| Electronics > Beginners |
| Puzzled about Online UPS + GFCI Behavior |
| << < (3/6) > >> |
| Messtechniker:
Facing a similar problem too. I was planning for a small UPS in case the electricity for may gas central heater fails leaving me cold. The supply of gas is ensured in the case of a mains power blackout. They use gas operated gas pressure controllers. :-+ So me thinks a small UPS might be nice since my central gas heater draws only 17 W max. The problem is, however, that the flame sensor is of the ionization detection type, thus needing a permanent neutral connection. Now if I insert an UPS, the GFCI is likely to blow - see above. I have asked several professional electricians (one old hand and one with best marks fresh from professional training (Elektromeister)) to recommend a suitable UPS for this scenario. They simply do not have the know how. Another one said "simply try". :scared: Well I'm not going to mess around with gas apparatus not knowing what I am doing. As to my question how they install such systems in hospitals, for example, they said. "We get a complete package from the manufacturer and simply install that". :-//. Go figure. So I am still at a loss what to do. |
| DrDeke:
--- Quote from: SeanB on September 30, 2018, 11:56:57 am ---The UPS in the diagram is line interactive. It does do dual conversion, but notice the block called dynamic bypass, which is normally going to have the input and output connected directly via a IGBT or relay switch. If power fails, the dynamic bypass will open around 1ms after the first missed mains zero crossing without voltage rising above 20V event, and the inverter stage will then use the stored energy in the HV stage to start supplying the load, and the battery to main bus converter will come out of standby to start charging the main DC bus, or will change mode from acting as charge controller that floats the battery bank to inverter using the battery bank. --- End quote --- Unless I'm fundamentally misunderstanding something (which is possible), I don't think that's how this UPS works. I have put multimeters on the input and output receptacles of the UPS and watched the input voltage fluctuate over time, while the output voltage remains constant. This suggests to me that the output is being powered by the inverter at all times. The section in the manual describing the dynamic bypass function also seems to suggest that this is how it operates: "The UPStation GXT provides an alternate path for utility power to the connected load, in the unlikely event of a UPS malfunction. Should the UPS have an overload, over temperature, or UPS failure condition, the UPS automatically transfers the connected load to bypass. Bypass operation is indicated by an alarm and an illuminated Bypass LED." Also, for what it's worth, you do hear a mechanical sounding "click" from the unit when putting it into or taking it out of bypass mode. |
| janoc:
--- Quote from: 6PTsocket on September 30, 2018, 02:34:02 pm ---Can somebody please tell me what is the reason for double conversion? 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? Why would you need inverter AC power at any time there is AC available from the mains? Why is the bypass " dynamic", whatever that means? Thanks. Sent from my SM-G900V using Tapatalk --- End quote --- It can - that's called an "offline UPS". However, those are only the cheapest and crappiest units because if you need also power conditioning and seamless switchover when the mains fails, they can't deliver. See e.g. here about the differences: https://www.upspower.co.uk/what-are-the-key-differences-between-online-offline-and-line-interactive-upss/ |
| DrDeke:
--- Quote from: 6PTsocket on September 30, 2018, 02:34:02 pm ---Can somebody please tell me what is the reason for double conversion? 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? Why would you need inverter AC power at any time there is AC available from the mains? --- End quote --- In the marketing text, you usually see double conversion UPSes suggested for use with "critical loads which can tolerate absolutely no interruption to their power supply." It is true that the output of a double conversion UPS should remain completely unchanged during interruption or restoration of input power, whereas other types of UPSes can have brief interruptions / phase discontinuities / etc on their output during such events (as shown on the oscilloscope capture in this thread). That said, I have never personally run across a load which seemed to suffer from the switching time on a standby or line-interactive UPS. I suppose it's possible that some equipment would be damaged by or run incorrectly during those events. Or maybe it's more that some loads are some combination of very expensive and in need of very high availability, and their owners don't want to take any chances. For me personally, I ended up with my double conversion UPSes for a different reason. Some years ago, I lived in a house which suffered fairly frequent power outages (thus wanting a UPS in the first place), and also suffered from chronically low voltages during the summer because the utility transformer serving that and several nearby houses was undersized/overloaded. Throughout the day as air conditioners turned on and the load on the transformer increased, the voltage as measured at a receptacle in the house would decrease and when it got below the UPS's low-transfer voltage (somewhere around 96 V for the UPSes I was using at the time), the UPS would transfer to battery power, thereby removing several amps of load from the supply circuit. The lighter load would cause the voltage to recover slightly, enough to make the UPS transfer to line power. The resulting increase in load would cause the voltage to dip again, sending the UPS back to battery power. This cycle tended to play out until either the UPS batteries were drained or the UPS itself had failed from the constant, frequent switching. After letting the smoke out of several APC Smart-UPSes in this manner, my roommate and I ended up getting a couple of these double conversion UPSes on eBay and never looked back. The one I've still got, the GXT1500, can run on line power all the way down to 73 V (if loaded to 70% or less - 93 V at full load), while maintaining a steady 120 V output. (The input current to the rectifier would, of course, increase as the input voltage decreases, to maintain the input power.) |
| Bratster:
--- Quote from: Messtechniker on September 30, 2018, 03:02:51 pm ---Facing a similar problem too. I was planning for a small UPS in case the electricity for may gas central heater fails leaving me cold. The supply of gas is ensured in the case of a mains power blackout. They use gas operated gas pressure controllers. :-+ So me thinks a small UPS might be nice since my central gas heater draws only 17 W max. The problem is, however, that the flame sensor is of the ionization detection type, thus needing a permanent neutral connection. Now if I insert an UPS, the GFCI is likely to blow - see above. I have asked several professional electricians (one old hand and one with best marks fresh from professional training (Elektromeister)) to recommend a suitable UPS for this scenario. They simply do not have the know how. Another one said "simply try". :scared: Well I'm not going to mess around with gas apparatus not knowing what I am doing. As to my question how they install such systems in hospitals, for example, they said. "We get a complete package from the manufacturer and simply install that". :-//. Go figure. So I am still at a loss what to do. --- End quote --- Not sure if this is hijacking a thread or not, But why do you think adding a UPS would cause your GFCI to trip? in this thread, the only reason the GFCI was tripping is because he was using a GFCI tester which is supposed to trip it. Sent from my Fi Moto x4 using Tapatalk |
| Navigation |
| Message Index |
| Next page |
| Previous page |