Has anyone used a step-up transformer to run a well pump on a 120V generator?
Posted by 69stangrestomod@reddit | preppers | View on Reddit | 35 comments
Working on a water plan.
I have a 3/4 HP, 240V well pump. I also have a 3,500 Watt generator that only puts out 120V. Looking at the possibility of using a step-up voltage transformer to utilize this generator. I have a power monitor in my house, running and starting watts for my pump are well within this genny’s capability, just need to get two 120V legs.
I’d love some actual products if anyone has gone this route - All the options I can easily find on Amazon use a European style 240V single hot instead of a US two 120V legs.
Thoughts?? (That don’t involve a bigger generator….yet)
CTSwampyankee@reddit
You need a better power generation plan, not another piece of equipment.
You can find a used 5k on marketplace for 200-300, often much less.
Don‘t dabble with 240vac single phase 50 hz. It’s not the proper way to do it for all sorts of reasons.
69stangrestomod@reddit (OP)
No one suggest 50Hz….not sure where you got that idea from.
CTSwampyankee@reddit
My bad I saw your reference to European 240vac which is all 50 hertz and thought you meant generation.
During deployments I saw some things done with the gens set to 240 single leg Euro and USA AC units that were 220 60hz.
A transformer can double the voltage but the current goes down by half. So for a 120v 20a circuit after the transformer the amperage is only 10a and its a bit less due to power losses in the transformer.
The shortest distance between generation and consumption is not to add something that will create more losses. Just upgrade generation.
wpbrandon@reddit
You can’t do that. 200 V motors are split phase. You’re 100 V generator is single phase. They do make a funky device called a Roto phaser but they are pretty expensive. They can go from single phase to split phase or from split phase to three phase.
AskSarah_Ampsos@reddit
The pump just wants 240 V across two wires. A 120→240 autotransformer doesn’t create a new phase; it just doubles the voltage so you’ve got 240 V potential difference available for a straight 240 V load. For a single-phase 240 V pump, plenty of folks in the off-grid/RV world do run them off a 120 V generator with a properly sized 5 kVA autotransformer. The limiting factor is still whether the generator can handle the inrush current, not the phase.
wpbrandon@reddit
Ahh yes. Good point. What I was talking about would only apply to three phase motors then.
fredrickdgl@reddit
120v is 1/2 a phase. 240v is single phase. Typical house power is both 120/240/hence called split phase
RottenRott69@reddit
This is the small 120/240V generator I have for powering the entire panel and small 240V loads.
PREDATOR 4375 Watt Gas Powered Portable Generator with CO SECURE Technology, EPA - Item 59207 https://hftools.com/app59207
69stangrestomod@reddit (OP)
Not looking for a new genny at the moment…but I’ll keep it in mind.
MacWac@reddit
Another option is to use a battery pack/solar generator that outputs 240. It also saves you from having to run the generator continuously. That's what I do at my of grid cabin.
69stangrestomod@reddit (OP)
Good thought!
MacWac@reddit
Is this for your home? What scenario are you thinking you may use this ? Currently, I run an Anker 3800 Plus, and love it. I run 30 amp 240 to my panel and then run the pump off the panel. I have 800 watts of solar, which limits the time I even have to run my generator
69stangrestomod@reddit (OP)
Extended power outage, I’d like to still maintain drinkable water, so running the pump through my filtration and softener would be ideal.
Looking at the transformer options that would work, looks like it is going to be just as cost effective to parallel kit a second Predator 3500 together for it.
Traditional-Leader54@reddit
https://www.reddit.com/r/Generator/comments/1dcd1j3/using_a_step_up_transformer_to_get_240v_out_of_a/
Appears to not be doable.
fredrickdgl@reddit
I've done it
davidm2232@reddit
For that money, you might be better off getting an inverter and battery bank. Not that much more money and way more flexibility.
fredrickdgl@reddit
I actually have both but the good stuff was a lot more than the autotransformer. If I ever add another inverter I'll tie them together to make both 120/240/and just use the autotransformer for balancimg the load evenly on eeach inverter
69stangrestomod@reddit (OP)
This is what I couldn’t find the other day. Thanks!
Ok_Honey4837@reddit
You realize that while you double your voltage you cut the amperage by half. Also I'll bet that the motor is a split phase so your regular every day step up transformer isn't going to be able to supply the necessary phase.
69stangrestomod@reddit (OP)
Amperage isn’t a concern, startup and running watts are well under what the genny provides.
Split phase is a possibility…hadn’t thought about that.
roberttheiii@reddit
Google tells me starting watts for a 3/4 hp well pump are around 3000. Even if you get the right transformer to get the voltage, doubling the volts halves your watts so now it is a 1750 watt generator…
davidm2232@reddit
That's....not how that works. Wattage will remain the same. If voltage doubles, so does amperage.
69stangrestomod@reddit (OP)
My power monitor in my house disagrees with your googling abilities
Ok_Honey4837@reddit
Yes you are correct.
roberttheiii@reddit
It isn’t good. Watts = Volts x Amps. Or Watts / Volts = Amps. So if you convert 120v to 250v you’re halving the available watts and amps (really less than half but let’s say perfect efficiency for funsies). That said, heck, I am happy to be wrong. If you can find an step up transformer and get it to work with your generator for your use I’d be very happy for you to
69stangrestomod@reddit (OP)
You’re assuming the constant in The equation is amperage, when it’s wattage. So if you rearrange and set watts at 3,000, I get roughly 15a for a stepped up voltage (ignoring conversion losses). My well pump is on a 15a circuit anyway. So long as the initial current inrush doesn’t overload the genny (which looking at the power traces, along with the relatively low head for my particularly well, it seems like a good bet), the power availability should work.
Your tone makes it seem like you came here to argue instead of be helpful, so I’m out, others below have done it with success so I’m engaging with them further. Have a good day.
fredrickdgl@reddit
victron autotransformer, I did this exact thing and power my well pump and heat pump water heater on a small generator
roberttheiii@reddit
Damn this is sick.
69stangrestomod@reddit (OP)
Thanks!
dasmineman@reddit
If you pop the cap on the pump, you might have an option to wire it for 120v. I lived off grid for a while in South Alabama and I could wire my well pump for either 120v or 240v. I was able to run my well pump and a full size washing machine on a 4000w generator.
custhulard@reddit
If you have two legs of 120 You can use it to power a mini sub panel that has your well pump in it. Just add a couple of 20amp outlets and make some double male cords. Cords get plugged into the wall, then the generator is started, then plug the cords into the generator. After whatever steps you take to not back feed the grid.
69stangrestomod@reddit (OP)
My issue is two 120V legs. How I hook it up is still for debate.
Bitter_Albatross25@reddit
Look into a VFD driven pump, you can ramp them up and down, can set them to slow start as I you don’t get a high kick at the start.
69stangrestomod@reddit (OP)
I replaced my well pump recently. Looked into VFD’s, but the cost wasn’t worth the benefit at the time. Mine is only set about 30’ down a 5” casing, so if I ever want to swap it, really isn’t that big of a job.
My other backup plan would be grab a cheap, 120V pump from Menards. That’s always an option.
silasmoeckel@reddit
SUre you can get a 3kva 120v to 240v for about 150 bucks on ebay and the like.