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J1772 Hydra - charge two vehicles with one charger
- Thread starter nsayer
- Start date
Cottonwood
Roadster#433, Model S#S37
I could see this as a very nice addition to the house/garage with limited total power and two Teslas. Putting the Hydra on the output of a HPWC with a Tesla connector on one output of the Hydra and a J1772 on the other Hydra output, with the Hydra in "share" mode would be pretty sweet. Plug both Teslas in and each gets half power. Need to charge one quickly, then all you have to do is unplug the other one.
Cottonwood
Roadster#433, Model S#S37
It's supposed to, but as a mentor of mine said, "If it hasn't been tested, it doesn't work!" :wink:
Undoubtedly that's a fencepost error in the firmware. The spec says you're supposed to give, like a 2% duty cycle "cushion" at the top and bottom end.
One thing I've considered a couple of times for the Hydra is for it to detect "balancing" at the end of the charge cycle and reduce the pilot down to minimum and give the rest of the power to the other car. One reason I haven't done that is concern that a 6A pilot may trigger errors (like this).
Yes. I don't have a Tesla, but I have observed them using the Hydra, and they do the right thing.
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If you're at all handy with power tools, building a Hydra is not hard.
The trickiest part is getting the high current paths correct. Making the QD terminal crimp connections is very critical if you want to avoid overheating that leads to component failure (and in the worst case, possibly a fire).
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Or better - put the Hydra in sequential mode and plug the needy one in first. If it finishes, it will switch automatically to the other car.
I don't know if anyone is interested, but I have a design for a Hydra board that replaces the inlet handling circuitry with a GFI. The idea is that with a GFI, one could replace the J1772 inlet with just a power cable, making the Hydra a straight-up two-headed EVSE (no host EVSE required).
Since I've sold a grand total of two Hydra boards so far, would this alternative configuration make anyone more likely to want to build one for themselves?
Since I've sold a grand total of two Hydra boards so far, would this alternative configuration make anyone more likely to want to build one for themselves?
It has always adjusted it's current down as far as I know, and know we know that on firmware 5.9 it will adjust back up as well.
Firmware 5.9: Smart Charging finally works!
This is basically turning the Hydra into the equivalent of the Chargepoint CT4000 except using OpenEVSE guts, no?
I personally don't have a need for such a beast, but when I get my second plug-in I am going to seriously consider one, though don't have a strong preference for either at this point.
Yes, although the guts aren't OpenEVSE. They're my own open-hardware design, though I will admit that they are heavily "inspired" by OpenEVSE.
I'm curious why you would put a GFI on the inlet side of the Hydra. This doesn't seem like a logical place for it. If the Hydra has been modified so it no longer needs a host EVSE, then it has to have it's own contactor. Why wouldn't you put the GFI downstream of the contactor where it's normally installed in an EVSE? You really should have a separate GFI sense on each branch.
I think we should team up on this one... OpenEVSE with a second port - HYDRA with GFCI. I think the resulting design would be the same by taking either angle.
TonyWilliams
Active Member
If you put the GFI on the input then it will catch faults in the logic power supply as well as the vehicles. Of course, it won't be able to cut off the power in those cases, but it will at least stop operating and alert the owner to a problem.
In the case of the Hydra, there's only a single GFI, so it needs to be able to catch faults on both vehicles (again, we're assuming it's the "dual head EVSE" configuration where there is no host EVSE). Of course, a GFI event will fail both vehicles, but GFI events are so rare (I think in a year of heavy involvement in EVSEs and Hydras I have seen one GFI fault, and it was not reproducible) that it's not worth doubling the GFI circuit to cover each vehicle separately.
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I have resisted selling complete units because I don't have the kind of product liability insurance or UL approval such a product as a complete product needs.
A 40A inlet/30A outlet EVSE is straightforward and would supply each vehicle with 20A simultaneously or 30A singly. It'd basically be the reference design as it currently exists.
Bummer. Thanks for answering.
I was thinking it would be a nice product and could actually help w/the EV charging situation at my work. It's not at all bad right now due to EV/PHEV drivers observing good etiquette, an internal list of EVs/PHEVs (w/license plates, owner names, etc.) + EV valets.
However, a tethered J1772 Hydra (so it doesn't get stolen) would be actually quite nice... We have numerous cars charging w/only 3.x kW OBCs or less (e.g '11 - '12 Leafs, Volts, Plug-in Prius, Ford PHEVs, etc.), so this wouldn't slow them down much/at all. Our Chargepoint EVSEs have 30 amp output max.
That's our situation at my workplace as well. We don't tether the Hydras (we have 2 and I have approval for a 3rd), but they have "nests" that they live in inside the building after hours.
I'd be happy to help anyone build a Hydra if they live in reasonable proximity to the Hacker Dojo in Mountain View (SF Bay Area).
The new EVSE variant boards are now for sale at store.geppettoelectronics.com. Fully assembled boards are available, so assembling a Hydra can be done without any soldering.
In addition to the GFI, there is a real-time clock chip and the firmware can do day-of-week differentiated charge timing for those on ToU electric tariffs. So the Hydra can begin charging both cars late at night, and in sequential mode, switch automatically from one car to the other. The clock can also do automatic DST switching, if enabled.
For those with high powered designs in mind, there's also a contactor adapter board to allow the 12VDC relay outputs to control line powered contactors instead. It's conceivable someone could make one capable of charging two cars at 40A or a single car at 80A with the right components.
On the off chance that it would inspire someone... I built a "Mega-Hydra" EVSE. It's perfectly tailored for the two-Tesla garage. It can charge two cars simultaneously at 25A or a single car at 50A. In fact, if you upgraded the power cable from 8 gauge to 6, you could do two cars at 30A (with a 75A rated circuit) or one at 50.
I did it to prove the concept of using my contactor adapter boards to control line-powered contactors.
I looked into getting UL approval, but that's almost as much money as a model X, it turns out. But it's not hard to build your own if you're at all handy with tools. In fact, you can get all the parts readied so that no soldering at all is required - even for the Mega variant.
I did it to prove the concept of using my contactor adapter boards to control line-powered contactors.
I looked into getting UL approval, but that's almost as much money as a model X, it turns out. But it's not hard to build your own if you're at all handy with tools. In fact, you can get all the parts readied so that no soldering at all is required - even for the Mega variant.
Cottonwood
Roadster#433, Model S#S37
I would love to hear if you think this would work.
My idea is to connect the input of the Hydra to the output of an HPWC, using cable rated to 100 Amps. I would then connect one output with a 100 Amp contactor to the original HPWC MS cable, and the other output through a 100 Amp contactor to a 75 Amp J1772 cable/connector that I have. This would allow me to charge my MS as well as my Roadster from the HPWC. Is there a way to allow the MS connector side to be limited to 80 Amps and the J1772 side to 75 Amps when there is only one connector used. When both outputs are used, I would want the 80 Amps in to be shared, giving each output 40 Amps.
If you think that this will work, I will probably buy one of your controller cards and start acquiring the rest of the parts. If it works, this will be a nice add on to a Tesla HPWC to support Roadsters and other J1772 compatible EVs.
My idea is to connect the input of the Hydra to the output of an HPWC, using cable rated to 100 Amps. I would then connect one output with a 100 Amp contactor to the original HPWC MS cable, and the other output through a 100 Amp contactor to a 75 Amp J1772 cable/connector that I have. This would allow me to charge my MS as well as my Roadster from the HPWC. Is there a way to allow the MS connector side to be limited to 80 Amps and the J1772 side to 75 Amps when there is only one connector used. When both outputs are used, I would want the 80 Amps in to be shared, giving each output 40 Amps.
If you think that this will work, I will probably buy one of your controller cards and start acquiring the rest of the parts. If it works, this will be a nice add on to a Tesla HPWC to support Roadsters and other J1772 compatible EVs.
I don't have any direct experience with the HPWC. Obviously modifying it will void its warranty. I think that at the end of the day it may be a lot easier to simply construct the EVSE variant of the Hydra with two J1772 cables. With 6 AWG input wire with 90 degree insulation, and with 75A contactors, you'll be able to do one car at 75A or two at 37.5A. In principle, it would be almost exactly the same thing I did with my Mega Hydra, but taken one "notch" higher.
I went with 50A simply because I wanted to not have to hard-wire it (as an experimenter I am always plugging and unplugging), and because I presently only have a 30A car anyway (and only a 40A circuit in any event). Also, the 50A contactor I sourced was particularly inexpensive.
The only tricky part is that you have to kind of squish 6 AWG wire to get it to fit through the GFI coil. But it can be done (it was done by an OpenEVSE builder once upon a time).
The "splitter" variant board requires a J1772 pilot and proximity line on the inlet, and requires J1772 pilot signaling on the output. If the HPWC can be coerced into working that way, then in principle you could "insert" the Hydra inline and break out an additional J1772 plug. But for the cost of an additional J1772 cable, you get to keep your unmodified HPWC as a backup. I think that'd be valuable.
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Here's a picture of the Mega Hydra, btw.
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