23 Apr 2003, 15:00, mark lewis (1:3634/12), wrote to all:

Hi mark.

I've already read Tom's reply, he did very good.

 ml> i've several 12volt, 11Ah batteries here that i'm wanting to 
 ml> charge and load test...

 ml> can i charge them with a standard car battery charger? what 
 ml> settings should i use?

You didn't state what type of battery, but from the context I assume gel-cell type.

With a lot of care, you CAN use a car charger, but you MUST use a current
limiter.  11AH batteries should be charged at 1.1A for 10 hours.  

Gel-cells have a thermal runaway problem when they get near their full
charge point, they will overheat and then short out, killing the battery
and causing a lot of swelling of the plastic case.

 ml> what's the best way to load test them to see if they are still 
 ml> good?

Put a 12V automotive bulb on them that draws about two Amps, like a dome
light bulb.  A tail light will run about three Amps, a stop light about 5
Amps, and a headlamp about 8 Amps.

 ml> what does the 11Ah (Amp hours) really signify?

Exactly what it says, Amps x hours.  That 11 AH should put out 1.1 Amp for
10 hours, or 11 Amps for one hour, or 5.5 Amps for two hours, etc.

 ml> how can i tell how much load time i should get on the batteries?

See above.  A safe test would be about 2.2 Amps for five hours.

 ml> if i connect these batteries in parallel, the voltage stays the 
 ml> same and the amperage capability of the set is increased... are 
 ml> the Ahs just added together? ie: three of these would give me 
 ml> 33Ahs

Exactly!

 ml> i've also two "speciality" packs... they are 6 2volt 25Ah all 
 ml> tied in series to give a single 12volt unit but i don't remember 
 ml> (as above) which way the Ahs go... i'm wanting to charge these as 
 ml> well and ensure that they are all up to snuff...

In series, the AH remains the same, but the voltage increases, just as you
have stated.  Charge rate is always 10% of the AH, so those
"packs" would be charged at 12V, 2.5 Amps for 10 hours.  If you
have a 2V charger and have access to the connectors between the cells, you
would do MUCH better to charge and test each cell individually.  So long as
the pack is not connected to anything else, there is no need to disconnect
the connectors between cells for individual charging and testing.

 ml> when it all comes down to the end, i'm wanting to tie these all 
 ml> together in parallel to go for 12volt, ??Ah so as to boost my 
 ml> uptime on my UPS' when commercial power is off...

Sounds good.  You have three 12V {at} 11AH, for a total of 12V {at} 33AH, and two
packs that together will give you 12V {at} 50AH.  With _everything_ connected,
you would have 12V {at} 83AH.

Your computer will need about 120 Watts to run with monitor, a wee bit more
to start up, but lets not worry about that, as it will already be running
in most cases.  Excluding lots of annoying formulas, Watts is basically
Volts times Amps.  To get 120 Watts from a 12V system, you will need to be
pulling 10 Amps.  If you do that for two hours, you have used 20 AmpHours. 
If all your cells are working and fully charged, you should have about
83AH, and get about eight hours running time for the FULL computer.  Triple
that with the monitor turned off, or about 24 hours.

 ml> lastly, what guage wire should i use to connect these? the last 
 ml> time i did this, several months ago, i was using some 
 ml> (supposedly) "heavy duty" two wise extension cord (like the brown 
 ml> ones we use in the house but heavier, definitely not the outside 
 ml> orange ones) and melted the insulation on the wire between the 
 ml> battery pack and the UPS due to the load... i'm just now looking 
 ml> at it and it appears to be 18ga stranded ;-(  i'm thinking that i 
 ml> need something more substantial... like 12ga or 10ga... the 
 ml> problem is being able to connect "stay-cons" to the wire to 
 ml> connect to the battery terminals...

Ouch!  "Heavy duty" usually means the rubber insulation is
thicker and can be dragged around a little without wearing through!  Agree,
18ga is way too small.  I use 4ga, but only because that's what I had
around.  :-)

12ga wire is rated for 15 Amps, and that would probably be good enough, but
those cells can easily put out 100A if shorted, and you are paralleling a
bunch of them.  I would recommend 8 gauge, and in any case, nothing smaller
than 10 gauge.  

As far as the connectors, my "standard" UPS uses 14 gauge wire to
connect to 7AH batteries.  In your case, I would get connectors that will
crimp to 12 gauge wire for the 11AH batteries, and use 12 gauge for each of
the 11AH batteries.  Use 10 gauge for connecting the 25AH batteries, then
clamp or bolt all the (+) ends to a piece of 8 gauge wire for connecting to
the UPS.  Same for all the (-) ends.

There's nothing more unsettling than having the lights go out, then
smelling wire burning!

You also have to consider the increased load on the UPS's internal charger
when the power comes back on.  All those batteries will likely cook the UPS
while trying to re-charge.  


     Good luck...  M.

--- Msged/386 TE 06 (pre)