| T O P I C R E V I E W |
| axf |
Posted - Sep 29 2008 : 6:10:39 PM
Hi, a friend of mine gave me an older APC uninterruptable power supply (Backups 400) unit. It's working quite alright, it just needed a new 12V battery and all was well or so I thought. I measured the output of the plugs when running from mains and it's 120VAC like it should be. When I disconnect the mains it lowers itself to about 100VAC. I tried adjusting the resistor for v out and it only raises it about a volt or two. Is this normal for a UPS or should I investigate further? |
| 5 L A T E S T R E P L I E S (Newest First) |
| axf |
Posted - Oct 03 2008 : 2:32:43 PM
Ok, so I checked out the black wire (Hot) and got this picture on my scope. I'm actually amazed than anything runs off this waveform but then again looking to the output of a ups is all new for me. Any tips I can get on correctly grounding the scope to the ups? I'd really like to not kill my oscilloscope by trial and error
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| Maxtron |
Posted - Oct 01 2008 : 01:01:26 AM
Most ups output a square wave wich is more acurate than a sinus wave the reason for that is i think that if you look at a sinus wave the efficiancy is at about 95%and that you can actually fit a square wave into it.It all comes down to usable power and should not be less than 5% and by the looks of it you got about 20% loss there.You can do another experiment and install a bridge rectifier(without filter cap)and then check the voltage but i doubt if there is gonna be any(much) difference.What i noticed as well is that some ups use a 7-10V(14-20V centre tapped) winding on either side and by chopping the square (regulating the square to 7V) you get a more reliable(regulation) output when the battery starts to drain.
Download Attachment: SINE.BMP
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| axf |
Posted - Sep 30 2008 : 11:10:41 PM
I was reading anoth thread about a 220/230VAC inverter and saw audioguru's reply stating that the waveform generated by the inverter is more complicated than a regular multimeter may be able to analyze. Is it possible the UPS may be outputting a modified sine wave of 120VAC but my multimeter is only reading 100VAC
http://www.aaroncake.net/forum/topic.asp?TOPIC_ID=7698 |
| axf |
Posted - Sep 30 2008 : 11:25:21 AM
Thanks for the reply, I'm awaiting my new digital scope for a few more days. Yes, the battery voltage is a good 13 volts :)
So all I can really do at the moment is look around and ponder. When you say dry capacitors, I'm assuming you mean the solder joints as well? |
| Maxtron |
Posted - Sep 30 2008 : 01:01:36 AM
Check battery voltage,Check (i asume mosfet half-bridge,H-bridge)one of the mosfets is not switching properly or check for dry connections from xformer to pcboard and around transistors or open drive resistor(s).If oscilloscope is available do a wave check on either side of the xformar(centre tapped)from the centre tap.I am not familiar with that specific ups but at some stage there should be a circuit regulating the ac output to about 110V to compensate for battery voltage drop.Check around there as well for dry electrolytic caps.
Cheers. |
SINE.BMP