UPS/Battery backup thoughts and questions
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@bearer Thanks and that makes sense about a fraction of the battery capacity. But doesn't a the inverter in a UPS suffer the same limitation?
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@Dougal1957 Cheers Doug. I'm not too worried about bulk. The plan is that I'd instigate this after I've first moved the printer into my garage so I'll have more room and it won't matter what it looks like.
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@deckingman Next time I see any on site I'll take a pic or 2 for you
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Hi,
The simplest approach would be a UPS of needed capacity to handle the outages.
Is that just too expensive?
Frederick
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@fcwilt said in UPS/Battery backup thoughts and questions:
Hi,
The simplest approach would be a UPS of needed capacity to handle the outages.
Is that just too expensive?
Frederick
As per my OP if you read it, you'll see that is the solution I put forward. But it just seems a bit daft to have an inverter converting from DC to 220V AC at around 85% efficiency, then a PSU converting that AC back to 24v DC with another loss due to efficiency. Why not cut out the "middle men" and just have DC backup?
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Unless I missed it, we are missing a key fact from this discussion: What is the pattern of outages at your printing site?
For example, at my house, I have a fair number of mains outages that last less than 3 minutes. Often just a few seconds. In the three years I've lived here, outages that last more than a few minutes have only happened twice. And both of those were 8+ hours. A UPS that could keep my 1300+ watt mains bed heater for 8+ hours is certainly physically possible, but it is more bulk and expense than I desire.
Therefore...
I've elected to put my smaller, 12 or 24 volt bed, printers on a small UPS. My printer that is big enough to have a mains bed, the logic (and motors and so forth) are on another small UPS, the bed is not UPS, it is mains only. Obviously, the printer has to have to power cords.
This has worked very well. All short outages have been perfectly covered, and I've not had a long outage during a long print. Maybe someday I will; if it happens, Cest La Vie.
So let's ask it as a question: What is the typical pattern that you are trying to mitigate? Have you considered covering only the "90th percentile" (using that term very loosely) outage occurrences ?
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@deckingman said in UPS/Battery backup thoughts and questions:
As per my OP if you read it, you'll see that is the solution I put forward. But it just seems a bit daft to have an inverter converting from DC to 220V AC at around 85% efficiency, then a PSU converting that AC back to 24v DC with another loss due to efficiency. Why not cut out the "middle men" and just have DC backup?
There is engineering elegance to do it directly, bypassing the 220V stages. There is operational elegance, and robustness, in purchasing a totally "off the shelf" solution and just plugging it in and having it work.
Me, personally, on a 'backup' system, I'm going to go for operational elegance & robustness every time.
Having said that, Telcos have done this for ages. They run ALL THE TIME on 24V from batteries (or is it 48V? I don't remember) and their incoming utility and power distribution keeps those batteries charged.
Assuming that Lead Acid batteries are used, "simple parallel" at 24V is NOT a good strategy. Lead Acid batteries will lose capacity rapidly if held at their nominal voltage for long periods of time. They will not "be there when you need them" in terms of ability to deep discharge.
Instead, they need a battery charger designed for lead acid batteries. One that will 'charge' vs. 'float' at proper voltages. These voltages are all within the operating range of a Duet. So a three way connection of battery charger, batteries, Duet should work just fine.
With one caveat: Some battery chargers are also "maintainers" or "de-sulfate" devices. These put out very short spikes of voltage WAY WAY above charge/float, to stop (or even remove) plate sulfation. Obviously, such spikes should not go into a duet.
Summary: I, personally, would not worry about the losses and would just use off the shelf components. If you do choose to go 24V battery, it seems OK to connect charger/battery/duet all in parallel. Pick a charger that does NOT de-sulfate.
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@Danal most telco stuff now is -48Volt supply but in the earlier days of Cell sites it was +24V and there are still some of the kit around the batteries tend to be deep discharge Gell type cells and the control systems are designed to disconnect the batteries from the output when they fall to a certain voltage to save the cells (They can be expensive to replace)
Doug
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We run quite a few Harmer & Simmons modules in the field (for 48V telco stuff
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These are quite expensive but last very long (we have some modules older than 20 years).
I would personally go for "operational elegance" as Danal nicely describes because dealing with DC charging and batteries can be dangerous stuff (I've experienced a 24V battery explosion (due to bad maintenance), it was not pretty...) -
@whosrdaddy said in UPS/Battery backup thoughts and questions:
We run quite a few Harmer & Simmons modules in the field (for 48V telco stuff
).
These are quite expensive but last very long (we have some modules older than 20 years).
I would personally go for "operational elegance" as Danal nicely describes because dealing with DC charging and batteries can be dangerous stuff (I've experienced a 24V battery explosion (due to bad maintenance), it was not pretty...)This of course is very true I to have seen this the Harmer and Simmonds I have used where all 24V Systems using SM24-50 or SM1800 rectifiers but they do tend to be huge.
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@deckingman this Quint UPS’s are a 24vdc in 2vdc out. So you power supply is providing the power to the ups, which obviously charges the batteries and also runs your system. When power is lost, it switches over to batteries. There is no conversion between Ac and dc past the initial power supply. As far as I am aware with them, you can install as big of a battery system as you like. Having separate power supplies means you don’t have to replace yours
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@samlogan87 said in UPS/Battery backup thoughts and questions:
@deckingman this Quint UPS’s are a 24vdc in 2vdc out. So you power supply is providing the power to the ups, which obviously charges the batteries and also runs your system. When power is lost, it switches over to batteries. There is no conversion between Ac and dc past the initial power supply. As far as I am aware with them, you can install as big of a battery system as you like. Having separate power supplies means you don’t have to replace yours
That almost sounds too good to be true. I'll have to give that some serious thought. Many thanks.
BTW are you based in New Zealand?
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So the one question nobody's asked is "How much do you want to spend?"
Solar charge systems (without inverters) and 24v LiPo batteries are becoming cheaper and cheaper. There are even used LiPo batteries for sale on Ebay at a fraction of the cost of new ones and while it's really easy to kill lead acid batteries it's really hard to kill a LiPo so they usually have plenty of life to them. -
@gtj0 I guess if I went the "normal" UPS route I'd be looking at £150 to £200 ish. So that sort of budget. I like the idea of using Li-ion batteries. All my power saws and drill drivers that I used to use for deck building are Li-ion (18 and 36v). They don't run down slowly like NiMh or NiCd but keep full power right up until the time when they need charging. I've seen a few 24v golf cart/electric bike batteries that might do the job.
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Yeah there don't seem to be too many who do the dc to dc UPS's. We are heavily aligned with Schneider Electric and use their RTU's, PLC's and HMI's. We also use their power supplies usually but they don't do a DC to DC UPS which we wanted. And like I mentioned earlier, Phoenix Contact have different communication cards you can put into the Quint range that you could integrate into the Pi to give you comms for auto shut down etc, or just use the IO on the front. There is a battery mode relay so you could run that to the Pi with a timer to shut it down after a period of time. They are not the cheapest but at least you get the UPS and battery charger all in 1. I have a brewery which runs off a Pi and I am forever having to reload raspbian (I have a master backup of the OS and the brewing webserver), if we have a power outage or it gets disconnected and it corrupts the SD card. I could see this being a headache using the Pi's for printers as well. You could certainly fix that with the UPS although you can now get UPS's for Pi's by themselves anyway.
Here is an earlier prototype of the retrofit Pump Station Controllers we do. We usually put all the gear into the main panels. We were playing around with cabinet sizes to get it as small as possible. It has change a bit but you can see the QUINT power supply on the left and then the UPS next to it with the battery down the bottom just for size reference.
And yeap. I am in Christchurch NZ.
Regards,
Sam -
Hi Sam,
Those Phoenix contact DC UPS's are a bit pricey - about £200 here in the UK. But, the company I was looking at also do a Mean Well one which looks very similar for about £37 which seems maybe too cheap. Could you take a gander at the spec and let me know what you think? Here is a link https://uk.farnell.com/mean-well/dr-ups40/ups-module-24v-din-rail/dp/3003013#anchorTechnicalDOCS
BTW, my daughter married a Kiwi who originates from Wellington. They live in Canberra but a couple of years ago they put together a road trip for my wife and I so the 4 of us "did" NZ starting in Aukland at the top of North Island all the way down to Te Anau on South Island taking in Christchurch along the way. Is it still all held together with shipping containers since the earthquake or have they finally fixed all the cracks?
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Hi Ian,
They look like they would work as well. I use the odd Mean Well power supply for small projects (including my printer and brewery) and they are good. We have some data loggers that have a 4.5v to 7.5v external power supply connection so use the Mean Well 15W 5V units. At that price you may as well give it a try. Phoenix Contact do a lot with Oil and Gas and will probably have all the certifications to suit. I use their Radioline Radios as well, and much like the UPS and power supplies are not cheap.
Oh cool. Are they enjoying it over there? Did you enjoy the trip? I am originally from the North Island but live down here now. I think the South is much more spectacular. Christchurch is definitely on the mend. It has been a long drawn out process but all the containers that were shops in town are now buildings. The city is gettings its vibe back which is nice. If you are ever back down this way let me know.
Regards,
Sam -
Can't a solar charge controller be used for this application? I'm curious...
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@Edgars-Batna said in UPS/Battery backup thoughts and questions:
Can't a solar charge controller be used for this application? I'm curious...
For charging a DC 12/24v cells off a larger DC supply they are a great solution (because you can pick them up very cheaply). We do exactly this on our club safety boat where the main motor (it's electric) has a 60V battery pack, but we have a 12V cell in there to run the rest of the electrics and lights. This simply has a 10Euro consumer solar charge controller between it and the main battery bank. Works well.
