Sizing well pump inverter (first post)

[inetdog]

All I can tell you is that some generators are over-rated and some are under-rated. I guess the Honda is "under rated". I do not remember what the start-surge rating is but I know that it will easily start up to a 1.5 HP 3-wire pump with a CSCR (cap start cap run) control box.

LRA is just an estimate. Once the motor starts to spin even a tiny amount the LRA goes down. LRA only lasts for a fraction of a split second.

With generators, you have a different mechanism behind surge overload tolerance than with inverters (except when talking about inverter-output generators).
1. The current from a generator is limited in a hard sense by the resistance of the generator windings. That limits the short circuit current and to some extent the current which can be delivered without a major voltage drop.
2. The current is limited in a more flexible sense by the heating effect of the current in the output windings. If only one half of a 240 generator or one phase of a three phase generator is loaded, it is possible to hit the thermal limit in a minute, more or less, while staying within the capability of the prime mover (engine).
3. The power delivered by the generator in a steady state is limited by the maximum power that the engine can develop. And as the speed starts to lug down, the power output will decrease even with the throttle full open. The maximum power of the engine may or may not also be limited by the available engine cooling, if it is a weak design. But in the very short term (seconds) the kinetic energy of the rotating mass of the engine and the generator can deliver a very large power surge as it slows down.

The off-grid inverter is limited by the battery and wiring resistance, the thermal protection, and the resistance of the output elements. If the inverter is conservatively designed, there will be a substantial surge possible until the circuit overheat causes the protection to kick in. A less conservatively designed inverter will just shut down in response to the current rather than the built up heat.

[Mike90250]

The pump starts will be for household usage, so multiple starts to refill pressure tank drawdown. Probably a few starts in the morning, nothing during the daytime and again heavier in the evening. The 4548 is just shy of what we need and with other loads running concurrently it might not work so well. Is there any problem using an inverter that's a bit too large for the rest of the household needs?

So without the solar contributing, it's going to hit the battery bank pretty hard early in the AM, when the batteries are soft from all night

We don't really need a 6k inverter except for the one load. The rest of the time it probably will not exceed 3k or so. I don't think the tare losses between the 4548 and he 6048 are significant.

My normal loads are 200 - 300 watts. Till the toaster or microwave are fired up. The only time I've ever pulled more than 3KW, was when the house was under construction and the floor dude clipped into the power panel to run a 3HP floor sander.
I watched my batteries get lower and lower for 2 days before I saw what he had done, then the contractor tried 2 generators and finally had to rent a 10Kw tow behind generator to run the sander. I was amazed the inverter would run that huge motor. The XW's are really beasts.

Mike, just curious what welder you are using with PV? I had basically written off using a welder without generator support.

30 year old 240VAC, 200A Lincoln MIG with huge tapped transformer in it.

[Texas Wellman]

All I can tell you is that some generators are over-rated and some are under-rated. I guess the Honda is "under rated". I do not remember what the start-surge rating is but I know that it will easily start up to a 1.5 HP 3-wire pump with a CSCR (cap start cap run) control box.

LRA is just an estimate. Once the motor starts to spin even a tiny amount the LRA goes down. LRA only lasts for a fraction of a split second.

Do you mean a 5k inverter with 10k surge capacity? I guess I don't understand how the EG3500 can start a 1.5 hp pump. The locked rotor amps would have to be lower than the max AC output of the generator? 29.8A? I would thing the larger motor would be more difficult to start. I got the 3 wire pump and the cap/start cap/run for the lower starting power requirement, although, I'm not sure it matters terribly looking at the start requirements of the pump.

[Texas Wellman]

You have the Grundfos SQ confused with the SQ Flex. The Flex is the solar pump, the SQ is the regular pump.

The difference is that the SQ only accepts AC power and has a built-in soft-start that plays very nicely with inverters (no start surge). The SQ Flex will accept either AC or DC. You can buy a SQ for under $1,000 easy on-line, just do a search.

Thanks for the replies. For now I am going to run what's down the hole. The make or break switch would work great if this was an irrigation pump but it's a non starter for a household pump. The difference between the grundfos pump and the 1hp I have was exactly $1719. Hopefully I won't be paying this out on the other end in solar equipment. Do I regret not spending it upfront? a little, but if I can use quality equipment that will work I won't regret it for too long. I am hoping something like a Xantrex 6048 inverter will make things work. I am planning on a 560AH battery bank for the house but will I have problems with power spiking during the surge current? I do not know what the weak point is regarding the start current through the inverter. The pump will run for less than 40 minutes a day total and the household budget is 5k watts. Am I making an error in sizing the batteries specifically regarding the pump which is the largest load? Thanks again for the help.

[jtbartlett]

The pump starts will be for household usage, so multiple starts to refill pressure tank drawdown. Probably a few starts in the morning, nothing during the daytime and again heavier in the evening. The 4548 is just shy of what we need and with other loads running concurrently it might not work so well. Is there any problem using an inverter that's a bit too large for the rest of the household needs? We don't really need a 6k inverter except for the one load. The rest of the time it probably will not exceed 3k or so. I don't think the tare losses between the 4548 and he 6048 are significant.

Mike, just curious what welder you are using with PV? I had basically written off using a welder without generator support.

[Mike90250]

Thanks for the replies. For now I am going to run what's down the hole. The make or break switch would work great if this was an irrigation pump but it's a non starter for a household pump. The difference between the grundfos pump and the 1hp I have was exactly $1719. Hopefully I won't be paying this out on the other end in solar equipment. Do I regret not spending it upfront? a little, but if I can use quality equipment that will work I won't regret it for too long. I am hoping something like a Xantrex 6048 inverter will make things work. I am planning on a 560AH battery bank for the house but will I have problems with power spiking during the surge current? I do not know what the weak point is regarding the start current through the inverter. The pump will run for less than 40 minutes a day total and the household budget is 5k watts. Am I making an error in sizing the batteries specifically regarding the pump which is the largest load? Thanks again for the help.

My old tired battery setup of 400ah PbH2So4 and the XW6048 started the 1/2 hp pump fine, and ran welder and air compressor fine.

You mention 40 minutes run time, is that 1 start cycle, or several throughout the day/night ? If daytime, the PV will pick up the load and the batteries just level it out.

The chart in the XW-6048 manual indicates that for 10 seconds, it can supply just over 50A , the 4548, right at 40 amps on the AC output.
http://www.solar-electric.com/lib/wi.../XW-manual.pdf sheet 103, pdf page A-3

[jtbartlett]

I know for a fact that a good quality 3500 watt genset will start and run up to a 1.5 HP pump (Honda EG3500). It's also a good thing that you have a 3-wire as a 2-wire consumes 2x the start power (per Franklin). For an inverter you should try about a 5K. There was another poster (don't remember the forum) who had similar questions and he got his inverter to successfully start his pump.

When you do need to change the pump look into the Grundfos SQ, which has a built-in soft-start and a much more efficient motor. They are available in up to 1.5 HP.

Do you mean a 5k inverter with 10k surge capacity? I guess I don't understand how the EG3500 can start a 1.5 hp pump. The locked rotor amps would have to be lower than the max AC output of the generator? 29.8A? I would thing the larger motor would be more difficult to start. I got the 3 wire pump and the cap/start cap/run for the lower starting power requirement, although, I'm not sure it matters terribly looking at the start requirements of the pump.

[jtbartlett]

Thanks for the replies. For now I am going to run what's down the hole. The make or break switch would work great if this was an irrigation pump but it's a non starter for a household pump. The difference between the grundfos pump and the 1hp I have was exactly $1719. Hopefully I won't be paying this out on the other end in solar equipment. Do I regret not spending it upfront? a little, but if I can use quality equipment that will work I won't regret it for too long. I am hoping something like a Xantrex 6048 inverter will make things work. I am planning on a 560AH battery bank for the house but will I have problems with power spiking during the surge current? I do not know what the weak point is regarding the start current through the inverter. The pump will run for less than 40 minutes a day total and the household budget is 5k watts. Am I making an error in sizing the batteries specifically regarding the pump which is the largest load? Thanks again for the help.

[inetdog]

1. If you are dead set on not replacing the pump (which I can sympathize with), then look at getting a full Variable Frequency Drive (VFD) or at least a solid state soft start aid. That will allow you to get by with the smallest possible inverter.
2. If this is a centrifugal (impeller) pump, which it almost certainly is, you should start the pump against a closed valve to minimize the power required as the pump accelerates up to speed. Then after a few seconds automatically open the valve slowly. This will also minimize the starting surge requirements.

[Texas Wellman]

Similar thread with results:

http://forum.solar-electric.com/show...00-watts-solar!

[Texas Wellman]

I know for a fact that a good quality 3500 watt genset will start and run up to a 1.5 HP pump (Honda EG3500). It's also a good thing that you have a 3-wire as a 2-wire consumes 2x the start power (per Franklin). For an inverter you should try about a 5K. There was another poster (don't remember the forum) who had similar questions and he got his inverter to successfully start his pump.

When you do need to change the pump look into the Grundfos SQ, which has a built-in soft-start and a much more efficient motor. They are available in up to 1.5 HP.

[Mike90250]

If you want to run a large pump, you need a large inverter or a large generator. You can stack a couple 40 gal pressure tanks to stretch your water time, but running a generator 3x a day for 10 minutes of pumping, will kill the genset from cold running. You may be better off biteing the bullet for the big inverter, several pressure tanks, and save the genset for foul weather battery charging.

[Sunking]

I pulled the 230v off of the Franklin motor spec sheet. Not sure why its 230 but that's what it says.

A 240 volt ac motor will have a spec of 230 volts. This is to account for line loss. For engineering and design purposes the code is different for motors. Normally you standard circuit the conductor is based the breaker size. Not so with motors and transformers.

[jtbartlett]

I pulled the 230v off of the Franklin motor spec sheet. Not sure why its 230 but that's what it says. My static level is 261' and the hole is 500' with a pump hung at 470'. Unfortunately for me, a 1/2 hp motor doesn't cut it.I have resigned myself to the fact that this isn't going to happen with an inverter and that I will have to fill a bulk tank under generator power. An outside tank is not possible, winter is too cold and long. An underground tank is not possible, 20"to bedrock. So...it's going to be inside, under the stairs. Also I just noticed the post under DC pumping (sorry). Would I be better off using a DC pump to pressurize the house tank or is it easier to just stay with AC. I understand there are losses and such but I'd probably need a DC>DC converter. Similar losses? Also, what sized pump is suitable for this application? My load calculations just went out the window with the pump changes. I don't have a real good idea how much water we actually use so it's a bit tough to tease out the specifics. I'd bet we're under 200 gallons a day without conservation. Is there any additional strain on the well pump using a generator to pump up a bulk tank? The cycling will be drastically cut so that's probably good. Does a well pump need pure sine or will AVR hurt it in the long run?

Any thoughts on sizing a generator to run a 1hp pump with ~10k surge? My box store troy bilt 7500/10500 strains heavily when the pump is turned on. I'd love to have an ISUZU driven 12k diesel but it's tough to justify the 6k price just for a well pump! Thanks for any help possible. Sorry if this seems a bit scattered but I just made the decision today to ditch the inverter driven pump. I would need waaay too much of a system for just 1 load and the rest of the time it would be waste, nice to have, but waste. Thanks

[Mike90250]

I have a 1/2 hp deep well pump, that consumes 1,000w @ 240V when running (pumping 160'). As reported my my inverter's control panel.

I would expect a 1hp pump to consume about 1800W @ 240V. You get a little better efficiency with larger gear.


Your locked rotor power of 42A @ 240V would be 10,080 watts, a bit of a strain for most inverters and battery & cable systems.
What does work in your favor, is the long wire going down the well, that resistance will reduce the peak the motor will pull.

US systems are 60hz, 240V. 230V is not a standard household voltage.

I can state that my lights don't even blink when my pump kicks on. (Xantrex/Schnider XW-6048, 6Kw, 48V)

If you have an above ground tank, you can pump 500 gallons to it in the daytime, when you have sun (unlimited power) and use a much smaller pump to pressurize your water for night time use, instead of the 1Hp pump kicking in 4 times a night, sucking the batteries down.