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Grid Backup without Solar. (UPS Inverter/Charger with automatic transfer back to Grid)

rickst29

Solar Enthusiast
Joined
Mar 27, 2021
Messages
712
Location
Reno, NV
It feels strange to ask about this configuration within the the solar-oriented forum, but here it is:

Friends have asked me to recommend and possibly install a back-up only battery inverter-charger for their home, covering only bedroom lights plus a plug-in fan and kitchen lights plus the main fridge. (About 6000 watt-hours to cover the minimal loads for 4-6 hours per outage. I strongly prefer to build a 16s DIY LiFePO4 battery (I've done a few in the past). Backup only: Unlike my own grid-connected solar home, he will not have gird-tie with solar power pushing energy to the grid, and he will not be configuring for time-shifting.

Their concern is with NV Energy "extreme fire risk" blackouts in Incline Village NV USA (Near the California border, north Lake Tahoe). This is on the Nevada side (NV Energy) and not the CA side (PG&E). With no power ever being sent "backwards" (new permits, new meters, etc.), the installation can be completely downstream. I've identified 4 possible products so far, and I list here them with my "feelings of concern". Can you offer hints concerning these possible choices?

1) Schneider Conext XW PRO. It seems to have high reliability, but costs the most (by far) and might be a lot more challenging to configure. My feeling is "overkill".

2) Samlex EVO-4248SP. Seems fairly easy to configure. Split phase is not needed at their house. The neutral-ground bond in this unit is auto-switched, depending on whether the grid is present. (That's nice, compared to the issues being discussed "at considerable length" WRT the EG4 units). The 4200W power rating is lower but adequate, the inverters do have good headroom for starting up the household fridge compressor. The big question concerns the reliability of switching modes - back to grid pass-through when "the grid" returns. I do not see this small unit discussed much here, it is sized only a bit larger than some RV "all-in one" load centers. Does anyone have experience with it?

3 and 4) EG4 products (6000EX-48HV or 6500EX-48). They're very cheap, and I worry that a large proportion of the build cost is invested in un-needed MPPT SCCs, rather than the Inverter/Charger and the transfer switch. Their documentation materials indicate that they prefer to communicate with their own battery BMS, and this forum is filled with zillions of posts about "error 61' in communicating with those proprietary battery packs. (The packs themselves are sold at a reasonable price, but likely contain an inferior DALY BMS, and the cells aren't compressed. They're also small, just 100Ah each. I have built bigger and better battery packs.) I can certainly configure the 'User' battery mode, but I worry about (a) the Inverters running with unbalanced loads and (b) "issues" of bonding versus unbonding the neutrals to ground, and (c) it's ability to switch back to grid - including any possible "issues" with the 'neutral' current paths.

I'm inclined to recommend the Samlex, but hoping to hear from you all before I do that. The EG4 products are both fairly new, has anyone seen them successfuly switch back to grid when configured in UPS mode?

Thanks in advance.
 
It feels strange to ask about this configuration within the the solar-oriented forum, but here it is:

Friends have asked me to recommend and possibly install a back-up only battery inverter-charger for their home, covering only bedroom lights plus a plug-in fan and kitchen lights plus the main fridge. (About 6000 watt-hours to cover the minimal loads for 4-6 hours per outage. I strongly prefer to build a 16s DIY LiFePO4 battery (I've done a few in the past). Backup only: Unlike my own grid-connected solar home, he will not have gird-tie with solar power pushing energy to the grid, and he will not be configuring for time-shifting.

Their concern is with NV Energy "extreme fire risk" blackouts in Incline Village NV USA (Near the California border, north Lake Tahoe). This is on the Nevada side (NV Energy) and not the CA side (PG&E). With no power ever being sent "backwards" (new permits, new meters, etc.), the installation can be completely downstream. I've identified 4 possible products so far, and I list here them with my "feelings of concern". Can you offer hints concerning these possible choices?

1) Schneider Conext XW PRO. It seems to have high reliability, but costs the most (by far) and might be a lot more challenging to configure. My feeling is "overkill".

2) Samlex EVO-4248SP. Seems fairly easy to configure. Split phase is not needed at their house. The neutral-ground bond in this unit is auto-switched, depending on whether the grid is present. (That's nice, compared to the issues being discussed "at considerable length" WRT the EG4 units). The 4200W power rating is lower but adequate, the inverters do have good headroom for starting up the household fridge compressor. The big question concerns the reliability of switching modes - back to grid pass-through when "the grid" returns. I do not see this small unit discussed much here, it is sized only a bit larger than some RV "all-in one" load centers. Does anyone have experience with it?

3 and 4) EG4 products (6000EX-48HV or 6500EX-48). They're very cheap, and I worry that a large proportion of the build cost is invested in un-needed MPPT SCCs, rather than the Inverter/Charger and the transfer switch. Their documentation materials indicate that they prefer to communicate with their own battery BMS, and this forum is filled with zillions of posts about "error 61' in communicating with those proprietary battery packs. (The packs themselves are sold at a reasonable price, but likely contain an inferior DALY BMS, and the cells aren't compressed. They're also small, just 100Ah each. I have built bigger and better battery packs.) I can certainly configure the 'User' battery mode, but I worry about (a) the Inverters running with unbalanced loads and (b) "issues" of bonding versus unbonding the neutrals to ground, and (c) it's ability to switch back to grid - including any possible "issues" with the 'n eutral' current paths.

I'm inclined to recommend the Samlex, but hoping to hear from you all before I do that. The EG4 products are both fairly new, has anyone seen them successfuly switch back to grid when configured in UPS mode?

Thanks in advance.

Since split phase 120/240 VAC is not needed possibly a Samlex EVO 24 VDC to 120VAC inverter. I have the Samlex EVO 2224 and very happy with the Inverter Charger. The system runs a freezer, fridge, dehumidifier, 2 computers and printer with router & hub, TV and lights and charges e-bike batteries. The loads you listed seems could be powered by this unit. Or a 24 VDC Samlex EVO 4024 inverter/charger could supply more power for the ability to add more loads in the future if needed. An 8s 24 Volt battery with 280 AH cells would give 6720 wh battery capable of the listed needs or place 2 banks of 8s 24 Volt 280 AH cells in parallel for over 13 Kwh battery.

A little more about the Samlex EVO-2224-Inverter-Charger with built in transfer switch that is listed:
The frequency and phase of the backup Inverter Section are always kept synchronized with the AC input source. This facilitates “extremely fast” transfer time of up to 16 ms. Also, transfer from the Inverter Section to the AC input source and vice versa takes place at zero crossing of the voltage waveform – this ensures (i) negligible arcing / erosion of Transfer Relay contacts and (ii) negligible Electromagnetic Interference (EMI) associated with arcing.

This synchronized feature also helps the wear & tear on loads when the auto transfer switches from one AC source like the Grid/Generator to the Inverter/Charger and vice versa. The transfer switch has always worked well & properly for the Samlex EVO-2224-Inverter-Charger.

Certainly the Samlex EVO-4248SP is a good choice if 120/240 VAC split phase is ever needed in the future or if a 48 VDC system is preferred.

The Samlex EVO-4248SP is on my short list of inverter/chargers when my system is upgraded to 120/240 VAC split phase power.

On a side note... Talking with Samlex America tech support recently and they said the Samlex EVO-4248SP would be stackable sometime in the near future. Just needed further testing of the firmware as the hardware already supports it.

Hope this helps...
 
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Since split phase 120/240 VAC is not needed possibly a Samlex EVO 24 VDC to 120VAC inverter. I have the Samlex EVO 2224 and very happy with the Inverter Charger.... The system runs a freezer, fridge, dehumidifier, 2 computers and printer with router & hub, TV and lights and charges e-bike batteries. The loads you listed seems could be powered by this unit. Or a 24 VDC Samlex EVO 4024 inverter/charger could supply more power for the ability to add more loads in the future if needed. An 8s 24 Volt battery with 280 AH cells would give 6720 wh battery capable of the listed needs or place 2 banks of 8s 24 Volt 280 AH cells in parallel for over 13 Kwh battery.

A little more about the Samlex EVO-2224-Inverter-Charger with built in transfer switch that is listed:
The frequency and phase of the backup Inverter Section are always kept synchronized with the AC input source. This facilitates “extremely fast” transfer time of up to 16 ms. Also, transfer from the Inverter Section to the AC input source and vice versa takes place at zero crossing of the voltage waveform – this ensures (i) negligible arcing / erosion of Transfer Relay contacts and (ii) negligible Electromagnetic Interference (EMI) associated with arcing.

This synchronized feature also helps the wear & tear on loads when the auto transfer switches from one AC source like the Grid/Generator to the Inverter/Charger and vice versa. The transfer switch has always worked well & properly for the Samlex EVO-2224-Inverter-Charger.

Certainly the Samlex EVO-4248SP is a good choice if 120/240 VAC split phase is ever needed in the future or if a 48 VDC system is preferred.

The Samlex EVO-4248SP is on my short list of inverter/chargers when my system is upgraded to 120/240 VAC split phase power.

On a side note... Talking with Samlex America tech support recently and they said the Samlex EVO-4248SP would be stackable sometime in the near future. Just needed further testing of the firmware as the hardware already supports it.

Hope this helps...
Thank you for advising me of your experience with the smaller unit, and your note regarding synchronization of the waveforms between Inverter and Grid (applicable to most Samlex models). The surge power should be sufficient for the fridge, although the EVO-4024 would provide a lot more headroom (at $300 higher cost, plus the cost for bigger main panel breaker). Wiring is simplified by avoiding split-phase, so I'll be recommending one of those two units.
 
I'm running a Chinese hybrid (24v 3.5kw) in UPS mode and as far as switching from grid to battery, it works ok and near-instantaneous. When the grid comes back, it takes its time to switch back, but I have learned that this is normal.
 
I'm running a Chinese hybrid (24v 3.5kw) in UPS mode and as far as switching from grid to battery, it works ok and near-instantaneous. When the grid comes back, it takes its time to switch back, but I have learned that this is normal.
That is because once you are on the inverter you must reach the "Battery power to utility" low voltage set point. If you want to maintain more of your batteries capacity plus operate more like a traditional UPS you would set this as high as it would allow.

Some companies do make large scale UPS systems. They would operate like a computer UPS that transfers immediately back to mains as the preferred power supply. Not cheap in comparison to the hybrid solar powered inverter setups.
 
Thank you for advising me of your experience with the smaller unit, and your note regarding synchronization of the waveforms between Inverter and Grid (applicable to most Samlex models). The surge power should be sufficient for the fridge, although the EVO-4024 would provide a lot more headroom (at $300 higher cost, plus the cost for bigger main panel breaker). Wiring is simplified by avoiding split-phase, so I'll be recommending one of those two units.

Just a note that the Samlex EVO series needs the RC-PLUS remote control to program the inverter/chargers. The manual for the remote is extensive very detailed on how to program the Samlex EVO series (manual attached).



 

Attachments

  • Samlex EVO-RC-PLUS Rmote Contlol Manual.pdf
    4.5 MB · Views: 3
The extreme risk is now, like in hours, not days and you may not have the time to build. So for the short term one of those (I hate the term)”solar generators” built by a multitude of different companies now. Not cheap for a good one. For a small load like you described, a small cheap quiet generator 2 to 3kw to get them passed this heat/wave and manually connect cords or install a interlock breaker & plug. Later, un rushed, with time to plan and get good equipment, install a great system.
 
That is because once you are on the inverter you must reach the "Battery power to utility" low voltage set point. If you want to maintain more of your batteries capacity plus operate more like a traditional UPS you would set this as high as it would allow.

No not really, I was just testing the UPS function, or was cycling the batteries really shallow. On startup, with batteries nearly full, it doesn't immediately switch back to grid, but the unit immediately senses the grid as the LCD indicates that there is grid power. Others who also bought the same unit thought that they were defective, but there's a discussion here that some inverters do this by design.

Though I've got two more 12v inverter-charger hybrids on UPS (one 3kw toroidal and 1kw portable) in the first floor for appliances / electronics, they do switch back to grid immediately regardless of any battery level.

Some companies do make large scale UPS systems. They would operate like a computer UPS that transfers immediately back to mains as the preferred power supply. Not cheap in comparison to the hybrid solar powered inverter setups.

Yep I've worked near several datacenters and these are huge.
 
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No not really, I was just testing the UPS function, or was cycling the batteries really shallow. On startup, with batteries nearly full, it doesn't immediately switch back to grid, but the unit immediately senses the grid as the LCD indicates that there is grid power. Others who also bought the same unit thought that they were defective, but there's a discussion here that some inverters do this by design.

Though I've got two more 12v inverter-charger hybrids on UPS (one 3kw toroidal and 1kw portable) in the first floor for appliances / electronics, they do switch back to grid immediately regardless of any battery level.



Yep I've worked near several datacenters and these are huge.
Sorry my bad. It also depends on preferred operating mode setting. The battery to utility set point would only apply when using SBU, SOL and not UTI modes. I had not thought it out completely before posting.
 
They're also small, just 100Ah each.
100 Ah is 5 kWh, you said you wanted 6 kWh. So two would be more than ample for your stated requirement.

While you could build your own with an AIO inverter and a DIY LiFePO4 battery, ready made server rack batteries are way easier to set up and not that much more expensive per kWh.

Alternatively it's a job for a Bluetti or EcoFlow portable power stations with a battery extension module or two.

Whichever way you go, install a critical loads panel powered by these units while having the AC charger input connected to a non-critical grid powered supply circuit.
 
It feels strange to ask about this configuration within the the solar-oriented forum, but here it is:

Friends have asked me to recommend and possibly install a back-up only battery inverter-charger for their home, covering only bedroom lights plus a plug-in

Don't do this. They are your friends now, but if something bad happens, and you put it together, then what? Homeowners can do their own electrical work or pay a pro to take on the liability. Do you want to take on the liability for a system you aren't in control of?
 
I have built a similar system using a diy lifepo4 battery made from 16x 280ah cells with a jk BMS active balancer. I have used a SunGoldPower bluepower tp6048 which is the same as the mpp solar lvx6048 which seems to be more well known on this forum.

So far, it's working well, except for one issue I am currently working on (and started a thread on somewhere else in the forum) is that when switching the priority mode from solar-battery-grid to solar-grid-battery I get a little bit of a blip. Enough to reset some things in the house like tvs and media players and sometimes clocks. But everything else has been smooth so far. I have an esp32 that connects it all to my Home Assistant where I am doing to automation of switching the grid mode on and off depending on peak/off-peak billing time.

I am not currently using the solar feature of the hybrid inverter. I thought I would be able to find a good solution that saved money due to not having the solar mppt features, but these hybrid all in ones seemed to be cheaper anyway.
 
So far, it's working well, except for one issue I am currently working on (and started a thread on somewhere else in the forum) is that when switching the priority mode from solar-battery-grid to solar-grid-battery I get a little bit of a blip. Enough to reset some things in the house like tvs and media players and sometimes clocks.
Check the inverter's setting for AC input voltage range. There are two options: Appliances (default) and UPS.
UPS mode is meant to have a faster cut over time.
 
Check the inverter's setting for AC input voltage range. There are two options: Appliances (default) and UPS.
UPS mode is meant to have a faster cut over time.
Yes, I have made that change. I couldn't find any clear description of the difference between those two, but I do have it set to UPS now and it seems to make no difference in the speed of transfer. Still blipping.
 
Just an update on my SunGoldPower BluePower TP6048 blipping when switching from battery back to grid, sungoldpower support indicated that this was because it was not designed to switch priority modes while actively operating. So, I setup a relay to cut off grid power to the inverter and keeping the inverter in Solar/Grid/Battery priority mode, that causes it to default to the battery. Then, when I use the relay to close the circuit and turn on grid power, the inverter switches back to Grid. When done this way, it does it near flawlessly. So, I think they need to do a firmware update to fix that issue, but I have setup my relay to be remotely controlled so it is working well for me.
 
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