Midnite Solar Rosie HF Inverter 27kW Surge Test

[Midnite Beta Tester]

Stopped by Midnite again yesterday, Friday. Only the backside of the booth was disassembled. Inverter display still wired up! OK, lets play a bit. I am told it takes 8-12 hours to assemble the booth. Same for tear down. I did a couple videos of some testing. Applied just over double the Inverters continuous rated load of 6.8kW. I put 14kW on her and then waited to see when the breaker would trip or the inverters protection would shut her down. The 250 amp breaker gave up first. She was pulling 350+ amps for about a minute+. Ignore the AC volts reading on the cheapo Vichy meter. A new battery in it made no difference. Ran test again and my Fluke meter showed a steady 239 VAC.

 

[Midnite Beta Tester]

Second test from Friday. Loaded up Rosie with 8kW of resistive loads, then turned on four air compressors, 15kW surge, 7kW running. So 15kW total running load and the 250 amp breaker let go after holding 45+ seconds at 380+ amps, 43.8 VDC.

 

[sunshine_eggo]

If you mentioned it, I missed it, but are you actually verifying inrush currents on the motors?

I'm starting to wonder if these things have a clever way of behaving somewhat like a soft starter - feeding only what it can supply without crapping its pants until the load reduces its demand.

 

[Hedges]

If you mentioned it, I missed it, but are you actually verifying inrush currents on the motors?

I'm starting to wonder if these things have a clever way of behaving somewhat like a soft starter - feeding only what it can supply without crapping its pants until the load reduces its demand.

Well, Midnight said they have a clever way to protect the transistors. Could it be a soft-starter as you suggest? But usually inverters give all they can trying to start a motor, and that's what motors need. Such current surge heats transistors fast (current squared).

And those compressors appear to have a clever way to start and run regardless of what voltage is presented to them. Including, I think, 48VDC or square wave. Universal motors are quite forgiving. Universal, in fact.

 

[Midnite Beta Tester]

If you mentioned it, I missed it, but are you actually verifying inrush currents on the motors?

I'm starting to wonder if these things have a clever way of behaving somewhat like a soft starter - feeding only what it can supply without crapping its pants until the load reduces its demand.

Yes they do! OCP, Over Current Protection. And yes, to protect the FETS. It's set conservatively right now so they don't blow up. They have 6 units working, when there are 10-12 then that protection will be backed off for hardcore testing of the surge limits. How much, how long, thermal temps etc.

 

[Midnite Beta Tester]

And those compressors appear to have a clever way to start and run regardless of what voltage is presented to them. Including, I think, 48VDC or square wave. Universal motors are quite forgiving. Universal, in fact.

A scope and a CT were used to check the inrush on the 4 pumps. 15kW was the number. I was there watching the engineer at the time.

 

[Hedges]

A scope and a CT were used to check the inrush on the 4 pumps. 15kW was the number. I was there watching the engineer at the time.

15kW inrush total for 4 compressor motors at once? Or per motor? And you said that was measured on a different inverter, correct?

What I'm curious about is how much inrush Rosie can deliver, and how large a induction motor it can start. That matters for things like well pumps. I think the DeWalt compressors have universal brush-type motors so more difficult to extrapolate from them to induction motors.

 

[Midnite Beta Tester]

15kW inrush total for 4 compressor motors at once? Or per motor? And you said that was measured on a different inverter, correct?

What I'm curious about is how much inrush Rosie can deliver, and how large a induction motor it can start. That matters for things like well pumps. I think the DeWalt compressors have universal brush-type motors so more difficult to extrapolate from them to induction motors.

The pumps can only be started up together, so yes, 15kW total inrush for them. Midnite has a well pump set up in their engineering dept. Outside the building. I have not seen it but I understand it's in the 2-3 hp range and designed to represent a deep well, 200-300 feet maybe? I'll find out next week exactly what kind of pump, size etc. The Rosie has no problem starting it.

 

[SolarPrep]

Sounds like a great inverter. The Midnite Solar people are great to deal with.

 

[Midnite Beta Tester]

At least some DeWalt compressors of that style apparently have brush-type motors.
Those are far easier starting.
Customers need to see how Rosie performs with induction motors, in particular how large an induction motor deep well pump it can start.

Did an inrush test today with the Rosie and a 2-3HP well pump. Did not get a chance to pull the pump and get specific details. Next opportunity I'll find out exactly what it is. Based on the running amps it appears to be a 2-3HP pump.

43.88 amps per leg inrush current with 12.2 amps per leg running current. The pump is configured to represent a well depth of 150-200 feet. Rosie didn't even notice!

 

[Midnite Beta Tester]

But would it start my 240v well pump? Last I checked the in rush was 42+ amps PER LEG ?

Based on the test I did, The Rosie would not even notice when your pump starts.

 

[Hedges]

43.88A x 240V = 10,531W (or VA)
Reasonable surge for a 5kW inverter to deliver. Should be easy enough for 6.8 kW Rosie.

43.88A surge / 12.2A running = 3.6 ratio
Relatively low surge, less than the 5x I assume and have measured for a very limited set of motors.
My central A/C compressor, for comparison, says "minimum circuit amps 16.4", "LRA 57" which is 3.5 ratio. Very similar I guess. It doesn't actually quote running amps, and I haven't measured.

12.2A running x 240V = 2928 VA running.

A 2 to 3 HP well pump should meet most customers needs.
Some have larger pumps for deeper wells, might need more.
Any well pump produces much more water than needed for household use. Ideally there would be a lower horsepower, lower volume pump for 500' to 1000' wells.

"designed to represent a deep well, 200-300 feet maybe?"
By that do you mean a pressure relief valve, so during testing it is delivering water flow at 100 to 150 psi?

 

[Midnite Beta Tester]

Two well pump charts I found. The basic one is what I used to get in the ballpark. The detailed chart leads me to think the pump is closer to a 1.5-2HP range. Grabbed a pic of the well simulator, or at least the fancy culvert pipe it's made out of.

 

[Midnite Beta Tester]

As the booth was being torn down I snagged a couple pics of the load lighting up top. It's clear that the guy installing them did actually run out of space to add more 300 watt bulbs...

 

[Quattrohead]

HaHa that is mental. Should think about a few dryer heater elements next time LOL. Only joking.

 

[Shunt Czar]

1. Is this inverter equipped with fault detection such that, if an output switch or controller fails, that it will disconnect the output with a physical relay, to prevent large DC outputs that can damage loads?

2. A serious test is to connect full load to the inverter and bake it in a 120 degF chamber or room until everything is at full temp. Then repeatedly hard short the output. I'd do it myself but I can't afford the inverter to try it.

 

[Midnite Beta Tester]

1. Is this inverter equipped with fault detection such that, if an output switch or controller fails, that it will disconnect the output with a physical relay, to prevent large DC outputs that can damage loads?

2. A serious test is to connect full load to the inverter and bake it in a 120 degF chamber or room until everything is at full temp. Then repeatedly hard short the output. I'd do it myself but I can't afford the inverter to try it.

Midnite has a nice sub zero freezer. -80 or more. I may put one in it, load it up and see how it goes. North Pole and the Arctic Circle need inverters too!

 

[Shunt Czar]

Midnite has a nice sub zero freezer. -80 or more. I may put one in it, load it up and see how it goes. North Pole and the Arctic Circle need inverters too!

I meant +120 degF

 

[Midnite Beta Tester]

I meant +120

A 2 to 3 HP well pump should meet most customers needs.
Some have larger pumps for deeper wells, might need more.
Any well pump produces much more water than needed for household use. Ideally there would be a lower horsepower, lower volume pump for 500' to 1000' wells.

"designed to represent a deep well, 200-300 feet maybe?"
By that do you mean a pressure relief valve, so during testing it is delivering water flow at 100 to 150 psi?

Yes, the pressure is higher than typical, no gauge but 100-150 sounds about right. I did pull the pump and it's 1.5 HP so smaller than I had said it appears to be, but not a wimpy 3/4 HP pump either!

 

[Hedges]

Yes, the pressure is higher than typical, no gauge but 100-150 sounds about right. I did pull the pump and it's 1.5 HP so smaller than I had said it appears to be, but not a wimpy 3/4 HP pump either!

Picture shows model 2243009203 Franklin 3-wire pump

Franklin Electric 2243009203 Super Stainless Water Well Motor 4" 1.5 HP 230V 3-Wire Single-Phase

Franklin Electric 2243009203 Super Stainless Water Well Motor 4" 1.5 HP 230V 3-Wire Single-Phase

www.rcworst.com

"CONTROL BOX REQUIRED"

Franklin Electric 2823008110 Standard Submersible Motor Control Box 1.5 HP 230V 1PH For 3-Wire Motors

Franklin Electric 2823008110 Standard Submersible Motor Control Box 1.5 HP 230V 1PH For 3-Wire Motors

www.rcworst.com

That appears to enable starting windings for a split-phase motor.
Is there any sort of easy-start installed as well? Or just Franklin's control box?

I don't use a well pump at this time. I think pressure from the couple hundred feet of head is resistance it has to start against.

Does the test setup have something to maintain back pressure from the previous time it started? Or does it start against atmospheric pressure, only experience more resistance as flow builds?

To make a well pump simulator I would consider an adjustable pressure relief valve and gauge to simulate depth, and a captive air tank on the pump side to hold pressure simulating head when starting.