1.5 hp 240v AC deep well pump start up surge of 40amps

[VeritasCupitor]

I'm a beginner. I know this topic has been discussed before, but the advice for inverters is beyond my budget. I would like to have a system for emergency use only. This would be to run the pump for about 15 minutes at most 3 times a day. The pump is AC "230" volts (240V) with a running amps of 10 and a startup surge of 40.17 amps. Measured with a TRMS clamp. Total well depth = 181'Pump depth = 140'Water table = 79' Pump output 20 gpm. I have 2 12V LiFePO4 230 Ah batteries on the way. Still need panels, charge controller, and inverter. From what I've read 24 volts would be better. I will be adding a plug to the well pump power line in order to run a cord to the inverter. Any advice on whether the 2 batteries are enough, and an affordable (< $1K) pure sine low frequency inverter? I will also use the system to power other items intermittently. I've seen conflicting reviews on the Santan Solar used panels, and I don't need a pallet load. Sorry if this seems redundant but I would appreciate useful advice. (replacing the pump is not an option).

 

[sunshine_eggo]

Neighbor uses this one (24V version):

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for his 3hp Grundfos pump at 700' depth. Yes. seven hundred, but he only got about 7gpm.

Run was about 18-19A @ 240V.

Surge was never measured, but it was published at 5X run.

Ran it like a champ until he downsized to 2hp, so he could power the pump purely via PV.

You'll almost certainly want 24 or 48V.

My concern is that your batteries can't handle that kind of surge.

Downside to this unit is it's VERY heavy, and it has a VERY high idle consumption... around 100W, so just turning it on and powering no loads would drain your batteries in about 2 - 2.5 days.

 

[Hedges]

Only if you find an inverter under a grand that spec's 9600W for 3 seconds.
Sunny Island spec is 11kW. It's 120V so would need auto-transformer.

Midnight Rosie has spec 15kW for 60 seconds.

12V x 230A (assuming 1C discharge) x 2 = 5520W, not enough.
Do those batteries and BMS support 2C discharge for a couple seconds? That's what you need.
Compare to a lead-acid car battery: 700 CA at 8V = 5600W from a single battery. Two in series might do it, depending on low-voltage cutout setting (and how fast voltage drops to 8V, think battery CA test is for 60 seconds.)


How many panels you need depends on how many kWh/day, so how many gallons you need and how many hours it takes to pump. But would be nice to have enough panels to produce 2400W, so about 3600W STC (more maybe for degraded panels.) If pumping all day I'd suggest 4800W, half facing morning and half facing afternoon sun.

 

[OffGridForGood]

I would like to have a system for emergency use only. This would be to run the pump for about 15 minutes at most 3 times a day.

emergency use only, inverter can be off most of the time, switched on when needed per above.

and it has a VERY high idle consumption... around 100W, so just turning it on and powering no loads would drain your batteries in about 2 - 2.5 days.

but OP is only interested in temporary back up, so will not be leaving it on, unused, = not an issue for their use case.

My concern is that your batteries can't handle that kind of surge

very likely

startup surge of 40.17 amps. Measured with a TRMS clamp

40A 240v 9600W = 24v x 400A although only for a short start up period, this is likely going to trip the BMS's on two parallel 1C rated 100Ah LiFePO4

For emergency use, mostly stored long term at high SOC = AGM maybe better lower cost solution.

 

[VeritasCupitor]

emergency use only, inverter can be off most of the time, switched on when needed per above.


but OP is only interested in temporary back up, so will not be leaving it on, unused, = not an issue for their use case.

very likely


40A 240v 9600W = 24v x 400A although only for a short start up period, this is likely going to trip the BMS's on two parallel 1C rated 100Ah LiFePO4

For emergency use, mostly stored long term at high SOC = AGM maybe better lower cost solution.

Hello, thank you all for the replies. The two batteries currently on their way are two 12V 230Ah. The pump surge should only last for about one second. And yes the inverter will only be on when needed. Wouldn't the capacitor in the inverter be the most affected by the surge? Do the batteries really take that much of a hit? How many of the 12V 230Ah batteries should it take to cover the well pump running for 15 min for 3 times a day max? I'll think about the AGM batteries. Thanks again.

 

[sunshine_eggo]

Hello, thank you all for the replies. The two batteries currently on their way are two 12V 230Ah. The pump surge should only last for about one second. And yes the inverter will only be on when needed. Wouldn't the capacitor in the inverter be the most affected by the surge? Do the batteries really take that much of a hit? How many of the 12V 230Ah batteries should it take to cover the well pump running for 15 min for 3 times a day max?

While lead acid can take huge hits, it's limited by voltage sag.

LFP batteries are limited by the BMS to a maximum current. Surges beyond maximum are allowed, but that depends on the BMS and the duration of the surge.

What are the discharge ratings for your batteries?

 

[Hedges]

Wouldn't the capacitor in the inverter be the most affected by the surge? Do the batteries really take that much of a hit?

Batteries take all the hit. Capacitors can't even supply 8 milliseconds of one phase. They're only good for the higher frequency PWM switching used to synthesize sine wave. Capacitors only supply current to the extent there is ripple in battery voltage.

You need a battery/BMS able to carry the starting surge for a couple seconds. Some BMS have specs for overload vs. time.

10kW resistive load powered by 23kW of inverter, 48V battery carries 16Arms ripple (48App).
That was while 217A on average was being drawn from the battery, so capacitors did help each cycle.
Inverters loaded to 40% of continuous rating.

 

[VeritasCupitor]

While lead acid can take huge hits, it's limited by voltage sag.

LFP batteries are limited by the BMS to a maximum current. Surges beyond maximum are allowed, but that depends on the BMS and the duration of the surge.

What are the discharge ratings for your batteries?

I'm not sure of the discharge rates. These are the less expensive LiFePO4 ones the are recommended on Will's site:
(LiTime 12V 230Ah Plus Low-Temp Protection LiFePO4 Battery, Built-In 200A BMS, Max 2944Wh Energy)
BMS：200A
Max. Continuous Output Power：2560W
Max. Continuous Charge Current：200A
Max. Continuous Discharge Current：200A
Max. Discharge Current 5 Seconds：600A

How would I determine the discharge rates?
Regarding the surge duration, I would assume that if a standard clamp meter can't catch the surge (which requires a TRMS meter to measure), then the surge should be less than 1 second.
Thanks.

 

[ChrisG]

I struggled with the same well pump issue with high surge at my cabin. I took a different approach where I changed the pump (out of need) to a Grundfos SQ soft starting pump. This allowed me to 1)have a new pump 2)require a much smaller generator to start it in full outage situation and 3)significantly decease inverter and battery amps needed.

 

[Hedges]

600A for 5 seconds sounds great. If it really does that should be all you need.

Clamp ammeters with surge [edit: "inrush"] function should work. I got the Harbor Freight Ames 1000A one.
I'm still not sure if it will measure DC surge or only AC.

 

[sunshine_eggo]

600A for 5 seconds sounds great. If it really does that should be all you need.

Trusting the cheap batteries to perform as advertised is the bigger issue.

Clamp ammeters with surge function should work. I got the Harbor Freight Ames 1000A one.
I'm still not sure if it will measure DC surge or only AC.

I see this labeled typically as INRUSH. and... checking the HF listing for that meter, it is labeled INRUSH.

@VeritasCupitor
CRITICAL that you use beefy cables rated for the current, with a minimum of voltage drop AND properly installed/torqued. For every % voltage drop, you get a % increase in current.

200A * 25.6V = 5,120W
600A * 25.6V = 15,360W

 

[OffGridForGood]

From what you have reported above, sounds like you have already pulled the trigger on the batteries and equipment - now you can just try it out and see what happens, hope to see a follow up report if it all worked (or not) to close the loop on this discussion.

 

[Hedges]

Maybe a soft-start will help.

I wonder if a couple automotive starting batteries in parallel with lithium would help in this case?

 

[OffGridForGood]

I wonder if a couple automotive starting batteries in parallel with lithium would help in this case?

Do you mean the lead acid would be better for the starting current delivery? or just that since these are not BMS controlled, they will not be subject to high current cut off like the LiFePO4 packs?

 

[sunshine_eggo]

they will not be subject to high current cut off like the LiFePO4 packs?

Yep. They act as a backstop to the LFP basically. The thing I don't know is if the LFP will recover without breaking and reconnecting the circuit.

 

[VeritasCupitor]

Thanks again for all the advice, So any advice on an affordable pure sine low frequency inverter? And how many of the "LiTime 12V 230Ah Plus " batteries would be required? I'm guessing a sub $1K inverter might not be able to cover the requirements.

 

[sunshine_eggo]

Per post #2

1.5 hp 240v AC deep well pump start up surge of 40amps

I'm a beginner. I know this topic has been discussed before, but the advice for inverters is beyond my budget. I would like to have a system for emergency use only. This would be to run the pump for about 15 minutes at most 3 times a day. The pump is AC "230" volts (240V) with a running amps of...

diysolarforum.com

Beast of an inverter that I've personally seen handle a 3hp grundfos pump @ 700' depth.

$760

4 total in a 24V configuration, 2S2P, would probably cover it.

 

[VeritasCupitor]

Batteries take all the hit. Capacitors can't even supply 8 milliseconds of one phase. They're only good for the higher frequency PWM switching used to synthesize sine wave. Capacitors only supply current to the extent there is ripple in battery voltage.

You need a battery/BMS able to carry the starting surge for a couple seconds. Some BMS have specs for overload vs. time.

10kW resistive load powered by 23kW of inverter, 48V battery carries 16Arms ripple (48App).
That was while 217A on average was being drawn from the battery, so capacitors did help each cycle.
Inverters loaded to 40% of continuous rating.

View attachment 172275

Hi Hedges, thanks for the feedback. Electrical is my weak area. Are you saying that I would require a 48V battery? And a 20,000 watt inverter?

 

[Hedges]

This would be to run the pump for about 15 minutes at most 3 times a day. The pump is AC "230" volts (240V) with a running amps of 10 and a startup surge of 40.17 amps. Measured with a TRMS clamp. Total well depth = 181'Pump depth = 140'Water table = 79' Pump output 20 gpm.

Hi Hedges, thanks for the feedback. Electrical is my weak area. Are you saying that I would require a 48V battery? And a 20,000 watt inverter?

24V should be sufficient, but 48V has much equipment available and would support other things.
If only for water, look at Sunshine's suggestion and see if inverter can be switched when needed.

I like Sunny Island, of course. Available on eBay used or new, $1200 to $2500. But would require a transformer for 240V. Look for a brand with native 120/240V.

The inverter needs to supply 240V x 10A = 2400W continuous, 240V x 40.17A = 9640W surge for a couple seconds. (30 milliseconds or 100 milliseconds won't cut it; that's only enough to fast-trip a breaker typically more than 5x breaker rating.)

Lots of low frequency inverters, and some high frequency, will supply a few seconds surge 200% of rating. So 5kW inverters would probably do it, including SMA, Schneider, other heavy ones with LF transformer. Some high frequency ones surge well too. Any HF inverter (legitimately) rated 10kW should also work.

2400W/12V = 200A, doable. 2400W/24V = 100A, reasonable. 2400W/48V = 50A, easy.
Starting surge 800A @ 12V, possible. 400A @ 24V, doable. 200A @ 48V, reasonable.

Lead-acid could do any of those; the starting batteries in my truck are good for 800A and there are two in parallel. My home system has 48V 405Ah, 24kW of inverters, 44kW surge (not that I've tried, would be 900A 2.25C)

45 minutes/day at 20 gallons/minute. 900 gallons/day. The volume is reasonable.
It would be better if you could pump 6 hours continuous per day or more drawing only 300W. 180' is 90 PSI. Small positive displacement pump? Is a lower wattage deep well pump available that can do the head? I don't know what the options are.

People us MicroAir Easy-start for air conditioners. That requires access to starting windings. Is your pump 3-wire or 2 wire? It is also possible that slow-starting a deep well pump wears it out faster - somebody said bearings ride on film of water.

 

[Hedges]

But to do any of those amperage with lithium, battery needs to have a BMS that supports the current, including surge for the time needed.

Only for emergency, you said. Consider a generator. This one says "max starting 9000W" and price is $880.

https://www.harborfreight.com/generators-engines/generators/9000-watt-gas-powered-portable-generator-with-co-secure-technology-epa-59206.html