Very low mains voltage with hybrid inverter. Would it work to correct it?

[LlamaSolar]

I have a client that has his dentistry clinic in a very rural area in Mexico. He is connected to a overloaded transformer from the electric company that he shares with pretty much half the town, causing the mains voltage that he gets to get as low as 190V Phase to phase during constant loads, lower during startup of his compressors. 84V Phase to Neutral during startup of his compressor.

I'm thinking a hybrid inverter can solve the issues he is having using peak load shaving, and battery backup when the mains get too low. Specifically the Sol-Ark 8K-2P-N, with the possibility of adding a second one in parallel once his loads grow.

Do you know if hybrid inverters can work in such low mains voltage without resorting to going off grid? Because if it's too low for it, then perhaps I'd instead get an off grid inverter, and save the client some money.

Any input or related experience would be appreciated.

Cheers!

 

[timselectric]

It can't correct the grid voltage.
It would just switch to off grid mode.
I would use an off grid AIO and a battery charger from the grid.
This would give you correct voltage at all times. As long as the AIO is sized correctly.

 

[ricardocello]

Maybe double conversion is the way to go.
The inverters are always providing nice clean power from batteries.

The horrible grid gets connected to chargeverters to keep the battery bank filled.
Not cheap, but he would have the best power in town all the time.

 

[Hedges]

"Compressors" - how big a compressor does a dentist use?

Large motors are a severe load for inverters, which need to deliver surge lasting a couple seconds at wattage 5x greater than running power rating.

The grid has a good surge capability, with voltage drooping due to resistance of windings.
Split-phase motors struggle to start at reduced voltage.
How high does line voltage get, and can compressor tolerate that? How about 10% to 20% higher?
A buck-boost transformer (large enough to give surge) could help compressor start from the grid.

Voltage of grid would still droop, but I'm thinking of charger + inverter (on-line UPS) feeding other equipment, while buck-boost transformer takes care of motor. The 190V L-L would be just fine for something like Chargeverter that operates on anything 120V to 240V.

 

[hwy17]

I would be concerned if my dentist was running on an inverter and it wasn't a Schneider XW.

 

[robbob2112]

"Compressors" - how big a compressor does a dentist use?

Large motors are a severe load for inverters, which need to deliver surge lasting a couple seconds at wattage 5x greater than running power rating.

The grid has a good surge capability, with voltage drooping due to resistance of windings.
Split-phase motors struggle to start at reduced voltage.
How high does line voltage get, and can compressor tolerate that? How about 10% to 20% higher?
A buck-boost transformer (large enough to give surge) could help compressor start from the grid.

Voltage of grid would still droop, but I'm thinking of charger + inverter (on-line UPS) feeding other equipment, while buck-boost transformer takes care of motor. The 190V L-L would be just fine for something like Chargeverter that operates on anything 120V to 240V.

Would an easy-start type device help with that?

 

[Hedges]

That was the first thought that crossed my mind.

EZ-start recommends their devices for A/C only to consumers, other (e.g. industrial) customers should contact them.
The required torque vs. time profile may differ.
Compressors have an unloader, I think just vent line when power switched off. Pressure would rise as it started turning. Unloading for an extended time should work, or a larger volume (coil of tubing). Modifications depend on model.

I'm surprised it doesn't have issues due to brown-out.
I'd like to restore voltage with buck-boost, more ideally automatically switched based on line voltage (transformer taps.)

But is this an induction motor?
Some compressors like the DeWalt ones Midnight demoed (inverter starts 4x compressors at once) are brush-type so essentially immune to brownout. Substituting compressor could be the best approach if presently induction motor. But of course have to understand application, is it oil free, medical grade air, etc.

 

[ricardocello]

I would be concerned if my dentist was running on an inverter and it wasn't a Schneider XW.

You misspelled Victron!

 

[v_green57]

If the issue is low voltage, but not losing power completely, a constant-voltage ferroresonant transformer may be a simpler answer:

Sola/Hevi-Duty Products | Sola CSV Hardwired Series Power Conditioners

Superior voltage regulation of ±1% sets the Sola CVS Series power conditioner apart from other power conditioning technologies on the market. Extremely tight regulation is accomplished by Sola/Hevi-Duty’s patented ferroresonant transformer technology.

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I have a 500vA Sola that I use to run a 500kV DC hipot - even a 1 volt difference on the AC side amounts to hundreds of volts on the DC side if I've got it cranked up testing cable. Gotta keep things stable.

 

[hwy17]

You misspelled Victron!

That would concern me for a different reason... That my dentist might be eruopean.

 

[wheisenburg]

Sol-Ark 8K-2P-N

Any idea what the surge current is for the compressor? Is it a 120 or 240 volt?

A Sol-Ark 8K is essentially 2*4K inverters. One for each leg. They also do not handle surges well. In fact they may struggle just to output 4K continuous on a single leg. Due to its transformer based low frequency design a Schneider 6848 by contrast can output 12K on a single leg for surges and 6K continuously.

You need to figure out your continuous and peak loads. You need to know this for the individual legs if you are planning to use a Sol-Ark. Other responders are correct that when using a hybrid in pass through mode the inverter can supplement the current. It can not increase the voltage. So depending on peak and continuous load requirements, you can figure out how much inverter power you need. Then you also need to make sure the batteries can provide that amount of power. The storage capacity may not be as important as the peak output. In my system the 2*6848 inverters will supply 24K watt peaks. The batteries are 100 amps * 50 volts * 3 = 15K watts. The batteries will trip before the inverters. Your system will be more reliable if the batteries can supply at least as much current as the inverters can use. I really should have 5 batteries and probably 6.

If a dentist is performing procedures having your power trip off line could be a safety concern.

For charging it is just a matter of making sure your charger can keep up with the continuous load which is typically way lower than peak loads. Your options might be a chargeverter or an additional inverter / charger. The additional inverter / charger, if you went that route, would be a dedicated device that would be wired to the grid and have the sole task of charging the batteries as needed. A dedicated inverter / charger could be programmed to do this. I looks like these chargeverter devices can do this automatically and when the battery is full they just go into a float mode.

I know of another user that built a system with 2*6848s to supply power and 1*6848 as the charger. He lived somewhere that had power quality issues as well as frequent outages. The system is working great last I heard. These are very heavy duty systems and they should last for years or even decades without issues. You won't have to worry about someone turning on a vacuum cleaner and taking the whole office down.

 

[sumpower]

Worked in Mexico and all I can add is that grid power destroys electronics. My number one concern if using solar/grid tie in Mexico.
I did not install any high frequency inverter to start motor loads.
I only installed XW pro's because of there unbalanced load capabilities. Some Outback Radian's in certain situations. Mainly because this is what I was familiar with.

I rewound several irrigation pump motors and refrigeration compressors motors in Mexico, all because these motors were killed by voltage sag.
Mexico and power quality do not go together in rural areas there.

 

[timselectric]

That's not a bad idea.
Two AIO's
One connected to the grid can maintain the battery and power the non voltage sensitive loads. While the other is only connected to the battery and powers the voltage sensitive loads.

 

[Gold Country Russ]

No matter what else he does, make sure that each motor load possible has an inverter, soft start, or even some modern single phase pump drives (Grundfos-Gould?) tolerate low voltage and can be applied to many applications other than just pumps.

 

[Berseker]

consider getting a voltage stabilizer, to modulate and smoothen the volage.....or get a dc charger and take the inverter offgrid