Hey party people, I have a “fun” issue I am trying to find an “easy” solution too, I am sure something like this has to be a thing, maybe I just don’t know what it’s called or I will have to DIY something.
I am using solar inverters ( Link to my build post ) that have a 10-20ms switching time from grid to battery, it’s been fine historically, but either the new gear I added is pushing that time up to the higher end, or I had a blip, a cutover, a cut back and a blip during the cutback and that went over the ~11-17ms holdup time on the servers power supplies.
I am looking for something that I can use as a holdup capacitor or something on the output side that would get me to ~60-100ms of wiggle room, but I am fine with up to ~1 min. I don’t want to get a set of separate UPSs as it is two 30-amp circuits that are each at ~60-70% utilization.
Capacitors DO NOT work on AC! Don’t even try it, you’ll destroy the capacitor, your health (capacitors have nasty stuff inside) and will likely cause a fire.
So, you’ll need said capacitor on the DC side and directly attached to the inverter leads with heavy gauge wire (minimum the same gauge as the leads themselves). But it’s extremely jank, so you really, really need to know what you’re doing! The fact you asked the question informs us you lack the knowledge to do so safely, so DON’T!
I think your brain short-circuited when you read AC + capacitor and did not comprehend when I said “I am looking for something that I can use as a holdup capacitor or something on the output side” I am well aware you can’t just slap a cap on the AC side of things. I am just using it as a descriptive expression of what I am trying to achieve.
I suspect the solution to be something like a UPS that uses super caps for the energy store and is more or less the same power design as a double-conversion UPS.
If your inverters aren’t switching over fast enough then I think your only options are replacing them with faster switching units or replacing power supplies that can’t handle the input fluctuations caused by the switch over.
Putting a capacitor in the circuit would be dangerous to both equipment and health but if you were going to try… you’d probably want to swap the existing output caps in the power supply with more capacity. But really… just try a different (possibly higher wattage) power supply. I imagine that’s where most if not all the sensitivity to dirty AC would come from.
I am assuming you’ve omitted the logic behind your solution because at it’s core: Add capacitors to problem and it goes away : is correct
but not practical
Proper way would be: Giga UPS being fed off mains AC only when DC reaches a specific threshold as the batteries would be charged by your solar panels
This is the opposite of how most function
But any N+1 UPS could handle your requirements handily
This would obviously be the ideal solution as your entire grid becomes smoothed by one of these big bastards: (I deliberately showed an old model with 99+% efficiency available for sub $1000 minus batteries)
So, most of the time they do and it’s fine, but almost every solar inverter I have seen when you put them in a pair, jump up from ~10ms to ~20ms on the spec sheet if not even worse than that. mpp-solar does have a double conversion model, so thats 0ms, but I don’t really want to go that route.
and again, people are getting hung up on the word capacitor, should I just use the word buffer or accumulator or something else? It is all pretty much supermicro PSUs, so, ~1.2kw/each (PWS-1K28P-SQ and PWS-1K23A-1R), so I don’t think thats gonna do it.
Think you snipped too much out of the thought, was imagining a 2U half-width double conversion UPS with zero batteries, just a cap back, or maybe a quiet flywheel or something else that you could put 2 next to each other in a 2U space and it was just a buffer. I have already spent ~$7,000 on my current setup, so, not looking to rip and replace it.
I am looking to handle exceptions, this blip that took me down was during the night Hurricane Helene came through, but while I was asleep, so my assumption is that the grid side had an issue after recovering from the first one and it happened after the inverters decided the grid looked good again only to fail back to the grid right as it had an issue and tried to turn around and go back to the battery source and that was not fast enough during the odd ping pong event.
I also live in a smallish townhouse, so, I don’t really have the room for a big smexy unit.
The diagram shows that the inverter in the “UPS system” is always in use. If you’re willing to accept the losses of always doing AC > DC > AC conversion then you should look to reconfigure your existing inverters to never pull AC and only put power from mains into the system after being converted to DC.
I mean, if it was a constant issue, I would suck it up and move over to something like mpp solar 5048MK but need to check and see if they work with my LiFePo4 batteries BMS. However, my power bill is already in the $600 range, not sure I want to add ~10% to that.
Guess I could also move to a EG4 12kPV or a EG4 18kPV so get down to 10ms on a single inverter instead of the two SPF 3000TL LVM-ES I am using now to get 240V/ dual 120
If you look at the bottom of the page you linked note that the device uses an “online UPS topology” which means that it always runs power through the inverter. So it wouldn’t be fundamentally different to transitioning your existing system to always run through the inverters and only using mains via a conventional AC > DC battery charger.
Yeah, so the current ones run in “UPS mode” and are more or less “Line-interactive” similar to my old dual APC SMT3000RM2U and the 5048MKs are “Online” aka double conversion, but, it does eat more power, make more heat, etc… I am already fighting heat, had to add an extra 10K BTU AC unit in here to keep the heat manageable, so, ideally, would like to stay in the line-interactive area, just trying to handle exceptions, I can flip the input breakers all I want and everything is fine, the system has been running for ~2+ years and this is the first ever issue I have had where they let me down. This is really me chasing down corner/edge cases.
You may want to just tolerate the odd glitch then. I doubt any makeshift solutions are going to work.
If additional losses are out then I think you’re only other option would be finding the smallest(cheapest) capacity UPS that can still handle the current you need.
That’s what I was afraid of, was hoping someone had a knowledge nugget I did not for this kinda issue.
The UPS route would be rather expensive, would be something like 2 2700/3000va UPSs and I would have to get them upstairs and lose the 4U in rack space for them again. My hampster farm likes to eat.
