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I need to do some work off-grid, and I only have a 1000W generator to drive my power tools, which easily draws twice that (and probably more when starting up) when cutting steel.

Instead of getting a new Honda generator that's powerful enough (minimum 1500$ for 2kW where I live) I was thinking of getting some kind of device that would even out the power draw. The tools usually only draw high currents for half a minute, tops, which would mean a energy usage of about 30s*100A=3000As=0.9Ah, each time. Typically, I would just have less than ten of those peaks, meaning I would require something that could deliver peaks of 100+A (1200VA) and be charged for about 10Ah. It needs to provide 220V AC, not DC.

I was browsing around for "super capacitor" and such, but I only found electronics bits. Then I remembered that a UPS serves a similar purpose, but they don't seem to be able to provide the short bursts of current I require (without costing many thousands of dollars).

I also thought about getting a cheap inverter hooked up to a spare 150Ah battery, but "cheap" and 2000W doesn't seem to appear in the same listings ;-) Found some generic cheap Chinese ones, but the reviews all claimed it would only really supply 500 Watts, so I guess there's a reason they're cheap ...

So do people have a tip on how I can achieve not killing my generator without it costing an arm and a leg?

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    AC electricity does not work that way, there's no way to put a battery or ultracap on AC. The best way to store power for tools is air.
    – Harper - Reinstate Monica
    Commented Apr 17, 2018 at 7:08
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    You're overthinking this. just get a bigger generator, and sell the old one. Whatever you do is going to cost similar (or more) and mean you have to carry around a large battery bank as well as a generator.
    – Digital Lightcraft
    Commented Apr 17, 2018 at 9:29
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    I would be interested to know the outcome, as the last inverter I used would trip out VERY easily on any sort of start-up spike. For example I tried to use my 500w to power a single 240v studio photography flash and despite the flash being rated at just 100w, it tripped immediately.
    – Digital Lightcraft
    Commented Apr 17, 2018 at 9:53
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    no, a UPS doesn't do that at the cost ranges you're talking about. You would need an online UPS (the most expensive kind) sized for motor start (again expensive). Cheap power tools do nothing to ease their locked-rotor draw because that would make them cost more, and it's unnecessary with unlimited utility power. "Cheap" is really what this is all about, isn't it? You seem underprepared for the financial commitment of succeeding off-grid, and my recommendation is a lot more research about off-power-grid living, which the Internet is flush with.
    – Harper - Reinstate Monica
    Commented Apr 17, 2018 at 16:02
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    @oligofren oh! Well that makes more sense! Sorry for being grumpy. Yes, needing to use an AC power tool in a remote location once is a most frustrating situation, and there is no cheap way to do it. GM's first hybrid vehicle, the 2004 Silverado truck, included a 120/240V inverter that was precisely for that problem. Unfortunately they bought back almost all of them, so they could EOL support. Even more unfortunately, no other hybrid maker has picked up on that idea.
    – Harper - Reinstate Monica
    Commented Apr 17, 2018 at 19:14

2 Answers 2

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AC power cannot be stored because AC is dynamically changing (to be more precise, alternating). It requires very expensive hardware to arbitrage it for other types of energy which are storeable, and in the sizes you need, the cost of that hardware is well beyond the scope you established in your question. That leaves:

  • Hand tools. Exercise your arms.
  • Smaller tools. A Dremel may be going too far, but plainly it won't trip your generator! If you're using a 9" grinder (1800W), use a 5" grinder (210-360W).
  • Battery powered tools. This is the direct way to do the energy storage you want. You may even find you can get chargers that will charge direct off your solar without need for gen at all. In your question you claimed a rather light duty cycle, and that should be well within the range of battery tools. (If that was falsely stated, GIGO.)
  • Air, as DDS discusses at length. Gas powered air compressor + air tools. Energy storage is done with an air tank, and those are way cheaper than batteries with no energy conversion required.
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Buy a (petrol-fired) air compressor and pneumatic tools, or go for a bigger generator. (Good) Inverter can cost nearly as much as a generator, also remember that an inverter rated for 2kW has a substained rate of about half. I found on Amazon this 3kW inexpensive inverter, check if it may be good for you. Anyway, with an inverter it's important that the battery can provide all the instantaneous power needed, and also that the wires are thick enough: 3000W@12V -> 250A it needs really big wires (60mm^2). Also remember that motors may require a start-up current that can be more than 7 times the 'rated'.

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  • An air compressor is as expensive as a big generator and still requires a power supply of several kilowatts. Are there affordable options that can fill a pressurized container that will be able to drive a pneumatic grinder?
    – oligofren
    Commented Apr 17, 2018 at 10:06
  • 7 times! Wow. Not aware of that.
    – oligofren
    Commented Apr 17, 2018 at 10:07
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    You can find a petrol-fired air compressor like this: agrieuro.com/…, so you'll avoid all the hassles of electricity (and you won't need high surge er for electric motors). And use the gen you already own for light duty appliances.
    – DDS
    Commented Apr 17, 2018 at 13:30
  • 7 times if the appliance doesn't have a soft-start or a power inverter, if the appliances have them startup current became lower. Also remember that a regular (70Ah) car battery can store only 840 Wh of power, that is about 10 minutes of work with 3kW draw. And to recharge will take about 10 hours
    – DDS
    Commented Apr 17, 2018 at 13:34
  • @DDS soft starts and power inverters are features found on rather high-end tools, that is not the economic stratum we are operating on in this question.
    – Harper - Reinstate Monica
    Commented Apr 17, 2018 at 16:23

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