UPS problem

[roltex_rohit123]

I have a computer UPS which had a small 12v 7.5 amp battery sealed lead acid type in it. it was used for a backup of my computer for 15 min. now the battery in it has detoriated and i want to replace it with a 60-100 amp lead acid battery flooded type. I checked the terminal ratings of the UPS. It charges at abt 17.6v and 8 amp when tested with multimeter. There are two adjustable resistors I think they are for voltage and current settings. but I need some advicing before I do this. anyone having experience or can give a good advice?

 

[Reloadron]

Who is the manufacturer and what is the model number of the UPS?

When you say 17.6 Volts and 8 Amps how did you measure that? Both numbers seem high for a UPS with a 7.5 AH sealed lead acid battery. Dis you measure the charge voltage across the battery in circuit and the charge current placing the meter in series with the battery?

I have run a good number of UPS units off an external automotive battery with good results, however, the best choice is to use a deep discharge external battery like a marine or RV type battery. I have never seen a charge voltage above about 14.5 volts.

Ron

 

[roltex_rohit123]

Who is the manufacturer and what is the model number of the UPS?

When you say 17.6 Volts and 8 Amps how did you measure that? Both numbers seem high for a UPS with a 7.5 AH sealed lead acid battery. Dis you measure the charge voltage across the battery in circuit and the charge current placing the meter in series with the battery?

I have run a good number of UPS units off an external automotive battery with good results, however, the best choice is to use a deep discharge external battery like a marine or RV type battery. I have never seen a charge voltage above about 14.5 volts.

Ron

I exactly dont know the manufacturer of the UPS, but it served me well for 5 years. though i used its battery mode only a few times. the current measurements were taken without the battery and the voltage measurements with the battery. but the voltage rating I think was not correct since in India we keep it 18volts and the battery charged to only 12.6 volts and kept idle for an hour it dropped to 12 volts. and when connected it would charge upto 17.6 volts. actually the charging ampers were high since the battery is to be charged very quickly. this is according to Indian needs. there is a lot of power cut and we have to charge our batteries soon. even our inverter batteries last only about 3-4 years. this UPS I am trying to light fluorescent tube 28 watt and a computer of about 300-400 watts. the UPS is a 600 VA. i think I should keep the battery extra large so that it would last me long. I woul also add a float to the circuit if needed and does not harm the circuit. or adjust the variable resistors. I aslo have no idea about the variable resistors. are they the current and voltage adjustments or just cycle and voltage adjustments?

 

[Reloadron]

OK, without a schematic of the charging system it is hard to tell what those two resistors actually do. They could be used to adjust voltage and current but it becomes hard to tell. You could run the unit charging a battery and try adjusting those pots being real careful to return them to where they were originally set. You would do that while monitoring the voltage across the battery and place a current meter in series with the battery.

The UPS units I have and have opened I never noticed resistors to adjust the charge voltage or current.

Next, I am sure you understand that using a larger battery will not increase the 600 VA rating of the unit you have. It will afford a longer run time if that is what you want to do.

Last but not least, remember that a general purpose UPS does not put out a sine wave but rather a modified square wave in most cases. This waveform is not suitable for some devices. It works fine for a PC and monitor in most cases but could destroy some devices.

Someone else may have some thoughts on this.

Ron

 

[aquamon]

I wouldn't change any settings in the UPS.
I wouldn't advise using a flooded Pb-acid either as you will regret later from acid contamination.
Try and use a sealed automotive 12V and leave alone for 5-years or more.
If you messed with the voltage for charging, set it back to around 14.2V MAX.
17.6V charging a 12V Pb-Acid will destroy it.
8Amps on a UPS by its own charging circuit is already too much.
I suspect your UPS is faulty.

 

[Reloadron]

I didn't really catch this part:

now the battery in it has deteriorated and i want to replace it with a 60-100 amp lead acid battery flooded type.

You really want to avoid using a wet cell battery or "flooded" type battery as aquamon points out. A sealed battery is fine. When I see the term flooded used I assume like the old car batteries we would add water to.

Also, again for a 600 VA UPS using a 12 volt 7 AH battery the charge voltage and current sound awfully high?

Ron

 

[roltex_rohit123]

I just want to increaase the backup time not the 600 va rating. on the UPS the manufacturer is told ADVIK but I am not sure. it could be a brand of some big company. the measurements of the charger were taken without battery connected for current and with battery connected on terminals. I will try the Deep cycle battery for it. It would cost more but certainly last more. and since there is a frequent powercut problem of overcharge wont be there for a 100 ampere battery. hope this method was right. or now the battery is not in a condition to be tested. it has swollen due to a reaction on adding water and cracked on 2 cells.

 

[Reloadron]

I just want to increaase the backup time not the 600 va rating. on the UPS the manufacturer is told ADVIK but I am not sure. it could be a brand of some big company. the measurements of the charger were taken without battery connected for current and with battery connected on terminals. I will try the Deep cycle battery for it. It would cost more but certainly last more. and since there is a frequent powercut problem of overcharge wont be there for a 100 ampere battery. hope this method was right. or now the battery is not in a condition to be tested. it has swollen due to a reaction on adding water and cracked on 2 cells.

OK, but understand something if I have this right. You can't actually measure current unless the current meter is in series with the load. There needs to be a load like a battery out there or some form of load. If you use a meter and select current measuring and place that meter directly across the leads that would go to the battery you are effectively for all purposes placing a dead short across the charger system. That would explain the very high current of 8 amps you came up with. Additionally the high voltage you are seeing is open circuit voltage with no battery or load out there. I am sure that will drop with a battery in the circuit. Do not ever try to measure current placing the meter across the terminals.

On another note I am sure you have noticed the wire gauge to the battery terminals is large in these devices. This is for good reason as those batteries deliver a high current when the UPS is under a full load. Since adding a larger battery that battery will not be as close to the circuits as when using the internal battery I very strongly suggest you go with a larger wire gauge to connect the external battery! Good clean connections are very important!

Ron

 

[roltex_rohit123]

OK, but understand something if I have this right. You can't actually measure current unless the current meter is in series with the load. There needs to be a load like a battery out there or some form of load. If you use a meter and select current measuring and place that meter directly across the leads that would go to the battery you are effectively for all purposes placing a dead short across the charger system. That would explain the very high current of 8 amps you came up with. Additionally the high voltage you are seeing is open circuit voltage with no battery or load out there. I am sure that will drop with a battery in the circuit. Do not ever try to measure current placing the meter across the terminals.

On another note I am sure you have noticed the wire gauge to the battery terminals is large in these devices. This is for good reason as those batteries deliver a high current when the UPS is under a full load. Since adding a larger battery that battery will not be as close to the circuits as when using the internal battery I very strongly suggest you go with a larger wire gauge to connect the external battery! Good clean connections are very important!

Ron

Ohh I got it Ron!! thanks. Thats why the wires from my multimeter got hot and soft in 3-4 seconds. But what can I do now? the battery is of no use to be connected. all I have is just the UPS without battery. how could I measure the current now?

 

[aquamon]

I just want to increase the backup time

Well, usually if you past 15 minutes the output FET's will overheat and be stressed which will blow when power is restored.

Maybe your UPS has a battery timer cut-off, also.

So, doing this for more battery time may fail.

I use automotive batteries solely for a better replacement/availability and not for increased battery run-time and don't recommend latter.

Maybe you can try placing a 12v 'puter case fan inside on FET's. if running past 15 minutes, if allowed.

 

[Reloadron]

Ohh I got it Ron!! thanks. Thats why the wires from my multimeter got hot and soft in 3-4 seconds. But what can I do now? the battery is of no use to be connected. all I have is just the UPS without battery. how could I measure the current now?

I wouldn't worry about it. It worked before and will likely work again despite its bad experience. I would get the larger battery and go with it. Just remember what was covered here. I have done it before and it has worked out just fine. Let's assume the charging system is still OK. It will take longer to charge a larger battery but overall things should work.

Ron

 

[roltex_rohit123]

Well, usually if you past 15 minutes the output FET's will overheat and be stressed which will blow when power is restored.

Maybe your UPS has a battery timer cut-off, also.

So, doing this for more battery time may fail.

I use automotive batteries solely for a better replacement/availability and not for increased battery run-time and don't recommend latter.

Maybe you can try placing a 12v 'puter case fan inside on FET's. if running past 15 minutes, if allowed.

If the FET's blow can i replace them with a higher rating ones?

 

[crutschow]

If the FET's blow can i replace them with a higher rating ones?

If they blow it's more likely from overheating, which is mainly a function of the heat sink size. You may need a larger heatsink.

 

[Reloadron]

If they blow it's more likely from overheating, which is mainly a function of the heat sink size. You may need a larger heatsink.

Or maybe add a fan? All my larger units have fans for cooling.

Ron

 

[roltex_rohit123]

yes I will add a computer fan to it. it will consume power from the battery but would prevent the FET's from overheating.

 

[jamied_uk]

i am using 100 ah battery 12 volts 230 volts ac inverter @300 watts connected to pc using max amps of 4 amps input and am
getting static on s video connection on tv when using inverter is it a case of need 1000 watt inverter?

any ideas would be helpfull

 

[roltex_rohit123]

i am using 100 ah battery 12 volts 230 volts ac inverter @300 watts connected to pc using max amps of 4 amps input and am
getting static on s video connection on tv when using inverter is it a case of need 1000 watt inverter?

any ideas would be helpfull

I didnt exactly get you. be a little more explanative. do you mean you use 300 watts from a 1000 watts inverter? or you suggest a 1000 watts inverter. see.. the SMPS is rated 300 watts but justnormal machine running we do not use more than 100 watts. the CRT moniter uses most of the power. what is this static on the video connection? what does this mean. please explain me better may be i could help..