RE: (ET) Battery Question

["David Roden (Akron OH USA)" <roden ald net>]

On 16 Jul 2002 at 15:55, Hazen, Dwight L wrote:

> If he leaves the two
> batteries in parallel all the time they will discharge each other. This 
> will
> cause a decrease in life of the batteries.

I have heard of this, but have never seen it happen.  It could be that it 
actually is self-discharge, which occurs in every lead battery.  However, 
AGM batteries (such as Optimas) have very low self discharge.  If kept 
clean 
and dry they can hold a charge for many months.  I have some rather 
elderly 
Hawker Genesis batteries here that have been sitting, untouched, for 
almost 
18 months.  An open circuit voltage test indicates that most are still 
over 
90% charged.

> Find the biggest battery that is rated for this service. In
> this case I would think Gel cells might be the way to go. 

East Penn or Sonnenschein gel batteries are long lived but must be charged 
carefully.  The Optimas are still an excellent choice.  Hawkers would also 
be good. 

The Optima group 31 deep cycle batteries are supposed to return to the 
market late this summer.  These would give excellent capacity, far more 
than 
he needs, at a mass of about 72 lb each.

Before replacing the existing batteries, he should make sure he's charging 
them correctly.  He may be undercharging.  Here are some Optima charging 
guidelines from Bill Dube', a sort of Optima Guru from the EV discussion 
list:

-- begin quoted text --

You can charge the battery at any sane current until the voltage reaches 
15 
volts. You hold the voltage at 15 volts and allow the current to taper off 
to less than an amp. The battery is "fully charged" at this point. It may 
not be completely equalized, however. To equalize the battery, you pass a 
2.0 amp currrent (with no voltage limit) though the battery for one hour.  
 

When the batteries are new, you want to do this equalizing routine every 
time or nearly every time. It helps to open up the plates and bring the 
battery up to full capacity. Also, the cells are "growing" in capacity and 
may not be doing so equally. To prevent reversing a cell, you want all the 
cells to be "full" each time and thus you must take extra care to be sure 
that they are starting out equally charged.  

In my opinion, as the pack ages, you probably don't need to do this 
equalizing routine as often. The over-charge does accelerate aging to some 
degree. I think the doing an equalizing charge perhaps once per week is 
probably about right once the pack has 30 cycles or so.  

-- end quoted text --

Keep in mind that Bill is talking about a battery pack for a road EV which 
is used daily, so adjust his figures accordingly for a battery used only 
occasionallly.

Me again.  To restore some of the capacity of chronically undercharged 
batteries, your friend might try a long, slow equalization charge at about 
1/2 amp with a voltage limit of 15.5 to 16 volts.  This can take as long 
as 
a week or two, and the batteries should be checked periodically to make 
sure 
they're not venting (gassing too much and releasing the gases from the 
valves).  

Cycle them a few times in succession, and charge again.  He may find that 
the capacity comes up enough to work just fine.


David Roden - Akron, Ohio, USA
1991 Solectria Force 144vac
1991 Ford Escort Green/EV 128vdc
1970 GE Elec-trak E15 36vdc
1974 Avco New Idea 36vdc
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