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BackupPowerWithModifiedUPS WARNING: MY MODIFIED UPS HAS STOPPED WORKING - LOOKS LIKE I DAMAGED IT!!  From the left, the levels should be: +164 0 -164 0 +164 0 -164 0 +164 but there is a leading transient I suspect I could repair the unit but I have no circuit diagram. SUMMARY: Features of the modified UPS during normal, line-powered operation: During power outage or when you take the modified UPS out into the field: FUTURE PLANS: Ron's (KG7OH) Battery Backup and Solar Cell Notes: MODIFICATION:  CAUTIONS: DISCUSSION: Here's what happens: The UPS is plugged into house AC power. It converts the 120V AC to 12V DC to charge the internal battery. Then it converts the DC back to 120V modified sine-wave AC to power other units. The AC output goes to the power supply which converts the AC back to 12 volt DC that powers the transceivers. Of course, I need the 120V AC from the UPS to power the computer so that the computer can convert it back to DC to power the computer components. The transceivers are designed to run on 12V DC so that you can power them from your car battery when you operate mobile. You will have noticed that there are a lot of power-wasting operations going on there. Asking computer manufacturers to build equipment that operates on 12 V DC is a bit of a stretch. But junking that $170 power supply is a savings. So, I went looking for a UPS that also had a 12V DC output terminal and I couldn't find one. Why? Probably because it wouldn't normally be used by non-Ham people and a variable-voltage 11-14V DC output (the battery voltage will vary with charge and configuration) would be hard to specify. Also, you would probably want to add a fuse and possibly some additional filtering to clean up any hash in that battery output. Anyway, I'll be looking into a number of issues in the next few days. One issue is that the battery in the UPS will not operate the equipment for long on that 9 amp-hour battery - about 7 minutes at half-rated-power or 3 minutes at full-rated-power. But an automotive battery could be attached and would last a long time, especially when you realize that those transceivers are typically only transmitting a small fraction of the time. The UPS serves as a trickle charger. Here's a list of power requirements that matches my office needs fairly well.  If I were manufacturing a UPS/DCpower unit, I would think about adding other things like additional DC filtering and USB charging outputs. Time to get out the oscilloscope and see what's going on in those UPS units! New info on power backup for office and ham gear. Well, it works - sort of. I did some rewiring and moved the battery out of the UPS and attached my UHF/VHF radio to it. I was able to receive for an extended period of time and also transmit briefly. However, the UPS got warm and the battery voltage dropped several volts during transmit. I was using a small 5 amp-hour battery; a large 80 amp-hour battery should solve the voltage-drop "problem". One question was - why did the UPS get warm? The answer is because the UPS does not actually generate DC and then convert back to AC when attached to a 120V power source. There is a relay in there that connects the input AC to the output AC when 120V input is present. The UPS only generates DC to charge the internal battery for use when the AC input goes out. That's fine for small power loads for a short period of time but probably not o.k. for generating power for a 100W transmitter for long periods of time. Another "problem" is that when generating AC from the battery, this UPS does not generate a sinusoidal output, it generates a "modified sinusoidal output". Here's a picture from https://www.dougv.com/2010/03/active-pfc-enabled-psus-are-not-compatable-with-most-low-end-ups/  The "modified sinewave" (in red) might be more accurately described as a "modified squarewave". So, when power goes off, that is what is fed to your computer, etc. The question is does it matter? And I think the answer is - not really for most equipment. The days of large, heavy 60 Hz transformers and vacuum tubes and giant high-voltage filter capacitors are mostly gone. Today's AC-to-DC power converters typically chop up the input waveform at a 25 KHz rate so that they can use small tranformers (inductance is proportional to frequency) to lower the voltage down to e.g. 12 Volts. So the "modified sinewave" lookis like a 25 KHz, 50% duty cycle square wave at a 120 Hz rate after the chopper. This might require a little more filtering to get to 12 VDC than would be necessary for the chopped 60 Hz sinewave but the difference is probably not noticeable. The problem (as mentioned in the referenced article) would occur if the equipment receiving the modified sinewave detected the anomalous input and shut itself down, defeating the UPS function! Some inexpensive UPS units advertise that they generate a pure sinewave output. It might be better to buy one of those in case you have some equipment that will not tolerate the "modified sinewave" input. So, I think this will work as long as we are using the UPS as a DC source and a trickle charger for a high-capacity battery. But, I probably still need my power supply for normal operations. |
