Inverter Management

[haycord]

I'm curious how others manage their portable Inverters (ie: RICH Solar PSW RS-V2000). For example, assume Grid down and a modern Refrigerator is on the Inverter - and the AGM batteries reach their minimum SoS and continue discharging for whatever reason (doesn't matter here) and there is no LVD to protect the batteries or the appliances. Most smart appliances are not going to be happy as the 120vac output slowly tapers off to zero. This has to be a common issue...

Related scenario: The Refrigerator is on and a LVD disconnects the Inverter load to protect the batteries. The Refrigerator is still on obviously and someone restarts the Inverter - I assume the Inverter startup with the Refrigerator on is bad news. How is this issue typically handled?

Thanks

 

[Q-Dog]

Most inverters have a low voltage cutoff, a point where they will shut down if DC voltage gets too low. That number should be in your user manual. The AC voltage should not taper off, the inverter should shut down once the DC voltage gets too low.

 

[Mattb4]

...

Related scenario: The Refrigerator is on and a LVD disconnects the Inverter load to protect the batteries. The Refrigerator is still on obviously and someone restarts the Inverter - I assume the Inverter startup with the Refrigerator on is bad news. How is this issue typically handled?

Thanks

If the refrigerator startup surge is more than the inverter can handle it will go into overload upon startup fairly quickly. If the inverter has a soft start capacity it will attempt to cycle up. If your refrigerator is one of those Internet connected, talking/walking and self aware units it might dislike not having perfect power upon startup. But the most likely scenario if the inverter is properly sized, and you have sufficient battery capacity, is it just starts up.

It is not a good idea to short cycle refrigeration compressor motors by quick power off and back on.

 

[haycord]

The RS-V2000 does a shutdown at 10.2V but by then the AGM's are at 0 volts. The AC feed to the Refrig slowly going from 120 to 0 is going to wreck it IMO. The Inverter Op Manual says to be sure the loads are disconnected before startup. Sounds like a wreck waiting to happen, thats why I am curious. Thanks

 

[hwy17]

no LVD to protect the batteries or the appliances. Most smart appliances are not going to be happy as the 120vac output slowly tapers off to zero.

The AC voltage should not be dependent on the DC voltage. Any good inverter can maintain solid 120vac as the DC voltage tapers down, until the inverters shuts of for LBCO.

 

[Mattb4]

The RS-V2000 does a shutdown at 10.2V but by then the AGM's are at 0 volts. The AC feed to the Refrig slowly going from 120 to 0 is going to wreck it IMO. The Inverter Op Manual says to be sure the loads are disconnected before startup. Sounds like a wreck waiting to happen, thats why I am curious. Thanks

Your response makes no sense. If the battery voltage is at 10.2vDC to shut down the inverter it is more likely to rise backup slightly after the inverter disconnects. This is due to battery voltage slump under load. The 120vAC is turned off much like a switch turns off power.

 

[Q-Dog]

The RS-V2000 does a shutdown at 10.2V but by then the AGM's are at 0 volts. The AC feed to the Refrig slowly going from 120 to 0 is going to wreck it IMO. The Inverter Op Manual says to be sure the loads are disconnected before startup. Sounds like a wreck waiting to happen, thats why I am curious. Thanks

When the battery reaches 10.2 volts the inverter will shut down. The battery can't be at 2 different voltages at the same time.

 

[haycord]

The AC voltage should not be dependent on the DC voltage. Any good inverter can maintain solid 120vac as the DC voltage tapers down, until the inverters shuts of for LBCO.

Good point. Maybe the RICH is a bad choice because the auto shutdown (10.2V) is below 0 volts on the AGM batteries.

 

[MisterSandals]

(10.2V) is below 0 volts on the AGM batteries.

How can 10.2V be below 0V?

Is this a southern hemisphere thing?

 

[haycord]

Your response makes no sense. If the battery voltage is at 10.2vDC to shut down the inverter it is more likely to rise backup slightly after the inverter disconnects. This is due to battery voltage slump under load. The 120vAC is turned off much like a switch turns off power.

Agreed. But at the point of auto-disconnect the Refrig has to have suffered. I'm sure the Inverter can't boost the out to 120v if the input is at 20vdc and declining for example.

 

[haycord]

How can 10.2V be below 0V?

Is this a southern hemisphere thing?

In Texas. Below zero is a bad choice of words on my part. My AGM chart says 11.5V = 0 volts, so actually the 10.2V disconnect will never be reached in theory.

 

[haycord]

In Texas. Below zero is a bad choice of words on my part. My AGM chart says 11.5V = 0 volts, so actually the 10.2V disconnect will never be reached in theory.

Sorry, 0%.

 

[Mattb4]

Sorry, 0%.

Capacity.

What happens to a battery under load is its ability to maintain voltage drops. So your inverter setting at 10.2v will likely leave very little capacity though you will see voltage come back up to a few percent capacity after it disconnects. As already mentioned the 120vAC is maintained by the inverter until it can't due to insufficient DC voltage. It turns off the AC output before the DC voltage drops below that level. So no taper down of 120vAC output. It is cut off.

ETA: Incidentally the low voltage cutoff of most mobile inverters is too low in my opinion for saving the life of your batteries. Ideally with a AGM you would only want to pull it down to 50% capacity before recharging it. That would be at about 12vDC under modest loading. Too bad simple inverters have no way to adjust low voltage cutout.

 

[haycord]

Thanks everyone. I know I over-analyze everything but I can't grasp how the Inverter can output 120V ~600W when the AGM batteries are nearing 0% and the disconnect still has not activated. It must being pulling HARD on the remaining battery. I'm just trying to learn how not to cook and $2500 Refrig. Thanks

 

[MisterSandals]

I'm just trying to learn how not to cook and $2500 Refrig.

This is a huge concern of mine too. I'm been messing around with a stupid Schneider SW4048 and its idiotic software makes setting it up impossible and it cuts out more times than my heart can take. I wait until the fridge cycles off before messing with anything, and even then, i turn the breaker off first and turn it back on long after things settle.

 

[hwy17]

It must being pulling HARD on the remaining battery.

Yes, the inverter will draw higher and higher current from the battery to serve the same AC load, as the battery voltage is dropping.

 

[hwy17]

Your response makes no sense. If the battery voltage is at 10.2vDC to shut down the inverter it is more likely to rise backup slightly after the inverter disconnects. This is due to battery voltage slump under load. The 120vAC is turned off much like a switch turns off power.

I believe some inverters have different LBCO and low voltage recovery levels to deal with this. Like turn off at 10 turn on at 11.

 

[Mattb4]

I believe some inverters have different LBCO and low voltage recovery levels to deal with this. Like turn off at 10 turn on at 11.

Yes, you do not want the inverter cycling back on and than off as the load hits and the voltage drops again. Though I wonder if a starter type lead acid battery with a really high inverter load could cause it to happen.

 

[Hogheavenfarm]

I manage it by moving everything from my conventional fridge into a chest freezer I converted to run as a fridge, an old Aussie-land trick. The chest freezer takes much less power to run than a standard fridge, and the johnson control unit cycles it between 33 degrees and 39 degrees. But I only do that if the power has been off for 5 hours or more.

 

[haycord]

Y'all confirmed my concern. I want to have a system that can be operated by my wife in my absence so I don't' want a list of technical maneuvers that she would have to follow. I'm currently designing a Manually Resettable LVD for the load-side of the Inverter that will trip on loss of power and/or a pre-selected falling voltage. I think that is the only reliable option that I can see now - apparently its not commercially available.

Thanks again.