Downgrading UPS?

[Curious.George]

I just inherited several APC RT2200 (SURTA2200XL) UPSs with "add-on" battery packs. Due to their size (ampacity), they require 20A branch circuits.

I'd like to use them on standard 15A branch circuits. I like the extended up-time they'll afford (esp with the add-on packs!) moreso than the power handling capability.

So, I can easily replace the power cord to workaround that obstacle. And, probably replace the breaker with one of a lower rating. (The output connections are all NEMA 5-15R so there shouldn't be a Code issue, there) But, I can't prevent the UPS from trying (and succeeding) to service a 20A load (short of a firmware hack).

If I take care to ensure my load never exceeds the ~15A (in addition to the above changes), is there ever any condition where the UPS could try to PULL more than 15A from the mains? I.e., would the UPS ever be "surprised" to find the breaker tripping in what it considers "normal operation"?

[eccerr0r]

Re: Downgrading UPS?

add a few more loops of wire around the current transformer to detect current to fake a 20A situation? Or is it hall effect?

I doubt it will ever pull more than 15A unless you pull 15A (and don't forget to add in charging current).

(The battery side, however, is a different story. I was able to get a true sine inverter and found the battery side current draw is really unpredictable except after reaching some sort of steady state...)

[petehall347]

Re: Downgrading UPS?

i do not understand this bit "But, I can't prevent the UPS from trying (and succeeding) to service a 20A load"
surely the load takes what it wants from the 20 amps available ? whether its anything from zero to 20 amps . or is online not a pass through situation ?
i cant see why it should matter so long as the load never exceeds 15 amps .

[Curious.George]

Re: Downgrading UPS?

add a few more loops of wire around the current transformer to detect current to fake a 20A situation? Or is it hall effect?

That's an idea. I'd have to have a look inside to know for sure.

I doubt it will ever pull more than 15A unless you pull 15A (and don't forget to add in charging current).

Not just charging current. Most of these units run "test/calibration" cycles WHILE powering their loads. I would imagine they do this by imposing some sort of load on themselves (?) but I've never checked to see just how big of a load that is.

If it first isolates itself from the line, then it wouldn't really matter (much). OTOH, if this load is added to the normal load, then it could be reflected back to the mains.

(The battery side, however, is a different story. I was able to get a true sine inverter and found the battery side current draw is really unpredictable except after reaching some sort of steady state...)

These are double conversion, pure sine inverters. So, the load is always powered by the inverter and reflected back to the mains along with conversion inefficiencies and charging currents. By contrast, the cheaper "standby" or line-interactive units really only present the load to the mains plus any charging current (which can intentionally be limited).

[Curious.George]

Re: Downgrading UPS?

i do not understand this bit "But, I can't prevent the UPS from trying (and succeeding) to service a 20A load"
surely the load takes what it wants from the 20 amps available ? whether its anything from zero to 20 amps . or is online not a pass through situation ?
i cant see why it should matter so long as the load never exceeds 15 amps .

The designers of the UPS could have assumed that they had a 2400W supply available to them, when on mains current -- that's the design spec.

They could see that they are currently powering (on mains) an 1800W load (e.g., a 15A branch circuit's capacity) and feel confident that they can pull another 100W to charge the batteries.

Or, could know that the 1800W that they are delivering to the load has a 200W conversion loss added (90% efficiency) -- but safely handled by the 2400W mains that is supposedly available (but actually isn't!)

I want to know what sort of assumptions were likely made by the designers so I can safely derate the output and KNOW that the UPS will never "freak out".

[eccerr0r]

Re: Downgrading UPS?

It's a good question what it uses as a test load; I have a feeling it must use the actual load as it is - using a dummy load wouldn't really test if the battery would simply die with the real load. And having a full capacity dummy load should be fairly easily spottable in the device if it had one, but if there was a power outage during the selftest then the system would be dead...

[Curious.George]

Re: Downgrading UPS?

It's a good question what it uses as a test load; I have a feeling it must use the actual load as it is - using a dummy load wouldn't really test if the battery would simply die with the real load. And having a full capacity dummy load should be fairly easily spottable in the device if it had one, but if there was a power outage during the selftest then the system would be dead...

If there was no load on the unit, then there would be no "test". E.g., most of them initiate a test cycle when they are first powered on. You can't count on a load being in place, at that time (e.g., I always turn everything off before powering down the UPSs so there's nothing there when it comes back on).

If they use the actual load as the test load, then a test would cause the output to fall off even in the presence of mains voltage (because they would have switched off of the mains, effectively simulating an outage).

I should see if I can scrounge up some "dead"/weak batteries and run a test: does the output fail during a test cycle (because the mains are switched off and the device relies on the weak battery, exclusively)?

There may be some middle ground where they can note how quickly the battery voltage is falling under whatever load you have attached and using that to make an assessment of the battery's integrity. But, if the battery has been too far depleted, the load might be dropped.

[I know that if the battery is not present it complains before it even gets started]

Schematics would, of course, make this easier to resolve...

[budm]

Re: Downgrading UPS?

Just think the UPS as 1600W generator when it runs on batteries that can handle 1600W load, 15A breaker on your breaker panel to limit how much total current you can draw from the outlet.
I look at the user manual, I do not see any circuit breaker on the front or the rear panel at all.

Your model has output rating of 1600W/2.2KVA.
VA and Watts:
https://switchon.eaton.com/power-ess...-101/va-watts?
https://www.power-solutions.com/watts-va

Double conversion UPS system:
http://www.apc.com/us/en/faqs/FA157448/
https://standbysystems.co.za/ups-sys...nversion-mean/

http://www.apc.com/shop/us/en/produc.../P-SURTA2200XL

[Curious.George]

Re: Downgrading UPS?

Just think the UPS as 1600W generator when it runs on batteries that can handle 1600W load, 15A breaker on your breaker panel to limit how much total current you can draw from the outlet.

If the unit is NOT connected to the mains, then all is well -- it delivers its rated power from the batteries until the batteries are depleted. The utility is never impacted. The problem lies when the unit is connected to a branch circuit that is insufficient to satisfy the needs of the device, as envisioned by its designers.

I look at the user manual, I do not see any circuit breaker on the front or the rear panel at all.

Dunno. I've not brought them in the house as they -- with their external battery packs -- are very large. Women tend to not appreciate these sorts of things "cluttering up the place"

Your model has output rating of 1600W/2.2KVA.

Correct. At an input PF of "> .95" let's just call it unity and treat the UPS as a PFC for the "load(s)". Then we can just talk watts reflected back to the input branch circuit.

At ~90% efficient (89.1), that 1600W of power delivered to the load would represent 1778W at the mains. Add to that the 120W that it delivers to the charging circuit and you're already at 1900W -- more than 100% of a 15A branch circuit.

[This assumes the charging power is delivered at 100% efficiency wrt the mains.]

If the test cycle adds to this, then things are even worse.

Given that you'd normally derate a 15A circuit to ~12A (1440W), its clear that you don't want the UPS to THINK it can even begin to approach its rated load capacity.

Tweeking the current sense as suggested by eccer0r could, possibly, be a clever dodge. Trick the UPS into thinking that it is delivering more current to its load than it actually is. But, who's to say how the software will interpret that? Will it report efficiencies of 105%? Will the software crash because it wasn't expecting such computational results? Will it wonder why so much power (charging circuit) is being drawn when it has switched OFF the load?

<shrug> Hard to say what the designers had in mind and how "integrated" the various aspect of the design are, in fact. Does the left hand know what the right is doing??

[CapLeaker]

Re: Downgrading UPS?

I just inherited several APC RT2200 (SURTA2200XL) UPSs with "add-on" battery packs. Due to their size (ampacity), they require 20A branch circuits.

I'd like to use them on standard 15A branch circuits. I like the extended up-time they'll afford (esp with the add-on packs!) moreso than the power handling capability.

So, I can easily replace the power cord to workaround that obstacle. And, probably replace the breaker with one of a lower rating. (The output connections are all NEMA 5-15R so there shouldn't be a Code issue, there) But, I can't prevent the UPS from trying (and succeeding) to service a 20A load (short of a firmware hack).

If I take care to ensure my load never exceeds the ~15A (in addition to the above changes), is there ever any condition where the UPS could try to PULL more than 15A from the mains? I.e., would the UPS ever be "surprised" to find the breaker tripping in what it considers "normal operation"?

That what I did to the SMT-2200 tower. I just put a different end on. Runs like that for 8 years my computers, network, NAS, all the PSU's for the ham gear etc. Never popped a fuse. For me it wasn't the power it can deliver, it was more how long it could provide the power to all that gear. It uses four 18Ah batteries, 2 in series, then the 2 parallel making a total of 48V 36Ah.

[eccerr0r]

Re: Downgrading UPS?

Eh no, there is always a load for testing. The parasitic load of inverting is a load in of itself!

Pathetic load, but it's a load, and if all you're powering is nothing, that's good enough of a test!

[Curious.George]

Re: Downgrading UPS?

That what I did to the SMT-2200 tower. I just put a different end on.

By "end on" do you mean "mains plug"?

Runs like that for 8 years my computers, network, NAS, all the PSU's for the ham gear etc. Never popped a fuse. For me it wasn't the power it can deliver, it was more how long it could provide the power to all that gear.

But what's the total load that it sees (W/VA)? In my case, its not uncommon to have 500 - 1000+W loads on each UPS. In those cases, I'm primarily looking for help coasting through switching transients, dim outs, brown outs, etc. so I want ampacity.

In other cases (e.g., for this workstation), the loads are much smaller (maybe 50W, total, for the workstation, monitor, router and "modem") so I'm looking for up-time (WHr)/

E.g., the box that runs my local DNS, TFTP, DHCP, font, lpd, etc. services draws less than 20W. But, it runs headless and is located UNDER some furniture (to keep it out of the way) so if I have to wire up a console to troubleshoot a boot problem (i.e., if it fails to transition cleanly to multiuser), it's a real PITA. So, I want to keep it "up" for as long as possible.

It uses four 18Ah batteries, 2 in series, then the 2 parallel making a total of 48V 36Ah.

?? 24V batteries? Are you sure it isn't 4 12's in series?

I'm looking to move everything to operate off of a 48VDC bus and maintain that with a pair of solar cells behind an MPPT charge controller. Hence the need to discard the 24V UPSs in favor of 48V units.

[Curious.George]

Re: Downgrading UPS?

Eh no, there is always a load for testing. The parasitic load of inverting is a load in of itself!

Pathetic load, but it's a load, and if all you're powering is nothing, that's good enough of a test!

But you're only powering "nothing" between the time you switched the UPS on (which initiates its self test) and the time it takes you to hit the power switch on the "real" load.

I'll drag out my Watt's Up and look at how the UPS appears to the mains. The "test" cycle is long enough that I shouldn't need to drag out a DSO and voltage/current probes. (If I can't "see" the test load on the Watt's Up, then it's insignifant to these other speculations)

[CapLeaker]

Re: Downgrading UPS?

[QUOTE=Curious.George;842035]By "end on" do you mean "mains plug"?

Yes.

The total load is about 1200W with all the ham gear, computer, monitor, TV and that big 12V 50A linear PSU etc. I was looking for run time, lesser the capable amperage. There are four 12V 18Ah batteries. 2 batts in series make a 24V pack, times 2. The Two 24V packs are hooked up in series again to make 48V. I think I did not clarify this properly in my last post. I've used to to run a echolink node to my 70cm repeater.

[Curious.George]

Re: Downgrading UPS?

The total load is about 1200W with all the ham gear, computer, monitor, TV and that big 12V 50A linear PSU etc.

OK, so even with the losses reflected to the mains from conversion inefficiency (~10%) and the ~120W that it diverts to battery charging, you're still below the nominal loading for a 15A branch circuit (1440W).

I'll try to drag one out of the garage, today, and see what sort of load it presents when it goes into "test" mode. And, whether it deliberately isolates itself from the mains when it does that or if the test load is reflected back to the mains, in addition to the other loads.

(Ugh, this is going to be tough on my back!)