The J1772 Hydra Helps You Charge Two EVs At Once

There are plenty of electric vehicle (EV) chargers out there that are underutilized. This is particularly common where older EVs are involved, where the cars may only be able to charge at a few kW despite the charger being capable of delivering more. [Nick Sayer] regularly found 6.6 kW chargers being used by vehicles that could only draw down 3.3 kW at his work. Thus, he built the J1772 Hydra as a nifty double-adapter to charge two cars at once.

The Hydra comes in two versions. One is a “splitter,” which is designed to be plugged into an existing J1772 AC charger. The other is a version designed for permanent installation to an AC power supply as an EV charger in its own right. Either way, both versions of the Hydra work the same way. In “shared” mode, the Hydra splits the available AC power equally between both cars connected to the charger. When one completes, the other gets full power. Alternatively, it can be set up in “sequential” mode, allowing one car to first charge, then the other. This is great when you have two cars to charge overnight and don’t want to wake up to shift the plugs around.

It’s a neat hack that could be useful if you’re running older EVs that rely on slower AC charging. We’ve seen other DIY EV chargers before, too. Expect hacking in these areas to become more commonplace as EVs grow in popularity.

20 thoughts on “The J1772 Hydra Helps You Charge Two EVs At Once

      1. Why the derision for people that speak Sarcasm as their mother-tongue? For some of us, it’s only on good days that we can be bothered with markup to help you straight-speakers along. …

        … …/s

    1. It is as safe as the J1772 standard allows. The EVSE version has a GCM and a GFI just like the spec requires. The splitter doesn’t but that’s because you plug it into an EVSE that has those already.

      It amuses me greatly that people just assume that people who design their own things are ignorant jackasses without taking the time to look and see first.

    1. Early EVs were marketed and sold as if ICE vehicles didn’t exist. Rather than acknowledging their shortcomings compared to ICE and responding, they competed against themselves with varying trim levels that offered different charging speeds.

      The Leaf SV was decidedly better than a Leaf S, but in reality the differences were small and both suck compared to an ICE. Full disclosure, I have a Leaf SV and it’s a decent little runabout.

    2. This was a lot more common ten years ago when the Hydra was first designed and built.

      Now you can get a circuit-sharing EVSE from ChargePoint, but I can confidently state that the Hydra was the first one ever designed, made and used.

  1. I was expecting a switching method, car A for half an hour, car B for half an hour, etc, making sure that both vehicles receive as much of a charge over night as they could while being fair. (Advantageous if you have a better rate at night, and concerns over 1 car being charged at the detriment of the other).

    1. “Hey charger, tomorrow I am leaving for work an hour earlier than usual and my wife is going to visit her mother in the afternoon. Can you please make sure both cars are properly charged?”

    2. I know that’s how the Chargepoint stations I installed a few years ago (could) work. It was a while ago but iirc you could set it depending on if it was fed by an 80 or a 40 amp breaker. With two cords on 80 it would feed both cars a steady 40 but if all it had was a 40 it would switch back and forth between both cars at 40 amps. I don’t remember the duty cycle but I’d imagine it was shorter than a half hour but I’m not sure.

    3. It’s not a bad idea, but I designed it to let one car finish and then switch. I figure if you want to have the cars get evenhanded charging like that then giving each 50% power is at least going to be less hard on the contactors.

    1. One possibility is that there is only one charger in a place where installing a additional charger means convincing someone stubborn, aka you don’t own the place.
      Another possibility is that this is done for the fun of it like many of the things we see here, aka look what I have done, isn’t it cool.

      1. The splitter variant was done to share commercial EVSEs that were installed in a parking lot. Adding more EVSEs as demand grew was just way more expensive than could be justified. And at the time (ten years ago), LEAFs and Volts that charged at 3.3 kW were very common, so sharing was no skin off anyone’s nose but allowed more folks to charge.

        Our company moved and now we have a parking lot where the EVSEs effectively have single dedicated parking spaces, so sharing isn’t feasible.

        Meanwhile, I made the standalone EVSE variant for our home because I had a single 40A circuit put in, but we then got a 2nd EV. Adding a 2nd circuit and EVSE would have been far, far more expensive than the Hydra, and the Hydra is more than adequate for our needs.

  2. EVs are all about BG GUBBMNT CTRL of US! Where U can go – Wen U cn go – How oftn you cn go – Hw much it $$ to go – Why RU going? Et-Cetera… All is TRACKD. Forcin’ EVs on all peeps meens THEY PWN us ALL. One chg point per EV meens ALL EVs are under central/collective GUBBMNT CTRL. U-Must Embrace-It, Accept-It… OK Com-Rad? [Yea U hv NO choice.]

    1. Dude. Settle down.

      The government doesn’t know how much of my electricity is used to charge our EVs and how much powers the blender that makes our margaritas.

      I like EVs because they have *all* the low end torque, are quiet, and we have very cheap electricity where I live. I don’t make claims about them being “green” or anything else. They fit my needs and lifestyle. Your mileage quite literally may vary.

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