Easy Small cabin Question: inverter

[OffGridForGood]

I am able to run my jet pump without any issues. Also runs my entire cabin with basic lights, outlets, a lcd tv and dvd player. It has also run my wife's 1500w hair dryer for those occasions she really needs her hair to look good in the woods!

Well ya just never know i guess!, at least the system can handle a hair dryer! - good to hear your system can handle the jet pump. Do you know the Hp rating on your pump? mine is only 1/3Hp and I am expecting to be able to start it.
I did consider the Growatt, and the very similar MPP Solar 3048 as these can be expanded with parallel units, and upgrade to 120/240 easily too.
In the end I chose the MPP 2724 (which does NOT support parallel inverters) based on it meeting my needs, lower cost, and since I already have twin MPP 6048's in my shop I felt confident in MPP's equipment. {there are some commentors that believe Growatt and MPP are made by the same factory, but I am not sure if this is true}
Playing with the 2724 and an undersized battery (all that I have until the 280Ahr cells arrive) I can report that the 2724 and the small battery has run everything I can throw at it around my pasture including angle grinder, drills, large electric impact & lights. The unit fits in a rack I have on the rear of my ATV so I can literally drive along the fence line, and run tools anywhere -even a 1000 feet from my nearest outlets - and pull out a grinder and cut steel using the small inverter and a battery alone in the ATV. very handy I have to say.
I believe I made one error when I ordered the 8S BMS for this set up - I assumed 100A would be sufficient, but the MPP specs list being able to handle up to 123A, I sould have ordered a 125 or 150 BMS, since the 280Ah cells can take that amperage draw, and the MPP will cut out if I exceed the 123A for too long. Darn. Should have read the specs more closely before ordering the 8S BMS.

 

[OffgridMatty]

My pump is a 1 hp and runs on 115v or 240. I’m running it on 115. Needed the 2 batteries as the growatt gave a low voltage daily when I only had one.

 

[OffgridMatty]

Start up watts are about 1200w and pulls about 900-850 while running.

 

[OffGridForGood]

Start up watts are about 1200w and pulls about 900-850 while running.

Great info - thanks!
I have not been to my cabin since getting the MPP 2724, putting it through some testing around the homestead it has been great at running hand tools and lights etc.
The MPP rating indicates a max of 123A x 24VDC which if I figure on 15% losses, would be 21A AC -should be plenty to start the 1/3Hp pump motor.
Having sufficient battery amperage will be key. Once I get the 8 280Ahr cells I ordered for my DIY battery, then I will make a trip up to the cabin to test it out.

 

[OffGridForGood]

Start up watts are about 1200w and pulls about 900-850 while running.

So you figure you hit maybe 10A 120VAC, starting the pump.
-your pump may have higer inrush for a second or two, without a very good meter it is a challenge to get a measurement I have found. Hope to be okay with the MPP 2724, as long as I can supply it with 123A @ 24VDC.

 

[MichaelK]

Start up watts are about 1200w and pulls about 900-850 while running.

To me those numbers are suspect? Could you please go into detail as to how you came up with those numbers, and what instrumentation exactly were you using? With running watts ~850, I'd think your starting watts would be ~3400W.

 

[OffgridMatty]

Just looked at my Inverter load when it starts up. No way it ever gets close to anything over 1500w. Maybe the 850w is where I’m wrong. It’s only pulling 5-6 amps if I remember correctly.

 

[OffgridMatty]

I dug a little deeper. My amps are 6. So running wattage is about 700w. The 850 must have included the other cabin loads also. Sorry for the misinformation.

 

[MichaelK]

Just looked at my Inverter load when it starts up. No way it ever gets close to anything over 1500w. Maybe the 850w is where I’m wrong. It’s only pulling 5-6 amps if I remember correctly.

Sorry, but I think you are fooling yourself. The maximal inrush current demand is within the first 500 milliseconds or so, and your display is not going to capture that. It just isn't fast enough

What you really need is a clamp meter that is capable of reading "inrush current". I have a Uni-T216C, which works as accurately as an expensive Fluke meter that I first got.

When I was first starting out, I tried more or less what you are doing, trying to look at startup surge with a regular meter. For a blink of an eye I saw 17A, so I thought "oh, the inrush is 17A". After getting an inrush meter, I saw 38A, more than double what that blinking number was.

 

[OffgridMatty]

All I know is it works and that’s all I really care about. I’m not that concerned about the details. The specs on the pump 6 amps. I’ll take their word for it. ??‍

 

[OffGridForGood]

With running watts ~850, I'd think your starting watts would be ~3400W.

Typical 1Hp motor will be FLA of 9-10 Amps, and starting will be 2.5X (or more) depending on motor winding classification. ie 3000 W as you noted.
I wouldn't be surprised to see 25 -30 amp inrush (LRA) however they may not be able to measure this breif current draw, especially if they are relying on the AIO display for the loading information rather than a meter.
References: NEC Table 430.247, & 430.52

 

[OffgridMatty]

It’s also a 1/2 hp pump. I’m full of bad info this evening. I guess looking at the specs before I post is a good idea.

 

[OffGridForGood]

t’s also a 1/2 hp pump. I’m full of bad info this evening. I guess looking at the specs before I post is a good idea.

Well, I am not any better: i see i posted the wrong reference - should be NEC 430.248
I agree with you on the main point: It Works! and that is ultimately what we are all striving for.

I have struggled in the past with attempting to calculate motor in-rush currents.
We always fall back on testing with a meter, however we should be able to predict the in-rush, and thus plan a suitable system (battery bank, inverter breakers fuses) to suit. In researching the topic I happened upon some information from the company Fluke who make high quality electrical meters. From there information I learned that it takes a special meter (such as the Fluke 370 or 381) that incorporate a special in-rush funtion just for measuring the peak current during that initial 200+ milliseconds. And yes, it is not uncommon for the inrush to be 4-8 times the FLA of a motor. This seems impossible to some people as they point out the motor is on a circuit with a breaker that may be 20 Amps, and the breaker doesn't trip. But the reason for this is the breaker is essentially a temperature driven divice and the short peak is not sufficient time to heat it up to the tripping point. Search Time-Current curves for the breakers and see the relationship. I myself fell into this trap: from 430.248 and 430.52 I had the information to select the appropriate breaker for the motor circuit and I thought "there ya go" that "must be" the max current, but no, not so fast. The breaker is able to allow considerably higher current to flow, for a short period of time, and the breaker size is not an estimate of the in-rush amperage.

Getting back to your 1/2Hp pump motor and my 1/3Hp motor, both will have FLA in the 4-6Amps range (120VAC) and will need circuit breakers of 15-20A size but the actuall in-rush currents can be much higher.
Working backwards on your system: you have a 3kW inverter and 200Ah of available battery and as you say, "it works"
I am hoping for the same outcome, with my slightly smaller 2700W inverter and 280Ah of available battery, my inverter lists max 123A x 24 VDC (the 8S LiFePO4 will be about 25.6VDC) (approx 3149VA) but the snag here will be what the equipment internally will handle, losses in efficiency and short term overloads. This is where high end equipment really shines as they often can handle significant overloads and for longer than a fraction of a second.

 

[OffgridMatty]

Thanks for all the background on this topic. Just to clarify one point. I am running two 24v batteries in parallel so I think I actually have 400ah and about 10kwh total. The pump wouldn’t start with just the one battery so I had to double the capacity. Hope this is helpful.

 

[OffGridForGood]

Thanks, and naturally it is not the Ahr that matter, but the max Amps output, and with two batteries, x2 of the output that one can handle.
I have realized for my set up, I ordered the 280Ahr cells and and 100A BMS - then relized during our discussions that the AIO can handle 123A input current, and I should upsize the BMS to 150A to be sure the BMS doesn't shut me down. Two batteries with 100A BMS each would also work.
At this point I may as well just try it. waiting on the cells for now.

 

[OffGridForGood]

And Finally the cells arrive, so I put together a DIY 8S using 280Ah EVE cells, and yeah I used the Daly 100A output BMS rather than buying a new BMS, and I am just going to try it out next time I go up to the cabin. Maybe soon since the weather is improving and it will be more fun in mild temps.

Edit: I ended up going with a 150A BMS, and this has run perfectly, starts and runs the well pump fine, and runs everything I need in the Cabin. Great to have a mobile battery and inverter set up.

 

[ArtDeco]

Very interesting idea, i already have an RV style 12V 'transfer pump'/truck battery, that I used in the past to move water from a barrel I would fill (winter use) so the generator only ran a few minutes to get the well pump to fill the barrel. The transfer pump was basically to get water to the sink for coffee and filliing a pot. I am thinking I can easily put up some 12V lights and keep things simple. For running the well and some small tools for working on the place, I am thinking about a fridge cart style set up like Lithium Solar did here: solar PV is optional, and the cart set up would be useful for portable power around my homestead as well. I could build it using two 24V packs, and still be able to connect these in series for 48 volt as well, use a 3024 inverter that would fit on a cart easily. Still playing with options.
I like the 12V idea, a small step down buck transformer on the 24V could supply it too instead of a truck battery, lots of options.
Who was that earlier said none of the answers will be easy or simple?

"Simple and easy" comment was me. I was hoping for simple and easy, now I would rather have "safe and working" ....

 

[ArtDeco]

Very interesting idea, i already have an RV style 12V 'transfer pump'/truck battery, that I used in the past to move water from a barrel I would fill (winter use) so the generator only ran a few minutes to get the well pump to fill the barrel. The transfer pump was basically to get water to the sink for coffee and filliing a pot. I am thinking I can easily put up some 12V lights and keep things simple. For running the well and some small tools for working on the place, I am thinking about a fridge cart style set up like Lithium Solar did here: solar PV is optional, and the cart set up would be useful for portable power around my homestead as well. I could build it using two 24V packs, and still be able to connect these in series for 48 volt as well, use a 3024 inverter that would fit on a cart easily. Still playing with options.
I like the 12V idea, a small step down buck transformer on the 24V could supply it too instead of a truck battery, lots of options.
Who was that earlier said none of the answers will be easy or simple?

"Simple and easy" comment was me. I was hoping for simple and easy, now I would rather have "safe and working" ....

 

[OffGridForGood]

The follow-up to my small portable system:
I bought the MPP 2724 small inverter. This unit has it's own outlets built right into the side of the inverter(4-standard recepticals and two USB) - so no electrical outlet panal required, just plug stuff directly into the side of the Inverter. {Safe and Working }
I ended up ordering in a 150A BMS to go with the DIY battery, and ended up using EVE 304Ah cells (x8) for a 24volt 7.9kWh battery.
This set up runs everything at the cabin and the well pump (a small jet pump, 1/3hp/120volt) starts up and cycles without any problems at all.
I have this portable unit in our greenhouse for the starters, and we will move it into our RV for the summer. In the Fall time it can go back into the Greenhouse for the end of season stuff, or be used around the property in areas too far from the main system outlets.

 

[12VoltInstalls]

bought the MPP 2724 small inverter

wish they had a 2712 model