48 volts UPS charging question

[GaleHawkins]

We have a Best 5.3 KVA system that was in the office complex we leased and the batteries died. It appears to have been installed years ago and not maintained. The spill proof batteries where dry when we pulled them out. Not knowing if the inverter error message was for real or because of the old batteries we did not want to pay $600 for a new set so I picked up 4 new deep cycle batteries at Wal-Mart. Since they are not sealed like the others we just left the front off of the case and assembled the 48 volt pack in front of the unit and made the connection. In just a few hours it brought the 4 new batteries to full charge and seems to be working fine.

My question has to do with battery charging principles. While I found one thread on this subject it was more of opinions than facts or links to other sources. If I build a second 48 volt pack and connect it in parallel, how will that effect the charger? Does a battery charger try to exceed its ability because of the change in load or just work normally but for twice as long to bring the batteries back to a full charge in the event of a power outage or both or some other answer?

I know the UPS output is fixed and my only desire to see if I can more or less double my run time without destroying the charger in the Best Unit. Over the past year we have just had the lights to blink a few times but if you are out in the utility room where the Best is hard wired into our electric system you can here it change over from time to time but not detect the loss of power visually. After hours we plan to only have 3 servers drawing a max of 500 watts. Thanks with your help on this charging question.

 

[technome]

No, the battery charger will not exceed it limits. The added 48 v pack will not cause undue hardship, but will require slightly more than twice the time to charge. "Slightly" due to the added internal resistance of the added batteries. Run time will basically be doubled

Before you add an another set, check the batteries are not excessively "gassing", produced by excessive charging voltage. This should not be an issue due to the circuitry designed for sealed batteries. Simple remove the cell covers, you should not see gas bubbles, maybe occasional small bubbles are OK, large and numerous bubbles, are not good, in a fully charged battery set. The room these batteries are in should have a small amount of air exchange, all open cell batteries do produce a small amount of hydrogen gas, (from first hand experience, it is explosive). As long as they are not contained in an airtight room they are safe.

 

[josepablomir]

Please consider the following:

1) The internal charger of the UPS could be not enough to charge the now bigger battery bank. The same 5, 10 or 20 Amps provided by it will be divided by every 48-Volts sub-bank you are connecting, and this will affect the recharge-cycle of the batteries which WILL affect the life-cycle of the batery's electrolyte. This could cause excesive overheating in the charger circuitry because of the extra charging-time.
Maybe you will need to by the "charger upgrades" offered by Best Power Techn. to guarantee a correct operation. Remember that your UPS is a PROTECTION device ussually intended to support CRITICAL EQUIPMENT!

2) By connecting batteries (or series of batteries) in parallel you are going to reduce the MTBF and the life expectancy of the whole bank. One damaged battery in one of the 48 volts series will repercute in all the other series connected in parallel. In the same way, one serie could reach overcharging conditions before the other.

Hope this help,
Jose.-


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Pablo Mir

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