The subpanel (actually a fuse box) to the AC is entirely within the garage, so it’s easy to tap off of. The only trouble is that the existing cable is sized for the 30A of the AC. Clearly, this cable runs up to my breaker box somehow, but I haven’t yet figured out how. The best-case scenario is that there’s a big channel that I can feed an extra cable through.
Weirdly, there’s another garage outlet that’s on the same circuit as my dishwasher and guest bathroom lights. I only know this because I managed to trip the breaker while charging the Tesla from that outlet and running the dishwasher. This was actually fine until the heating cycle.
I think it’s time to go through the whole house and map out every outlet and light… the notes in the breaker box do not tell the whole story.
If you are installing, I don’t think your HOA has much leg to stand on to prohibit it. A conduit is fairly normal and should be allowed like conduit for solar.
A solution does exist. You need a transfer switch based on contactors (same stuff that’s in your AC actually) that is wired to the same wire from the A/C thermostat that trips those contactors.
This is assuming you are using an old style A/C and not a modern inverter unit.
This would cause the EV charging power to be cut every time the A/C turns on, which would be just fine as a solution in that it would not affect your life at all. You’d most likely gain plenty of range even on the hottest summer night.
Right–something like that would be optimal. The duty cycle on the A/C isn’t going to be more than 30% or so, which leaves plenty for charging.
The thermostat must have enabling wires down to the ground floor but they aren’t in an obvious place. They must be there, though, so I’ll keep looking.
A truly ideal solution would just always enable the A/C, but disable the secondary circuit when it’s drawing more than some setpoint current. I could actually build that device trivially (and safely), but I doubt I could make it meet code. Maybe something is already out there, though.
Thermostat would normally be set to “off” but the temperature would get monitored by software. (running a script on an android device or something). When the temperature gets high enough to start the A/C, the script would communicate with the car, telling it to lower it’s charging current, then, once it gets a response from the car, it would tell the wifi thermostat to turn on into A/C mode.
This would work, and it would be perfectly safe as every hardware component would be totally code compliant and legal. The drawback is that it could be a lot of hassle to overcome various roadblocks in the way of doing seemingly trivial things (like communicating with the car) and there are many ways that software bugs could cause the system to crash or occasionally trip a breaker.
You would need an app that can send a command (there’s a standard interface) to a smart wifi thermostat like this one, that is compatible with standard HVAC systems. It would run on android or iOS as root and somehow hijack this Tesla API, haven’t looked at how you’d actually accomplish this but no doubt there are code examples.
Then the core logic is just :
mode = car_charging
while(True):
read temperature, read setpoint from Honeywell wifi thermostat. Set thermostat to off.
If temperature > setpoint and mode == car_charging:
ping Tesla
if Tesla found
turn off charging
wait
turn on thermostat
mode = HVAC
if temperature is less than setpoint and mode == HVAC
turn on thermostat
ping Tesla
if Tesla found
turn on charging
wait
mode = car_charging
(this is way more readable with tabs)
That’s way more complicated than what I had in mind :).
There are various devices available like this one. You run a wire through the sensing coil, set a trip current level, and fiddle with the time delay.
A short delay in switching out the other circuit is fine. A typical circuit breaker can go for ~100 s at a 2x overload condition. The sensing and switch should take <1 s, which is plenty safe.
The only problem is that I haven’t found a device yet that is dual-pole, 240v, and “normally closed” (or double throw).
I could use that relay to drive another, bigger one, but now it’s getting more complicated. I’d like to use off-the-shelf components for simplicity if nothing else. And really I’d just prefer to pay an electrician to avoid hassles with code, etc.
Where is your air conditioner in relation to your condo? Just run a new line to that and you’re done. that frees up the 220 fuse box in the garage for the car. which is the location you want it to be in the first place.
The A/C is basically inside the garage and in a relatively convenient location. Running a line parallel to the existing A/C line would indeed be ideal, but the geometry is non-obvious.
I did some probing around in the garage to see what’s what and I now at least fully understand the electrical situation.
One unfortunate bit: a subpanel that I installed with my grandfather (just after I bought the condo, and before I knew anything about wiring) and that taps off of the A/C to provide some 120v plugs is absurdly out of code. The 240v line running to the A/C is just /3 romex (presumably 10/3, but I can’t tell). That is, no dedicated neutral. We tapped off that and (unbeknownst to me, until today) used the ground as neutral. Ugh. That now needs to be completely ripped out as there’s no way to bring it into code without a neutral available.
I did at least find the thermostat control lines. So I can use those to drive a relay instead of a current sensing system.
To learn more it looks like I need to tear down some drywall… no time like the present.
Secondary box is disconnected. Jesus. At least I only used that circuit for low-current battery chargers and shit, but still.
I can follow the A/C coolant line from the downstairs condenser/pump to the upstairs evaporator/fan. So I know there’s a way down, though my knowledge of fire code is that there’s going to be some fireblocks somewhere on the way down. Needs further investigation…
You may be right :). Well, as said I may end up just sticking with 120v charging. I’d actually popped the breaker once when running the dishwasher (discovering at that time that the dishwasher was on the same circuit). But I was able to trivially move the dishwasher to a different circuit, so that at least isn’t a problem anymore.
Actually, I think my problems are relatively simple at this point as long as I’m not too ambitious. I’ve found the thermostat control line and can use that to control a relay. The relay shuts down the car charger when engaged. This is a simple device to build, though I need to research the electrical code a bit to ensure I’m not missing anything.
Worst-case, I put in a manual switch. Means I have to choose between A/C and charging on any given night, which isn’t great but I can live with it.
I’m genuinely confused at this point. You live on the 3rd floor of a condo. You have a garage that is part of the building. you have an air conditioner compressor unit that’s “basically” inside the garage. Is this a standard Compressor with coils are they somehow separated? I don’t see how a standard unit can be inside the garage.
What I’m suggesting is that you treat the AC unit as if it’s a new install and run the wire (in conduit) up the adjacent wall (but not attached to it).
If you can run it through an interior wall then drywall is nothing in this equation. It’s an afternoon and a few dollars to replace an entire sheet of it.
It’s a reasonably typical unit. There is a box containing the compressor, coils, and a fan. It vents to the outside via a mesh “window”. The unit is largely boxed up in drywall and wood framing but there is an access panel on the inside. This is also where the power cabling goes in. From the box, upward goes an insulated line for condensed freon, an uninsulated return line, and a 2-wire line from the thermostat.
I know the freon lines go up to the attic, then jog over a ways, and then down into the evaporator. The breaker box is also a short ways off. If I can run a new power line alongside the freon lines, I can easily get to the breaker. But that’s two stories and there are probably firebreaks that make running a line challenging. Still looking into it.
The existing A/C powerlines take a different and clearly more convoluted path. It’s pretty obviously not possible to run another cable alongside here.
Drywall, and knockdown, and paint. But the real problem is my neighbor in the way.
My situation is actually somewhat unusual–I have a personal, finished garage but am in a multi-story, many-unit building. A common garage would be way easier, at least in CA, since it would already have high-amp electrical for the lighting. And a normal single-occupant house would be easier since there would be no pesky neighbors or weird convoluted routes to deal with.
Furthermore, I still have plenty of alternatives available to me. I’m only pursuing this because it increases my convenience slightly. As said, 120v charging is sufficient, and this would be true even if my commute were 4x as long. I can also easily charge at work. And in the absolute worst case, I could just visit public charging stations occasionally. Combined with shopping trips, it would hardly take any additional time from my schedule.
The sheer flexibility of EV charging as compared to gas makes it very practical.
What’s the problem? I think Dr S. wants to do something non-standard, but an electrician can install a charging station if he’s willing to pay. He’s in CA, and CA law already provides that HOAs can’t restrict installation of charging stations beyond what’s reasonable.
Incidentally, there are now a ridiculous number of Model 3s at work. From just my usual parking area I see three reds, a white, a dark silver, and a blue. And a teammate just got her delivery notice for Friday (light silver). It would not surprise me if there were 2-3 times this many across the whole campus.
There may actually already be more Model 3s than Ss at this point. Certainly more than Xs.
All right, I’m gonna build this bitch. Got a NEMA-certified electrical box with internal mounting plate. Ordered a 50 A DPDT relay with 24VAC coil. A grounding bus bar. Some “Danger High Voltage” stickers :).
I think it’s all pretty reasonable, actually. Even if the relay fails closed somehow, it still sits behind a 30 A fuse and breaker.
Home Despot has all the remaining bits like armored cable and plugs (guess I’ll go for the 14-50 since that seems to be the default). Shouldn’t be more than about $300 total.
The only thing I’m not super happy about is that the 24 V is driving the relay directly. My experience from PCB work is that you always isolate high voltage from low with a transformer, optoisolator, etc. But the relay in the existing A/C is also driven directly so it’s clearly not against code. And relays are pretty safe, really, since there’s no electrical path between the low and high voltage parts. Still, it bugs me a little.
