| Electronics > Beginners |
| Puzzled about Online UPS + GFCI Behavior |
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| SeanB:
Double conversion is typical in audio and video use, where you do not want even the briefest dip that can cause lights to flicker. Of course there they are bigger units, that run the entire room. Another place is medical, where the briefest mains failure has a chance of causing machinery malfunction that might be attached to a patient and keeping them alive, thus the double conversion for life critical, and simple medical isolation transformers for those that are merely critical and do not have built in battery backups. |
| Messtechniker:
--- Quote from: Bratster on September 30, 2018, 06:08:55 pm --- But why do you think adding a UPS would cause your GFCI to trip? --- End quote --- Because I am expecting the UPS while mains powered to cause a current imbalance on the neutral line. Dependent on the construction of the UPS. I haven't found anyone who would reliably recommend a specific type of UPS which will definitely not trip the GFCI. The other problem may be that the UPS disconnects the neutral line from the central gas heater thus floating it so that it won' t work. Connection of the central gas heaters neutral line to mains neutral is mandatory for operation of the heater. |
| SeanB:
No UPS I have around causes a trip of the mains, especially those that plug in, as a GFCI is a mandatory fitment here on all socket outlets. There are a few that pass neutral through, and some that break it, but most do not break neutral as they are designed for polarised outlet use only. |
| David Hess:
--- Quote from: drussell on September 30, 2018, 06:01:34 am --- --- Quote from: David Hess on September 30, 2018, 04:02:45 am ---Not all UPSes pass neutral through. There was a change in this requirement a few years ago. They can be identified by measuring the hot and neutral voltages to ground which will be 60 volts (floating) instead of 0 and 120. --- End quote --- Interesting. I have never seen a UPS that was also some kind of isolation transformer. It would still blow a GFCI though, if you send any current back through the ground since that current is not returning through the input neutral, even with an isolation transformer. --- End quote --- APC mentions it here and I have run across it several times in standby UPSes. I do not know what online UPSes do but they might disconnect neutral when on battery power only; it is not something I have ever specifically checked. --- Quote ---If the UPS is also isolating ground, then :scared: --- End quote --- Ground always goes straight through. |
| David Hess:
--- Quote from: 6PTsocket on September 30, 2018, 02:34:02 pm ---Can somebody please tell me what is the reason for double conversion? Why would you need inverter AC power at any time there is AC available from the mains? --- End quote --- An online UPS by its very nature suppresses all line irregularities including surges and dips so it might be thought of as a super power conditioner. If the online UPS has power factor correction, then it also corrects the power factor of the load. --- Quote ---Why can't the battery charger, battery and inverter be simply bypassed all the time there is AC available and kick in when power fails? --- End quote --- Some online UPSes support this mode of operation as well. --- Quote ---Why is the bypass " dynamic", whatever that means? Thanks. --- End quote --- An online UPS has to be able to bypass in the event of inverter failure or if the load exceeds the capacity of the inverter. |
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