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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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APC Back-UPS 280B faulty - looking for ideas
I have a APC Back-UPS 280B that has stopped working correctly.
I've had experience in troubleshooting basic electronics and since the layout of this thing is primarly discreet components (only one small IC if I remember correctly), I believe that I might be able to fix it. However, I can't find anything at all about it on APC's website or anywhere else (schematics, user guides, nothing). Symptoms are as follows: In testing it using a 40 watt light as a load, the output voltage across the light is normally about 125 VAC. When the plug is pulled, that voltage drops to about 85 VAC.This was how it was behaving when the problem was first discovered (power outages caused computre to go down), so the internal settings were all as they came from the factory. Initially suspecting the battery, I checked the voltage on the battery in the normal running (i.e., charging) mode. Voltage on the battery was somewhere around 13+ VDC and when the plug was pulled dropped only slightly to somewhere around 12 and 1/2 VDC and held steady. I interpreted this as the battery and the charging circuitry of the 280B were basically good. The setting on the potentiometer for the output voltage of the inverter section was physically set originally at about 2/3 full scale. With a 40watt load and the unit unplugged (output voltage at outlet around 85 VAC), I turned the pot up to full scale. This resulted in the output climbing to around 119 VAC. Although I can (just) get the output up to a "working" level, I would not trust it, it's stability, or load handling since something has obviously gone wrong with it. I do not own or have ready access to a 'scope so I could not examine the output waveform or frequency (I own a Fluke 27 Multimeter) It would be nice to have this working again as I do have an application for it, however: 1) Paying someone to fix it would cost as much as buying another one 2) I can't justify buying another one as I don't have the money for it 3) If it is only a component or cold solder joint that has gone bad, it should be very cheap for me to fix, however: 4) I have no schematics or info on this to help locate where the problem is so I'm a little at a loss, not being familiar with which levels and where to check. If I can't fix this I'm pulling the battery and trashing the UPS which would be shame since I'm sure it is a simple fix once the problem is located. Any assistance, ideas, or even places I could look to find literature on this UPS would be appreciated. Thanks! - Jeff |
#2
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Sounds like a weak/bad battery.
You did not post that you performed the proper test on the battery. Find out the MAXIMUM current output available under UPS mode of operation. Place a suitable load on the output, calculate that your computer is not overloading the unit. Most UPS units will NOT handle both the computer and the monitor for very long. Then pull the plug while monitoring BOTH the AC output voltage AND the battery voltage at the SAME time. FYI it is normal for the meter reading voltage to drop to below 90 volts when the UPS detects a no load condition. 40 watt light bulb is simply not large enough to test the output, since most computers alone have 300 watt power supplies. UPS sealed lead acid batteries last ALMOST 2 years before they should be replaced. Occasionally one will last a bit longer, but for full back up performance, replace them every two years. David |
#3
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dkuhajda wrote: Sounds like a weak/bad battery. You did not post that you performed the proper test on the battery. No, I didn't. However, from the fact that the AC output dropped to 85 volts but the battery still held at around 12.5-12.75 without really sagging led me to believe it was probably ok. Find out the MAXIMUM current output available under UPS mode of operation. Place a suitable load on the output, calculate that your computer is not overloading the unit. Most UPS units will NOT handle both the computer and the monitor for very long. Then pull the plug while monitoring BOTH the AC output voltage AND the battery voltage at the SAME time. This is what I did (i.e., monitoring both the AC output and the battery level) although not with a computer for a load. This is only a 280 VA unit not intended for really large loads. I was planning on using it for my wife's CPAP machine since we occasionally have power outages at night. The 40 watt lamp I used was just convenient. FYI it is normal for the meter reading voltage to drop to below 90 volts when the UPS detects a no load condition. 40 watt light bulb is simply not large enough to test the output, since most computers alone have 300 watt power supplies. So there not only is a maximum load but also a minimum load for a given UPS? I could understand there being a voltage foldback for a no load condition depending on the design of the unit, but a 40 watt bulb pulls 1/3 amp. That isn't totally trivial as the UPS is only rated for a bit over 2 amps max (depending on application of course). Seems like an extremely narrow operating range. So you're saying that if I put a 150 volt bulb on this (over half the maximum rated load), the output voltage should increase? (assuming the battery was good) UPS sealed lead acid batteries last ALMOST 2 years before they should be replaced. Occasionally one will last a bit longer, but for full back up performance, replace them every two years. Yes, I have no idea how long it was in there (I got the unit from a friend) so it could be that old. However, I still would expect a bad battery to not be able to hold a voltage of over 12.3 volts under load even if that load is 1/7 of the maximum load rated for that UPS. This is a fairly lightweight unit and using it as a UPS for a 40 watt load did seem plausible. - Jeff |
#4
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"Jeff Wiseman" bravely wrote to "All" (28 Aug 04 17:52:25)
--- on the heady topic of "APC Back-UPS 280B faulty - looking for ideas" JW From: Jeff Wiseman JW I have a APC Back-UPS 280B that has stopped working correctly. JW I've had experience in troubleshooting basic electronics and JW since the layout of this thing is primarly discreet components JW (only one small IC if I remember correctly), I believe that I JW might be able to fix it. However, I can't find anything at all JW about it on APC's website or anywhere else (schematics, user JW guides, nothing). JW Symptoms are as follows: JW In testing it using a 40 watt light as a load, the output voltage JW across the light is normally about 125 VAC. When the plug is JW pulled, that voltage drops to about 85 VAC.This was how it was JW behaving when the problem was first discovered (power outages JW caused computre to go down), so the internal settings were all as JW they came from the factory. JW Initially suspecting the battery, I checked the voltage on the JW battery in the normal running (i.e., charging) mode. Voltage on JW the battery was somewhere around 13+ VDC and when the plug was JW pulled dropped only slightly to somewhere around 12 and 1/2 VDC JW and held steady. I interpreted this as the battery and the JW charging circuitry of the 280B were basically good. JW The setting on the potentiometer for the output voltage of the JW inverter section was physically set originally at about 2/3 full JW scale. With a 40watt load and the unit unplugged (output voltage JW at outlet around 85 VAC), I turned the pot up to full scale. This JW resulted in the output climbing to around 119 VAC. JW Although I can (just) get the output up to a "working" level, I JW would not trust it, it's stability, or load handling since JW something has obviously gone wrong with it. I do not own or have JW ready access to a 'scope so I could not examine the output JW waveform or frequency (I own a Fluke 27 Multimeter) I recall that most multimeters are calibrated with pure sinewaves and their internal precision rectifiers measure the average value of the waveform. Thus depending on the shape of the BUPS's output waveform the reading may be inaccurate. The meter may indicate a correct reading from the normal AC line but then read low when the BUPS is running. I think an AC RMS meter would be needed for a proper calibration. JW It would be nice to have this working again as I do have an JW application for it, however: JW 1) Paying someone to fix it would cost as much as buying another one JW 2) I can't justify buying another one as I don't have the money JW for it JW 3) If it is only a component or cold solder joint that has gone JW bad, it should be very cheap for me to fix, however: JW 4) I have no schematics or info on this to help locate where the JW problem is so I'm a little at a loss, not being familiar with JW which levels and where to check. JW If I can't fix this I'm pulling the battery and trashing the UPS JW which would be shame since I'm sure it is a simple fix once the JW problem is located. Any assistance, ideas, or even places I could JW look to find literature on this UPS would be appreciated. Thanks! JW - Jeff I would try loading the BUPS to a significant percentage of its ratings and see how the output voltage is affected. If there isn't much change, say less than 10%, then I would suspect the reference voltage or the feedback divider chain. Resistors do go open circuit, capacitors get leaky, solder joints and connectors can go bad, etc. A*s*i*m*o*v .... Transformer designers take turns doing it. |
#5
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Asimov wrote: "Jeff Wiseman" bravely wrote to "All" (28 Aug 04 17:52:25) --- on the heady topic of "APC Back-UPS 280B faulty - looking for ideas" JW The setting on the potentiometer for the output voltage of the JW inverter section was physically set originally at about 2/3 full JW scale. With a 40watt load and the unit unplugged (output voltage JW at outlet around 85 VAC), I turned the pot up to full scale. This JW resulted in the output climbing to around 119 VAC. JW Although I can (just) get the output up to a "working" level, I JW would not trust it, it's stability, or load handling since JW something has obviously gone wrong with it. I do not own or have JW ready access to a 'scope so I could not examine the output JW waveform or frequency (I own a Fluke 27 Multimeter) I recall that most multimeters are calibrated with pure sinewaves and their internal precision rectifiers measure the average value of the waveform. Thus depending on the shape of the BUPS's output waveform the reading may be inaccurate. The meter may indicate a correct reading from the normal AC line but then read low when the BUPS is running. I think an AC RMS meter would be needed for a proper calibration. I believe that the Fluke 27 does read true RMS (it was a $300 meter 14 years ago). The fact that the 40 watt bulb also goes extremely dim when the plug is pulled also reinforces my believe that the reading is likely reasonable. I would try loading the BUPS to a significant percentage of its ratings and see how the output voltage is affected. If there isn't much change, say less than 10%, then I would suspect the reference voltage or the feedback divider chain. Resistors do go open circuit, capacitors get leaky, solder joints and connectors can go bad, etc. When I get the chance I'll try a 150 watt bulb (that's over half the UPS's max rating) but I still find it a little difficult to believe that a 280 VA UPS wouldn't work properly to protect a 40 watt load but I'm not real familiar with the normal operating conditions of these. I have a Tripplite 550VA UPS that will continue to properly supply just a simple 14 watt flourescent light when it is unplugged with no side effects (although its UPS type may be different than the APC I have). And although circumstantial, I'm still convinced that there is a non-battery related failure in the APC. If I could track down a schematic or something it would really help. - Jeff |
#6
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FYI if you plan on using it on any kind of motor or inductive load, you
need a different UPS. The APC units for computers are not designed for use on any kind of motor or coil, in fact they even state they should not be used on a heavy resitive load. Check APC's web site for the specifications of that model. David |
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