We are now approaching the time of year when our National Grid is stressed. Winter months mean more demand for electricity and potentially less availability of renewable resources like solar and wind farms. The sun’s radiation and availability time is less and whilst it can be windy, turbines are idled back to prevent damage from overrun With this in mind, its even more likely that your UPS system will have to kick-in and fill momentary power breaks or even longer if there is a complete mains power failure.
Most uninterruptible power supplies use Valve-Regulated Lead-Acid (VRLA) batteries with a 3-5 year or 7-10 year design life. Often users don’t check the overall health of their UPS batteries and only uncover an alarm condition when they are the most exposed. Their systems crash and they have to wait for the mains power to return before they can reboot. The life expectancy of any battery (including VRLAs) will vary dependent upon a number of factors.
A proactive maintenance inspection and testing will help to ensure that the batteries powering your uninterruptible power supply are ready for any power failure. Here are some useful tips that can help with battery maintenance.
UPS Batteries Checklist
1. UPS Location and Environment
The VRLA batteries within your UPS system provide electrical power by way of a chemical reaction. It is important to ensure that the ambient temperature of the room the uninterruptible power supply is placed within is between 20-25 degrees centigrade and this means in most cases temperature-controlled. It is important to remember that whilst UPS system can typically operate up to 40degreesC without derating, for every one degree rise above 30degreesC battery life can half. This means that at 35degreesC you may not get more than a year from a 5 year design life battery.
Humidity can also be important as can placement away from air conditioning units which can leak excess moisture onto the UPS cabinet. Excessive dust and corrosive fumes should also be avoided.
When positioning the UPS system ensure that there is easy access to side panels, connectors and the front panel. This is importance during general operation and preventative maintenance visits. Easy access should also ensure connected load and mains power cables are not disturbed and ideally the UPS system should be installed with an external maintenance bypass switch. Most UPS require at least 100-150mm around the UPS for good air flow and it is important to ensure that air flow is maximise – don’t block air intakes or outlets or fan grills.
2. UPS and Battery Maintenance
VRLA batteries may be ‘maintenance free’ but this is not actually the case. A visual inspection is important as part of a preventative maintenance visit which could identify a bulging case or electrolyte deposit on terminals. Both can be signs of high internal impedance and that a battery is near to or has failed.
It is also important to have easy access to battery terminals to ensure that connections are tight and that the correct torque settings are applied. Over tighten a battery terminal and it can loosen inside the battery leading to a potential break or poor connection with internal lead plates.
Good access to the battery terminals also allows for onsite battery testing using a hand-held meter and probes. The batteries may be internal to the UPS but more likely for three-phase UPS systems and/or long runtimes the batteries will be in external battery cabinets or on open or enclosed racks or stands.
3. Battery Cycle Management
Battery calculations are an art form. Lifetimes can be quoted in terms of discharge characteristics at specific temperatures and cycles. When we talk about cycling a battery we mean a complete charge/discharge cycle. When a UPS system is first installed it may take around 5 complete cycles before the battery set reaches its calculated runtime. The runtime provided is the peak and from then on with each cycle performance will degrade. Your UPS battery should provide 200-300 complete cycles but it is importance to monitor performance and preferably with dummy load banks to ensure full availability.
4. VRLA Battery Degradation
Most VRLA battery lifetimes are calculated to reach no less than 80% of their useful capacity. Below this value, a battery’s performance can degrade rapidly and lead to other the failure of other batteries within a battery string. It is important to remember that a battery set or string is only as strong as the weakest battery in terms of electrical performance.
Performance curves are also non-linear for VRLA batteries. This means that the runtime available below 80% capacity can rapidly tail off leaving little battery support for the UPS inverter when the mains power fails.
5. Replacement Battery Options
It is rare to hold spare batteries on site. The first reason for this is that batteries need to be matched in terms of age. If you replace a battery within a 2 year old or more battery string, the new battery will degrade in performance quite rapidly to that of the ‘older’ ones. This is why UPS companies always recommend a complete battery swap-out or change.
If you do take your UPS system off-line also remember that you can only store batteries without charge for around 4-6 months. Even when not in use a battery will self-discharge and could reach a depth of discharge from which it is impossible to recover the battery – no matter how intensive the recharge regime. Degradation during storage can be slowed by storing VRLA batteries at 10degreesC or less but this is not recommended long term.
6. VRLA Battery Alternatives
There are today several alternatives including Lithium-ion (Li-ion) alternatives, super capacitors, fuels cells and flywheels. Each of these UPS battery alternatives requires a different type of maintenance regime and initial investment profile. Of the different types Lithium-ion batteries appear to be the most promising and offer a direct alternative to VRLA batteries. Within Europe and the UK there are now several Li-ion enabled UPS systems in test within IT and data centre environments. Whether Li-ion UPS become a standard will depend on cost and availability as VRLA batteries have a far lower cost-base and require less sophisticated battery charging and management.
For more information on UPS battery maintenance or to arrange an inspection or battery testing please contact the Eco Power projects team on 0800 612 7388.