DCP 650VA UPS circuit

[Nipuna]

Have you placed the components intact after replacing the battery. I remember you were experimenting with a comparator IC?
What are the ratings of the battery that you have replaced? (is it a 12V, 7Ahrs?)

What happens if you power on the UPS now? Any beeps, indicators?

My battery is 12V 7A.

I have placed everything correct. After replacing LM339 Self turning off problem that i told you earlier corrected not the one i told you yesterday.

I have replaced the LM324 IC then UPS started to work. After that I charged UPS for 8 hours I think Now The error came again. That is

without connecting the AC line UPS beeps for 1 minute then Turns off by it self Doing Long Beep and Lighting the yellow LED. After connecting the Monitor and Computer when power gone UPS turn off by it self Doing a Long Beep.

[Neo]

It seems a problem in the voltage comparators. Have you checked the ratings when you replace them? (I'm sure you did replace exactly the same item). Ask your dad to trace through battery unit to voltage comparators and then from there to step-up.

Also, try calling the seller and ask for the circuit diagram. I don't see any other way to find the circuit diagram for this unit.

[Nipuna]

Ok. I will try then if there is a problem i will tell you

Thanks

[Saman]

I knew two good UPS brands in Sri Lanka. One is Sola (Australian) sold by Adelphi. They have given a superb service to me at my door step. Real value for my money. But I don't know whether they exist or sell them now. Even after 11 years, it still works with my dad.

The other brand is APC (American brand made in China) sold by Fentons. They have also given a superb after sale service to me as well.

Both of these companies maintained a team of qualified engineers and technicians who were very kind and helpful to customers.

Before about 6, 7 years, all these started to happen. A few people had started computer shops in Unity Plaza and started to undercut each other that resulted in selling lowest quality products with no guarantee period at all.
Guarantee is about replacing the old unit with a new one within the agreed period. But these people refuse to do that. They try to repair them with a set of completely unqualified staff (I have many personal experiences).

The main point is, there is nobody I know that I can recommend 100%. I heard Metropolitan is good (especially after sales service) but their products are bit expensive. At Unity Plaza, I tried almost everybody. The only place I can recommend 50% now is Tech Information Systems. I only got one hardware replaced quite recently and they did that without having to answer nonsense. The rest of the hardware I bought from them are working fine.

We need to convince everybody in Sri Lanka regarding this crisis. Join with https://robot.lk/viewtopic.php?f=34&t=1339 and let everybody know about your idea.

[Nipuna]

I have Repaired My UPS by my self i will Tell this in here later.

Thanks

[Herath]

Looking forward to hear. I have the same UPS model with the same problem. I am going to have a check on it today. It was lying around for about 5 months. I can't ask for money from my parents for a new one. I am still studying. No job

[Herath]

There is an amber LED on my UPS. And the manual says that it should be turned on while charging the battery. But it never came up since the first day I started using this UPS. I am wondering if the charging circuit is malfunctioning.
And I took the UPS apart. Just going through the components to find a clue about how this charges up the battery.
There is a 17.6V winding on the secondary side of the transformer, it goes to the board. And rectified, filtered and regulated via LM317T. I am checking more on the circuit.

Anyway I am wondering why this UPS doesn't startup with a dead battery while connected to main power line (battery is dead, zero volt even on multimeter. Just a slight movement of the needle). And why doesn't it try to charge the battery off the main power??. All I do is cursing the people at unity plaza who sold this to me.
( I had a power cut in today morning too. Anyway, I have backed up my important data, just in case )

[Neo]

Hi Herath,

Welcome to ROBOT.LK !!! A place where people share their technical experiences for the benefit of people. (Update member details and write up something about you on the relevant section under Member Area).

If you follow the discussion between me and one of our senior members (Nipuna) (who is busy doing his A/L this month. Make a wish for him ), you might have seen that his father(who has technical skills) was talking about a quad voltage comparator. Voltage comparators are usually used to identify whether charging is necessary and to cut of charging when the battery is fully charged. You may find this and see whether the path to that form battery and step-down is malfunctioning.

Make sure to do these things with extreme care as you work with live power. There might be some situations where you need to test while the USP is powered. So take extreme care on yourself.

Good luck!

BTW: where did you buy this?

[Herath]

Well, First wishing Nipuna good luck with the exam.

And I checked the circuit further. And I am checking the details of the components in the circuit.
Battery charging unit is working. And the transformer is also in good condition. Stepdown is working.( i read about 16 volts AC, when the 220V primary is powered externally. That 17.6V winding is used to chrage the battery). I will find some reference circuits of LM339 and check the board further.
And I found that the UPS use PWM technology . There are two PWM ICs,LM324 and SG3524.

(Edit: LM324 is a quad op-Amp, A/L syllabus has a little part on op-Amps. )

And I have a question,I am not sure if the UPS can recharge a fully dead battery, can't they?. Will i have to charge it externally with another charger?.

I bought this from Colombo.(Barclays Computers to be exact). And the UPS gave up after about 1 and half year. Although it had warranty, i did not want to carry it all the to colombo from home traveling about 80km.

[Neo]

If the battery cells are dead (out of re-charging capability of chemicals) you won't be able to charge it. If the battery is new, then of cause you can charge it from the beginning with UPS circuit.