In this episode of the Pipeliners Podcast, Russel Treat welcomes back Andre Scholtz from Solarcraft to discuss designing reliable uninterruptible power supplies (UPS) for field applications. They delve into the differences between UPS systems and solar power supplies, the importance of understanding load requirements, and the various types of UPS systems and their applications.

Russel and Andre emphasize the importance of understanding the specific requirements and environmental conditions when designing UPS systems. Proper design, monitoring, and maintenance can significantly enhance the reliability and longevity of these systems in the field.

Field UPS Power Show Notes, Links, and Insider Terms

• Andre Scholtz is the Technical Director at Solarcraft. Connect with Andre on LinkedIn.
  • Solarcraft, Inc. is a Houston-based full-service manufacturing company that engineers and builds industrial Solar Power Systems, Backup Power Systems, Control Panels, and Electrical Shelters for critical automation and communication.
• Uninterruptible power supply (UPS) is a device that provides backup power to electrical systems during power outages or fluctuations. It has an internal battery that allows connected devices to run for at least a short time when the primary power source is lost, protecting equipment from damage.
• Load is the consumption of power from the instruments being used in the system.
• Online UPS is always powering the load through an inverter, providing continuous and clean power.
• Offline UPS powers the load directly from line power until it switches to the inverter during a power failure.
• Line Interactive UPS corrects minor power issues like brownouts and frequency changes while also switching to inverter power during failures.

Field UPS Power Full Episode Transcript

Russel Treat: Welcome to the “Pipeliners Podcast,” episode 344, sponsored by Solarcraft, providing high quality engineered solutions for powering, sheltering, and operating critical field automation infrastructure. Find out more about Solarcraft at Solarcraft.net.

Announcer: The Pipeliners Podcast, where professionals, bubba geeks, and industry insiders share their knowledge and experience about technology, projects, and pipeline operations. Now, your host, Russel Treat.

Russel: Thanks for listening. I appreciate you taking the time, and to show that appreciation, we give away a customized YETI tumbler to one listener every episode. This week, our winner is Mahesh Iyer with Shell Pipeline. To learn how you can win this prize, stick around till the end of the episode.

This week, we speak with Andre Scholtz of Solarcraft who joins us to talk about designing reliable field UPS power. Andre, welcome back to the Pipeliners Podcast.

Andre Scholtz: How are you doing, sir?

Russel: I’m doing well. The last time we talked, we talked about solar, and this time I want to talk to you about UPS. UPS is uninterruptible power supply. Really the topic here is designing reliable UPS.

Last time we talked about understanding load as it relates to the solar. How is understanding load related to UPS different from understanding load as it relates to the solar panels themselves?

Andre: That’s a good question. It’s not very different. UPSs and solar power supplies are inherently the same thing, that they are a form of energy input where you also store the energy, but you continuously power the load.

Knowing how big the drain on the system is is absolutely crucial for the design of it. Really what you have is a bucket full of water that you knock a hole in the side with of a given size, and you have to make sure that bucket stays full. If you want it to stay full for more days, you’re going to have to put more bucket in. Determining or knowing the size of the drain is fundamental and it’s absolutely the first step.

What we mentioned before as a recap is that, it is OK to look at data sheets and their numbers for all the equipment that you need to back up, but you just have to keep in mind that very often people put maximum numbers over there, that is not the real continuous draw.

You are far better off measuring the load that you need to back up than calculating it from vendors’ data sheets. Once you have calculated it like that, then you can sit down and get into the UPS system, picking batteries, picking power supplies, choosing redundancy options, things like that.

Russel: The other thing about UPSs in the field, is it’s not uncommon to have UPSs in places where my primary power is utility power and the UPS is there to provide ongoing operation for a period of time should I lose utility power.

Distinct from a solar system, which would have batteries in a solar kit, and you try to keep it running all the time, a UPS in some cases are there to hold the load for a period of time. Understanding that period of time can be really critical. Am I going to hold that load for an hour, four hours a day, three days?

Then what is the nature of the load I’m holding and am I holding just monitoring load, but I’m not actually going to be able to run motors and such? There’s a little bit about understanding that aspect of what you’re doing with UPS that’s unique.

Andre: Yes, absolutely. You don’t even have to have the same input voltage into a UPS as the output voltage. You would think that you do, but more often than not, it doesn’t really matter what power is available, because a UPS and specifically a dual conversion online UPS has a rectifier on its input side, a battery charger, so to speak, maintaining a set of batteries who in turn feed an inverter that feeds the load.

What voltage do you have to put into that rectifier? You just pick a rectifier that suits the input power. Then you pick an inverter that suits the output power. We can run a 240 volt “split phase” load from a single phase 480 volt input, for instance. You don’t have to have them exactly the same.

What’s also important, having an online UPS means that your rectifier must be capable of absolutely, always supplying the input power to that inverter, which in turn powers the load, but also have residual power left to charge the batteries for when a power failure reconnects.

You can’t have, say, a one kilowatt input for a one kilowatt load. You have to have about a two kilowatt input for a one kilowatt load. You just have to balance it and know which components need to be which size, which have to be which voltage for a given load size that you spend so many hours calculating.

Russel: I’m a sailor. I watch some YouTube channels. One of the big trends in sailboats, particularly for people that are long distance cruisers, is they’re moving away from diesel propane.

They’re moving to all electric sailboats using lithium batteries and charging systems and solar arrays and wind power, even to the point that they’re driving their engines with electrical power versus motor driven. Fascinating, the complexity of managing those loads and how they do that. It’s not unlike the conversation we’re having now.

Andre: Just like solar systems, if you have to maintain a given load for, say, a day–a 24 hour backup is a common number–as it pertains to things in the field in the middle of nowhere, very often, you would size your battery bank according to how long does it take somebody to get there once the thing makes an alarm.

If a UPS sits in a manufacturing plant somewhere with people all around, you don’t need a lot of backup. Very often, you only need to bridge how long it takes between the power failure and the generator starting, maybe 10 seconds, maybe 15 seconds.

Out in the boondocks, now it’s a different story. How long does it take a guy to get there on Christmas Eve when everybody’s been drinking? That may be a two day backup right there.

Russel: There are places in Wyoming and other places like that where it may take me a full day to get to some place, just to plan the trip and make the journey, depending on what time of year is and conditions of the roads and all that.

Andre: The majority of the money in a UPS system goes towards rectifiers, inverters, switchgear, labor, making the enclosure and everything. Making the enclosure a little bigger just to accommodate more batteries doesn’t add to the price that much.

Also, batteries do have this characteristic that the more batteries you put there, the longer the whole battery bank lives. In fact, it’s again one of those somewhat exponential things, where if you put two times more battery than you need, the bank will last four times as long.

If you put three times more battery than you need, the battery bank probably lasts nine times as long, something along those lines. So just do it.

Russel: That’s good advice, for all kinds of reasons. Tell me a little bit. As we were teeing this conversation up, you were talking to me a little bit about various kinds of UPSs. What are the various kinds of UPSs? How are they different?

Andre: There are two big distinctions. The one kind of UPS would be an online UPS. The other one is an offline UPS. An online UPS, also called a dual conversion UPS, is what I’ve mentioned a minute ago, where the loads are absolutely always powered by an inverter.

None of the line power, with all its messiness and on and off ness, ever makes it to the loads. The inverter is always straight from a battery bank, which is always maintained by a charger, so to speak.

If you go to your favorite big box store and you buy a car battery charger and a car battery and a little inverter in the same section where you would find the battery chargers, you can make yourself an online UPS right there.

You plug the charger into the wall. You connect it to the battery, connect the inverter to the battery. You plug your computer into the inverter. Now, it doesn’t matter if you pull the plug out of the wall. The inverter is still just being fed from a full battery. It’s a very bad UPS, but it explains the thing.

Russel: It explains the principle.

Andre: Yeah, what does an online UPS look like. An offline UPS has a battery bank off to the side with a charger connected to it. It maintains the battery bank full. Then there’s an inverter connected to that battery bank that is always on, but it’s not feeding the load.

Between the line power that feeds the rectifier and the load is a relay that flips or chooses between sending power to the load from the wall or the line power or from the inverter.

The most–-what do you call it–prominent characteristic of an offline inverter is there’s a tiny little gap, maybe 20, 30 milliseconds, in the power supply if there’s a power failure, from a relay flying through the air and hitting the inverter side of it. Now you’re being powered from the inverter.

Not every load cares about that. Certainly, a computer wouldn’t. A refrigerator wouldn’t. A microwave wouldn’t care. Once in a while, you may encounter sensitive electronics that are not properly buffered. Cheaper PLCs, for instance, are not happy with an offline UPS. You have to give them an online UPS.

That’s the big difference. Is the inverter always supplying the load? Or is there a relay between the inverter and the line power, and when the power fails, it’ll flip to the inverter side of it?

There is a third kind. Many inverter charges are just like that. They call them line interactive UPSs. It does happen that, say, the incoming line power at 110, 120 volts would have somewhat of a brownout. Maybe the 110 volts drops to like 90 or 80. In that case, the inverter will boost a bit and lift the voltage to the load. Or if the frequency gets out of whack, it’ll take over and correct it.

It interacts with the line power. It fills in gaps. It’ll also certainly take over when the power fails altogether. It’s not a common form of UPS. There’s three, but really just two.

Russel: Interesting. The line interactive is interesting to me. If I were going to speculate about the future, I would say you’re probably going to see more of those.

Andre: Good point. They were around. When you buy inverter chargers, many of them are just that. They are offline UPSs. If you pay a little bit more, they’ll be a line interactive UPS. It’s becoming more and more frequent or more common now.

Russel: Given where we’re moving in terms of computers and everything else, that, to me, makes more sense. I want to talk too about environmental considerations. We’ve been talking primarily about remote field sites.

In our world, in my world, you find UPSs used in three different situations. One situation would be an indoor UPS that is backing up power around a bank of computers. It’s got nice, conditioned AC power coming into it.

Another type would be I’ve got a UPS. It’s in the field, but it’s in a building. That building at some level of environmental control. It’s got a door and maybe an air conditioner to keep the temperature under 85. Then the last type is it’s just out in the freaking boonies. It is what it is. How do those three different situations impact designing your UPS?

Andre: The first thing that comes to mind is the more controlled the environment is, the cheaper the UPS is. That’s just a fact, for two reasons. The one is every inverter out there will derate as it gets hotter. They’ll publish a given output power at room temperature, like 25 degrees Celsius.

They would also, in their data sheet, say, “For every 10 degrees, it drops so many percent of the output power.” What you think is a five kilowatt output may in fact, when it’s really cooking, may only be capable of delivering three kilowatt without shutting down.

Blowing fans on them helps a bit, but not if it’s 120 degrees outside. In that case, we have to preemptively derate inverter systems to be able to handle really high temperatures. You don’t just go and pick your favorite inverter from Amazon and build a reliable field UPS that supports a safety system. You’ll embarrass yourself. There are better equipment out there. Don’t use the rubbish.

Another issue, conversely, is with batteries. The colder you make them, the less their capacity is. Every battery data sheet usually has a little capacity over temperature chart. For lead acid batteries, if it says 100 amp hour on the battery, that will be at room temperature, 25 degrees Celsius. What’s that in Fahrenheit? It’s like 72.

By the time the battery is at zero degrees, which may be, say, when there’s snow on the ground, it will only be a 70 amp hour battery.

When you design this battery bank for a given backup time, you have to go and make sure if I need to have 100 amp hours’ worth of load that I have to back up, I can’t just put 100 amp hour battery because in really cold weather that’s going to be a 60 or 70 amp hour battery, you have to put more of them.

That’s important for people to design this stuff, but it’s also very important for people who get quotes from people to build UPSs to discern whether these people actually know their business or not. Do they derate inverter output for temperature? Do they derate battery capacity size for coldness?

Russel: What about the temperature? For extreme heat?

Andre: Batteries perform better when they’re hotter, but they die quicker. It’s like a teenager on cocaine. They bounce around, but they’re going to die young. What kills a battery or ages it prematurely is frequent and deep cycling, and especially sitting discharge, and then also heat.

If you shade a battery bank properly, even in a place like New Mexico or West Texas, it’s not a big deal. The common modern crop of Gel and AGM batteries are perfectly capable of that.

If you have a big battery bank, they normally don’t track the air temperature during the day. The battery will never get as hot as the air does, it’s too heavy, especially if you have a big battery bank and you put them next to each other. Don’t separate batteries, you get them as close as you can together, make them touch each other so that you have all that mass in as little of a space as possible.

Then they tend to track the daily mean temperature, the average between day and night. During the day, the outside of the box may be really hot, but when you feel the batteries, they’ll be cool to the touch. In that case, you’re fine. If you put that box in the sun, that will not be the case, so get it out of the sun.

I don’t know, big problem for us is Kuwait. It gets phenomenally hot over there. At that point, you absolutely can’t use the lithium batteries anymore unless you spend energy on keeping them cool. There are particular mixtures of lead acid batteries that are designed for high temperatures for UPSs, such as the Fahrenheit series.

Russel: That actually answers another question I was going to ask you is, what’s preferred lead acid or lithium, and I guess it depends on what the use is.

Andre: Yeah, that’s true. Also, and how heavy can you tolerate it being?

Russel: Right. Interesting.

Andre: Lithium batteries don’t do so well when it’s cold. They discharge fine, but they are very hard to charge when it’s freezing outside. People do make lithium batteries that have internal heaters.

For UPSs that works wonderfully because you would keep them charged and the discharging can happen colder than the charging can happen. You just got to make sure you’re able to afford those batteries actually. They’re not necessarily much smaller, but they certainly are a whole lot lighter.

You can cycle lithium batteries much more frequently and deeper than you can lead acid batteries. On the whole, UPSs don’t cycle that much anyway. The power failures are not as frequent. For something like solar, that’s different, but for UPSs especially field UPSs lead acid batteries, they do just fine lately.

Russel: Interesting. What about battery capacity and temperature? You talked about this a little bit. Certainly, the amount of load and the length of time I can power the load diminishes as I get colder. Then as I get hotter, I can still support the load, but the useful life of the battery diminishes.

Andre: That’s right. Let’s say a battery bank in really hot conditions, like excessively hot with the sun shining on the box, would probably be three or four years or so. Then it’ll be dead. In a very cold place, if you properly compensated for that loss in capacity, you’re probably good for 15 or 20 years if you don’t put rubbish batteries there.

As long as you know how much the capacity drops with temperature–you can just find it right on the battery’s data sheet if it’s a good battery–and you compensate for that, in cold environments, your batteries will live way longer than they do in hot places.

They’ll perform a little better, but the performance is cheap. It’s not something to chase. It’s longevity which is what you’re chasing with batteries.

Russel: Last subject. What’s necessary? What should you be doing to maintain UPS batteries? We’ve talked about just how you use them. Are there any other things that you should be doing to extend the useful life of the batteries themselves?

Andre: That’s a loaded topic right there. Here’s the two extremes. Putting a charger in a box with a battery or two batteries in series, on a pole, maintaining a small load in the countryside, you’re not really going to do anything. You’re going to put an alarm on the battery voltage, but you fall back on good design to make sure the thing will last long.

The reason is there are very few batteries there. A battery bank is much like a chain where one link’s failure will cost you the entire battery bank or some costly exercise. Replacing one battery in a battery bank is a bad idea.

Most of the serious maintenance and monitoring that you would do on battery banks to make sure they live long comes with very large battery banks, such as you would find in server rooms and things like that. There, they go all out. They would measure, such as an electric car would, the voltage on every cell in that system.

You would have active battery balances that take energy from the cell with the highest voltage and stick it in the cell with the lowest voltage. You do that for a second or two. Then you monitor again. You repeat and repeat until everything is nice and balanced and you can keep it like that.

That way, you can also tell if one of these batteries is taking up too much charge, or, if you have such a fancy system that you can measure the resistance of every particular battery, you can flag the bad ones.

If you can flag them early enough while every other battery is still within spec, then you can replace that battery with a new one. Otherwise, if you don’t monitor like that, the battery bank as a whole tends to go south.

I don’t know if we’ve got time for this, but here’s an example. If you have four balloons that you put on one piece of pipe with your little pipe manifold…These balloons were manufactured on the same day. They came from the same packet. They’re equally old. You connect them to your little pipe. You blow on one end of the pipe. You would expect all four balloons to inflate at exactly the same rate.

If you leave them inflated, such as you would with a UPS–it’s a terrible analogy–and you deflate them again, that balloon will not be as stiff and tight as it was when it was new. It’ll kind of be limp.

If you then replace one of those balloons with a brand new one and you try to inflate them again, you may find that the new, tight one doesn’t even inflate at all. The other three that are old will inflate more, but you’re still going to keep blowing to a particular pressure.

Why is it a good analogy? It’s because a charger doesn’t know the individual battery voltage, such as these common charges are. They just look for a combined voltage. If you have two 12 volt batteries in series, it could be your charge is aiming for 28 volts. One of your batteries is at 10 volts. The other one is at 18 volts. Both of them are dying, but the charger doesn’t know it.

Monitoring becomes way more important the more you have in series and the more batteries you have at a site.

Russel: That makes sense. Andre, I’ve got to say, that kind of understanding about how batteries work and how they work in groups. I’m thinking a little bit about electric cars and how they do their batteries.

If you don’t know this, if you don’t understand this, you would think, “If I’ve got one segment of batteries that’s gone bad, I could just pull that segment out and put a new segment in. I’m going to be fine.” That’s not really the way it works.

It’s a system. Putting something new in an old system, it’s just not going to work the same way as putting complete new versus “Can I find something out of an old system that’s not dead but is more in the same shape as the ones I’m working on?” It’s like everything. It gets more complex.

Andre: I don’t want to honk our horn too much, but at Solarcraft, we’ve learned all these lessons. We’ve made every mistake.

By now, when we design a new UPS, we know, for a given location, for a given load, what should this battery bank look like, how can we maybe change the loads to make it more reliable, how can we change the installation, where it is on the site, to make the whole thing more reliable, all such things.

Russel: I say this all the time. Experience is what you get when you didn’t get what you wanted. Wisdom is what you get if you can learn the right lesson.

Andre: Certainly, yes.

Russel: Doing the same thing, working in the same environment, if you can learn and build wisdom, then that’s some real value. Certainly, you guys have that. Anyways, again, awesome conversation. Every time I talk to you, I learn something. Really appreciate your time. Thank you, Andre.

Andre: Thank you very much. Appreciate it.

Russel: I hope you enjoyed this week’s episode of the Pipeliners Podcast and our conversation with Andre. Just a reminder before you go, you should register to win our customized Pipeliners Podcast YETI tumbler. Simply visit PipelinePodcastNetwork.com/Win and enter yourself in the drawing.

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Transcription by CastingWords