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Testing an APC 600W UPS by powering my fridge

Delmar

Solar Addict
Joined
Dec 9, 2019
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Lake Conroe Texas
I am installing a small UPS to run my Moms TV and satellite dish during short-term grid down. Measured around a 100W draw. The backup system needs to be granny-proof autonomous so purchased a APS sine wave BR1000MS. Cost was $160 including tax & shipping.

The UPS is supplied with an internal 24V AGM Battery rated 130WH (5.4AH x 2). Per the specs a 100W draw should run for 43 minutes. Plugged in the UPS for around 4-hours and measured the battery pack at 27.6V, figured that was close enough to fully charged.

For the first test I unplugged my full-size fridge to ensure a long runtime. It draws a similar 100W so should be a fair comparison to grandmas TV. Connected the fridge to the UPS while on wall power for a few seconds, then unplugged the UPS from the wall. The fridge continued to run with no problem.

fridge.jpg

Closely monitored the fridge and UPS for 33 minutes until the capacity indicator was under 3 minutes remaining. I could sense a slight warmth from the UPS while running at minimal 17% capacity, and only the smell of new electronics. Never did I feel or smell any electronics cooking.

After turning off the UPS for a minute the battery measured 23.4V. Considering that was not true resting voltage I am not concerned. Did not test the surge capacity while starting the fridge from the small batteries. I will replace the internal batteries with a pair of external 35AH Harbor Freight AGM in series, cost will be $117 for the pair after my 20% coupons. Capacity @ 24V = 840WH. With a 100W draw I estimate should run for 4.6 hours. Will add a second pair if grandma complains about the runtime.

Pictured for size comparison is one of the two Harbor Freight batteries next to the APC 24V pair. I will return to Harbor Freight when they restock another battery. Did not want to steal the one running my Belkin UPS.

UPS.jpg
 
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Looks good, with such a low load compared to its full rating it should be able to keep that up for as long as you can supply it with DC. Does it have a fan built in? At worst if you found it did start to get too warm after an extended period a fan should take care of it.

The charger is pretty limited, pulling 70AH of battery up to charged from flat is going to take days with that. Keep an eye on the temperature when you first try charging as if it doesn't have a fan built in you may find heat problems there.
 
There is no fan, and surprisingly little ventilation holes. If I can sense the UPS getting hot I may add a thermostatically controlled 24V fan. Additionally I may just Swiss cheese the housing for cheap insurance.

APC has a patent that uses the same H-Bridge to charge the batteries so should not have overheating problems. I also plan to charge the batteries from wall power or solar panels.
 
It looks like an entirely switching design from pictures via google rather than any use of a chunky transformer so that would help a lot with heat. Chunky transformer types also used the transformer for charging and prolonged charging could actually cause things to get hot enough to break thermal fuses.
 
Connected the two Harbor Freight batteries to the UPS. Voltage as received was 26.08V and after around 10 hours increased to 27.29V. Ran cooler while charging the batteries than discharging. Everything worked perfect, what could go wrong?

UPS HF.jpg

Connected my TV with a 100W load. Disconnected the UPS from the wall and had a revolting discovery: the UPS ignores actual battery voltage and instead calculates the AC load based on the standard battery capacity. Ran for the same 43 minutes as listed in the specs and shutoff. The running battery voltage just before it shutoff was 25.10V. I figured the "Pro" version would be smarter.

Contacted APC to see if there is a method to change the default battery capacity. Found nothing in the PowerChute software, and running a self-test seems to have no affect.
 
All hope may not be lost. There was another thread on the forum a while back where someone reconfigured an APC UPS via an internal serial port header. A few searches doesn't turn it up but if you search around you might find it and get some ideas from it.
 
The serial port was on the higher-end units (see circle) and used a different version of PowerChute. I have one on my old 5U-case beast.

ups serial.jpg

The consumer versions use an CAT5>USB cable with a basic version of PowerChute. Will see if APC responds with a solution.
 
Not the UPS status serial port, it was an internal serial header not intended for user access.
 
Delmar >> I'm experimenting with a APC 1400 rack mount, solar charging and a 200Ah battery bank..
The battery meter is way off..goes flat as if it had the stock batteries in it, but it's not cutting off.
The beeper is annoying. so i had to disconnect it also.
other than that, it's working good..
 
I'm experimenting with a APC 1400 rack mount...battery meter is way off...goes flat as if it had the stock batteries in it, but it's not cutting off.
What is the model number of your APC 1400?

Alternately I am looking at a SUA1000XL that is factory setup for continuous run with external batteries. Stupid expensive new so am looking for a good used one. Not approved by Bernie Sanders.
 
Changed course and purchased the APC SUA1000XL that I knew dang well would have worked perfect in the first place, as it was designed for an external battery pack and continuous operation. But I became seduced by the new & pretty packaging of the modern UPS. The design of the SUA1000XL is over 18 years old so is probably safer for me to be messing with anyway. Yes I have a UPS fetish.

Price used was $240 shipped including a pair of brand new 18AH batteries so I consider to be a good deal. When paired with the Harbor Freight 35AH batteries I will have 1.3KWH of capacity that will easily run a 100W load for more than 8-hours (runtime graph).

Bought the matching Anderson connector for the external batteries. Waited for the UPS internal batteries to match the voltage and plugged them in. Didn’t blow the external 15A fuse. So far no smoke and everything is performing well.

The UPS is rated for 800W, and the low-frequency design with massive transformer should have great surge capacity. But it still won’t start my fridge. Very surprised that it wouldn’t.

18AH battery.jpg 35AH battery.jpg
 
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I'm still not sure what transformer has to do with surge capability. Current has to come through transistors, from capacitor or battery.

Maybe it is because lightweight transformerless inverters use a boost circuit to charge capacitors to a voltage at least Vpeak of AC, and can't respond with more current. Low frequency with transformer primary at battery voltage has thousands of battery amps available.

UPS is probably designed for computer applications without motor starting surge, so just puts out peak current/watts on its label. Doesn't have nearly as many transistors in parallel as a general purpose inverter.

Just using a DMM, not a scope, I caught an 8A 960W peak.



Figure 4x to 5x nameplate rating to start a motor (I've measured that with a scope for window A/C). Although, the nameplate on fridge may refer to defrost element, so possibly not that bad.
 
I'm still not sure what transformer has to do with surge capability. Current has to come through transistors, from capacitor or battery.
Thank you very much for that insight! During the previous fridge test I only had the internal 18AH battery pair connected. Figured that would be more than enough.

Connected the external 35AH battery pair and the fridge started! The UPS gave one complaining beep otherwise ran fine. I likely will not run grandmas fridge from the UPS, but its good to know I have the ability.

Another variable…in the previous test I unplugged the fridge for about 15 minutes for the pressure to bleed down. This test was unplugged for a couple of hours.
 
I'm still not sure what transformer has to do with surge capability. Current has to come through transistors, from capacitor or battery.

Maybe it is because lightweight transformerless inverters use a boost circuit to charge capacitors to a voltage at least Vpeak of AC, and can't respond with more current. Low frequency with transformer primary at battery voltage has thousands of battery amps available.

You are on the right track.

'HF' types have a boost section to generate a high voltage DC supply and then PWM that to produce the AC output but they typically, I'm going to say in almost all cases, only output a fixed duty cycle PWM signal. Their only method to regulate the AC voltage is to regulate the HVDC supply. In the lower end of the market the HVDC is usually pretty loosely regulated in order to not blow up transistors with high current flows, ie, this is how they deal with being cheap rather than engineering their way out of the issue.

'LF' types, that even actually try to regulate their output must vary the PWM duty cycle since it's the only way they can regulate. With the low impedance DC supply that is the battery they can throw a lot of current around to ensure the AC output is regulated and a will formed sine wave too. Of course an elcheapo LF will do badly at this but even so it will do better than the typical HF design.

We must also take care to not confuse surge with short term over rating, they are two different things.
 
From my formal education in switching power supplies (graduate level) I learned how selection of inductor could produce less ripple, or provide faster response to transients. It was a trade-off. And that most of the power dissipated in the transistors was during transitions, not steady-state. So when you clock it faster for less ripple, faster response, it became more inefficient.

Taught by career academics, it missed most of the practical aspects. But went deep into stability, root-locus, etc. which (while complicated mathematically) is good because that is where most engineers do badly. If we are lucky, we get products designed by someone who knows what he is doing. But future product generations don't always maintain that.
 
Hedges >> said....

Figure 4x to 5x nameplate rating to start a motor (I've measured that with a scope for window A/C). Although, the nameplate on fridge may refer to defrost element, so possibly not that bad.

I said >>> My fridge claims to use 6.5A, but when i measure it running, it is only drawing about 3A... So maybe the defrost element draws the 6.5A, or maybe that's the compressor start amps ?
 
Hedges >> said....

Figure 4x to 5x nameplate rating to start a motor (I've measured that with a scope for window A/C). Although, the nameplate on fridge may refer to defrost element, so possibly not that bad.

I said >>> My fridge claims to use 6.5A, but when i measure it running, it is only drawing about 3A... So maybe the defrost element draws the 6.5A, or maybe that's the compressor start amps ?

I would guess 3A is just what the motor draws under mild conditions. Probably more under higher temperatures, when pressures are higher. The defrost (or icemake thaw to release cycle) could also be more. But I expect starting current to be several times nameplate, for 10's of milliseconds.

I tested a window air conditioner with scope. Starting amps was 4x nameplate, running was 1/2 of nameplate:


There was one defrost cycle in the earlier link of refrigerator.
 
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