Unlocking A Locked-Down Inverter

There was a time when a mains inverter was a heavy, expensive, and not particularly powerful item, but thanks to switch-mode technology we are now spoiled for choice. Most inverters still work with 12 V or 24 V supplies though, so when [Chris Jones] was looking for one to run from 36 V batteries, he found a limited supply. Sadly the Greenworks model he ended up with was affordable, but locked to a particular battery by means of a serial line between battery and inverter. Buy the special battery? No, he did what any hacker would do, and modified the inverter to do without it.

Tracing the serial link led to a mystery chip, probably a microcontroller but without available data. It in turn had a line to an 8051 derivative that seemed to be the brains of the operation. Acting on a hunch he pulled down the line with a resistor, and as if by magic, a working inverter appeared.

As you might expect, here at Hackaday we abhor such tricks by manufacturers, and thus any moves to circumvent them are to be applauded. It would be extremely interesting were anyone to have the Greenworks battery to subject to some reverse engineering of the profile.

Meanwhile if this is a little complex for you, there is a much simpler way to make a rough and ready inverter.

21 thoughts on “Unlocking A Locked-Down Inverter

      1. You made it political with the mention of “capitalism” right off the bat genius. Hence why I made my comment.

        And my point still stands. If you agree with them being able to brick equipment sent to Ukraine at will, then you agree with it being done in America as well. It doesn’t change just because you like one group of people but despise the other.

  1. On one hand, it’s a nasty move to lock you in to their batteries.

    On the other hand, an inverter can draw a lot of current and there’s sense in ensuring it’s plugged to a legit pack that can deliver the required current without catching fire. Both for their liability and users’ safety.

    A nice middle ground would be a clearly marked bypass jumper or screw terminals for an aux battery, but hidden safely behind a case removal, to deter the average idiot and make it clear you’re taking your own liability.

    1. I guarantee the instructions say not to use the inverter underwater or when wet, it’s not too much trouble to add a line that says “For safe operation use a battery that is rated for a continuous discharge of XYZ amps”.

      I think the major issue is that it’s designed to take batteries from Greenworks proprietary battery sled. I wouldn’t be surprised if the resistors act as analog ‘smarts’, where Greenworks 40 volt batteries with different amp hour and current supplying abilities have different sized resistors that connect to the tool, letting the tool know how much it can draw from the battery safely.

      1. This is common. The battery management system is either in the battery or the device. For example the Milwaukee M12 batteries are dumb batteries. The battery management system is in the device. So the deed choice is responsible for not damaging the battery pack.DeWalt 20v packs are the same. The metabo hpt 18v and 36v packs on the other hand have the management system in the pack. The packs will shut themselves off or limit current to protect the pack.

    1. It might be that the mystery chip was ensuring the battery had the right chemistry, or the capacity to handle the amount of current that the inverter required. If that’s all it is, bypassing it is fine. But it falls upon him to ensure his replacement battery pack matches the original pack exactly, spec for spec.

      It’s also possible the serial data included the pack’s temperature and/or charge level, and would shut the inverter down if the pack was misbehaving. That would make it more of a safety issue.

      The best path would be for him to continue exploring, and to try to decode the data flowing to the mystery chip.

      1. I agree if it isn’t charging the battery. But, if a charging circuit is also enabled you are taking a big risk if the chemistry of your LIPO replacement is incompatible with the OEM battery.

      2. They do so by being very conservative about how they charge and discharge the batteries, staying far away from voltage extremes and consequentially not using a good part of the battery capacity.

  2. Like other people have said, they probably locked it down for “safety” reasons to ensure a battery with proper specifications was used. HOWEVER, that’s still no excuse for doing such a thing. I’m of the opinion that if you buy something, anything, without knowing how it works and what it’s limitations are, it’s on YOU if you do something stupid. The rest of us shouldn’t suffer because a small handful of people are too lazy to do a tiny bit of research on the things your buying so you know what your doing!

  3. For those interested in inverter technology, there’s a manufacturer in Australia who’s about to do something rare:

    open-source the designs and IP. Well, not soon, but in 2 years.

    Latronics make inverters and my first one from them finally gave up this year – I bought it in 1996, so I’ve no complaints. I bought a replacement and my reseller made sure to tell me that the warranty was going to be 2 years instead of the usual 3, because the company will close in 2 years, and when that happens, the designs and IP will be released to open-source. The founders are ready to move on, and I’ll be keen to grab some schematics and other information when it happens. It’ll be good to have the data needed when any repairs are required.

    Not affiliated, just a happy customer.


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