Re: (ET) AGMs in an ET?

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

On 6 Apr 2002 at 10:29, Christopher Zach wrote:

> Quick question? Anyone ever thought of using AGM batteries in an 
> Elec-Trak?

Not so quick answer.

You won't find a 12v battery of any type that fits into the same space as 
a 
golf car battery and has the same watt-hour capacity (ah * voltage).  
Group 
24 fits nicely; it has about the same L x W but is not as tall.  Its watt-
hour capacity is ~much~ lower.  (For an example, I use group 24 gel 
batteries -- see below -- and they have a capacity of about 400 wh at 75 
amps.  A standard golf car battery will deliver over 790 wh at 75 amps, 
roughly twice as much.)

However, Concorde (and probably others) make an AGM type golf car battery. 
This should fit just fine -- but note that even this battery does not have 
as much capacity as a standard flooded golf car battery.

So should you use AGMs (or gels)?  They do have the advantages of needing 
no 
watering and of never making any acid mess.  

AGMs (not gels) are excellent for very high current applications, such as 
road EVs that are used for racing and/or driven hard.  Delivering 750-1000 
amps on demand is their great strenth.  However, this kind of power 
density 
is wasted in an ET, which really doesn't need or want that kind of current.

And all VRR (valve regulated recombinant, or "sealed") batteries cost a 
LOT 
more, and have less capacity.  They seldom have as long a cycle life as 
good 
golf car batteries, so their cost per unit of use time is much higher (in 
a 
road EV, AGM batteries cost between 2 and 3 times as much per mile).  They 
also require a more sophisticated (and possibly expensive) charger.  This 
is 
probably not an issue for Christopher, since he has a solar setup, but for 
most other ETers it is.  

So are they worth it?  I don't think so -- unless you have access to them 
for free, or very cheaply.  As I've posted before, I use East Penn group 
24 
gel batteries.  I am satisfied with them so far.  However, the only reason 
I 
use them in the ET is that I had quite a few of them on hand (still do).  
If 
I were fitting new batteries otherwise, I'd use plain old flooded golf car 
batteries.


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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