Agreed. And the most common motor load in a residence is the fridge.
Are there any guidelines or rules if thumb for the duration and magnitude of surge current / power ti start an average refrigerator?
Eg4 inverter future
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Are there any guidelines or rules if thumb for the duration and magnitude of surge current / power ti start an average refrigerator?
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
I don't know, but I would bet that the newer refrigerators have a much smaller surge than the 30-year-old fridge that got put out in the garage.
zanydroid
Solar Wizard
Inverter drive fridge should be low. I think most grownup fridges are inverter drive by now.
Cheap chest freezer is pretty damn high.
Cheap chest freezer is pretty damn high.
As in how high?
zanydroid
Solar Wizard
I didn't do very careful testing of it, and I unfortunately bought the wrong clamp meter (no surge measurement). It's somewhere > 3A. I don't plan to try it again with smaller than 1500W supply.
My testing was:
Questionable Ryobi MSW inverter @300W: no way, instantly killed. Was hoping it would at least suffer through the MSW. My inverter fridge could start but with a terrible running noise, so I didn't want to keep it on.
Inverter generator @3000W: no problem. Could start freezer and run fridge + microwave and kettle.
So 3kW of HF power could start freezer no problem - exactly what I was looking for.
Could it start the freezer even when other loads such as microwave wire running (on High, otherwise cycling could have been off)?
Toaster ovens and coffee makers also cycle but I don’t know about electric kettles…
zanydroid
Solar Wizard
This wasn't a controlled test, it was during a power outage... If I get a chance again I'll give it a shot. The feeling I got is that it can easily handle all of those small appliances. Like one of those full 1800W ones (toaster oven or microwave), and then all the small ones combined.
With respect to how those appliances cycle, it depends. I've tested many with grid power and power meter.
If you have the cheapest ones, they are all or nothing cycling. Classic microwave and classic Toaster oven. Instant Pot as well.
Inverter microwave are ramped smoothly (and this is supposed to be easier to work with anyway as an appliance). High end toaster ovens like Breville with precise temp control are ramped.
Most kettles are all or nothing. I haven't tested my Stagg to see if its PID is on-off or ramped.
Apart from the classic microwave I know all of those are pure resistive loads. Dunno what kind of load magnetron presents when it's run on/off.
My favorite non-cycling electric load is an electric charcoal starter (~600W).
Alternatively, as long as you can know exactly when the freezer starts, you can measure current on the leg powering the fridge.
Subdood
Photon Wrangler
Would one 5.1KWh (48v 100ah) battery be enough to start/run a 6.5KW single phase inverter, assuming the load is 5KW or less? Assuming there is no grid, and no solar? What about if there was sufficient solar?
zanydroid
Solar Wizard
Not sure how single phase would affect things
I went back to the other thread about the XW and the discussion about min sizing was around lead acid batteries, so it’s not transferable to LFP.
If there is enough solar then the MPPT output would eventually be paralleled to the battery output before going into the inverter, which would take the load off the battery.
If you have solar to cover 100% of the load then BMS shutdown (presuming the battery takes more than expected of the load) will not cause an issue, but it is very unlikely to have a BMS shutdown in this case.
I went back to the other thread about the XW and the discussion about min sizing was around lead acid batteries, so it’s not transferable to LFP.
If there is enough solar then the MPPT output would eventually be paralleled to the battery output before going into the inverter, which would take the load off the battery.
If you have solar to cover 100% of the load then BMS shutdown (presuming the battery takes more than expected of the load) will not cause an issue, but it is very unlikely to have a BMS shutdown in this case.
Runs my 6000watt split phase inverter under load with a single chins 100ah 48v battery. Less load the longer the runtime but it works even at high loads.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
The Amp hour rating of the battery only determines how long the inverter will run on a given load.
Whether the inverter can run at full power is determined by the total Amps the battery(s) can produce. For a 6.5KW inverter... I will assume a 94% efficiency. That means at full power the battery needs to provide (6500W/.94)/52V=133A,
Most 48V server rack batteries have BMSs with only 100A discharge capability. Consequently, a single battery would not be able to provide enough current for a continuous 6500W. At about 4.9KW the current draw from the inverter would trip the BMS to shut down. There are a few server rack batteries that have 200A BMSs. A single one of these would be able to handle a 6.5KW inverter at full power.
Some of the wall-mount batteries that are coming out also have 200A BMSs. As an example, the wall-mount battery that EG4 just released has a 200A BMS and could run a 6500W inverter at full load.
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timselectric
If I can do it, you can do it.
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But only for about 45 minutes, at full load.
Subdood
Photon Wrangler
Thanks for the reply. Yeah, I know a 6.5KW load would be over 100A for the battery, my question is with say just a couple KW load, with no solar and no grid, the battery ought to be able to start the inverter? I was thinking along the lines if the battery had enough "juice". Something about enough power to charge the inverter's capacitors. May not even be a relevant question.
Another question- my array is rated at 3.6KW, with the 5kwh batt fully charged, and it being a sunny day, the inverter ought to be able to handle a 6.5KW load, correct?
One more- if the inverter is in SBU mode on a sunny day, and you have say a 4KW load. As long as the battery is not near low voltage disconnect, both the PV and battery ought to be able to provide power to the load, correct? How much of that 4KW comes from the array and how much from the battery?
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Most server rack batteries have precharge and current limits that pretty much eliminate the old pre-charge problem.... I would not worry about that. As long as it is a 48V battery with a capacity of just a few amps it will start the inverter. (I have used 10A power supply on the battery input to start up an inverter.... I just could not put any load on the inverter.) Once there are a few amps to get the inverter to turn on, it is 'just' a matter of how much current is needed by the load on the inverter.
The only answer I can give is 'probably'. However, the definitive answer depends on the internal design of the inverter. I don't have enough experience on systems with undersized batteries to say much more than that.
Again, my definitive answer is 'Probably'. Unfortunately, most of the lower-cost inverters don't explain things to that level of detail. Furthermore, it seems like people see different behaviors on different Inverters.
I would expect the inverter to use everything it can from solar before it taps into battery power. However, people have reported odd behavior with the various settings so I can not say with confidence that they all behave the way I suspect.
BTW: I suspect that a lot of the settings are not independent of each other. Consequently, 'SBU' might behave differently depending on what some of the other settings are. This would explain why people observe seemingly different behavior between two different inverters. (Not to mention all the different firmware versions that can change things)
Capn D
New Member
Good question. I have replacement 6000EX New in box.
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