[ausev] AGM batterys

[gary]

I have gel SLA's in my trike with manual balancing connectors, we used 
AGM SLA's in the Porsche with the Rudman regulator system, and floodeds 
(FLA's) in the MR2 with no individual battery monitoring.

The downside to SLA's is that you will need to monitor each battery.  
With FLA's, you can "overcharge" to bring the lower ones up and the 
worst case is that some of the higher ones vent.  You can top them off 
and they are still fine.  SLA's have a one-way valve, when they vent 
they are permanently damaged.  If each battery is not monitored and you 
are charging by pack voltage then it's likely that eventually some will 
be low and some will be high which results in constantly overcharging 
some and letting others get weaker.

The easiest way to monitor each battery is to bring a fused lead out to 
a connector.  For safety, the pack should be broken up so that each 
connector only has 4-6 batteries to keep the voltage lower.  There is a 
risk of popping a fuse while monitoring or charging which means 
disassembly and replacement.  Adding these monitor leads is a lot of 
extra work and money and is only the simplest method.  The best method 
is an automated battery monitoring system which can vary in price all 
the way up to the cost of the pack itself and is a lot of work to 
install.  For a DIY EV, the manual system is fine but means extra 
maintenance to put a meter across each battery and top off the low ones 
individually.  It is better to have a temperature compensated charger 
for SLA's, both for the pack and individual batteries.  The max allowed 
charging voltage varies quite a bit with temperature so on hot days the 
charge voltage needs to be reduced to prevent overcharging and damage.

I used SLA's because I wanted to design something for the general public 
and watering seemed like something people wouldn't want to do, and 
providing easy access to all batteries can be a challenge.  I bought 
some of Lee Hart's battery monitoring kits which are affordable 
automated systems to make it as low maintenance as possible.  Since 
then, lithium batteries have gotten cheaper and SLA's have gone up.  I 
don't think SLA's are worth the trouble.  Now I will be using FLA's for 
an economy version and lithium for a high-end version.  Trojan's seem to 
be the gold standard for FLA's so that might be your best bet.  The 
AGM's can put out more current for racing, can be mounted in 
inaccessible places if needed and in any position, but won't last nearly 
as long.  They will also be more expensive, more work to install and 
more work to maintain.

Gary Krysztopik
www.ZWheelz.com
www.aceaa.org
http://voices.mysanantonio.com/drive_electric_san_antonio/ 
San Antonio, TX



Joby Wieser wrote:
> I have read a lot of talk about people here using flooded lead acid batterys, watter miser caps ect.  It looks like my first set of sams club flooded batteries are nearly toast.  I have been reading about AGM batterys and they seem to have many advantages.  Has anyone on the list used them?  Are there drawbacks Im not aware of yet? (aside from the extra cost).
>
> Joby in Fbg
>
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