UPS doesn't take load (APC BE700-SP) - Page 1
Forum section: electronics / repair

author: rodrigopires
author_rank: Regular Contributor
timestamp: September 30, 2020, 10:56:46 am
content: Hello everyone! I have a APC UPS model BE700-SP that doesn't take load when the power is off.-With power on it has 230VAC output (grid power) and works well.-With power off and no load (baterry powered) it has 230VAC output.-With power off and with load (baterry powered) it shuts down and starts intermitent beeping.The problem is that i have power with no load but if something is connected it shuts down power and goes crazy beeping. How do i diagnose the problem?Note: The battery was replaced, original one was completely dead won't even charge. New battery 12v 7.5 AhThanks everyone for the time dedicated to my problem!

author: shakalnokturn
author_rank: Super Contributor
timestamp: September 30, 2020, 12:10:32 pm
content: A good starting point would be checking the battery/ies.If their internal resistance is too high they'll be going too low in voltage under load.

author: PaulAm
author_rank: Frequent Contributor
timestamp: September 30, 2020, 03:08:33 pm
content: How old are the batteries? They do go bad over time.Depending on the model, the firmware may adjust an internal battery constant based on the periodic battery test. I had one APC where that constant had drifted to the point of having a 3 minute run time at 20% load with brand new batteries. After correction, it gives me 45 minutes at the same load. Took forever to track that down and APC does not encourage end users to fiddle with it.

author: rodrigopires
author_rank: Regular Contributor
timestamp: October 02, 2020, 04:20:58 pm
content: My mistake but forgot to mension that i had change the original battery to a new one. Original APC battery was dead probably it was left uncharged for too long so i bought a new one and charged to 100% before installing.

author: PaulAm
author_rank: Frequent Contributor
timestamp: October 02, 2020, 04:26:45 pm
content: If it's hooked up to a Linux system you can use the apcups software package to find out what the current value of the battery constant is and, modify it, if necessary. If the value looks good, you may have a hardware problem.If you have a Windows system, you're more limited. Can't help you there.

author: masterx81
author_rank: Frequent Contributor
timestamp: October 02, 2020, 05:37:49 pm
content: Can also try to install the windows software and if possible run the runtime calibration.Sometimes i've also found new batteries totally dead. Who store them doesn't always do the maintaining charge. If i receive a battery with less than 12v i'll send it back.Now i not know the logic of the "remaining time" calculation, but if the sw not have the calibration runtime function, it's possible to leave it discharge with low load, an let the ups "learn" then new value?

author: Shred
author_rank: Contributor
timestamp: October 03, 2020, 09:55:10 am
content: The BE700 is a “dumb” UPS, so it probably doesn’t have the runtime calibration like the more advanced APC SmartUPS models. I’d try a new battery from a different supplier. Sometimes SLA batteries sit on the shelf for years before you buy them.The other thing is to check that the battery has the correct sized spade terminals. The correct battery will have a wider, thicker spade terminal than the common “burglar alarm backup” type 12v SLA battery, Using the cheaper battery with the smaller spade terminals will limit the output of the UPS, since these batteries have a higher internal resistance than the ones designed for this application.

author: rodrigopires
author_rank: Regular Contributor
timestamp: October 03, 2020, 04:59:45 pm
content: The battery currently in use is new and I completed the charge with a smart battery charger before applying it to the UPS. In addition, I tried to power the UPS with a bench power supply (12v) and the result is the same: no load, everything is fine, but as soon as I apply the minor amount of load it beeps and does not stop until its disconnected from the battery (supply). I don't know much about the inner working of this, but to me it looks like some kind of current sensing that is triggering the problem.

author: james_s
author_rank: Super Contributor
timestamp: October 03, 2020, 05:15:03 pm
content: I'd check the battery cables and solder joints where they connect to the board inside the unit. If you have high resistance somewhere that can cause this to happen. Another thing to check for is leaky surface mount electrolytic capacitors, I've seen UPS's that have a bunch of those in them. I wouldn't put a lot of effort into fixing a basic UPS like that though, I have found that it's very easy to get them, with usually nothing wrong except for a bad battery. I've been given several of them and have bought a few others, rarely paid more than $20 and usually most of that is the shipping.

author: shakalnokturn
author_rank: Super Contributor
timestamp: October 03, 2020, 05:50:46 pm
content: What voltage do you measure at the battery when loaded?

author: TheMG
author_rank: Frequent Contributor
timestamp: October 03, 2020, 06:19:54 pm
content: Just because it's a "new" battery, doesn't necessarily mean it's any good.Where did you purchase the battery from? What brand is it? What's the date code on it?Could be a dud battery too, I've seen that happen, especially with the cheaper brands.Measure the voltage when you apply the load to the UPS, voltage should not drop below about 11.5V under load, depending how much load you put on it.Also make sure the terminals fit nice and snug on the battery terminals. If they seem loose, you can squeeze them with a pair of pliers before putting them back on to make them a bit tighter.

author: james_s
author_rank: Super Contributor
timestamp: October 03, 2020, 06:25:30 pm
content: I have also had a brand new battery be defective. Out of about 10 UPS batteries I have bought over the past few months one of them was bad right out of the box. It showed over 12V but would not carry a load so that is definitely worth checking.

author: rodrigopires
author_rank: Regular Contributor
timestamp: October 03, 2020, 06:57:44 pm
content: Did some further testing and came to these results: it does not support inductive loads (electric drill) max current was 5mA while beeping continuously (drill trigger pressed); It can take to some extent resistive loads (heating elements and tungsten filament light) was able to successfully power a 40w incandescent light but not a 60w. Curious fact is that even with the 40w some times it worked ok other times it showed the same behavior (no power output and beeping continually).As for the PCB all looks like straight from the factory: no corrosion, no heat spots, electrolytic capacitors with no leak and no bulge, battery cable is well soldered on both sides of the board.The unit itself was given to me free of charge, but the new battery was about 20 euros, so I was hoping to see it runningThe new battery is an Ultracell UL7.5-12. As far as date code the only marking I see are "UUL7949". With resistive load I was able to draw more than 10A from the battery so at the very minimum the UPS should provide 100W of output right? And as I stated the problem is the same when connected to my bench power supply (12v 60A) so I never assumed it to be a faulty battery.

author: shakalnokturn
author_rank: Super Contributor
timestamp: October 04, 2020, 12:15:08 am
content: Bench supply test is ok if you have considered the wire resistance when connecting.Being able to draw 10A from the battery sounds good but still isn't giving the battery voltage. (I can get 10A short circuit current from a solar panel although in that case it's close to zero useful power...)At the best modified sine UPS's aren't comfortable with inductive loads, the ringing caused by the fast dV/dt could be triggering a secondary side OVP if such a thing is monitored on your model.Things that may be worth checking are primary side (12V side) decoupling before MOS stage and secondary side snubbers.

author: james_s
author_rank: Super Contributor
timestamp: October 04, 2020, 03:42:27 am
content: If the drill is a variable speed type it won't like that either. Triac speed controllers and light dimmers don't like the modified sine wave, which is really just a square wave with dead time. These UPS units are designed to power computer equipment with switchmode power supplies, not power tools and other devices.