It is known that the duration and quality of equipment operation depend on the quality of power supply. Unwanted shutdowns, voltage dips (or, on the contrary, too high voltage) - all this does not contribute to long and high-quality work. Finally, some equipment (for example, medical equipment) must always work without failure, even during emergency power supply modes. Therefore, to ensure high-quality power supply without interruptions, a UPS is used.
The larger the load that needs to be supported in emergency mode, the more powerful the UPS must be.
Often, UPS suppliers not only install the UPS at the customer's site, but also commission it and instruct staff. Further, as a rule, the UPS is serviced either by its own technicians, or by the service department (often chosen on the advice of the supplier). The usual service interval is one year.
However, customers prefer not to delve into exactly how the test is carried out - whether the UPS is being tested under load, whether the service signals are analyzed - such questions are usually not asked by customers . Unfortunately, sometimes verification procedures do not go beyond signatures in acts.
As long as there are no failures in the network (or the UPS operates normally), the client is obviously satisfied with everything. But with the next accident, the equipment either shuts down or fails altogether - and this is all because the UPS did not work.
Alas, the second happened in one of the medical institutions - due to a non-operating UPS, one of the expensive components of the tomograph went out of order . In addition to the obvious losses due to the need to purchase and install the site, the client got a worse problem - the inability to diagnose patients for a long time.
The UPS is serviced by the technical service that commissioned the UPS. According to the entries in the maintenance log, the UPS must be in good working order. However, in an accident, it did not work. Why?
But because almost all technical specialists who service the UPS completely forget that the UPS, generally speaking, has batteries installed. And it depends on them to no less (and even more) whether the UPS can work normally in the emergency mode of the network.
Most UPSs (even the most expensive ones) control the voltage on the battery block in ENTIRE (as a rule, the batteries in the block are connected either in series or in series-parallel). The voltage on the battery pack is almost always within acceptable limits (even if the actual battery capacity is close to zero). This means that the UPS will not issue any errors and warnings about the installed batteries.
An important remark - sufficient voltage on the battery is by no meansdoes not mean sufficient capacity - we have met a huge number of batteries with normal voltage, which sagged almost to zero even with minimal load.
It is worth noting that the instructions for almost every UPS honestly say that in addition to the UPS itself, you should also check the batteries installed in it. And technicians do not like this terribly - as a rule, they say something like “Is this what I have to turn off everything, unscrew all the bolts, remove all the jumpers, measure each battery with a tester and then put everything back together? No, thank you. "
However, this is exactly how you should approachto scheduled maintenance. Even so, it is worth keeping in mind the fact that voltage is not always related to capacitance - even if a disgruntled technician does all of the above, thanks to the tester, he only knows the voltage value. And this is often not enough.
After a long introduction, let's move on to the technical details: the UPS has 32 DELTA HRL 12-75 batteries with a capacity of 75 Ah. We need to determine the state of the batteries and whether it is worth replacing them with new ones.
Using the AEA30V analyzer, we will measure the battery characteristics and compare them with the data from the documentation (according to the documentation, the internal resistance of a fully charged battery should not exceed 5.2 mΩ)
The bar graph below shows the voltage and internal resistance values of all 32 batteries installed in the UPS:
So, the internal resistance of all batteries is higher than indicated by the manufacturer.
Even if we assume that the technicians measured all the batteries at least once, they could not suspect that something was wrong - according to the voltage values, all the batteries seem to be charged. But the internal resistance speaks about the real state of the battery much more - but the testers that the technicians use (if they use it) do not measure the internal resistance.
So, is it worth trying to restore the battery, or is it better to replace them immediately? To make a decision, let's check for real capacity two batteries out of thirty-two - with the best and with the worst characteristics of all.
Let's start with the worst battery (# 4). To test the battery, we use the EHIP Activator AEAC-12V:
An important note: when the battery is discharged with a current of 7.5 Amperes to a voltage of 10.5 Volts, it should give 75 Ah. The actual capacity of the battery is determined at the first discharge, the actual available capacity (real capacity) - at the second discharge after charging.
As you can see, the battery gave only 1.67 Ah. At the same time, pay attention to the charging time of the battery at each of the stages of the second charge (except for the last stage, at which the battery is equalized within three hours) - the battery simply "flew" these steps according to the control value - in other words, the voltage on it almost instantly reached the set values. This proves once again that it is far from always possible to draw a conclusion about the capacity by voltage.
Further - the "best" battery (No. 25):
As you can see, battery # 25 delivered 74.55 Ah. This means that we have a good chance to restore the batteries, which have characteristics similar to the battery No. 25.
It is up to the client to buy a new set of 32 batteries or buy only a replacement for those that have failed. The client chose the “saving” method, and we get to work.
We will service all batteries, except for No. 4 and No. 14 - their internal resistance is too high, and, as we saw earlier with the example of battery No. 4, the capacity of a battery with similar characteristics is close to zero.
We start by adding distilled water. But ... batteries are maintenance-free, aren't they? The documentation says so! But in fact, almost all "maintenance-free" batteries have a cover that can be removed using, for example, a clerical knife. And in the lid itself you can see a hole for the outlet of gases.
Let's take a closer look at the FIRST DISCHARGE data obtained during the control-training cycle:
It is worth noting that the capacity of the battery No. 8 is significantly lower than that of the others.
After the first discharge, we charged the battery according to the manufacturer's recommendations. To determine the actual available capacity, we perform the second discharge and, based on the data obtained, construct a histogram:
If we compare the values of the given capacity for the first and second category, you can see that the batteries are degrading in capacity - all the batteries (except for the battery No. 8) gave a little less in the second category than in the first. This degradation is due to the age of the battery and their improper operation (incorrect from a physical point of view - any battery loses water during operation and needs to be periodically refilled with distilled water, but the manufacturer declares the battery as maintenance-free). Of course, the degradation of the battery could not but affect the values of the internal resistance - they are much higher than the 5.2 mΩ declared by the manufacturer. Finally, you will notice that the batteries have uneven wear.
Why did it happen? Two main factors can be distinguished:
1) Arrhenius's law: the rate of chemical reactions increases with increasing temperature. In the customer's UPS, the batteries were distributed in four tiers in height - the higher the tier, the higher the temperature, and, as a consequence, the rate of chemical reactions.
2) The batteries initially had an imbalance and were installed immediately after purchase, without resistance selection and capacity verification. In the course of operation, this imbalance only worsened.
Conclusion: all batteries except No. 4, No. 8 and No. 14 are suitable for operation. Battery # 1 and # 15 can be saved as a backup.
As a result, the client bought 5 new batteries, and left batteries # 1 and # 15 as backup.
The customer has already "burned out" because of the non-operational UPS, and the technical service that maintained the UPS, for various reasons (from obvious laziness to the lack of necessary equipment), is unable to take adequate measures. In such a situation, the client could well “freak out” and, in addition to the tomograph unit, replace ALL batteries installed in the UPS. Considering the cost of one battery at 19,000 rubles, this would cost the client about 608,000 rubles.
However, during the tests it was found that even the worst battery has 83% of the capacity declared by the manufacturer (we do not take into account the battery with a capacity close to zero). This means that it is enough to replace only the faulty batteries, which the client did.