UPS Battery Failure
UPS Battery Failure
(OP)
Hi
I have a 40KVA ups and it's been three years since installation,the batteries are ten year design but they have failed instantly. The specs. on the are 90AH 12V in a serise combination giving 420VDC. I measured the ripple current and voltage and they are as follows 1.9A ac and 3.9V ac, IS this too high and if so do you have any documentation or could you point me to some useful liturature on ripple current?
B.F.H.
I have a 40KVA ups and it's been three years since installation,the batteries are ten year design but they have failed instantly. The specs. on the are 90AH 12V in a serise combination giving 420VDC. I measured the ripple current and voltage and they are as follows 1.9A ac and 3.9V ac, IS this too high and if so do you have any documentation or could you point me to some useful liturature on ripple current?
B.F.H.






RE: UPS Battery Failure
RE: UPS Battery Failure
I've done a lot of research on this problem myself and the values you stated for AC ripple seem very low. C&D's recommendation is no more than 5A (AC rms) ripple current per 100A-hr of battery capacity. Ripple voltage should be less than 0.5%rms of total DC float voltage.
Here is C&D's documentation on ripple:
http://www.dynastybattery.com/cd_dyn/contact/tech_support/2131.htm
How did your batteries fail? Did they fail a capacity test or fail to provide backup? VRLA (sealed) cells are notorious for opening without being detected until called upon to provide power. That is a major disadvantage for such a high DC bus voltage - you need many more cells which means that much more opportunity for that failure mode.
Have you verified that your float and equalize voltages are calibrated correctly (per battery manufacturer's recommendations)? I'm assuming you have sealed type batteries - equalizing is not good for them (it is beneficial with flooded or wet type cells) since the electrolyte is in a suspended medium and water can't be added.
High temperature is also a killer for batteries, though I'm sure this UPS is in a climate controlled room. There are many other factors that contribute to poor sealed battery performance in addition to their inherently inadequate design.
Please provide more details about your specific application and battery operating conditions such as float voltage, nominal battery charging volts per cell, ambient temperature, etc.
RE: UPS Battery Failure
RE: UPS Battery Failure
Were you able to find the failed battery(s)? How many failed?
RE: UPS Battery Failure
This is why the UPS industry to looking to go 'off-line', where the loads are fed from the utility directly during normal operation without the UPS being involved, yet within 4 to 6 milliseconds of a power disturbance, the batteries come in through inverters to pick up the loads.
This way, the batteries can be better 'taken care of' when 'off-line', and has a chance to really contribute when they are needed.
A lot of the UPS for PCs are of the off-line type. They are not always of good design, but they could be. The important thing is for the manufacturer to pay attention to taking care of the batteries [such as equalize charging them during off-line times]. Most UPS people pay a lot of attention in the 'boost mode' [when they take power from batteries to serve the emergency loads], yet precious little efforts in looking after batteries.
RE: UPS Battery Failure
RE: UPS Battery Failure
RE: UPS Battery Failure
What is one of the better battery testing analyzer on the market?
RE: UPS Battery Failure
http://www.mesta.com/PDF/UPS3500%20Specs.PDF
for typical UPS data offered by a UPS manufacturer.
RE: UPS Battery Failure
http://www.albercorp.com/ProdPageCellcorderCLC200.htm