Any Help appreciated

[almoudamer]

Hi to all
firstly, i would like to say am very happy to join such this good and helpfull forum

secondly, i have 2 problems and need advice from experts

1- i have a UPS , i want to know the best type of batteries to work with
lead acid / nimh / sulfaric acid ,blablabla

2-the ups operate from 24V, so i need to use 2 battries in series, each battery i need 100AH

i need a good battery charger schematic for them(24v)


i already using 2 sulfaric acid car batteries + normal battery charge which is
Center tapped transformer +2 diodes then easy comparetor circuit that cut off when the voltage at batteries become around 29V

but the battries alway loses from the acid inside and i have to add sterlized water in it, and now batties damaged after lessthan 7month only

can any one help here to solve these problems,
best regards
thx in advance

[anatech]

Hi almoudamer,
Normally you would use gel cells in that application, they make them smaller and also in 24V assemblies. Gel cells don't like deep discharge, nor will they do well if not properly charged. You could get by with NiMh, depending on your run time expected between recharges.

I think the main issue is recharging these cells properly. That means doing some research and creating the proper charging circuit. There are battery maintenance type ICs out there in the market. Again, research is needed. One thing that is for sure is that a simple uncontrolled current type charger with a simple voltage comparator will not do the job properly. Many use a mixture of constant current, possibly with different levels during charging, and an end voltage. From there, they may float charge the batteries. If you are using cell in series, things become more complicated as you need a way to properly charge each cell or battery independently. If you don't, one cell may be overcharged and actually reverse polarity. It's probably destroyed at that point.

Google and manufacturer application notes are your best friend right now.

-Chris

[eyoung]

If you want to use lead acid batteries you may want to observe a fully charged battery has 2.2v per cell 13.2 v per battery or 26.4v for 2 . You may just be over charging, an automotive charging system is usually 13.6-14.2v and has the ability to regulate amperage. A typical charger for slow charging has 2 to 6 amps capability. If these batteries are just for back up they should last for years . If gel batteries are too expensive you might consider marine batteries which are deep cycle batteries as they are meant to be used for longer periods without recharging.

Regards, Elwood

[almoudamer]

hello, first i would like to thx for the fast replies

let me tell u more about my situations

in my country electricity cut for 6hours and come 4hour, so, the ups should work for 6 hours, and after that i have 4hours to charge the batteries again
my charger is as i told, is center tapped transformer wih 2 diodes(half rectifier) and a voltage comparetor, 30A the transformer
the battery power is 24v x 100Ah = 2400w,so the output power from ups after losses is about 1700W
i have loading power of 220w , so the ups should work for around 7hours.

iam using 2 x lead acid battries in series
i searched a lot on net to find a good current and voltage controlled ciruit for 24v charging, but cannt find

best regards
thx in advance