Help with the ups circuit please

I have a desi UPS which is having the problem that it even starts its inverter even when there is electricity (no loadshedding). The UPS is in charging mode but suddenly switches to inverter mode repeatidly for few seconds and stops charging then again switches to Charging mode and back again. This cycle goes on for many times. I have contacted local mechanics which say that i have to replace the entire circuit kit. Can you please tell me what can be possibly wrong with this?

IMO: I think the relays have gone bad but it appears that there are two relays of the cicruit. I have posted the picture of the ciccuit please help me detect the problem?

NB: The pics on this forum have been down sampled. You can right click on the pics to open the high resolution one

Me too looking for someone who can little bit explain this circuit. I think the transformer is actually 12V charger for the battery and inverter transformer will be the big one.

There is a portion of the circuit which senses the AC input to the UPS and tells the PIC16Fxxx IC that AC is present or not. The value of input AC for detecting the presence is adjustable with the variable resistor "Mains LOW" near the transformer.

Somehow the PCI16F is sometimes getting the signal as if AC is not present. This may be due to some loose connection, bad component or the adjustment of variable is just at margin.

Look for any such fault in the narked area.

[quote=“nasirjavaid, post:2, topic:17406”]

Me too looking for someone who can little bit explain this circuit. I think the transformer is actually 12V charger for the battery and inverter transformer will be the big one.

[/quote]

The transformer on the PCB is for powering up the entire circuit board. Now you will wonder why the 12V from the battery can’t be used for this purpose. One of the main reasons is that circuit should operate even when battery is disconnected.

The big transformer outside this circuit board is actually inverter + charging transformer. It has a dual role.

u can use a ood led torch and light it at one side of pcb..anfd look through other side .. u camn easily identify which parts are loose are where connections are broken.. u can even see a hairline cracks inn the traces of pb with a good torch (costs 600-700 rs led high power zoom rechargeable) ..

Heat Gun is very helpful in such matters where reballing or tightening of circuits on boards is required. Otherwise, it is not an easy task to test every joint for fault.

You can use hair dryer as well if it has burning hot air.

@ijaz ahmad & @jhagra & @blogger. Thankyou for replying.

When i was trying to figure out what was wrong with this circuit i wondered if it is possible for someone with understanding of the electronic circuits to literally read these circuits like a story? I mean to know the path of the current and what everything on the circuit board is "doing"? I someone has the time please try to explain the path of the current in this circuit board.

I have a very rudimentary understanding of the electronic components and circuits and i would like to learn more about electronic circuits can someone tell me where should i start?

[quote=“generaluser, post:7, topic:17406”]

if it is possible for someone with understanding of the electronic circuits to literally read these circuits like a story? I mean to know the path of the current and what everything on the circuit board is “doing”?
[/quote]

Not every circuit is readable and understandable like a story especially if you see it for the first time but with experience, one can tell or guess (with reasonably accurate results) what the circuit is actually doing. For example, almost all power supply circuits are similar but there are variations as well.

[quote=“generaluser, post:7, topic:17406”]
I mean to know the path of the current and what everything on the circuit board is “doing”? I someone has the time please try to explain the path of the current in this circuit board.

I have a very rudimentary understanding of the electronic components and circuits and i would like to learn more about electronic circuits can someone tell me where should i start?

[/quote]

I wish I had time to explain it in depth but I don’t have it. The circuit under discussion is a control circuit (or a kit) for a UPS. It has various functions to perform like

1) Monitor if AC input is present

2) If yes, then check battery status

3) If battery voltage is low, start charging

4) Stop the charging when battery reaches a certain level

5) If AC input disappears, then disconnect the main transformer from AC mains

6) Start generating PWM (or square wave pulses) at 50Hz (which is then fed to external transistors mounted on big heatsinks)

7) Keep monitoring the battery level

8) Turn on Alarm / buzzer if battery is getting low and turn off inverter (the PWM waveform) if battery gets too low.

[quote=", post:4, topic:17406"]

The transformer on the PCB is for powering up the entire circuit board. Now you will wonder why the 12V from the battery can’t be used for this purpose. One of the main reasons is that circuit should operate even when battery is disconnected.

The big transformer outside this circuit board is actually inverter + charging transformer. It has a dual role.

[/quote]

Thanks Ijaz… yes I accept my less knowledge in electronics as I am just a hobby guy. I figured it also when I went to order my desi ups and saw the open ups there…

[quote=", post:8, topic:17406"]

Not every circuit is readable and understandable like a story especially if you see it for the first time but with experience, one can tell or guess (with reasonably accurate results) what the circuit is actually doing. For example, almost all power supply circuits are similar but there are variations as well.

I wish I had time to explain it in depth but I don’t have it. The circuit under discussion is a control circuit (or a kit) for a UPS. It has various functions to perform like

1) Monitor if AC input is present

2) If yes, then check battery status

3) If battery voltage is low, start charging

4) Stop the charging when battery reaches a certain level

5) If AC input disappears, then disconnect the main transformer from AC mains

6) Start generating PWM (or square wave pulses) at 50Hz (which is then fed to external transistors mounted on big heatsinks)

7) Keep monitoring the battery level

8) Turn on Alarm / buzzer if battery is getting low and turn off inverter (the PWM waveform) if battery gets too low.

[/quote]

The main issues in desi UPS are like

1- UPS does not disconnect charging even at 95% or battery charging, sometimes even if battery is 100% charged the ups continues to charge it…

2- Output AC voltage is more than 230V (in some cases more than 300V) and output DC voltage is more than 15V (for 12V battery)

3- UPS switches to UPS-MODE when input voltage is less than 190V / 180V etc

Can you please tell from the above circuit, which variables or settings we can use to adjust these things?

Appreciate your guidance in this forum.

[quote=“nasirjavaid, post:10, topic:17406”]

The main issues in desi UPS are like

1- UPS does not disconnect charging even at 95% or battery charging, sometimes even if battery is 100% charged the ups continues to charge it…

2- Output AC voltage is more than 230V (in some cases more than 300V) and output DC voltage is more than 15V (for 12V battery)

3- UPS switches to UPS-MODE when input voltage is less than 190V / 180V etc

Can you please tell from the above circuit, which variables or settings we can use to adjust these things?

Appreciate your guidance in this forum.

[/quote]

Ohh… my ignorance… Just Noticed the BATT LOW and MAINS LOW variables on the PCB… anyhow if there is something missing you can add please.

love you engineers for such a good information and helping each other i will also help

I purchase similar board shown in the picture (could not use it yet) and traced its schematic.

This board is a charge controller and provides PWM drive. Interestingly little transformer also provides 100Hz pulses for

the functioning of PWM.