[SOLVED] 12v 40 Ah Lead Acid Bty Charger...

Hello guys...

Firstly I am new to this forum and I am on a vacation of 20 days and would like to make something useful.

I've got a 12V 40ah Lead Acid battery. I placed it into a 650VA UPS (actually I did some google search before doing it). Well..the UPS is working but gives only few minutes backup like 5 or 10 minutes and the ups gets heated(Waited a day long, and got the same result). I again googled and found that the UPS is designed to charge 12v 7ah btys that's why the backup is less and gets heated up.

I managed to get a 12v Transformer-DC output with 4 to 5Amps(checked myself) from an old PMPO.

now my question is:- Is there any way to get these two things combined and get 1 or 2 hour backup??

-Thank you

If you use your transformer to build a regulated power supply with its output voltage set to just slightly less then the output voltage of the existing charger (.1V), then when the battery is really low, both chargers will supply current, as the battery voltage increases, you new charger will cut out but the old one will continue. Google around for the circuit of a 12v 5A charger circuit.
Frank

Check to see if the charge Voltage reaches 13.8V.

40Ah x12V is 480 watthours, so check your load, the inverter may only have 70% efficiency, Giving 350W for 1hr if the battery is good.

SunnySkyguy said:

Check to see if the charge Voltage reaches 13.8V.

40Ah x12V is 480 watthours, so check your load, the inverter may only have 70% efficiency, Giving 350W for 1hr if the battery is good.

Click to expand...

well...maths...Bty Charge is >13.8V and the load is 25W CFL

backup time is 5 to 10 Mins. Oh the Bty is good..!! I checked it yesterday with my friend's bty.

Any suggestions...?

---------- updated ------------

SunnySkyguy said:

Check to see if the charge Voltage reaches 13.8V.

40Ah x12V is 480 watthours, so check your load, the inverter may only have 70% efficiency, Giving 350W for 1hr if the battery is good.

Click to expand...

Bty charge is > 13.8V and the load is 25W CFL..

Bty is good...! I checked it Yesterday...

Any suggestions...?

just a suggestion,

the battery efficiency is at best about 80% (when its new)
the inverter efficiency say 70%
the Battery 40A/hr = 40W for 1 HR.

charge time required to replenish the battery 40A/7A * 1.2 HRs = say 7H

current drawn from battery for 650VA/OP = 650/12 = 54A *1.3 =72A

expected run time 40/72 = 0.5HR.

so if the unit was left on for more than a day,
and the inverter power drawn is <= 650W
then it seems that the battery is duff.
or the inverter is cutting out due to a timmer or overheating
or the battery connections are bad.
or the battery lead is not thick enough.

THINKER_KAM_MAN said:

just a suggestion,

or the inverter is cutting out due to a timmer or overheating
or the battery connections are bad.

Click to expand...

Thank you guys... for replying

I'll take these two reasons.

I doubled the wire (two 14 guage wires), so the second one seems less important to me..

The first one is important because I found that if I restart (OFF/ON) the UPS after cut off. it again gives backup for some time then cut off. It works like this for 3 or 4 times.

If it is due to a timer..then is there any way to deactivate it..? I don't think its the heat.

thank you

Thanks Guys..The problem is solved now.. Actually there wasn't any real problem. All I did wrong was, I never checked that thing with enough load. 25W is kind of low for that UPS. Today I connected a pedestal fan and WTF!!!? it ran for 2 hrs!!. I don't know how much watt it consumes, but it really worked.

Thanks guys..thank you very much for helping me and I will definitely come again with some real problems

Just wondering if my estimate was close of 350W for 1hr in 650VA UPS

If you got 2hr then was it a 175W fan? 230V? X 0.75A
Yes some UPS need 10% load.