps) will get you all you're ever likely to 
get with that battery.  Most likely though that cell will continue to be 
the 
weak link in your pack, and you'll end up replacing that battery.

> Will a full 36V charge balance the pack? 

It's better to treat the weak battery individually.  Don't be fooled by 
reading a higher voltage on it; that battery is more recently charged, and 
the good cells are pushing the voltage higher.

> Second, another of my tractors a full
> charged show white on the Voltage fuel gauge, but each battery as at 6.6 
> volts
> I thought they should be at 7.2V. 

When the charger is connected and operating, a battery at 7.2 to 7.5 volts 
is fully charged (at around 25 deg C).  Note that this is ^on charge^ 
voltage. When you disconnect the charger, voltage will fall rapidly at 
first, then more slowly.  Several hours later it will stabilise at around 
6.3 to 6.4 volts.


David Roden - Akron, Ohio, USA

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