Baby steps in the basement: Sizing 48V inverter/charger for furnace and well-pump back-up.

I'm hoping to piece-meal together a small system that would be expandable in the future for more off-grid power.  Initially, I was hoping to school myself by focusing on two essential items of the homestead-- the furnace (propane) for winter and the well pump for water.  As you might expect, non-winter months are not so crucial.  Even if the well becomes inoperative for a period, livestock watering can be done from the river near the house.  

I've already dabbled a bit with 12V-powered inverters for producing low-wattage 120V AC power.  What I'm envisioning for the current project is a 48V inverter/charger (Magnum Energy being one brand of interest) that would keep batteries topped up while grid-power is active, but be able to switch over to powering the furnace motor (120V) and well-pump (220V) if grid-power goes down.  A side angle here is the fact that I'm preparing to convert a 36V golf cart to 48V soon and this likely will involve several (3-4?....more?) 48V/30Ah LiFePO4 batteries.  Clearly one can get larger individual batteries, but I'm interested in keeping individual battery weight as low as possible so that they can be used in the golf cart (solar PV panel roof) in summer and shuttled easily to the basement for winter.

Questions arise around sizing the inverter/charger and battery bank for powering the furnace fan and the well-pump.  The furnace is less of an issue as it should be readily powered by an inverter of 4000-6000W (pure sine wave, peak surge watts nearly double the running watts). If memory serves me, the house well pump was ~2/3 - 3/4 hp submersible running at 220V and while the running amps/watts aren't terrible, the starting amps may be up in the 20s to low 30s.  So I'm more concerned about making sure the well pump won't trigger a system shut-down due to either batteries or inverter (or both) being under-sized.  A parallel string of 4 batteries each at 48V would yield 120Ah with internal BMS's sized for golf-cart amp surges (80 - 100A per battery...typically double that for short spike surges).  As finances allow, I would be integrating solar energy into the system as well as part of the expansion.  Input on this vision and design is most welcomed...  Thanks!

John Weiland wrote:I'm hoping to piece-meal together a small system that would be expandable in the future for more off-grid power.  Initially, I was hoping to school myself by focusing on two essential items of the homestead-- the furnace (propane) for winter and the well pump for water.  As you might expect, non-winter months are not so crucial.  Even if the well becomes inoperative for a period, livestock watering can be done from the river near the house.  

I've already dabbled a bit with 12V-powered inverters for producing low-wattage 120V AC power.  What I'm envisioning for the current project is a 48V inverter/charger (Magnum Energy being one brand of interest) that would keep batteries topped up while grid-power is active, but be able to switch over to powering the furnace motor (120V) and well-pump (220V) if grid-power goes down.  A side angle here is the fact that I'm preparing to convert a 36V golf cart to 48V soon and this likely will involve several (3-4?....more?) 48V/30Ah LiFePO4 batteries.  Clearly one can get larger individual batteries, but I'm interested in keeping individual battery weight as low as possible so that they can be used in the golf cart (solar PV panel roof) in summer and shuttled easily to the basement for winter.

Questions arise around sizing the inverter/charger and battery bank for powering the furnace fan and the well-pump.  The furnace is less of an issue as it should be readily powered by an inverter of 4000-6000W (pure sine wave, peak surge watts nearly double the running watts). If memory serves me, the house well pump was ~2/3 - 3/4 hp submersible running at 220V and while the running amps/watts aren't terrible, the starting amps may be up in the 20s to low 30s.  So I'm more concerned about making sure the well pump won't trigger a system shut-down due to either batteries or inverter (or both) being under-sized.  A parallel string of 4 batteries each at 48V would yield 120Ah with internal BMS's sized for golf-cart amp surges (80 - 100A per battery...typically double that for short spike surges).  As finances allow, I would be integrating solar energy into the system as well as part of the expansion.  Input on this vision and design is most welcomed...  Thanks!

John the magnum is currently discontinued. If you want to stick to the older transformer based units like the magnum then a samlex or victron would do it for you. If you are going lithium choose an inverter meant for them like the lux or sol ark type. I am liking lux these days.

Sorry John, the phrases "small system" and "run a well pump" can NOT be put into the same sentence.  Can you run a well pump solely off of solar, well sure, but it ain't gonna be small.  Take a look at the following chart...

A 3/4hp pump needs 31.4A at 240V for ~500 milliseconds to start.  That works out to be ~7500 starting watts.  Few inverters can handle that.  But they are out there.  I power my own 1hp pump with Schneider's XW+6848 inverter.  Beware of the cheaper Chinese-made inverters.  Although they may claim they can surge to 2X, that surge can only be maintained for at most one AC cycle, or ~ 16 milliseconds.  So, shop for an inverter that is DOCUMENTED to surge for at least five seconds.  Outback's Radian, Schneider's XW6848, and the Conext 4048 can surge that high.  All expensive, but all very much worth the money.

You'll be ahead of the game if you get a meter that can measure starting surge, also called "inrush".  I use and recommend the clamp meter UniT 216C.  You can find one on Ebay for ~90$.  I can also read AC/DC running amperage and AC/DV volts, plus ohms, so that one meter will meet all your solar needs.

I started out with 380Ah of battery at 48V, and I never try to run my pump unless I have at least 2000W of power coming in.  With 4500W of solar panels on rotating array mounts, I can run my pump from 8am till 4pm in summer.  Maybe 8:30am till 2:30pm in weaker November sun.

David Baillie wrote:

John Weiland wrote:I'm hoping to piece-meal together a small system that would be expandable in the future for more off-grid power.  Initially, I was hoping to school myself by focusing on two essential items of the homestead-- the furnace (propane) for winter and the well pump for water.  As you might expect, non-winter months are not so crucial.  Even if the well becomes inoperative for a period, livestock watering can be done from the river near the house.  

I've already dabbled a bit with 12V-powered inverters for producing low-wattage 120V AC power.  What I'm envisioning for the current project is a 48V inverter/charger (Magnum Energy being one brand of interest) that would keep batteries topped up while grid-power is active, but be able to switch over to powering the furnace motor (120V) and well-pump (220V) if grid-power goes down.  A side angle here is the fact that I'm preparing to convert a 36V golf cart to 48V soon and this likely will involve several (3-4?....more?) 48V/30Ah LiFePO4 batteries.  Clearly one can get larger individual batteries, but I'm interested in keeping individual battery weight as low as possible so that they can be used in the golf cart (solar PV panel roof) in summer and shuttled easily to the basement for winter.

Questions arise around sizing the inverter/charger and battery bank for powering the furnace fan and the well-pump.  The furnace is less of an issue as it should be readily powered by an inverter of 4000-6000W (pure sine wave, peak surge watts nearly double the running watts). If memory serves me, the house well pump was ~2/3 - 3/4 hp submersible running at 220V and while the running amps/watts aren't terrible, the starting amps may be up in the 20s to low 30s.  So I'm more concerned about making sure the well pump won't trigger a system shut-down due to either batteries or inverter (or both) being under-sized.  A parallel string of 4 batteries each at 48V would yield 120Ah with internal BMS's sized for golf-cart amp surges (80 - 100A per battery...typically double that for short spike surges).  As finances allow, I would be integrating solar energy into the system as well as part of the expansion.  Input on this vision and design is most welcomed...  Thanks!

John the magnum is currently discontinued. If you want to stick to the older transformer based units like the magnum then a samlex or victron would do it for you. If you are going lithium choose an inverter meant for them like the lux or sol ark type. I am liking lux these days.

Well John, Michael is right about inrush current. If you are using a 3/4 Hp pump you will want to oversize the inverter. Older transformer units had better surge capability but they have not moved on to the new standards for meeting UL 9540 rules for using Lithium Batteries. In some areas of the world that does not matter. Here in Ontario I have to meet all the latest standards. So, Michael suggested the 6048 which is a good unit but you would want to substitute a 10kw all in one inverter as a subsitute if you wanted to go for the transformerless units. I would also invest in a 3/4 horsepower pump with a soft start like a grundfos pump.
Cheers,  David

Excellent information, David and Michael, and I'm always so grateful for your feedback here.  

First, .... Magnum inverter.  Yes, I had assumed they were still around and keeping up with the battery developments as they occur.  Much thanks for the updated information on inverter/controller/chargers from you both and I will be researching these soon.  Perhaps like many, I like my drill to be a hammer or my car to be a tractor....in other words, I so often expect my infrastructure to do too many things.  Thus, I was hoping for an inverter/charger/controller that would handle my well pump surges *AND* be lightweight enough to be readily bracket-mounted onto my golf cart or wife's Polaris Ranger, both 48V (or soon-to-be).  Truthfully, there is a decreasing need for the inverter on the vehicles as so many of our tools now are cordless, battery-powered units.  So I should focus more on a good, high quality wall-mounted option for the basement,....which not only would provide well-pump and furnace back up power, but also power for the 2 sump pumps that save our butts during spring flooding around here.

Second and as noted, however, I'm still somewhat leaning towards a set of batteries that could be shuttled around for different uses. Since I'm not using the golf cart in winter, I would much like them to be light enough for my aging bones to move them into the basement to power the inverter and loads.  Clearly, the idea of running all loads noted at once is just not practical with the small- to moderate-sized system I am proposing, but the 48V/30Ah/100A-BMS batteries that I'm looking at, and sporting GC2-dimensions to neatly replace the old lead acid 6V heavyweights, are advertised as 8p, so I could parallel up to 8 of these for 240 Ah of capacity if need be.  Not a huge array, but not tiny either.  And from information here and other web sources, it appears best to avoid series connecting LiFePO4 batteries at present in favor of parallel connection if possible.  Thanks for any additional insights, comments, and corrections you can offer on these points.

David, is there some clear indication when shopping the inverter varieties out there as to which are using transformers and which aren't?  I generally look as the specs for confirmation of LiFePO4 compatibility, but admit to just assuming Magnum would have automatically done this to keep pace with the industry.  Also, Michael, I really am hoping to get the muti-meter you noted as my current 2, purchased many years apart, just really aren't up to snuff.  I've seen use of the clamp-type current meters being used to estimate amps pulled by a golf cart under different loads....can the AC side of your meter be used to read the current on my 240V well-pump wire?  This would be a handy tool indeed.....and Christmas is soon upon us! ;-)

On a newbie side-note, just so charged up (pun intended) to see wife's Ranger at 100% SOC in November just south of the Canadian border after only a few hours plugged into a single 380W panel/solar controller combo.  Thanks again and let me know if I failed to address and issue or question raised your respective posts.